DAMM BS422 Review: Mast Top Base Station Design for Australian Mines

The DAMM BS422 is a software defined outdoor base station that runs up to four carriers of TETRA, DMR Tier III, TEDS or analogue from a single 12 kg IP65 enclosure. It carries its own controller, so it needs no separate rack, and it is designed to be mounted at the top of the mast beside the antennas rather than in a shelter at the bottom of it.

Those two design decisions, a complete base station in a box small enough to go up the tower and a technology stack chosen in software, are what separate it from a conventional base station. They also change the site design around it, which is where the engineering interest lies.

This review works the BS422 against the deployment that suits it best in Australia, a mining operation running surface and underground on one network, and then sets out the band, duplex, power and compliance decisions that have to be settled before an order is placed here.

What Is in the Box

Four receive sensitivity figures are published for TETRA, and mixing them up is the most common way to get a coverage prediction wrong.

Note that diversity is worth 3 dB in the static case and 6 dB in the faded case. Two branches always give you combining gain; the extra 3 dB only appears once there is fading for the second branch to work against. DMR and analogue publish the same static pair, −124 dBm with diversity and −121 dBm without.

The controller is integrated rather than external, running Windows 10 IoT on an Intel Atom platform, so network management, gateways and voice and data logging run on the base station itself with no separate computer at the site. Capability is set by a USB dongle that fixes the number of carriers, subscribers, profiles and organisations, and those limits can be lifted remotely without pushing large files across the network. On a remote site that turns a capacity upgrade into a configuration change rather than a site visit.

The Four Capabilities That Change a Site Design

Mounting at the mast head removes the feeder

This is the most useful thing about the product and it is the least discussed.

A conventional base station sits in a shelter and reaches the antenna through 40 to 60 m of feeder, and that feeder costs you twice: transmit power on the way up and receive sensitivity on the way down. The BS422 is designed to go up the tower next to the antenna, and DAMM states the intent plainly, that mast top mounting removes the usual transmit and receive signal degradation caused by feeder losses.

Here is what that is worth. Feeder loss computed as K1 x √f + K2 x f from the coefficients in our own cable data, on a 50 m run with 0.5 dB allowed for jumpers and connectors:

A shelter mounted 25 W TETRA base station on 1/2 inch feeder delivers 12.4 W to the antenna. The BS422 delivers 25 W from the same 25 W transmitter, and recovers the same 3 dB again on receive. Six decibels of round trip system gain, for no additional DC power and no additional transmitter. At 168 MHz the effect is smaller but still real, 4.1 dB round trip on the same cable.

There is a cost on the other side. The active electronics are now at the top of the tower, so maintenance is a climb or an EWP rather than a walk into a shelter, the unit is in full sun and full wind, and lightning protection has to be right because the equipment sits at the highest point of the structure. DAMM specifies internal lightning protection, and the 0.08 m² wind area and 12 kg mass are small enough that most existing masts will take one without a structural rework, but the maintenance access question is a real trade rather than a free win.

Four carriers in one box, but not four full power carriers

The BS422 runs one to four virtual carriers and they can be different technologies. A single unit can carry a TETRA carrier, a DMR carrier, a TEDS carrier and an analogue carrier at once, which is the migration story: the old analogue fleet and the new digital fleet run from the same box on the same mast during changeover, with no bridge or gateway between them.

The part that is easy to miss is that the carriers share one power amplifier, and the published power table makes the consequence explicit.

Four carriers is 2.5 W each, which is 10 dB down on the single carrier figure. DAMM’s own footnote says the amplifier’s efficiency falls in a multi-carrier setup and that consumption may be limited by heat dissipation, which is exactly what that table shows.

This is why DAMM’s own scaling examples do not use four carriers. Up to eight BS422s connect at one site, and DAMM’s two published node configurations are eight single carrier units at the full 25 W, giving 31 traffic channels and one main control channel, or a two carrier configuration giving 16 carriers at 10 W and 63 traffic channels. Capacity comes from adding boxes, and power per carrier comes from using fewer carriers in each one.

Working the slot counts through Erlang B:

The shape of that table is why single carrier trunked sites disappoint. One carrier is three traffic slots and 0.46 Erlangs, which is a small fleet. The second carrier returns five times the traffic for one more pair on the licence. Trunking efficiency is worth the most at the bottom of the range, so the site sized at one carrier because the fleet is small today is the site most likely to need a return visit.

One spectrum constraint governs all of it. Each band version offers a window of up to 150 kHz for its carriers, and 75 kHz in the VHF mid band version, which is why that version is limited to one or two. The carriers are not independently tunable across the band; they have to be found together. On a 12.5 kHz raster, 150 kHz is twelve consecutive channels, and four aggregated 25 kHz TETRA carriers need eight of those twelve to be clear. In quiet spectrum that is nothing. In a congested band it is a materially harder coordination task than four channels scattered wherever they happen to be free, and it is the question to put to the Frequency Coordination Tool before the order rather than after.

The 6.25 kHz synthesiser step is worth noting on the other side of the ledger: it lands cleanly on the Australian 6.25, 12.5 and 25 kHz rasters, so the tuning granularity is not a constraint.

The same hardware is the base station and the repeater

The BS422 runs in simulcast or repeater mode for TETRA, DMR and analogue, and DAMM’s case for it is that a repeater built this way keeps full transmit power, full functionality when isolated from the master node, full network management, redundancy, alarm management and log system integration, which conventional repeater products generally do not.

Up to 10 base stations connect to a BS422 acting as master. With a server as master and IEEE 1588 synchronisation, up to 50 simulcast slaves are supported, and simulcast and non simulcast subnets can be combined into one network.

Combined with frequency sharing, which lets adjacent units run the same frequencies, this produces the capability that matters underground: DAMM states that with frequency sharing an indoor repeater system can be built without optical fibres, and that the same hardware serves as base station and repeater unit. One spare part covers the surface mast and the decline, and one management system covers both.

The architecture survives losing the link

TetraFlex replicates system information to every site with no central switch, so a site that loses its connection to the rest of the network keeps carrying local calls and data. Two BS422s at two sites can also act as one fully redundant base station sharing the same frequencies, which puts the redundancy in the antenna system as well as the electronics, and a second unit at a site gives hot standby redundancy at both controller and carrier level.

On an Australian mine this is the failure mode that actually occurs. The backhaul, whether it is a microwave hop over a range or a satellite service, is usually the least reliable element in the system, and a crew underground or on a haul road should not lose radio because a link on the surface dropped out.

For sizing that backhaul, the published per slot data rates are 12 kbit/s for TETRA IP payload, 20 kbit/s in tunnel mode, 10 and 18 kbit/s for DMR, and 0.4 kbit/s per node for backbone control traffic. A four carrier TETRA node is therefore a few hundred kilobits per second, which is a modest ask of a link that has to carry the mine’s other traffic as well.

Building an Actual Node: Antennas, Service Boxes and Power

The mast top argument creates a question the marketing material does not answer, and it is the first thing an integrator should ask. If the whole point is that each unit sits at the antenna with no feeder, what happens when a site needs eight units? Eight boxes with a transmit port and two receive ports each is a lot of coaxial cable on a mast whose selling point was the absence of coaxial cable.

The published antenna configurations are these:

That third row is the interesting one, because two units with four receive paths between them still need only two antennas. The mechanism is a cross connection: each BS422 carries an A-OUT port alongside its RX A and RX B, and DAMM’s installation guide describes the jumpers needed for a paired installation as two for TX/RX, two for GPS, and two for RX-B and A-OUT running between the two base stations. Each unit transmits and receives on its own antenna through its internal duplexer, and takes its second diversity branch from its partner’s antenna through that cross connection. No external multicoupler, and no feeder loss on either path.

Two things follow that matter for a node design.

Beyond two units, the antenna arrangement is not covered in the published material. The documented configurations stop at a pair. Whether four or eight units chain the same way, whether they need an external receive multicoupler, and whether the transmitters combine or each keeps its own antenna are questions to settle with DAMM before a high capacity site is designed, because the answer decides how many antennas go on the mast and whether any combining loss creeps back into an architecture that exists to avoid it. Ask it early. It is the difference between a two antenna site and a sixteen antenna site.

The service box count is set by power, not by network capacity. One SB422 supports up to two BS422s, and it cannot mix a BS421 and a BS422 on the same box. A second, redundant SB422 removes the single point of failure and raises the limit to four base stations at one location. So the eight unit node that DAMM quotes for capacity is four service boxes, not one.

The SB422 delivers 56 VDC at a maximum of 7 A, which is 392 W for both base stations combined, and that is a real constraint at the top of the range:

Two BS422s both running at full DMR or analogue power exceed what one service box will deliver. That is a specification question, not a disaster, but it needs answering before the single line diagram is drawn rather than during commissioning.

Two more practical points from the service box. The Ethernet between the SB422 and the base station requires Category 6A once the run exceeds 55 m, so the 100 m separation is not free. And the alarm inputs include a dedicated power reduction input and a TX off, base station idle mode input, which means a battery management system can be wired to drop transmit power or idle the transmitter on a low state of charge. On a solar site that is a genuinely useful feature and it is not mentioned anywhere in the sales material.

Worked Example: One Mine, Surface and Underground

Take an operation with an open pit and a decline, which is the configuration where the BS422’s capabilities compound. The requirement: one fleet, one talkgroup structure, one set of radios, working on the surface and underground, with emergency response able to talk across the portal.

Surface

Assume 350 radios across haul trucks, diggers, light vehicles, trades, supervisors, the processing plant and emergency response. Mining fleets are talk heavy, so take 0.02 Erlangs per radio in the busy hour as a planning figure.

Four carriers, and here the power table above stops being a footnote and becomes the design decision. There are three ways to build four carriers, and they are not equivalent:

Ten decibels of per carrier power costs 5.2 times the DC, 4 times the hardware and 5 times the solar plant. All three carry the same 15 traffic slots, and all three attract exactly the same licence, because the ACMA charges per spectrum access and four duplex carriers is eight chargeable accesses however many boxes produce them.

For an open pit with haul roads running out several kilometres, option A at 2.5 W per carrier is unlikely to reach, and the honest answer is B or C. For a compact site, a workshop precinct or an underground node, option A is the elegant one and it draws less power than a single carrier at 25 W. The point is that “a four carrier BS422” is not one thing, and reading four carriers off the datasheet without reading the power column is how a site ends up 10 dB short.

Whichever option, mast top mounting gives every one of them 6 dB back over a shelter installation on 1/2 inch feeder, and a second antenna gives 6 dB more on the uplink. Those two together are worth more than the entire step from option A to option C, and they cost no DC power at all.

The borefield 12 km out gets its own node. With frequency sharing it runs on the same frequency pairs rather than needing its own, which is the difference between one coordination exercise and two.

Underground

Underground, capacity stops being the problem and coverage becomes the whole problem. The crew in a decline is small, so one carrier per underground node is generous, and that is the configuration that gives full transmit power.

The link budget is unusually favourable because there is no feeder between the unit and the antenna:

Allow 30 dB for near field coupling and junction losses and 104 dB remains for attenuation along the drive. What that buys depends entirely on the drive:

Read the spread rather than any single row. A factor of four in an assumption you cannot get from a datasheet produces a factor of four in the number of units you buy. Straight, large section, smooth walled development sits near the top of that table; a real decline with bends, cuddies, level accesses, changing section and steel sets sits near the bottom, and every junction is a loss this model does not itemise. This is a sensitivity check, not a design. The design number comes from a survey or from a 3D model with the actual geometry in it, which is what the Leaky Feeder 3D Coverage tool exists to do.

So how does a BS422 repeater chain compare with the leaky feeder that would otherwise go down that decline?

Leaky feeder still wins on a long single drive. Radiating cable gives near uniform coverage along its length with predictable loss per 100 m, and for one long decline with little off it, the cost per metre is hard to beat. The economics and the design method are in our guide to leaky feeder coverage for underground mines.

The BS422 chain wins where the mine is a network rather than a tunnel. Portal areas, workshop cuddies, crusher chambers, magazines, multiple levels and stope accesses are where leaky feeder gets expensive, because each branch is another cable run and another amplifier. It also wins where the operational requirement is one network, because the underground units are the same hardware, the same management system, the same spares and the same trunked features as the surface, and no fibre is needed between them.

On most mines the answer is both. Radiating cable down the decline itself, BS422 nodes at the portal and at level accesses and infrastructure chambers, with frequency sharing tying them into the surface network. What the BS422 changes is that the underground infrastructure stops being a separate system with its own spares and its own management, which is where the operating cost of underground radio usually sits.

One boundary to be clear about. The published standards and approvals for the BS422 cover TETRA, DMR, analogue, multi-channel and railway EMC. There is no explosion protected certification in that list. For Australian underground coal, where equipment in a hazardous zone must be explosion protected, the BS422 belongs outside the hazardous zone or in appropriately certified housing, and that is a question for the mine’s electrical engineer rather than the supplier. Metalliferous hard rock is a different question and generally not a constraint.

Sensitivity, Diversity and Getting the Balance Right

The 6 dB between the two dynamic sensitivity figures is the most useful number DAMM publishes, and it is not the one that gets quoted.

Static sensitivity is measured with the signal fed by cable and no multipath. It is a bench figure. The dynamic figures are measured under the TU50 faded channel, which is what a moving user experiences: −118 dBm with dual receive diversity and −112 dBm without. DAMM separately quotes the diversity pre-gain from an external RX B antenna as up to 6 dB.

That 6 dB costs a second antenna and a second feeder and no DC power at all. Under a log distance model:

Roughly half as far again, and about twice the area.

The case is stronger than the range figure, because receive diversity works on the uplink and the uplink is usually the direction that is short. Take a TETRA class 4 portable at 1 W talking to the BS422, and the BS422 talking back to that portable’s receiver. Counting transmit power against receive sensitivity, since the base antenna gain applies equally in both directions and the feeder has been removed:

The bottom row is what gets ordered by default: the higher power setting, one antenna. It is also the worst balanced of the four. The base reaches 9 dB further out than the portable can talk back from, so a haul truck operator hears the controller clearly from a place where the controller cannot hear them. That failure is worse than no coverage, because a drive test that only measures received signal will not find it.

The top row is what nobody quotes: the lower power setting with two antennas, balanced within a decibel, drawing 95 W instead of 150 W.

Stack that with the mast top result and the picture is clear. A BS422 at the mast head at 10 W with receive diversity beats a shelter mounted 25 W conventional base station on 1/2 inch feeder with a single antenna, on the uplink, by about 9 dB, while drawing less power.

Two caveats. These figures are transmit power against receive sensitivity only, so a real budget still carries antenna gains, body loss and the fade margin you have chosen, and the portable numbers are one vendor’s published dynamic figures rather than a class minimum. And 6 dB of diversity gain is DAMM’s measured result under one fading channel; a site with little multipath will see less. Neither changes the direction of the conclusion. Work your own case in the Link Budget Calculator and the Coverage Predictor.

Specifying It for Australia

The BS422 is sold in frequency band versions with separate receive and transmit sub-bands, and both the ranges and the duplex spacing are fixed when the unit is built. This is the part of the specification that has to be right at order time, because the constraint is a filter, not a tuning range, and the software defined radio inside does not change it.

These are the catalogue versions as they appear in the ordering codes of DAMM’s product sheet of 19 January 2022. Treat them as a guide to how the product is structured rather than as today’s price list, for a reason set out after the table.

Now the Australian requirement. These splits were computed from the channel centre frequency formulas in RALI MS22 and RALI MS42, which is the only reliable way to read them, because the segment edges are not symmetric and inferring a split from them gives the wrong answer.

Three conclusions come straight off those two tables.

The two VHF versions are exact matches. Both carry the full band on receive and transmit with a tunable duplexer, and their standard spacings of 2.5 MHz and 4.6 MHz are precisely what MS42 requires. That is a better result than most imported equipment manages and it deserves saying.

The 450 to 470 MHz version is an exact match too. Order code 10520142 receives in 450 to 460 and transmits in 460 to 470 with a 10 MHz split, and MS22 segments S and X sit at 452.5 to 457.5 receive and 462.5 to 467.5 transmit, exactly 10 MHz apart with the base transmitting high. Segments T and Y are the same arrangement for government. The catalogue unit drops straight in. The constraint here is spectrum rather than hardware, because segments S and X are subject to a transition embargo on new assignments.

The 400 MHz version on that list does not fit the Australian 400 MHz band. Order code 10520141 receives in 410 to 420 MHz and transmits in 420 to 430 MHz. Australia does the opposite: base receive sits between 403 and 410.54 MHz and base transmit between 412.47 and 420 MHz, 9.45 MHz apart. The catalogue unit would try to receive on Australian base transmit spectrum and transmit in segment O, which is radiolocation primary with the mobile service limited to government use. The receive band, the transmit band and the split are all wrong.

This is a made to order item rather than a defect. DAMM states that other frequencies are available on request, and the catalogue already includes a non standard example: order code 10520133 pairs a 300 to 310 MHz receive band with a 336 to 346 MHz transmit band, a 36 MHz split. So the architecture builds custom splits. What matters is that the Australian 400 MHz band needs one, and that the quantity, lead time and price for a special build are different from a catalogue item.

Check the version list before you rely on any of this

One caution on the table above, because the sources disagree and the disagreement runs the wrong way for a confident conclusion.

The ordering codes come from the product sheet dated 19 January 2022. DAMM’s own brochure, dated 15 July 2022, is six months newer and lists frequency ranges that the ordering codes do not: 216 to 225 MHz, 406 to 430 MHz and a 430 to 450 MHz DMR variant. A 406 to 430 MHz version, if it exists, would reach segment E and change the conclusion above materially. DAMM has also published at least one later revision of the outdoor system flyer, version 4.0 dated 3 May 2024, which was not available for this article.

So the safe reading is this. The BS422 is built as paired receive and transmit sub-bands with a fixed duplex spacing, the catalogue is organised around European and global band pairs, and the Australian 400 MHz arrangement is not one of them as of the ordering list examined here. Whether a suitable variant has since been added to the catalogue is a question for DAMM, and it is worth asking directly rather than inferring from a brochure, because the answer decides whether this is a stock item or a special build.

The 400 MHz trunked answer

For a trunked system in the Australian 400 MHz band the specification is definite enough to write on the purchase order.

RALI MS22 states that “segments E and M are allocated exclusively to the land mobile service (trunked)”, and neither is government only. Segment E is base receive with channel centres at 406.1125 + n x 0.0125 MHz for n from 1 to 202. Segment M is base transmit with centres at 415.5625 + n x 0.0125 MHz over the same 202 channels. Subtract one formula from the other and the split is 9.45 MHz on every channel of the pair, with the base transmitting high.

So the order is a receive band covering 406.1 to 408.65 MHz, a transmit band covering 415.56 to 418.10 MHz, and a 9.45 MHz duplex spacing. The 3.5 MHz filter bandwidth on the UHF versions is comfortable for it: segment E is 2.54 MHz wide and segment M is 2.53 MHz wide, so one filter passband covers an entire trunked segment and the assignment can move within it later without new hardware. In the VHF high band the 1 MHz filter bandwidth covers only a third of the 3 MHz trunked segments, so there the filter has to be tuned to the part of the segment you are assigned.

One detail at the bottom of segment E. It begins at 406.1 MHz, and the 100 kHz immediately below it is the mobile satellite service band used for distress beacons and EPIRBs, protected under ITU footnote 267. Your mobiles transmit in segment E. A fleet transmitting a few tens of kilohertz above an international distress band raises a spurious emission question that will be asked, and should be, so keep the low channels of segment E in reserve rather than opening on them.

Where the other versions sit

The two rows worth flagging to anyone taking a European quote at face value are 380 to 400 MHz and 350 to 370 MHz. The first is the band almost every European public safety TETRA network runs on, so it is the version a European integrator will offer by default, and footnote AUS101 designates it principally for defence and national security. The second sits inside spectrum designated under AUS100 for the Australian Defence Force. Neither is a fault in the product; they are the versions built for markets whose 400 MHz band is not ours.

Channel Arrangements: What Each Mode Can Do Here

TETRA needs a 25 kHz carrier and the Australian 400 MHz plan is channelised at 12.5 kHz. Those are compatible, through a rule worth knowing.

RALI MS22 provides for land mobile at “6.25/12.5/25 kHz channelling” and builds the 25 kHz channel from the 12.5 kHz raster: “for the land mobile service, two 12.5 kHz channels may be aggregated if required. In HDAs and MDAs, the aggregation scheme is channels 1 and 2, 3 and 4, et cetera.” So a TETRA carrier centre is not free to sit wherever the synthesiser can tune it. It sits on an aggregated pair from the published raster.

There is also an efficiency test, and it is where the four technology modes stop being equivalent. MS22 permits a channel wider than 12.5 kHz within 100 km of high and medium density areas “only for systems carrying two or more circuits through a 25 kHz channel, that is, systems that achieve spectrum efficiencies equal to or better than one communications channel per 12.5 kHz”.

• TETRA puts four slots in a 25 kHz carrier, one circuit per 6.25 kHz. It passes comfortably and is permitted in any area.
• DMR Tier III on 12.5 kHz does not engage the rule.
• Analogue FM on 25 kHz is the single circuit case the rule prohibits in and near high and medium density areas. The BS422 supports 12.5 kHz analogue, so run it there. On a remote mine this does not arise.
• TEDS above 25 kHz has no land mobile channelling in the plan. The BS422 offers TEDS at 25, 50, 100 and 150 kHz, and MS22’s narrowband land mobile provisions stop at 25 kHz; its wideband arrangements at 150 to 750 kHz are for the fixed service. An exception is possible but MS22 requires it to be “accompanied by evidence to support the request” and decided case by case. Treat wideband TEDS as a regulatory project rather than a configuration option.

For a remote mining operation, which is where the BS422 is strongest, all four modes are available. The constraints above bite in and around the capitals.

Powering It

The BS422 takes −48 VDC SELV natively, or Power over Ethernet, so a telecommunications DC plant reaches it with no inverter in the chain. Power over Ethernet caps at 90 W with the transmit power limited accordingly, which puts it near the single carrier 10 W TETRA case, so it suits a repeater node rather than a main site.

Sizing a solar plant, with assumptions stated so you can change them: 3.5 peak sun hours as a conservative winter figure for southern Australia, 70% end to end efficiency covering soiling, temperature derating, the controller and battery round trip, three days of autonomy at 50% depth of discharge on a 48 V battery, BS422 load only.

Two things to be careful with here. DAMM’s published consumption table is stated at VHF, 160 MHz, so confirm the figure for the band you are ordering before the array is quoted. And the product sheet prints two consumption tables under the same heading with slightly different multi-carrier values, which is why the four carrier row above is a range rather than a number. The single carrier figures are consistent across both tables and match the brochure.

Read the power settings alongside the link balance table. Going from 10 W to 25 W is 3.98 dB of transmit power for 58% more array and battery, and on a site with receive diversity that 4 dB lands on the direction that was already the strong one. Mast top mounting delivers more than that, in both directions, for nothing. Size the plant in the BESS and Solar Designer once the configuration is settled.

The cable between the SB422 and the BS422

The service box can sit up to 100 m from the base station, and it feeds it at 56 VDC rather than 48 V. That is a deliberate choice and worth understanding, because the extra volts exist to be spent on the cable. DAMM’s own connection module terminates 2.5 mm², and at 200 W over 200 m of loop that gives:

Every row arrives comfortably inside the input range, so the volt drop is not the problem it first appears to be. The 56 V output has already solved it.

The loss is the problem, and only on a solar site. On mains it is 17.6 W of nuisance heat. On solar it is generation: 17.6 W continuous is 0.42 kWh a day, which is another 172 W of array bought to warm a cable. On a DC plant sized in the low kilowatts that is not a rounding error. Run the full 100 m only where the site actually needs the separation, and go up a size or two when it does.

Heat

The BS422 is rated for operation from −25 °C to +55 °C ambient, and separately for storage from −40 °C to +85 °C. Only the first pair matters for a working site. The unit also carries a stated maximum enclosure temperature of +85 °C as a PA protection limit, with power limiting above it, so the throttling behaviour is a documented design feature rather than a guess.

Australia’s highest recorded shade temperature is 50.7 °C, set at Oodnadatta in South Australia in January 1960 and equalled at Onslow in Western Australia on 13 January 2022. Shade maxima in the mid to high forties are an ordinary summer in the Pilbara, on the Nullarbor and through much of inland Queensland, which is where these systems get built.

The +55 °C rating is an ambient rating. An IP65 enclosure has no ventilation by definition, so it sheds heat through its skin, and mast top mounting puts it in full sun with nothing shading it while it dissipates up to 200 W of its own. On a 45 °C day the enclosure can be outside its operating rating while the weather station reports ten degrees of margin. DAMM’s own note that multi-carrier consumption may be limited by heat dissipation points the same way.

That does not make the BS422 unsuitable for hot country. It makes a sun shield a design item rather than an accessory: a separate shade panel with an air gap, mounted so it does not trap heat between itself and the box, and an orientation on the mast that puts the structure between the unit and the afternoon sun.

The failure mode is worth knowing because it is not a dead radio. Equipment near the top of its rating limits power, in the afternoon, which means the fault is temperature correlated and will not reproduce when the technician gets there in the morning.

Frequency Sharing: What It Buys, and What It Does Not

Frequency sharing lets adjacent BS422s run the same frequencies, and DAMM’s illustration is covering a railway line with two frequency pairs instead of a typical five. For a mine with a pit, a borefield, a haul road and a portal, the same logic applies and the benefit is real: fewer distinct frequencies to find, fewer frequency assignment certificates, and less coordination work under RALI LM8. In congested spectrum it can be the difference between a workable plan and no plan.

The one claim that does not transfer to Australia is the licence cost. DAMM’s brochure lists reducing frequency licence costs as a benefit, and the Australian fee model does not work that way. The fee schedule defines the unit of charge as follows: “Each spectrum access specifies the allowable bandwidth, frequency, geographical site and power of the transmission. All transmit spectrum accesses are chargeable spectrum accesses.” The site is part of the definition, so five sites sharing two pairs is still five sites of transmitters.

Work a five site corridor both ways and the numbers are identical. Figures are computed from the ACMA apparatus licence fee schedule, edition 2026-07, excluding GST, applying two chargeable transmit accesses per duplex carrier, one for the base and one for the mobiles:

Five distinct pairs or two shared pairs, that table does not move. What does move it is the density area, and for a mine that is the good news:

Four TETRA carriers cost $32,999 a year in a high density area and $350 in a remote one, because the rate for 403 to 520 MHz in a remote area is zero and the tax falls to the $43.75 minimum per access. TETRA’s 25 kHz carrier is taxed at twice the DMR rate in a city and the same as DMR in the bush, so the capacity advantage of TETRA’s four slot carrier is effectively free on a remote mine.

One trap worth naming, because the four carrier configuration invites it. Land mobile system licences are eligible for a low power discount of 90% and a micro power discount of 95%, and a 2.5 W carrier looks like it might qualify. It does not, on either test. Low power requires a radiated level of “8.3 watts EIRP or less and designed for operation within a radius of 2 kilometres”, and micro power requires 1.7 W EIRP within 200 m. A mine base station on a gain antenna covering a pit fails the EIRP test and fails the radius test, whatever the transmitter setting says.

There is also an engineering cost to frequency sharing and it is not regulatory. Adjacent sites on the same frequency is co-channel operation by design, which is a simulcast problem: overlap regions have to be managed and launch timing equalised. The BS422 gives you the timing reference through IEEE 1588 or GNSS, quoted at ±14 µs against the synchronisation source. It does not give you the overlap design, and on a corridor or a haul road that design is the job.

The Commercial Model: What the Dongle Controls

The hardware is only part of the bill of materials, and the licensing structure is where a quote grows in ways an integrator needs to anticipate. Every BS422 carries a USB dongle that gates its services, and the published ordering list shows what is metered.

A node licence, then a licence for every carrier. Carrier licences are per technology, and simulcast is a separate line from the base carrier: there are distinct part numbers for TETRA and TETRA Simulcast, for DMR Tier 3 and DMR Tier 3 Simulcast, and for analogue and analogue simulcast. TEDS is licensed by bandwidth, with separate 25, 50, 100 and 150 kHz items. That matters for the underground repeater chain in particular, because every repeater carrier down the decline is a simulcast licence rather than a plain one.

Subscribers, profiles and organisations are tiered.

Read the organisations column, not just the subscriber count. The 350 radio mine in the example above fits inside Medium on numbers alone, but Medium is a single organisation. A site running the owner’s fleet alongside contractors, a drill and blast crew and an emergency service that each need their own fleetmap and their own administration is a multi-organisation deployment, and that steps up to Large even though the radio count has not changed. On a mine, where contractor fleets come and go with the work, that is the tier decision that gets made wrong.

Gateways and encryption are licensed separately again. The list includes a packet data gateway, an application gateway including one port, a terminal gateway, a voice gateway including one voice stream, dynamic subscriber assignment, and air interface encryption as AIE Class 3 and TEA2, both per node. If the design connects to a PABX, a SCADA head end or a dispatch application, those are line items rather than included functions, and the voice gateway is licensed per stream.

TEA2 deserves an early question rather than a late one. It is a restricted TETRA algorithm and its availability depends on the customer and the jurisdiction, so establish whether it can be supplied to an Australian industrial operator before it appears in a security specification.

The redeeming feature is that the dongle limits are lifted remotely by running a file supplied by DAMM, with no large software distribution across the network. A capacity or feature upgrade on a site four hours from town is an email rather than a truck.

Compliance

The BS422 is certified against European standards: EN 300 394-1 for TETRA, EN 300 113 for DMR, EN 300 086 for analogue, EN 303 039 for multi-channel, and EN 50121-4 for railway environments, which is useful where a mine has rail.

The Australian equipment standards for land mobile are AS/NZS 4295 (2015) for analogue speech angle modulated equipment and AS/NZS 4768.3 (2018) for digital radio equipment, both covering 29.7 MHz to 1 GHz. RALI LM8 lists both, and describes AS/NZS 4768.3 as a voluntary standard. More usefully, LM8 states that the parameters of both Australian standards “are subsumed by those standards referenced above”, the ETSI standards being EN 300 392-2, EN 300 113-1 and EN 300 086-1. Those are the standards the BS422 is built to, which is a good starting position rather than a problem. LM8 gives two examples of Australian specific parameters that the ETSI standards do not carry: the extension of the frequency range from 470 MHz to 520 MHz, and maximum power limits.

None of that is the supply obligation. Supplying a radiocommunications transmitter in Australia runs through the Radiocommunications Equipment (General) Rules 2021, which set obligations against the general standards, the EMC standard and the EME standard, marked with the RCM under a supplier declaration backed by records. It is not a type approval the manufacturer holds on your behalf. Establish before the order who signs the declaration of conformity and who holds the compliance file.

The EME standard applies at the site rather than the box, and mast top mounting changes the assessment. The transmitter is at the antenna with no feeder loss between them, so the radiated power is higher than the same equipment would produce from a shelter, and the exclusion zone is calculated accordingly. It also puts a live transmitter at the point a rigger climbs to. Model it, document it, mark it, and settle the isolation procedure for tower work before the unit goes up. The RF EME Exposure Modeller will do the assessment.

Practical Rules

• Mount it at the mast head and count the gain. Removing 50 m of 1/2 inch feeder at 415 MHz is 6 dB of round trip system gain, more than the difference between the 10 W and 25 W settings, for no DC power.
• Read the power column next to the carrier count. Four carriers is 2.5 W each, 10 dB down on a single carrier at 25 W. Capacity comes from adding boxes; power per carrier comes from using fewer carriers in each box.
• Buy the second antenna before the higher power setting. Six decibels of receive diversity costs nothing to run and lands on the uplink, which is the direction that is short.
• Coordinate the carriers as a block, not as separate channels. They share a 150 kHz window, which is twelve consecutive 12.5 kHz channels, and four TETRA carriers need eight of them clear.
• Ask DAMM directly for the current version list. The 2022 ordering codes have no Australian 400 MHz pairing, the newer brochure hints at one, and there is a 2024 revision neither this article nor most resellers have. Specify receive in segment E, transmit in segment M and 9.45 MHz spacing, and find out whether that is a stock item or a special build before it goes in a schedule of rates.
• The VHF versions and the 450 to 470 MHz version are catalogue matches. Their standard 2.5, 4.6 and 10 MHz spacings are exactly what MS42 and MS22 require.
• Ask how antennas are shared beyond two units. Two units cross connect through the A-OUT port and need only two antennas. Four and eight are not documented, and the answer is the difference between a two antenna mast and a sixteen antenna one.
• Count service boxes, not just base stations. One SB422 runs two BS422s, a redundant pair runs four, so an eight unit node is four service boxes. Two units at full DMR power exceed the 7 A output of one box.
• Price the licences, not just the hardware. Carriers, simulcast, subscriber tier, organisations, gateways and encryption are all separate line items on the dongle, and the organisation count is the one that catches multi-contractor sites.
• Check the transmit direction, not just the split. The Australian VHF high band trunked pair transmits on the low side, as does most of 470 to 500 MHz. European practice is the other way.
• Size the power plant on the band you are ordering. The published consumption table is stated at VHF 160 MHz.
• Treat +55 °C as an ambient rating and shade the box. A sealed enclosure at the top of a mast in full Australian sun is not at air temperature, and the unit limits power above +85 °C enclosure temperature.
• Do not assume the low power licence discount. It needs 8.3 W EIRP or less and a design radius under 2 km, which a mine base station will not meet.
• Underground, get the drive attenuation from a model or a survey. A factor of four in that assumption is a factor of four in the number of units.

Frequently Asked Questions

What makes the BS422 different from a conventional base station? Two things. It is a complete base station with an integrated controller in a 12 kg IP65 box designed to mount at the top of the mast beside the antennas, which removes the feeder and about 6 dB of round trip loss at 415 MHz on a 50 m run. And it is software defined across four technologies, so one unit can carry TETRA, DMR Tier III, TEDS and analogue carriers at the same time without gateways between them.

How many carriers, and at what power? One to four per unit, sharing one amplifier, so the output per carrier falls as you add them: 25 W at one carrier, 10 W each at two, 4.4 W each at three and 2.5 W each at four. Up to eight units connect at one site. DAMM’s own node examples are eight single carrier units at 25 W giving 31 traffic channels, or a two carrier configuration at 10 W giving 63.

How much traffic does that carry? Four carriers is fifteen traffic slots and 8.11 Erlangs at 1% blocking. Thirty one traffic channels is 21.19 Erlangs and sixty three is 49.69 Erlangs, both at 1%.

Can it be used underground? Yes, in metalliferous hard rock. The same hardware runs as a repeater slave, up to 10 to a BS422 master or 50 with a server, and frequency sharing means an underground repeater chain can be built without optical fibres between the units. For long single declines radiating cable is usually still cheaper per metre; the BS422 wins where the mine is a network of levels, chambers and accesses and where you want one management system and one set of spares for surface and underground. Its published approvals include no explosion protected certification, so underground coal needs the unit outside the hazardous zone or in certified housing.

Which BS422 version should I order for Australia? For VHF, the catalogue 68 to 87.5 MHz or 146 to 174 MHz versions, whose standard 2.5 MHz and 4.6 MHz spacings match RALI MS42 exactly. For 450 to 470 MHz, the catalogue 450 to 460 / 460 to 470 MHz version, which matches RALI MS22 exactly. For the Australian 400 MHz band, a version receiving in segment E, transmitting in segment M and spaced at 9.45 MHz. The 2022 ordering list has nothing that fits, so confirm with DAMM whether that is now a catalogue item or a special build.

How many antennas does a multi-unit site need? One unit with diversity needs two. Two units with diversity still need two, because each takes its second receive branch from its partner’s antenna through the A-OUT cross connection. Four and eight unit arrangements are not covered in the published material, so ask before designing a high capacity site.

What is licensed separately from the hardware? The RF node, each carrier by technology, simulcast as a separate item from the plain carrier, the TEDS bandwidth, the subscriber tier, the number of organisations, the packet data, application, terminal and voice gateways, and the AIE Class 3 and TEA2 encryption. Limits are lifted remotely by a file from DAMM, so upgrades do not need a site visit.

Why not the 380 to 400 MHz TETRA version? Because in Australia that band carries footnote AUS101, designating it principally for defence and national security, with the Department of Defence normally consulted about non-defence use. It is the standard European public safety TETRA band, which is why it is the version most likely to be quoted by default.

Which sensitivity figure should I put in a link budget? The dynamic figure for the configuration you are building: −118 dBm with dual receive diversity, −112 dBm without. The static figures, −124 dBm with diversity and −121 dBm without, are bench measurements with no multipath and will overstate coverage. Never set a static figure from one vendor against a dynamic figure from another.

How much power does the site draw? 95 W for one carrier at 10 W TETRA, 150 W for one at 25 W, 200 W for one at 50 W DMR or analogue, and 90 to 115 W for four carriers at 2.5 W each. Idle is 20 W. Those figures are published at VHF 160 MHz, so confirm them for your band.

Does frequency sharing reduce my ACMA licence fees? No. The fee schedule charges per transmit spectrum access, and an access is defined by bandwidth, frequency, geographical site and power. Five sites sharing two pairs is the same number of chargeable accesses as five sites on five pairs. Frequency sharing reduces the number of distinct frequencies to find and coordinate, which is worth a great deal in congested spectrum, but it is not a saving on the annual tax.

Can TETRA’s 25 kHz carrier be assigned in the Australian 400 MHz band? Yes. RALI MS22 provides for 25 kHz channelling by aggregating two 12.5 kHz channels on a prescribed scheme, and permits channels wider than 12.5 kHz anywhere for systems carrying two or more circuits in 25 kHz. TETRA carries four, so it qualifies in any area. Analogue FM on 25 kHz carries one and does not, which restricts that mode in and near high and medium density areas but not on a remote mine.

Work the Numbers for Your Own Site

Every figure in this review was computed rather than estimated, and the same tools will do it for your configuration.

The LMR Trunked System Planner builds offered traffic from your talkgroups, sizes the channel pool against an Erlang B or Erlang C target, and maps the result onto real carriers and paired spectrum across a multi site network, which is the calculation behind the carrier and fleet tables above. The Frequency Coordination Tool runs the interference analysis against nearby licences, and it is the right place to test whether the carriers will fit inside one 150 kHz window at your site. The Coverage Predictor handles the surface coverage with your own terrain and fade margin, and the Leaky Feeder 3D Coverage tool handles the underground geometry that decides how many units go down the decline.

Related reading: P25 vs DMR vs TETRA for the technology choice and the carrier arithmetic behind it, Designing Leaky Feeder Coverage for Underground Mines for the alternative underground, How Much Does a Radio Licence Cost in Australia? for the full fee calculation, and What Is Erlang? for the traffic sizing.

If you are specifying a BS422 network and want the band, duplex, coordination, coverage and power plant settled before the purchase order, that is work we do as an ACMA accredited person.

Notes on Sources

• Headline specifications are from the DAMM MultiTech Outdoor Base Station BS422 brochure, version 3.7, dated 15 July 2022: dimensions, weight, wind area, temperature ratings, IP65 encapsulation, the 100 m SB422 separation, the SB422 ratings, synchronisation options, the standards list, and the frequency sharing and geo-redundancy claims.
• Detailed specifications are from the DAMM MultiTech Outdoor Base Station BS422 product sheet, document D105201-REF_BS422 Rev. 1.00, dated 19 January 2022, published in German: the ordering codes and their receive and transmit sub-bands, duplex spacings and filter bandwidths, the 150 kHz carrier window, the full sensitivity set, noise figure and IP3, the 6.25 kHz synthesiser step, output power ranges, the output power and consumption table, idle power, the +85 °C PA protection limit, PoE, connector list, per slot data rates, the eight units per node figure, repeater and simulcast limits, and the Windows 10 IoT platform and dongle licensing.
• The two documents disagree on the frequency versions. The brochure lists nine ranges; the product sheet describes seven standard versions and its ordering list carries eight codes, the eighth being an on-request pairing. The brochure also lists ranges (216 to 225 MHz, 406 to 430 MHz and a 430 to 450 MHz DMR variant) that do not appear in the product sheet’s ordering codes. The brochure is the newer of the two by six months, so the ordering codes are treated here as evidence of how the product is structured rather than as a current catalogue. DAMM has published at least one later revision, an outdoor system flyer version 4.0 dated 3 May 2024, which could not be retrieved for this article. Get the current version list from DAMM before relying on the frequency tables here.
• SB422 specifications are from the DAMM Service Box SB422 product sheet, document D10535001-REF Rev. 1.1, dated 22 May 2022: the 450 W maximum and 46 W idle consumption, the 56 VDC and 7 A output to base stations, the 100 to 240 VAC and −48 VDC input, support for two BS422 or two BS421 but not a mixture, the redundant configuration raising the limit to four base stations, the Category 6A requirement beyond 55 m, the alarm inputs for power reduction and base station idle, dimensions, weights and temperature ranges. Note that a German reseller’s ordering line describes the SB422 with a 200 W supply; DAMM’s own sheet states the figures used here.
• The antenna cross connection between paired units is described in DAMM’s BS422 installation and setup guideline, which lists the jumpers for a dual installation as two for TX/RX, two for GPS and two for RX-B and A-OUT between the base stations. That document could not be retrieved directly for this article and the description is taken second hand, so verify it against the installation guide for the revision you are supplied. Arrangements for more than two units were not found in any published source.
• The output power and consumption figures are published for VHF at 160 MHz. The product sheet prints two such tables under the same heading with differing multi-carrier values; single carrier values agree across both and match the brochure, and multi-carrier figures are given here as a range.
• Australian allocations are from the Australian Radiofrequency Spectrum Plan (2025 Update) 2021, Compilation No. 1, compilation date 9 October 2025. Footnote AUS100 designates its bands “for use by the Australian Defence Force and Department of Defence”; AUS101 designates its bands “principally for the purposes of defence and national security”; AUS91 limits the mobile service in its band “to Australian, State and Territory Government purposes”.
• The 400 MHz band plan is RALI MS22, January 2020, approved 17 January 2020. Segment limits, channel centre frequency formulas, the trunked allocation of segments E and M, the 25 kHz aggregation scheme, the efficiency rule and the exceptions process are quoted from it. Every duplex split in this article was computed from its channel centre frequency formulas rather than segment edges, and comes out exact: 9.45 MHz across 403 to 420 MHz, 10.0 MHz across 450 to 470 MHz and 5.2 MHz across 470 to 500 MHz.
• The VHF band plans are RALI MS42, approved 18 August 2016, covering 70 to 87.5 MHz and 148 to 174 MHz. The 2.5 MHz and 4.6 MHz splits and the per segment transmit directions were computed the same way from its Table 1 and Table 2.
• The embargo on 452.5 to 457.5 MHz and 462 to 467.5 MHz is described in RALI MS22 Appendix B, which records embargoes “Australia-wide on all new assignments” in those ranges other than for existing users transitioning out of 403 to 420 MHz. Check the current position before planning around it.
• Australian equipment standards are as listed in RALI LM8, May 2024 update: “AS/NZS 4295 (2015): Analog speech (angle modulated) equipment operating in land mobile and fixed services bands in the range 29.7 MHz to 1 GHz” and “AS/NZS 4768.3 (2018): Digital radio equipment operating in land mobile and fixed services bands in the range 29.7 MHz to 1 GHz”. The statement that their parameters are subsumed by the referenced ETSI standards is LM8’s own. Whether either is an applicable standard under the Equipment Rules for a given device is a question for the supplier, and was not verified against Schedule 5 for this article.
• Licence figures were computed from the ACMA apparatus licence fee schedule, edition 2026-07, and exclude GST, applying two chargeable transmit spectrum accesses per duplex carrier on an ordinary Division 4 land mobile system licence. The low power and micro power definitions of “8.3 watts EIRP or less and designed for operation within a radius of 2 kilometres” and 1.7 W EIRP within 200 m are quoted from the same schedule. These are calculations from published rates rather than a quote, and the ACMA’s assessment of an individual licence is the authoritative one.
• Feeder loss was computed as K1 x √f + K2 x f from the coefficients in our own cable data for CommScope LDF4-50A, LDF5-50A and LDF7-50A, on a 50 m run with 0.5 dB for jumpers and connectors. The formula reproduces CommScope’s published attenuation figures for those cables to three significant figures.
• Portable receiver figures are from the Motorola Solutions MXP660 data sheet: receiver static sensitivity −116 dBm guaranteed and −118 dBm typical, receiver dynamic sensitivity −107 dBm guaranteed and −109 dBm typical, transmitter classes 3 (2.8 W), 3L (1.8 W) and 4 (1 W), frequency bands 350 to 470 MHz. It is used as a representative TETRA portable rather than a class minimum.
• Erlang figures are Erlang B for the slot counts stated, validated against published tables, with the traffic model that goes with it: calls arriving at random and blocked calls cleared rather than queued. Fleet loadings of 0.015 to 0.03 Erlangs per radio are planning assumptions, not measurements.
• The underground reach table is a first order budget from the terms shown, with a 30 dB allowance for near field coupling and junction losses. It is presented to show the sensitivity to drive attenuation, not as a design. Real declines sit at the pessimistic end and the design figure must come from a survey or a 3D model.
• Temperature records are the Bureau of Meteorology figures of 50.7 °C at Oodnadatta, South Australia in January 1960 and at Onslow, Western Australia on 13 January 2022.
• Solar, battery and volt drop figures are computed from the assumptions stated alongside each table, with copper resistivity taken as 0.0172 Ω·mm²/m at 20 °C. The volt drop table is computed at the SB422’s stated 56 VDC output rather than a nominal 48 V, which is what makes the drop tolerable on small conductors.
• Licensing structure is from the ordering list in the BS422 product sheet: node and per carrier licences, simulcast as separate items, TEDS by bandwidth, the six subscriber tiers with their profile and organisation limits, the packet data, application, terminal and voice gateway licences, dynamic subscriber assignment, and AIE Class 3 and TEA2 per node. No prices are published and none are implied here. The observation about TEA2 availability is a question to put to the supplier, not a statement about DAMM’s export position.
• No deployment claims are made in this article. DAMM publishes mining sector material describing its systems in general terms; specific mine names that appear alongside vendor pages on trade websites are those sites’ own project directories and are not customer references.

Band plans, fee schedules and equipment specifications are all revised. Check the current edition of each before relying on a figure here for a design or a purchase order.