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Articles on RF Engineering
Every noIM₃ article on RF Engineering, newest first. Written by engineers, for engineers.
● 26 articles Page 1 of 5
RF Engineering FDMA vs TDMA Underground: Why Amplifier Group Delay Favours FDMA on Leaky Feeder and DAS Cascades On the surface, TDMA wins the spectrum argument: two calls on one 12.5 kHz carrier for DMR and P25 Phase 2, four on 25 kHz for TETRA. Underground, every signal reaches the radio through a cascade of cable, line amplifiers, repeaters and sometimes fibre, and every one of those elements delays it. FDMA has no slot clock and no guard time, so that delay costs it almost nothing. TDMA carries an inbound timing allowance of 1 ms for DMR and 389 µs for TETRA, and the delay tolerance where two copies of a signal meet scales with the symbol period, which is longest for the FDMA standards in common use. This article works the three delay questions with the numbers the ETSI and TIA material actually publishes, shows why a channelised amplifier at 12.5 kHz adds the delay of 16 km of cable in a single pass, and sets out the cases where TDMA underground is comfortable and the cases where it is not. 
RF Engineering 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 one 12 kg IP65 box, and it is built to sit at the top of the mast beside the antennas instead of in a shelter at the bottom. Removing the feeder is worth about 6 dB of round trip system gain at 415 MHz on a 50 m run, and the same enclosure works as a base station or as a repeater slave, which is what makes a single network across an open pit and a decline practical without fibre underground. The four carriers are not four full power carriers, though, and the 400 MHz version on DAMM's published ordering list does not fit the Australian band plan. This review works the capability against a surface and underground mine, sizes the carriers and the traffic, quantifies the mast top and receive diversity gains, and sets out the band, duplex, power and compliance decisions that have to be settled before the purchase order goes out. 
RF Engineering Duplexer, Cavity Filter, Combiner or Multicoupler? What Each One Actually Does Four devices sit between a radio and a shared antenna, they look similar in a rack, and buying the wrong one is expensive. This guide explains what each actually does: why filter selection is decided by fractional separation rather than the gap in megahertz, why a duplexer's rejection comes overwhelmingly from a tuned transmission null rather than from its filter skirt, why a hybrid combiner throws away three quarters of your transmit power on four channels while a cavity combiner costs a fraction of a decibel, and why fitting a receive multicoupler can leave a receiver deafer than connecting it straight to the antenna. Includes measured figures from five duplexer legs, catalogue data from 441 real parts, practical selection rules and an FAQ. 
RF Engineering P25 vs DMR vs TETRA: Which Digital Radio Standard Should You Actually Choose? On the nominal air interface calculation, P25 Phase 2, DMR Tier III and TETRA all land on one voice path per 6.25 kHz of carrier bandwidth. What actually separates them is how those voice paths land on whole RF carriers, and that decides how many transmitters you combine, how many transmit frequencies you licence, and what the ACMA charges you every year. This guide works the carrier and spectrum maths for each standard, prices the annual licence tax that follows from the choice under a clearly stated duplex access model, explains why a high density site and a remote site favour different technologies, sets out what Australia actually runs and where, and shows why receiver sensitivity figures cannot be compared across the three datasheets. 
RF Engineering How Much Antenna Separation Do You Need? Put two radio systems on one tower and the transmitter on one antenna can deafen the receiver on the next. The real question is not distance but isolation, measured in decibels. This guide opens with a worked rooftop example, then explains the three ways co-located antennas interfere, how to turn a receiver's tolerance into a required isolation figure, and how vertical and horizontal separation deliver it. It uses the ITU-R M.2244 formulas, shows why stacking beats side-by-side spacing, and is clear about where the formulas stop being trustworthy and measurement has to take over. 
RF Engineering What Is Noise Figure? Cascade Noise, the Friis Formula and Where to Put the LNA Noise figure is how many decibels of noise a stage adds on top of a perfect receiver, and in a chain those figures do not add. The Friis cascade formula divides every later stage by the gain ahead of it, which is why the first stage sets the system noise figure and why a lossy feeder run in front of the amplifier is the most expensive mistake on the tower. This guide covers noise figure, noise factor and noise temperature, the cascade formula, why passive loss equals noise figure decibel for decibel, a worked four stage chain that gains 2.9 dB purely by moving the LNA, how much gain is enough, the dynamic range you pay for it, Y factor measurement, and when chasing a lower noise figure buys you nothing at all.