This excellent and comprehensive presentation explored the aims and objectives of military communications, the hierarchy of army command, the different corps, what they do and what sort of communications they need. Also the often-conflicting requirements of speed, security, operational range, HF, VHF and UHF coverage and the physical/environmental requirements of the radios. In addition we were treated to asides and comments from The Crimea War, and the Inns of Court Regiment and its history dating back to the late 16th century.
The presentation was supported by a selection of radios that Michael had brought along. These included receivers, transceivers and panoramic displays, many of which are included in the following list.
G8MOB’s NOTES ON EQUIPMENT DISPLAYED
HF Receiving
Racal RA3701
Quite extensively used by the military for monitoring and point-to-point links with data systems eg Piccolo. Fully modular with numerous options.
Coverage: 15 kHz to 30 MHz.
Modes: AM, CW, USB, LSB and NBFM, [options for ISB and FSK].
IFs: 41.4 MHz and 1.4 MHz.
IP3: At 20 kHz spacings, +33dBm RF amp out and +25 RF amp in.
1st mixer is a Rafuse type switching quad FETs. 2nd is an IC.
Image and IF rejection better than 90dB (better in fact).
IF Filters: 6, 3, 2.7 U & L SSB, 1kHz and 300Hz. Options for more.
Can be remotely controlled by computer or external Racal controller unit.
One version has two receivers built in (RA3712) and is used in diversity data systems.
Various Racal-Dana frequency standards can be fitted or input from an external source (eg Rb).
Now superseded by the identically looking RA3791 with extensive DSP.
STC STR 8282
Covers 150 kHz to 40 MHz.
IFs: 70.050 MHz and 50 kHz (DSP at 50 kHz).
Modes: AM, CW, USB, LSB, ISB and NBFM.
Measured IP3 at 20 kHz spacing: +23dBm approx.
Measured Ist IF and image rejection: over 100dB.
Measured 2nd image rejection: approx 116dB.
13 bandwidths from 300Hz to 15 kHz.
IF selectivity is excellent. Some specs:
Mode -3dB kHz -100dB kHz
SSB 2.7 4.5 max
CW 0.3 1.5 max
AM/ISB 6 10.0 max
FM 15 25 max
Ultimate IF stop band is > 100dB in all cases. Exceptionally low differential phase distortion in the filters giving a true linear phase response (v important for fast data).
An early DSP receiver (1990s). ADC chip sourced from Tektronics. Very complicated DSP done the hard way.
1st mixer is a Rafuse switched DB quad FET (IC is a Siliconix Si8901Y)
2nd mixer is a most complicated image rejection design using two Si8901Y ICs followed by a complex polyphase network.
Usual provision for computer control and external frequency reference.
DSP output options: In phase and quadrature filtered baseband signals.
However don’t try to find one. Only about 150 – 200 made before STC taken over by Nortel and production stopped to make way for building phone systems. Additionally, there are reliability problems and spares are impossible to source. The fan noise will drive you mad in a quiet room. Most were taken by the “Government listeners”.
HF Transceiver
Philips / MEL PRC 2000
A nifty transceiver of the 1980s using Weaver’s third method of generating SSB. Covers 1.6 to 30 MHz. 20W PEP output. Built in auto ATU and a separate dipole outlet. Has effective voice compression/clipping. Runs off a 15V NiCad.
Can be fitted into vehicles with a mounting tray and external power source.
Not bought much by HMG (since we already had Clansman) but many sales abroad to third world countries.
Has a matching linear amp and auto ATU.
MEL SURF (“Selector Unit RF”)
Used with Clansman VRC321 HF SSB vehicular transceiver as a passive pre and post selector when two 321s have to be used in the same vehicle [eg at a HQ for a squadron/combat team net and the QM’s resupply net].
Spec when fitted to each VRC321:
“Less than 3dB reduction in S/N ratio with a 40W HF transmitter 15% off frequency in the same vehicle with 2 metres antenna separation”. [Ie a whip either side of eg a LandRover].
Approx 0.75dB loss on transmit and receive.
VHF receiving
Nems-Clarke 1303
1960s vintage, all valved. 24 valves.
Tunes 55 to 260 MHz in a single band using the American-made Mallory “Inductuner”
Modes AM and FM
F/E valve is a tiny ceramic planar triode for minimum noise. Measured the average noise figure at about 3.8dB. This compares with the latest Watkins-Johnson 8611 with a spec of 7 to 11dB. Front end module is of silver-plated brass. Each bandwidth has its own IF strip.
Separate meters for signal strength and centre tuning. (These are expensive products made by Honeywell)
Gives exceptionally low demodulated distortion. Had great difficulty in measuring the distortion on WB – well below 1% THD.
Used extensively by US Govt agencies, particularly NASA for telemetry for the Mercury and Apollo missions.
Factory price: $2,700 in 1963.
Several other versions made, some with two tuners fitted.
Has an optional add on panoramic adaptor but is exceptionally rare.
Norlin SR209-C EW receiver
Transistorised receiver of the late 1960s/1970s used primarily by US Govt bodies. Used in USN submarines.
Separate plug-in tuners cover 30 MHz to 12 GHz (I have four which cover 30 MHz to 1,000 MHz). Frequency display on a long film scale.
Modes: AM, CW, NBFM and WBFM
Many choices of bandwith from 10 kHz to 4 MHz; each comes on a PCB containing the entire IF strip and demodulator.
Separate meters for signal strength and centre zero tuning.
Modules for panoramic display and a digital display with DAFC (a “huff & puff” system).
Very similar to the WJ8730 series (using v similar plug-in tuners and the same Mallory Inductuner). Both factories in Gaithersburg, Maryland, not far from Washington DC.
Racal MA2313E Panoramic Display
Input: 21.4 MHz.
Display span from 100 kHz to 3 MHz.
Can switch IF inputs and audio from 2 receivers.
Matches the Racal RA1795 receiver (20 to 1,000 MHz) but will match any receiver with a panoramic output (ie prior the main IF filtering) of 21.4 MHz.
Eddystone 1061A/1 Panoramic Display
Inputs: 1.4 MHz and 100 kHz (switched internally)
Display Span: 1.5 kHz to 15 kHz
RBWs: 50, 100, 250 and 500 Hz.
Switchable log or lin display with up to 40dB switched attenuation to expand the screen log display range of 40dB. Made in the 1980s and 90s but dated now.
***
It is simply not possible to do justice to Michael’s fascinating presentation, which by any standards covered an extremely wide selection of pretty specialist equipment, and we are very much indebted to him for providing such an unusually interesting and entertaining evening.
John Longhurst G3VLH
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