Incorporating G2DYM Aerials & Garex Electronics

Quality English products hand-crafted to order












News & New Products - 20 November 2018

Proprietors;- Mr A.J. Nailer HNC BA G4CFY, Mrs J.R. Nailer. 


Phone UK 01305 262250 International 0044 1305 262250

Please email or phone for a quote or for a Paypal money request or for bank details. Payment can be by direct bank transfer or by credit/debit card or via Paypal to g4cfy@talktalk.net together with a note stating product required. Purchase of several items is likely to make a saving on postage.

Orders & quote requests to  jean@spectrumcomms.co.uk

Technical queries to  g4cfy@talktalk.net 

NEWS UPDATE 15th November 2018. The re-written book 1 of Technical for the Terrified now entitled Understanding Radio has be completed and printed and is available by Paypal payment of 15.33 or bank transfer of 14.50 to my personal accounts. See further details on the spectrum Amateur and Listeners pages.  The first article of the Radio Design & Construction series about a hybrid valve/transistor 20 & 80m AM/USB/LSB receiver is now ready for purchase at a cost of 2.50 direct to my bank or 2.85 to my Paypal email address antony.nailer@talktalk.net  The first article of the Understanding Radio series about Op Amps is still available at a cost of 2.00 to my bank or 2.35 to my Paypal account.  In the future I also intend to rework the last 20 something articles of Technical for the Terrified into a book called Understanding Radio Book 3.  

The HF SWITCHED PREAMP and HF SWITCHED PREAMP have been reworked to cover the full range of 1.8-30MHz.  Quartz crystals have been re-priced at 3.00 for New, and 1.50 for Secondhand.

A new 118-400MHz PREAMPLIFIER for Scanner enthusiasts has been introduced.  It is available in a small box for external 12VDC bench supply or vehicle application and also with integral mains power supply.  See the Scanner & Listener page.

 Understanding Radio Book 1 is a re-write of the Technical for the Terrified Book 1 published by Practical Wireless and compiled from 27 articles of that name previously published in PW Magazine between February 2005 and October 2008. The first chapter is a short revision for everyone who has not used algebra since leaving secondary or grammar school.  It should also be useful to youngsters still at school and trying to get to grips with it.  The articles have been reworked into chapters so there is now a natural progression of information through the book.  All the circuits have been redone and a lot of wasted space and unnecessary comments removed.  It runs to 112 pages, which is 10 less than the T4T Book 1 but there is a lot more in it. The writing style is aimed to be easy to read and should be of great value to readers of all technical levels.  Subjects include; Algebra, Resistors & Ohm's Law, Diodes and Rectification, Transistors - FETs & Valves, Transistor biasing, Amplifier Classes of Operation, Reactance & Resonance, Parallel Tuned Circuits, Bandpass Coupled Pairs, Small Signal Bipolar RF/IF Amplifiers, Small signal FET & Mosfet RF/IF Amplifiers, Oscillators, Mixers, Decibels, Modulation Modes, TRF & Superhet, Filtering in HF & VHF Receivers, Modes & Demodulation, Choosing RF - IF & LO, Phase Locked Loops, PLL in CB & 10M rigs, Antennas & Feeders.  Price 15.33 to my personal Paypal account antony.nailer@talktalk.net or through Spectrum, 14.50 by direct transfer to my bank.

 Now to make a start on re-writing T4T Book 2 into Understanding Radio Book 2.  


NEW PRODUCTS introduced or improved during 2017


Five relay switched 5-element Elliptic Low Pass filters for use in conjunction with wideband HF linear amplifiers. The standard board has the classic bands 80, 40, 20, 15, & 10m.  160, 60, 30, 17, & 12 are also possible. Two boards can be paralleled to give a 10 band facility. The relays are high sensitivity requiring only around 15mA each for activation from a 13.5V switching voltage.  There is insignificant passband loss for each filter and ultimate attenuation 'As' is specified at either -30dB or -40dB in excess of 3 times the cutoff frequency.  A notch just below the 2nd harmonic is typically 20dB further down than at As.

PCB Kit with pre-wound toroids 64.00 UK, 69.00 World.  PCB Built 78.00 UK, 86.00 World.  Box Kit 95.00 UK, 102.50 World.  Box Built 126.50 UK, 132.50 World.



RG58CU (Webro). 50 Ohm cable with PL259 each end and heatshrink strain relief. Available in standard lengths, 0.6m 5.50, 1.2m 5.85, 1.8m 6.75, 2.4m 7.00, 10m 13.10, 20m 19.10.  All including 1st class Post Office or Hermes carriage.  Other lengths +/- 60p/m.

Mini-8 (Sharmans).  50 Ohm foam-dielectric cable, 7mm OD. With quality long PL259 each end and heatshrink strain relief. Available in standard lengths, 10m 15.10, 20m 24.60.  Both including Hermes carriage.  Other lengths +/- 75p/m.

RG213 (Sharmans). 50 Ohm cable with quality long PL259 each end and heatshrink strain relief.  Available in standard lengths, 10m 24.60, 20m 43.10, 25m 51.10.  All including Hermes carriage.  Other lengths +/- 1.60/m.



RG59U Leads. 75 Ohm solid dielectric.  BNC to BNC with either moulded end or crimped end with adhesive heatshrink strain relief. 0.3m 5.50 pair.  0.6m 6.50 pair. 1.2m 6.00 pair.  

BNC to PL259. 0.3m 6.00 pair.  0.6m 5.10.  1.2m 5.35.  Prices include 1st class post.


2 way BNC switch box.  Response from common to each way is flat within 2dB from DC to 360MHz.  Isolation between ports is 20dB at 360MHz, 27dB at 200MHz, and >30dB below 140MHz. Price, 30.00 including Hermes carriage.

3 way BNC switch box. Response from 1 or 3 to common is flat within 2dB from DC to 350MHz.  Isolation from 1 or 3 to 2 is 20dB at 350MHz, and >32dB below 80MHz.  Isolation between 1 & 3 is 30dB at 350MHz and >40dB below 120MHz. Price 32.00 including Hermes carriage.

4 way BNC switch box.  Response from 2 or 3 to common is flat within 2dB from DC to 260MHz.  Isolation between 2 & 3 is 26dB at 260MHz, and 30dB at 200MHz, 40dB at 80MHz, 46dB at 30MHz and 52dB at 10MHz.  Isolation between 2 & 4 or 1 & 3 is 30dB at 260MHz, 37dB at 150MHz, 40dB at 125MHz, 50dB at 30MHz, and 56dB at 10MHz.  Isolation between 1 & 4 is 30dB at 240MHz, 36dB at 150MHz, 48dB at 30MHz and 54dB at 10MHz.  Price 35.50 including Hermes carriage.



This handy tester allows cables with PL - PL, or BNC - BNC, or PL - BNC to be tested inner to inner, outer to outer, inner to outer, and also a single end PL or BNC inner to outer.  It should be intuitive, with a wanted connection showing the LED ON and the unwanted connection with the LED OFF.  Price 30.00 including Hermes carriage.



Supplied either as a kit of parts to build the board shown in the picture as well as a drilled and labelled box, and all associated hardware, or ready built.  It is a stand alone Morse practice oscillator or digitally keyed Morse code generator that can be fed through the microphone socket of an SSB transceiver.

The boxed kit includes 3.5mm jack sockets for Morse key, and for logic input (+5V gives a tone) from a computer, and an output to drive an extension speaker, a SPST toggle switch, volume control, LED and holder, internal loudspeaker, PP3 battery holder and the necessary nuts and screws.  The kit even includes various coloured hookup wire and four stick on feet.  The battery shown in the pictures is NOT included.

PCB & Hardware kit 33.50.  Ready Built 42.50.  Prices include carriage by Hermes.


Price 59.00 including carriage by Hermes.

The Receive SPC Aerial Tuning Unit is based on the Series Parallel Capacitor ATU configuration used for transmit matchers which prevents the circuit becoming a high pass filter with certain choices of tuning capacitors and inductances.

It will work with long or short random wire aerials or with aerials fed with coax cable.  Unlike transmitting ATU's which must be low Q to avoid loss, the receive ATU should be high Q to enhance the signal as well as making the aerial resonant on the wanted frequency.  This high Q operation also reduces both unwanted signals and unwanted noise above and below the required band.

It is provided with a single wire yellow terminal post for random wire aerials and with a single wire black terminal post for a connection to ground. Also an SO239 coax socket for a coax downlead.   Output to the receiver is via another SO239 coax socket. 

The QRP TX SPC Aerial Tuning Unit is based on the Series Parallel Capacitor ATU configuration used for transmit matchers which prevents the circuit becoming a high pass filter with certain choices of tuning capacitors and inductances.

It will work with long or short random wire aerials or with aerials fed with coax cable.  In this version the inductances are wound on toroids to provide high Q, small space, and low unwanted coupling.  Power handling will be limited by a 100V rating of the polyvaricon capacitors and the impedance of the antenna being matched.  By definition QRP means up to 10W SSB in the UK.

With a random wire antenna presenting a high impedance at the required frequency the voltage when matched can be quite high and that is the limiting factor for this and all TX ATU's.  Indeed for really high powered transmission the variable capacitors are wide airspaced with flashover ratings in excess of 2kV.

When matching to a low impedance antenna only a small amount of inductance is required to achieve the match.  Conversely with an antenna a bit short for a quarterwave (or resonant at a higher frequency than required) more inductance and less capacitance is required.



The ATU is provided with a single wire yellow terminal post for random wire aerials and with a single wire black terminal post for a connection to ground. Also an SO239 coax socket for a coax downlead.   Output to the transceiver is via another SO239 coax socket. 

Price 85.00 including Hermes carriage.


VLF CONVERTER 100Hz - 100kHz

PCB & Hardware kit 53.00.  Ready Built 72.00. Inc carriage.

This Very Low Frequency Converter operates from as low as 100Hz and up to 120kHz.  The conversion gain is; 100Hz 0dB (unity), 1kHz 0dB (unity), 10kHz 2dB, 50kHz 4dB, 100kHz 2dB, 120kHz 0dB (unity), 140kHz -10dB, 160kHz -20dB, 180kHz -30dB.

The unit contains a 4MHz crystal controlled oscillator and a diode ring mixer (to cope with strong signals found in this region).  This means the output range will be 4.000100MHz to 4.100000MHz.

At low frequencies the mixer becomes in effect a modulator so the inbound signal mixed with the carrier produces a carrier and two sidebands.  This means that the receiver can demodulate this as amplitude modulation if tuned to precisely 4MHz.

At frequencies beyond the bandwidth of the receiver IF stages the mixed signal plus the carrier can be demodulated as a single sideband or CW signal.  It may be beneficial to use a CW IF filter if one is fitted to remove unwanted noise each side of wanted signal.

The unit is powered from an alkaline PP3 9V battery (not included) and draws only 21mA.  It is housed in a plain diecast box 120x94x34mm.


The HF Tuneable Receive Preamp comprises four bandpass coupled pairs of tuned circuits that together with a variable capacitor tune 1.8-3.8MHz Band A, 3.8-7.6MHz Band B, 7.5-15.0MHz Band C and 15.0-30.0MHz Band D.  The fixed value of top coupling capacitor in conjunction with the wide variation of tuning capacitance across the bands causes the circuits to be undercoupled at the low frequency end and critically coupled at the top end.

Gain specification.
On Band A 10dB at 1.8MHz, 13dB at 2.5MHz, 15dB at 3MHz and 16dB from 3.5 to 3.8MHz. 
On Band B 10dB at 3.8MHz, 12dB at 4.5MHz, 14dB at 5MHz, 15dB at 5.5MHz and 16dB at 7.6MHz. 
On Band C 11dB at 7.5MHz, 13dB at 9MHz, 14dB at 10MHz and 16dB at 14 to 15MHz. 
On Band D 7dB at 15MHz, 10.5dB at 17MHz, 13dB at 18MHz, and 15dB from 21-30MHz.

The gain is adjustable over a wide range, mid Band A -21 to +16dB, Mid Band B -28 to +16dB, Mid Band C -40 to +16dB, and mid Band D -30 to +15dB.

Connectors are SO239 unless otherwise requested.  There is also a 2.1mm DC connector and a twin red/black power lead 0.6m long to connect to a 13.5V bench power supply.

The unit shown in the pictures is the HF Switched Preamp version that can be transmitted through with 150W. RF switching will occur reliably with power as low as 500mW.

The unit is straight through with the power off.  With the power ON the relay is activated and the preamplifier is in line.  When RF is applied the switching circuitry deactivates the relay within 30mS and when the RF is removed the circuit holds the relay off for 500mS.  This prevents relay chatter when using SSB.  There is no provision for hard PTT switching.

HF Tuneable RX Preamp, box kit 58.50, ready built 102.00.

HF Switched Preamp, box kit 72.50, ready built 123.00.  Prices include carriage by Hermes.


SC3900F Conversion board for Galaxy Saturn & relatives.

PCB kit 19.00.  PCB built 22.50, including 1st class post.

 I have at last been able to add an eprom to give the UK band on the Galaxy Saturn homebase rig that has frequency readout. The conversion includes instructions to put the correct offset for the UK band and all channels reading correctly.  It should suit other mobile rigs that use the same chassis, similar to the Superstar 3900 but which have the coding wires all in a line GND P4 P5 P6 P7 B+ P0 P1 P2 P3.

The wires corresponding to P4-P7 and P0-P3 are unsoldered from the main board and resoldered to the SC3900F.  Then two 7.5cm lengths of 4-way ribbon wire connect from the SC3900F outputs to the P4-P7 & P0-P3 positions.  The NB/ANL switch is made available and used for USA/UK switching in conjunction with band-D, the USA HI band.

In addition there are connections to the board for 0V (ground), also +8V, and +13.5V from the DC input to the main board.  Offset is provided by means of a 4k7 trimpot (provided) to pull the clarifier down on UK.

The top pictures shows the view towards the front with the board suspended from the channel ribbon wire by means of a tie-wrap.  The bottom picture shows the band-D with the NB/ANL switch ON giving 27.601MHz (except for a dodgy segment on the 0).  

Spectrum Communications was established as a part-time business by Tony Nailer G4CFY in October 1978.  In August 1981 following the legalization of CB in the UK there was sufficient work and CB sales for both Tony & wife Jean for full time employment.  CB popularity declined steadily to a very low level by about 2000 and for the following 4 years sales were almost at unsustainable levels.  Following becoming an author with PW in 2004 and developing new projects for the Doing It By Design series, sales have risen back to make us busier than ever. I became author of another PW series In 2005 titled Technical For The Terrified.

G2DYM Aerials was purchased from Richard Benham-Holman G2DYM on 30 October 2006.  Garex Electronics was purchased from Peter Longhurst G3ZVI on 1 December 2011.