Incorporating G2DYM Aerials & Garex Electronics

Quality English products hand-crafted to order












15 December 2021

Proprietor;- Mr A.J. Nailer HNC BA G4CFY. 


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@spectrumcomms.co.uk together with a note stating product required. Purchase of several items is likely to make a saving on postage. You can also obtain products by using my Ebay shop https://ebay.co.uk/str/Spectrum-Comms and pay via Paypal.

Orders & quote requests and technical to  g4cfy@talktalk.net



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 Loop; PLL in CB & 10M rigs; Antennas & Feeders.  

Understanding Radio Book 2 has been printed and I have been selling it on Ebay since early June. It is a re-write of Technical for the Terrified Book 2 including all the articles 28-49 published in PW between October 2008 and April 2013 plus article 51 published in August 2013.  The articles have been condensed into chapters and unnecessary duplication of information has been trimmed back and then the subjects further expanded.   It runs to 114 pages and the subjects include Passive components, old and new; Equivalent circuits; Variable Frequency Oscillators; Crystal Controlled Oscillators; Feedback & Amplifier Stability; Singly Balanced Mixers; Analogue Low Pass Filters; Laying out Printed Circuit Boards; Measurements and Test Jigs; Receiving 100kHz - 30Mhz; Superhet Receivers; AGC of RF & IF Stages; Superhet with Tuneable IF; Coax & Twin Feeder; SWR/PWR Meters & the Noise Bridge; Aerial Impedance - Bandwidth & Gain; Aerials for Receive & Transmit; ATU's for Receive & Transmit.

To buy either books on its own including postage pay £17.00 to my personal Paypal account antony.nailer@talktalk.netor through Spectrum, or by direct transfer to my bank.

To buy both books together pat £32.00 to my personal Paypal account antony.nailer@talktalk.net or through spectrum, or direct transfer to my bank.


Stable VFO RX 9MHz IF Amplifier with AGC Receiver, single band
RX Front-end Filters, 5 & 10 band SSB Detector & CIO 9 or 10.7MHz Regen Receiver, four band
RX Mixer & Dual Front-end BP Filters SSB Detector & CIO 455kHz Piptone PT1000S
SSB IF Filter 6-Pole, 9 or 10.7MHz Audio 500mW Amplifier Kaytone KT2000
CW IF Filter, 5 pole 9MHz Super Sudden by G3TEX & G4CFY  


STABLE VFO, a rock stable FET VFO for 6.995 - 7.205MHz for a direct conversion for the extended 40 metre band, or 5.0-5.5MHz for 20m and 80m rigs with a 9MHz IF. The board includes upper band edge adjustment.  The Buffer type 2A, mounted on the top of the box, delivers 1.6V p-p into 50 Ohm with second harmonic 40dB down. Drilled Box and PCB kit with potentiometer £28.00 UK.  State required frequency when ordering. 


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Triple bandpass coupled receive filters.  DC diode switched with 5 bands to a board.  Kit 5A 80/40/20,15, & 10m.  Kit 5B 160/60,30/17/& 12m.  Insertion loss below 5dB on all bands. Switching DC resistance 1k Ohms, draws 8mA from 8V or 12mA from 12V.  Two boards can be interconnected for 10-way band switching.   board size 92 x 84 x 15mm.  

One PCB 5-band kit of parts £44.40 UK, £51.40 EU, £52.60 World.   

Two PCB 10-band kit of parts, £88.20 UK, £94.00 EU, £99.60 World.


RECEIVE MIXER & DUAL BAND PASS FILTER.  The board includes diode switched triple Butterworth bandpass filters normally supplied as 80 & 20m but can be any combination of the HF amateur bands to suit the constructor.  The filter feeds into a push-pull FET high level mixer with an untuned input and a tuned output at 9MHz (though 10.7MHz is an option) which is damped on the primary side to present the correct impedance for the Spectrum 9MHz SSB crystal ladder filter at 820 Ohms or with a change of resistor for the usual 500 Ohm 9MHz commercial SSB filters.

Local oscillator drive is into the low impedance of the sources of the FETs and needs to be 3V p-p for good mixing action.  PCB Kit £35.90 UK, £43.40 EU, £44.60 World.



Ladder filters using 6 crystals for 9MHz or 10.7MHz. Bandwidth at -6dB 2300HZ . Bandwidth at -60dB 6000Hz. Shape factor 2.6:1. Insertion loss 2dB. Termination 820 Ohms and less than 5pF. PCB size 60 x 27 x 15mm. Choose 9MHz or 10.7MHz.

Built £26.90 UK, £33.90 EU, £35.10 World.

 9MHz CW 5 pole CRYSTAL LADDER Filter 600Hz -6dB bandwidth. 8dB insertion loss, 820 Ohm termination, £23.90 UK, £30.90 EU, £32.10 World.


This circuit uses a single FET plus two AGC controlled MOSFET amplifiers to achieve a gain of 90dB and an AGC range of over 100dB. The supply rail is derived from a low drop out regulator providing stable 9.4V from a supply input of 10-13.5V.  The AGC level is presetable for meter set zero and there is another trimpot for fsd or S9 scale calibration.  It is designed to work with a 100uA meter movement. The input to the first FET includes a resistor to match the crystal filter, either 820 Ohms for the Spectrum 9 MHz filter or 560 Ohms for the usual commercial 9MHz filters.

PCB Kit £34.20 UK, £45.10 EU, £46.30 World. Includes tracked carriage.


SSB DETECTOR & CIO 9 or 10.7MHz. The board includes two carrier insertion oscillators (CIO) connected at the transistor collectors like Siamese twins.  This allows each to be selected by switching the base bias to the transistors.  This avoids the usual pulling effect of one oscillator tuning on the other.

The SSB signal is demodulated using an a singly balanced product detector followed by a low pass filter to remove any residual 9 or 10.7MHz IF or carrier signal.  Choose 9MHz or 10.7MHz.

PCB Built £31.20 UK, £37.90 EU, £39.10 World. Includes tracked carriage


SSB DETECTOR & CIO 455kHz.  The board includes two Carrier Insertion Oscillators (CIO) connected at the transistor collectors like Siamese twins.  This allows each to be selected by switching the base bias to the transistors.  This avoids the usual pulling effect of one oscillator tuning on the other.

The SSB signal is demodulated using a a singly balanced product detector followed by a low pass filter to remove any residual 455kHz IF or carrier signal.

PCB Built £22.20 UK, £28.90 EU, £30.10 World.


500mW AUDIO AMPLIFIER.A handy audio output stage using a TBA820M with a gain up to 48dB, 0.5W into a 8 Ohm load, low quiescent current, and low noise. PCB Kit £9.50.



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REGENERATIVE RECEIVER G3RJV-G4CFY  This is my development of the circuit described by George Dobbs G3RJV in April 2013 PW.  It comprises an FET infinite impedance detector and a conduction controlled Q multiplier or oscillator to enhance AM reception or receive and decode SSB signals.  It also includes an IC audio amplifier to drive a loudspeaker.  

Coil: Version A 1.8-3.8MHz uses 45uH, version B 3.5-7.5MHz uses 11uL,              version C 7.0-15.0MHz uses 2u6L, & version D 11.0-23.0MHz uses 1u2L. 

PCB kit and pots & polyvaricon £24.50 UK,  £27.50 EU, £28.30 World.  Conversion kit to 4 Band Receiver £14.50 UK, £16.50 EU, £17.25 World.

Knobs and phono socket NOT included.


G4CFY 4 Band Regen Receiver  This is a further development of the single band G3RJV/G4CFY Regen Receiver with optimization of the oscillator section of the receiver to cover the bands carrying the maximum number of SW broadcast and Amateur Radio traffic.  These are 1.8-3.25MHz, 3.25-5.85MHz, 5.85-10.53MHz, and 10.53-18.95MHz.  This is achieved by removing the coil from the receiver board and using an additional coil pack board.  To achieve the best operation over this total range it was necessary to also change the values of C3 and C5 of the single band version. 4 Band Kit excluding the knob £36.20  UK, £43.00 EU, £44.70 World.  



SUPER SUDDEN RECEIVER As featured in SPRAT Magazine from the G-QRP Club, design by Tex Swan G3TEX, PCB by G4CFY.

PCB (on its own) with a circuit diagram that matches the PCB layout £7.50 including P&P.

Complete kit of parts with circuit diagram that matches the PCB layout, and includes the special pulse transformer, £32.70 UK, £39.40 EU, £40.60 World. Including tracked carriage.


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PIPTONE. An end of message tone for 250mS for weak signal SSB use. The unit provides 50mV across a 600 ohm microphone. The tone and amplitude are presetable. A relay is included for receive and PTT switching. PCB size 44x25x17mm. 

Type PT1000S. PCB Kit £11.30 UK, £18.90 EU, £20.10 World. PCB Built £14.30 UK, £22.90 EU, £24.10 World. Prices include carriage.


KAYTONE. A name coined by Spectrum, this unit is the successor to the original Kaytone sold in 1979. End of message Morse K particularly useful for weak signal situations. Adjustable pitch, speed, and level. A relay is included for TX and RX switching making it suitable for all rigs. PCB size 58 x 39 x 15mm.   

Type KT2000. PCB Kit £16.80 UK, £25.40 EU, £26.60 World.  PCB Built £23.80 UK, £32.40 EU, £33.60 World. Including tracked carriage.

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