Incorporating G2DYM Aerials & Garex Electronics

Quality English products hand-crafted to order












19 August 2020

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.nettogether 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-Commsand pay via Paypal.

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

Technical queries 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 15.50 to my personal Paypal account antony.nailer@talktalk.netor through Spectrum, or by direct transfer to my bank.

To buy both books together pat 29.00 to my personal Paypal account antony.nailer@talktalk.net or through spectrum, or direct transfer to my bank.


Intermediate Licence VFO RX Mixer & Dual Front-end BP Filters Regen Receiver, single band
Intermediate Licence Crystal Oscillator SSB IF Filter 6-Pole, 9 or 10.7MHz  Regen Receiver, four band
Portland VFO v2 RX 9MHz IF Amplifier with AGC Super Sudden by G3TEX & G4CFY
5 Band 100W TX Low Pass Filter SSB Detector & CIO 9 or 10.7MHz Piptone PT1000S
5W Broadband HF Linear SSB Detector & CIO 455kHz Kaytone KT2000
RX Front-end Filters, 5 & 10 band Audio 500mW Amplifier CTCSS Encoder 



Here is a simple stable variable frequency oscillator running on 3.5-3.8MHz and suitable for the qualification of the UK Amateur Intermediate Licence.  It is also available as a 7.0-7.2MHz oscillator for the Intermediate Licence or as a local oscillator for a direct conversion receiver.  

It is a Colpitts Oscillator with the output taken from a link winding on the oscillator coil and fed through an FET buffer.  The output is low impedance and typically has the second harmonic 40dB down, which produces a sinewave on an oscilloscope screen that looks perfect.  

The PCB kit and tuning potentiometer 16.50 UK, 18.50 EU, 19.25 World.

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This oscillator uses a traditional Colpitts crystal oscillator running at 5MHz with output taken from the emitter of the oscillator transistor where it is rich in harmonics.  The circuit includes an elliptic low pass filter that can be linked in or out of the path from oscillator to output buffer.  Without the LPF in line the 2nd harmonic is only 1dB down on the 5MHz fundamental.  The third harmonic is 9dB down, the fourth harmonic just 20dB down and the fifth harmonic 28dB down.

Crocodile clips are supplied to enable the oscillator to be linked directly to the bypass or through the filter.  When the LPF is linked into the path the second harmonic is now 21dB down and the third harmonic 33dB down, etc.  This board used in conjunction with the Intermediate Licence VFO enables the student to compare the stability of crystal control versus free running oscillator and to demonstrate the use of a low pass filter to dramatically reduce harmonics generated in a circuit.

PCB kit 21.80 UK, 23.70 EU, 24.50 World

PORTLAND 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 25.50 UK, 28.30 EU, 34.70 World. Prices include tracking.   State required frequency when ordering. 


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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 76.00 UK, 81.50, 83.00 World.  PCB Built 86.50 UK, 92.50 EU, 94.00 World.  




Push-pull transistor HF linear covering the range 1.8-29.7MHz with full out for input levels between 37 and 97mW drive.  Harmonics typically are 2nd -42dB, 3rd -18dB, 4th -49dB and 5th -29dB.  This amplifier needs to be used together with a double Pi type low pass filter, details of which are supplied with the kit.

Full kit of parts with drilled heatsink. With pre-wound toroids 45.00 UK, 50.50 EU, 51.50 World.   Ready built and tested 50.50 UK, 56.00 EU, 57.50 World.  Tracking included.  The prices do NOT include the low pass filters.



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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 40.00 UK, 45.50 EU, 47.50 World. Single PCB built 54.50 UK, 60.00 EU, 62.50 World.  

Two PCB 10-band kit of parts, 77.50 UK, 83.50 EU, 85.00 World. Two PCB built 106.50 UK, 112.50 EU, 114.00 World. Prices include tracking.


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 33.00 UK, 35.80 EU, 42.20 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.

PCB Kit with wound toroids 18.50 UK, 20.50 EU, 21.50 World. PCB built 21.50 UK, 23.50 EU, 24.50 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 30.50 UK, 38.00 EU, 39.00 World.


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 FET product detector with an audio transformer in the drain circuit to select the audio and completely remove any residual 9 or 10.7MHz IF or carrier signal.  Choose 9MHz or 10.7MHz.

PCB Kit 21.50 UK, 23.50 EU, 24.50 World.  PCB Built 29.50 UK, 35.50 EU, 36.00 World.

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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 an FET product detector with an audio transformer in the drain circuit to select the audio and completely remove any residual 455kHz IF or carrier signal.

PCB Kit 17.00 UK, 19.00 EU, 20.00 World.  PCB Built 21.50 UK, 23.50 EU, 24.50 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 9.00.



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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.   Version A 1.8-3.8MHz uses 45u0H coil.            Version B 3.5-7.5MHz uses 11u0L coil.              Version C 7.0-15.0MHz uses 2u6L coil.             Version D 11.0-23.0MHz uses 1u2L coil. 

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, 30 including 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 9.00 UK, 11.00 EU, 12.00 World. PCB Built 12.50 UK, 14.50 EU, 15.50 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 14.50 UK, 16.50 EU, 17.50 World.  PCB Built 21.50 UK, 23.50 EU, 24.50 World. EU & World tracking 5.50 extra.

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Originally designed by Kenn Ginn then post designed and modified and a new PCB layout by Spectrum.  It produces all nine CTCSS tones that can be selected by a link or using a 9 way rotary switch. The unit is triggered by the microphone PTT and in turn provides a PTT output to the rig via an opto-isolator. The module includes a trimpot to set the tone level output to accommodate different microphone impedances.  PCB size 67x55x10mm.  PCB kit 18.00 UK, 19.50 EU, 20.50 World.  PCB built & tested 25.00 UK, 27.00 EU, 28.00 World.  Including P&P.