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@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 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 first print run was 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.net or 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.


RX L-TYPE ATU VHF Masthead Preamps RF Switched
RX SPC ATU 100kHz to 4MHz Receive Converter
QRP TX SPC ATU VLF/LF to 4MHz Receive converter
HF Tuneable Preamp 1.8-30MHz VHF Receive converters 2m, 4m, & 6m
HF Switched Preamp 1.8-30MHz Clara 2 Receiver
VHF Receive Preamp Transverters 2m, 4m, & 6m
110-400MHz Scanner Preamp VHF Transmit Amplifiers, 25/50/100W
VHF Station Preamps RF Switched 4001 FM 4m Transceiver



   For short random wire end fed aerials.  Gives improved signal strength and lower receiver noise from 200kHz to at least 21MHz depending on wire length.  Diecast box 114x64x55mm. Fitted with terminals for aerial and earth inputs, and phono or BNC or SO239 coax output.  Includes a switch for tuner or bypass.  State required output connector when ordering.  Ready Built £43.00 UK, £51.00 EU, £54.80 World.  

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For all types of antenna, except short random wires.  It has an SO239 socket for coax inputs and a binding post for direct random long and short wires.  It works from 1MHz to 32MHz and will tune high and low input impedances and provide a low impedance output via an SO239 socket to the receiver.  Housed in a two part stove enameled aluminium case 150x100x75.  Price £65.50 UK, £72.00 EU, £77.50 World.  Including tracking & insurance.


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 is limited by the 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 an antenna that is too short to be a quarterwave at a certain frequency, 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.

Ready Built £84.50 UK, £96.75 EU, £100.00 World.



1.8 - 30MHz.  Configured in 4 bands, Band A 1.8-3.8MHz, Band B 3.8-7.6MHz, Band C 7.5-15.0MHz, & Band D 15.0-30.0MHz..  Bands 1.8-15MHz flat gain of 16dB. Band D starts at 12dB at 15MHz rising steadily to 16dB at 18MHz thereafter flat to 30MHz.  Gain adjustable down to -20dB.  Runs from an external 12 or 13.5VDC at 20mA via a 2.1mm DC connector. input and output RF sockets are SO239. Two-part stove enameled box 150x100x75mm.  Weight 410gms. 

Box kit £64.00 UK, 73.00 EU, £80.00 World. Ready built £102.50 UK, £111.00 EU, £118.00 World.  


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Through handling power 150W. Fail safe operation, straight through path when switched off.  1.8-30MHz in 4 bands, with highly selective tuneable filters, reduces overload from strong broadcast stations.  Gain 16dB adjustable down to –20dB.  12/13.5V DC operation at 20mA.  SO239 in/out connectors. Two-part stove enameled box 150x100x75mm.  Weight 410gms.   

Box kit £73.00 UK, £82.00 EU, £89.00 World.  Ready built £121.50 UK, £136.50 EU, £140.25 World. Tracking & insurance included.



Narrow band station preamps for external 12/13.5V operation with typically 18-20dB gain. These replace the Garex Preamps, which had provision for a PP3 battery.  Weather Satellite 137-138MHz; Marine 156-161MHz,  & AIS 161-162MHz.   Two part stove enamelled box with choice of BNC, or SO239 connectors.   Ready built UK £42.50, EU £50.50, World £54.30, including tracking and insurance.

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The VHF and UHF bands are dominated in the UK by broadcast FM radio in the range 88-108MHz and by broadcast TV from 550MHz up to about 900MHz.  Any preamp that is wideband enough to include wither of these broadcast bands is likely to overload and then not be able to amplify the low power communications in the range 110-400MHz.  The preamp includes quite sharp high pass and low pass filters with a passband as shown in the screen shot.  The top of the screen is +20dB and the vertical scale is 10dB steps.  The horizontal scale is 100MHz steps. Gain is 0dB at 500MHz falling to more than -25dB to 1000MHz.  Passband gain is 18dB +/-1dB. The mains version is housed in an unpainted diecast box 120x95x34mm with BNC sockets and a 1 metre mains lead and plug. A 0.6m BNC-BNC lead is also included.

Ready Built only, £61.00 UK, £71.50 EU, £77.50 World. Including insured and tracked carriage.


This version  is powered from an external 12V supply.  It uses the same board amplifier boards as the mains version but is now supplied in an unpainted diecast box, which looks more rugged and is a little cheaper than the painted version shown in the picture.  It is supplied with a 0.6m RG58 BNC-BNC lead.

Ready built for external 12V in plain diecast box £41.20 UK, £49.50 EU, £53.30 World.

Ready built in black diecast box, £45.50 UK, £53.50 EU, £57.30 World.  Includes tracked carriage.  


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  For 2, or 4, or 6  metres. 100W through rated on transmit. RF & DC switched 0-20dB panel adjustable gain. 2m, 4m, & 6m types use BF964 with noise figure under 1.5dB. Over-voltage and reverse voltage protected.   Protected against transients and EMP at input and output ports. PCB size 68 x 46 x 28mm. Purpose made box 76 x 70 x 38mm. Fitted with SO239 connectors. DC supply 13.5V 80mA. 

Types RP2S, RP4S, RP6S, & RP10S. PCB & hardware kit £54.50 UK, £62.00 EU, £65.00 World. Ready built £78.50 UK, £84.50 EU, £92.50 World. Tracking & insurance included.



100W through rated on transmit for 2 or 4 or 6 metres. RF & DC switched and DC fed via the coax. Gain 20dB, NF less than 1.5dB. Supplied with a DC/RF Station Box with SO239 connectors for the shack. Heavy duty waterproof plastic box fitted with SO239 connector for feed coax and 1 metre of coax for connection to the antenna. Box size 82x80x50mm. Supplied with masthead fitting plate and releasable tie-wraps. Types RP2SM, RP4SM, & RP6SM. PCB & hardware kit £66.00 UK, £75.0 EU, £82.00 World.  Ready Built £88.50 UK, £98.00 EU, £102.50 World, including tracking.  


400W through rated on transmit for 2 or 4 or 6 metres.  RF switched. Supplied via separate wire DC feed.   Gain 20dB, NF less than 1.5dB.  Protected against reverse and over voltage and against EMC transients at input and output. Heavy duty waterproof box fitted with SO239 connector for feed line and 1 metre of coax to connect to antenna feed point. Box size 82 x 80 x 50mm. Types RP2SH, RP4SH, & RP6SH.  PCB & hardware kit £53.00 UK, £60.50 EU, £65.50 World.  Ready built £69.50 UK, £78.00 EU, £80.00 World, including tracking.  

Picture opposite is the RP2SH type with external 13.5V supply.

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VLF CONVERTER 100Hz - 100kHz

Converts up to 4-4.1MHz. High input impedance to suit any random wire aerial.  100kHz elliptic low pass filter for input range, diode ring mixer, crystal oscillator, bandpass filter at IF centred on 4.05MHz.  Gain is -22dB at the band edges and -18dB mid band. SO239 coax output to receiver and 4mm terminal post for aerial wire .  Runs from an internal PP3 battery. 

Box kit £57.00 UK, £65.50 EU, £68.00 World.  Box built £75.00 UK, £83.05 EU, £86.00 World. Prices include tracking.

Just 2 boards left and this will be replaced by a new and improved design of VLF/LF Converter to 4MHz, covering 3kHz to 300kHz and translating this to 4.003 - 4.300MHz.





This is a new version version and converts is up to 4.003 - 4.300MHz.

It replaces both the 100kHz & the 500kHz version both of which had a conversion loss of 18db whereas this unit has a gain of 9dB.   It has a high input impedance to suit any random wire aerial driving a 300kHz elliptic low pass filter to band limit the reception. This signal range together with a 4MHz oscillator signal feed into a diode ring mixer with matched germanium diodes.  Then another elliptic low pass filter to remove any oscillator mixer products with harmonics of the oscillator and finally an emitter follower to drive a low impedance receiver input.  There is an SO239 coax output to the receiver and 4mm terminal post for aerial wire.  It has a 1 metre DC lead to connect to an external 12V bench supply. 

Box kit £64.50 UK, £77.00 EU, £80.80 World.  Box built £83.00 UK, £95.50 EU, £99.30 World. Prices include tracking.



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Convert 2, or 4 or 6 metres to a receiver tuning 28-30MHz,  These are low noise and have a gain of 15dB and noise figure of 1.5dB. This design incorporating a diode ring mixer was put into production in November 2001 together with an improved oscillator and multiplier circuit. The Boxed version has panel adjustable gain, on/off switch and power LED. Fitted with SO239 connectors and has 1metre of lead for 13.5V bench power input. PCB size 95x45x17mm, Box size 102 x 84 x 40mm. Types RC2-10, RC4-10, & RC6-10. 

Convert 4, or 6 or 10 metres receive to a 2 metre transceiver. Same specification as the 10m IF versions.  

Types RC4-2, RC6-2, RC10-2. PCB & hardware kit £65.00 UK, £74.00 EU, £76.00 World.  Ready built £95.00 UK, £103.50 EU, £105.50 World.  Prices include tracking & insurance.




This single band receiver can be configured to work on 160m, or 80m, or 40m, or 30m, or 20m.  A version has also been made for 21.5MHz and successfully used as a Jupiter receiver. It uses a high stability Hartley VFO and runs from an external 12/13.5V DC supply. The product now uses a lower value of main tuning capacitor which gives a more linear scale.  Box kit £68.00 UK, £77.00 EU, £79.00 World. Box built £94.50 UK, £103.00 EU, £105.00 World. Includes tracking and insurance.

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Early commercial transceivers often had a transverter facility with a low level output from the transmit driver stage and a means of disabling the power output stage.  This meant there were two connections for an outboard transverter, one from the low power transmit port, the other for receive via the main antenna socket.  Some of the top of the range rigs still have this facility but most modern rigs do not have any transverter facility at all.  To use them with a transverter simply reduce the power of the transceiver to minimum and use a single connection to the transverter from the rig antenna socket.  

Add 2 or 4 or 6 metres to a rig with 10 metres,  or 4 or 6 metres to a 2 metre rig.  The transverter main board contains an attenuator in the transmit path and can be configured for 1-500mW or 0.5-5W drive levels and gives 300mW output. The RF sensing of the transverter will work at drive levels from 5W down to 100mW.  Below that drive level, hard switching is required. Class AB linear operation gives all mode use. The standard product includes a linear amplifier giving panel adjustable output 5 to 20W on 2m, or 5 to 25W on 4 or 6m.

All spurious and harmonic outputs better than 45dB below carrier.  Capable of withstanding long periods of transmit into bad SWR.  Receive side has panel adjustable gain 0-20dB gain and NF less than 1.5dB.   PCB size 150 x 93 x 18mm.     Box size 200x160x77mm. Suffix s is used for single IF drive arrangement, suffix d is used for dual IF drive version, the suffix L is for integral linear.

TRC2-10sL, 4-10sL, 6-10sL 10m 0.5-5W Single
TRC2-10dL, 4-10dL, 6-10dL 10m 1-100mw Dual
TRC4-2sL, 6-2sL 2m 0.5-5W Single
PCB kits £173.00 UK, £177.50 EU, £180.25 World. PCB's built £213.50 UK, £218.25 EU, £221.00 World.  Box kit £219.50 UK, £225.00 EU, £232.00 World.     Ready built £285.00 UK £289.00 EU, £296.00 World. Prices include tracking & insurance. 

Repeater shift for 2m output versions, add £8.50 to PCB kit or Box kit, £15 to PCB built or Boxed built.



TRANSMIT AMPLIFIER (20/25W) For Spectrum 0.3W Transverters. Two stage PTT switched class AB linear amplifiers for 2, or 4, or 6 metres giving a minimum of 20W out for the 2m version, and a maximum of 35W for the 6 metre version. Should not be run at more than 25W output. Antenna relay with high speed TX/RX switching makes it suitable for all modes including data and RTTY and Packet. PCB size 125 x 57 x 28mm. Types TA2S4, TA4S4, TA6S4.   PCB kit £110.00 UK, £119.00 EU, £125.00 World.    PCB Built £120.50 UK, £129.50 EU, £135.50 World.   Prices include tracking.

TRANSMIT AMPLIFIER (50W) Single stage switched class AB linear amplifier suitable for CW, SSB, FM, RTTY, and PACKET. 4m and 6m versions typically 7.5W in 50W out.  Switching circuit senses RF & DC and uses a monostable relay driver giving VERY FAST attack and a hold time of 250ms to 2s for SSB use. For data modes the hold function can be disabled. PCB size 102 x 72 x 55mm. Diecast box size 171x121x55mm with a heatsink 150x99x32mm on top. Fitted with SO239 connectors and comes with 1 metre of 42.0.2 red/black DC cable. Types TA50W4M, & TA50W6M. Ready built £146.00 UK, £153.30 EU, £160.30 World.  Price include tracking.

TRANSMIT AMPLIFIER (50W) & PREAMP   Linear amplifier and receive preamplifier together in one case with independent switching. Amplifier details as TA50W above, together with 20/26dB gain preamp. Types TA50WRP4M, TA50WRP6M.  Ready built £185.00 UK, £190.50 EU, £197.00 World.  Prices include tracking and insurance.

TRANSMIT AMPLIFIER 70MHz (100W) Single stage parallel pair of 50W devices in class AB for all modes, 20 to 22W SSB input gives 100W peak output when run on a PSU with 13.5V at a load current of 16A.  Rated for long periods on FM and Data at a continuous output of 50W.  Also can be used with AM with an output carrier power set to 25W and peak power of 100W.  RF sensed switching with fast attack and 500mS hang to avoid relay chatter when on SSB.  Unit includes a peak reading power meter that remains in operation whilst the unit is connected to the power supply even though the amplifier is not in operation.  Overall size 187x118x94mm. Type TA100W4M, Ready built only £233.50 UK, £239.75 EU, £247.00 World, including tracked carriage.

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70.2500 to 70.4875MHz in 20 channels in 12.5kHz steps. Originally AKD, then GAREX, now Spectrum. This rig is really easy to use, not menu driven and in the event of failure is easy to repair.  The default channel at switch-on 70.450MHz. Now upgraded to give excellent audio quality on receive and transmit.  RF output 25W or 5W presetable and switchable. Sensitivity better than 0.25uV for 20dB SINAD.  Audio output 500mW rms. Supply requirement 13.5V DC 4A on high TX, 1.5A on low TX, 130mA on RX.  This product is now being custom built to a high quality standard rather than down to the cheapest price. 

Type 4001S £195.00 UK, £203.00 EU,  including tracked carriage & insurance.


2001 PIC module to change to 12.5kHz channel spacing and add CTCSS. Supplied with replacement reference crystal, LED in-between channel indicator and handbook with new frequency listing. £22.50 excluding P&P.

4001 replacement PIC to change to 12.5kHz channel spacing. Supplied with replacement reference crystal and handbook with new frequency listing.  £8.50 excluding P&P.

6001 PIC module to change to 10kHz channel spacing and add CTCSS. Supplied with handbook with new frequency listing.  £20 excluding P&P.

Upgrade kit for 2m, 4m, and 6m versions for improved IF amplifier, better RX filter matching and improved transmit audio. Supplied with replacement IF filters 10M07 and LTW455HT and complete circuit diagram & board component layout.  £14 excluding P&P.

7003 upgrade to receive IF amplifier and transmit modulator section is pending post design work but is likely to be similar to the kit above except that the 21.4MHz first IF filter will not be changed.

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