All of these are suitable to demonstrate your skills for the Intermediate Radio Amateurs exam but see notes on the Ordering page!
This is a very simple AM receiver that I have designed specifically for group building projects for novice constructors taking their first steps into electronic construction. . Several schools are running events as part of the British Science Week in March 2019 with sponsorship provided by the Radio Communications Foundation; members of the public (young or old!) can book into the open event on March 16th at the National Radio Centre located at Bletchley Park (https://bletchleypark.org.uk/whats-on/build-a-radio-receiver) The receiver covers the amateur 160m band and the lower part of the medium wave band up to about 300m so there are plenty of powerful broadcast stations that can be heard with simple aerials. The professionally produced PCB has space for a PP3 battery and is switched on by plugging in your modern stereo 32R phones; the circuit is very simple using just four MOSFET transistors. Apart from the main tuning control, the smaller one is an RF gain control. The very detailed Spaxton building manual can be downloaded here. Readers may also hear of the Spade gadget - this is a specialised piece of test gear to help commission Spaxtons when being assembled inside modern buildings that act as a Faraday cage. Because the Spaxton has been heavily supported by the RCF, I am afraid that I am not normally able to supply individual orders, but we hope that this initial run of events will encourage schools and the RSGB to put on more events subsequently. For potential organisers, the guidance notes for event team leaders can be downloaded here. You can see below how simple the Spaxton is to assemble!
This is a simple Regenerative Tuned Radio Frequency (Regen TRF) receiver design for those just embarking on electronic construction projects; it is also suitable for Radio Club group building projects and as an introduction to short wave radio. You should be able to build it in a couple of evenings! It has two general coverage bands which can be chosen from MW or around 160m, and around 80m or 40m. These are chosen by alternative fittings for the four ready wound inductors. Because it is a Regen TRF it is ideal for the powerful broadcast stations of the Medium Wave (and the 'short' wave) bands, using Amplitude Modulation, which can be easily heard with a short aerial; so start by building it for the MW as a good confidence booster! Because it is a Regen TRF it can also copy the common modes of Morse, and phone Single Sideband used by amateur radio enthusiasts. It has three controls - the Main tuning, and RF gain control and the Regen control. It uses four transistors arranged as an RF amp, the regen stage and two for the audio amplifier. The audio amplifier is designed specifically for modern 32R stereo phones which turn the RX on when plugged in and there is also very smooth control of the critical point of oscillation. The kit includes 5m of aerial wire for an initial 'throw-out' aerial which is usually enough for MW reception. The price is 20 GBP.
You might wish to consider adding the Fosse CW TX to your Rockwell!
The Isle CW TX
This is a 1.5W single band CW transmitter, that uses a crystal or, depending on band, a ceramic resonator for frequency control. The band can be any one of those in the 20 - 80m group. The kit includes a 3.58 MHz ceramic resonator for 80m which can be pulled over several tens of KHz down from the nominal figure using the on board trimmer. For the higher bands you have to use a crystal which means that the trimmer will then only have a very limited tuning range. The single band version is shown below with a single crystal, however there is space for three 'crystals' which can all be in the same band if you wish, so that the single harmonic filter on the Isle PCB will serve for all three frequencies. If the extra crystals are in more than the single band, you need extra low pass filters - using the Dual LPF kit. TR control of the aerial relay (it has to be mounted elsewhere due to lack of PCB space) is semi-break in from the key and includes facilities for muting the RX. If wanted, the TX can be driven by an external frequency source such as the sim-mix kit instead of using 'crystal' control. The price for the single band version, including the 80m resonator, is 19 GBP; just add the extra crystals for 3 frequency operation. Standard QRP calling frequency crystals for 20, 30 and 40m are 3 GBP each.
This is the transmitter for those wanting to get on the air quickly with DSB phone! It is entirely compatible with other stations operating single sideband! It produces a peak output of 1.5W when used on a nominal 12v supply. It is normally for any single band in the 20 to 80m group. Frequency control is by the included ceramic resonator for 80m giving about 50 KHz coverage down from 3.69 KHz with the on-board trimmer; for the higher bands where ceramic resonators are impractical, you will have to use a crystal with a tuning range of just a few KHz - the prototype (with crystal) shown below is for 20m. Ceramic resonator or crystal control would be appropriate for a simple RX where its VFO is at reception frequency, but the Axe can alternatively be driven by an external LO signal derived from a mixer kit! This avoids the limitations of 'crystal' control! A SA602 is used for the balanced modulator which then drives an AD8055 high speed op-amp. Because the gain through these stages vary with band, the single drive level preset has to be set for that band which means that the rig is limited to single band operation. The output stage has three BS170 MOSFETs operating in parallel - these are ideal for the LF bands where a standing bias current is needed linear operation! The standard Axe can also be used to drive an external liner amplifier. The output stage is followed by low pass harmonic filters and the control circuits include RX muting and control for the TR relay which has to be mounted elsewhere due to lack o0f PCB space. Axe price is GBP 27; 7159 KHz and 14318 KHz crystals are available at GBP 3 each.
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