Advanced Projects

The Stone RX and Stoke TX

These are relatively simple superhet projects that together provide a 1.5W SSB phone transceiver for either 40 or 80m bands. They also use single sided PCBs to make electronic assembly easier.

The Stone RX (above) uses an Intermediate Frequency of 6 MHz with the VFO running at either near 1 MHz for 40m , or near 2.5 MHz for 80m. There is main tuning from the large knobbed PolyVaricon capacitor with fine tuning from a potentiometer controlling the reverse voltage (and hence capacitance) of a power diode. The superior LM317 regulator is used for those circuits needing good supply stability. The RX has a double tuned RF filter that feeds the first SA602 mixer, whose other input is from the separate JFET VFO, and outputs via a simple IF amplifier stage to the four crystal IF filter. The second SA602 mixer follows with the 6 MHz crystal controlled carrier oscillator tuned by a trimmer. This is followed by a discrete BS170 AF amplifier, the AFG control and then the LM386 audio output stage. The design allows for optional new CW and AGC kits shortly to be proven – see the Accessories page. The price of the Stone is £45.

When the Stoke TX is added (as below) they form a PTT controlled SSB transceiver.

When transmitting, your microphone audio is amplified in an adjustable gain speech amplifier that feeds the second mixer now acting as a suppressed carrier modulator. The signal flow through both mixers and IF amplifier is reversed using relays so that the unwanted sideband is removed by the IF filter, then mixed to band frequency in the other SA602, with its output amplifier now feeding the RF filter so that low level band frequency signals are ejected from the RX antenna terminal! There is also a special signal clipping feature in the IF strip which acts as a speech compressor during transmission, thus increasing the effective RF output power. The RF line up uses an expensive high speed op amp to minimize the parts count of the necessary adjustable gain amplifier which drives the high gate capacitance of the 1.5W peak IRF510 output stage (on the finned heatsink). It is followed by the harmonic filter and two TR relays to route antenna signals around it during reception. The two extra RX relays are supplied with the TX kit. (An early builder would also be good!) The Stoke price is £40.

The Ham RX and Hale TX

These are RX and TX designs for 20, 40 or 80m – the Ham Receiver is shown below and can be used on its own.

The Ham RX is a superhet which means that only one sideband is heard – this is particularly relevant for CW when compared to simpler RXs which hear both sidebands: it is also highly desirable for SSB phone reception and essential when the RX is used to drive the Hale SSB or CW transmitter. The Ham has a 10 MHz Intermediate Frequency which makes it a little easier for one set of parts to cover the relevant small section of the overall 2.8 to 6.5 MHz range for any one of 20, 40 or 80m bands. The receiver comprises a double tuned RF bandpass filter feeding the first SA602 mixer with a simple output amplifier, feeding into a four crystal IF filter, and then the second SA602 mixer (with carrier insertion oscillator) acting as a product detector. The audio pre-amp uses one half of a low noise TL072 op-amp with its second amplifier providing a switch selectable third order CW filter. Then follows an AGC stage, using both sections of another TL072, which feeds the AFG control and the output audio power amplifier. For transmission, two relays (supplied with TX) reverse the signal flow through the RX’s mixers and IF strip to eject the low level RF out of the RX antenna terminal, but for reception without the TX, there are small PCB links across the normally closed relay contacts. The first mixer is additive on 20m but subtractive on 40 and 80m, so there is an extra CIO coil for 40/80m to provide the normally used sideband for all bands. Compared to earlier designs, this RX now includes a good CW filter as well as AGC all on the main PCB! The RX price is £50.

The Hale Transmitter – this is driven by the Ham RX and so must be for the same band!

The photo above shows the Hale attached to the Ham RX. Tracks are cut in the RX so that two relays can be fitted there to reverse the signal flow in the IF strip and both mixers, which together with the TX relays then activates transmitter stages. The RF amplifier chain is linear for SSB signals, or the keyed audio tone for CW. A TL072 low noise op-amp is used for the microphone speech amp and for mixing in the CW sidetone oscillator output when that is activated. These drive the RX’s second CIO mixer to generate DSB which is filtered by the IF filter to remove the unwanted sideband before that is then changed to band frequency in the RX’s first mixer, and then the through the RX’s RF bandpass filter so that it ejects low level RF out of its antenna terminal! The first TX RF stage is a grounded gate RF amp with Drive preset, followed by the main RF amplifier that drives the output IRF510 power stage (with large upright heatsink) and the low pass harmonic filter. The Hale provides a Maximum output of 5W nominally on a 13.8v supply for both CW and SSB but can be used with care on higher voltages for increased output. Control is by the PTT switch of your microphone (dynamic type) for SSB or with semi break-in operation for CW. The control circuits mute the RX via the AGC stage. You should not need specialist test gear to set these kits up pretty well if you have a general coverage RX, multi-meter and the normal RF accessories of a power indicator, 50 Ohm dummy load and Aerial Matching Unit. A scope and two tone oscillator are desirable but not mandatory with a little patience!

The TX price if ordered subsequently on its own is £42 but if ordered with the Ham, the pair are discounted to £85.

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