Advanced Projects

The Ham RX and Hale TX

These are new 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.

The Queenie, Kingston and Phaser

Together they form an advanced CW TCVR for any single band of 20, 40 or 80m capable of single sideband CW reception if the optional Phaser kit has also been added. The Queenie RX is direct conversion with a strong product detector using 4066 electronic switches instead of the often used SA602. The line up has the usual double tuned RF bandpass filter, followed by an RF amplifier whose gain is controlled by a switch. This drives two electronic switches for the product detector, (with the unused pair available for the Phaser kit extra channel). These switches only limit when signals get near a few volts of RF so the RX is less liable to BCI which is really helpful dealing with the adjacent broadcast stations! They are followed by a grounded base low noise first AF stage, then an audio op-amp and the switch selectable 3rd order humped CW filter whose peak is nominally at 725 Hz. The AFG pot follows with audio output for phones or LS. The product detector switches are driven by anti-phase square waves at band frequency; when the RX is used alone, these are generated at band frequency by the VFO which has a PolyVaricon for Main tuning and a potentiometer for Fine tuning and offset cancellation. With the Kingston fitted, the VFO instead always runs near 4.67 MHz, which is then squared up, and tripled by extracting the third harmonic for 20m, with division digitally by 2 or 4 if required for 40 or 80m, which then drives both RX and TX.

Because the RX needs space for the optional Phaser kit, the LO trebling filter and dividers are on the Kingston PCB. The LO trebling/division scheme gives freedom to operate where you wish in the band without chirp, complex mixers or crystals! The special features are 5W output on nominal 12 volt supplies, with full break in operation so the band is heard whenever the key is up. Disconnection of the aerial when the key is down is done with a MOSFET switch because relays are not fast enough. There are the usual double Pi harmonic filter and sidetone oscillator which feeds into the RX audio amplifier with RX muting when the key is down. Much design effort has gone into the reception to transmission (and back) timing aspects to make certain there are no nasty thumps or clicks in your phones!

The Phaser kit is an optional extra that converts the RX from the normal double (meaning both) sideband operation into single sideband where the desired one is increased and the unwanted one is rejected. It is mounted in the space on the right hand side of the RX PCB. It uses the spare switches of the product detector, with extra audio stages to provide a second audio channel. These switches are driven by a phase shifted LO signal, with both audio channels having further phase shifting at 725 Hz so that they can be added or subtracted as required. The design is not suitable for phone SSB reception due to the intentionally restricted bandwidth necessary to keep matters simple! Apart from normal double sideband reception where either sideband can be heard, a switch allows acceptance or rejection of either sideband – most useful for dodging unwanted stations!

Interestingly, these designs have the potential of working on all three bands with another relatively simple pair of add-on PCBs, one for LO selection with two extra RF filters, and an earlier kit for adding two more transmitter LPFs! I did try this out with the Phaser but it was all a bit complex and rather tender so I am not currently offering the three band option – but I might yet return to it!

Pricing!

Queenie RX only – £42, Kingston TX (if ordered later) – £25, if Queenie and Kingston ordered together – discounted to £64, Phaser kit – £18. If Queenie, Kingston and Phaser all ordered together – discounted to £80. It would be good to have another early builder, let me know if you are interested and I can offer a further small discount!

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