The Stone RX and Stoke TX
Together these two form a relatively simple superhet TCVR with an output of 1.5W of single sideband phone for either the 40 or 80m band. They also use single sided PCBs to make electronic assembly easier. The key difference compred to a direct conversion rig is that they hear (and transmit) only a single sideband so a crowded band has far less unwanted signals on it.
The Stone RX (nearest the knobs) 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. It has main tuning by 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; it 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 the optional CW and AGC kits – see the Accessories page. Please ask me if you only want the RX!
When the Stoke TX (on left above) is added, 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. (If fitted, this is where the CW kit feeds in a keyed tone for CW.) 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 a high speed op amp to minimize the parts count of the RF amplifier chain which drives the 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. The price of RX and TX is £75.
The Ham RX and Hale TX
These are superhet RX and TX designs for 20, 40 or 80m using a bi-directional IF strip like the S and S above. But owing to the higher frequencies, higher RF output and extra circuits for AGC and CW, they use double sided PCBs.
The Ham RX 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 VFO 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 an 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 finally the output audio power amplifier – so no need of extra kits for CW or AGC! 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. 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.
The photo above shows the Hale transmitter (on left) attached to the Ham RX. The RF amplifier chain is linear for SSB phone signals and the keyed audio tone for CW. A low noise TL072 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, with one sideband being removed by the IF filter, then mixed up to band frequency by the VFO, through the RX’s RF bandpass filter and into the TX RF amp chain. This has a variable gain stage top allow for the different bands and to feed the IRF510 but configured for 5W output (on 13.8V) after the harmonic filter. 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 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! The price for the RX and TX is £90.
The Barle and Barwick
The special feature of these two kits is that they have the potential of THREE band operation! The Barle RX is a strong direct conversion RX (using MOSFET switches in the detector) for any one of the 20, 40 or 80m bands, having a RF amp stage ahead of the detector. The gain of the RF amp is switchable and the CW filter is also switch selectable. The local oscillator runs near 4.67 MHz which is trebled (by squaring and filtering) to 14 MHz and squared up again for the digital functions of keying, and division by 2 or 4 when 40 or 80m is the chosen band. This arrangement provides tuning freedom without being troubled by chirp due to TX stage high currents getting into the VFO. They have the usual PolyVaricon main tuning with an incremental receiver offset that is removed when transmitting. The Barle also includes a frequency shift facility (adjusted by trimmer) whose main purpose is associated with three band operation as explained below. The Barwick transmitter provides 5W on normal 13.8v supplies and includes the usual Low Pass Filters and sidetone oscillator. A new TX driver stage has been devised to ensure that output does not drop significantly on the higher bands! The T/R electronic switch has also been uprated for the higher power with full break in sequencing to ensure smooth click free operation as the key is operated. The single band Barle and Barwick occupy the two base PCBs in the above photo. The price for a single band transceiver is £80.
Three Band B and B!
The above photo is actually a three band B and B with all the extra facilities for all three bands – 20, 40 and 80m! The upright PCB nearest the front has relay selected RX Bandpass filters for two extra bands with electronic selection of the desired LO from the divider RX stages. Band selection is by DC from a centre off toggle which also controls the relay selecting the transmitter Low pass filters on the other vertical PCB. (Both these extra PCBs are standard and have uses for other rigs – see Accessories page.) The base RX VFO frequency shift facility now comes into its own to make the main PolyVaricon tuning position the same on all bands for the common QRP calling frequencies. (3.56 x 4 requires the ‘multiplied’ VFO on 14.24 instead of the 14.06 MHz needed for 20 or 40m!) The band kits include a centre off toggle to control this shift facility. The price for the extra band kits is £40.
Walford Electronics Ltd. 