Intermediate Projects


Halse and Hatch

The emphasis in this phone singe sideband design is ease of construction. The Halse RX can be used on its own but together they form a single band 5 Watt SSB TCVR for any single band of 20, 40 or 80m. The superhet's IF is 9 MHz which gives coverage of the 20 and 80m bands with a single VFO band near 5 MHz; and by just changing the VFO inductor it can work near 2 MHz for the alternative 40m band. Starting at the aerial, the receiver has a double tuned RF filter, followed by the first mixer which is an SA602 having its own discrete IF amp prior to the IF filter which uses four crystals in a ladder formation. The second mixer is also an SA602 which includes the Carrier Insertion Oscillator and can work on either sideband by the addition of an inductor. The first audio stage uses a pair of BS170 MOSFETs driving the AF gain control, which is followed by the audio output stage able to drive a loud speaker or phones. The RX PCB is nearest the front panel in the photo below. You can add the Mini CW kit, the Mini AGC, and or a digital frequency readout - the three digit one is most appropriate.

For transmission, the RX is switched over to produce low level SSB by installation of relays that come with the TX kit.  The microphone speech amplifier output is fed into the RX second mixer which now acts as a balanced modulator. The IF strip is then used in the reverse direction (with relays reversing the mixer inputs and outputs to reverse the signal flow), so that the IF filter removes the unwanted sideband and feeds into the other mixer to get to the desired band frequency. The RF BPF removes the unwanted mixer products so that low level SSB is actually ejected out of the RX aerial terminal! Then follows the TX RF amplifier chain with an IRF510 MOSFET for the RF output stage; this is designed to produce 5W on a nominal 12v supply, but as ever, it is highly dependent on actual supply volts at the output stage! This is followed by a double Pi harmonic filter with the inductors and capacitors adjusted for the chosen band. TR control is by your mic's PTT switch and this also mutes the RX when transmitting.

Prices are GBP 46 for the Halse RX, or GBP 79 for the Halse and the Hatch when ordered together. The Hatch is priced at GBP 36 when ordered on its own later.


The Culm

This is a new CW TCVR for any single band 20 to 80m. On 80m it uses a ceramic resonator for the VFO giving several 10s KHz tuning range. The RX is direct conversion with a PolyVaricon for the main tuning and a voltage controlled diode for the Fine tuning beat note offset, which is automatically cancelled when you go to transmit. The RX has an RF amp with an RFG preset, followed by a double tuned RF filter and then a pair of JFETs for the product detector. This is followed by the first audio amp and a humped low pass CW filter centred on 725 Hz , which feeds the AFG pot and the audio power amp for a LS or phones. For transmission, the VFO feeds digital gates for the RF keying which then drive a buffer stage and a pair of BS170 MOSFETs in the output stage for a nominal 1.5W (with a 13.8v supply) on any band to 20m. The transmitter output has twin pi low pass filtering and the TR control circuits automatically disconnect the LPF from the RX RF amp when transmitting for click, and thump, free full break in changeover! There is also a 725 Hz sidetone oscillator, with adjustable level, that feeds into the RX audio amp. The 3.58 MHz ceramic resonator can be replaced by a crystal of your chosen frequency for the higher bands where ceramic resonators are not suitable, or by a 4 MHz resonator that can drive the Digi-mix kit fitted with a crystal to for any band output (including 5262 KHz!) up to 20m - this has the advantage of giving approx 50 KHz tuning range instead of the very limited range with a crystal. The photo below has the Digi-mix piggy back on a 40m Culm. The plain 80m Culm is pictured on the Home page. The Culm price is GBP 42.


This is a very simple single band DC RX. It can be built very easily on a small piece of copper laminate so I am not going to do a kit for it! Full details are in Hot Iron E99.

Three 'Crystal' Isle

This is the simplest way to produce CW on more than one frequency! If all three frequencies are in the same band then no extra low pass harmonic filters are needed - see the simple page; but if they are for two or three bands then you also need a Dual LPF kit (plus the extra crystals) for the two extra filters not fitted on the Isle PCB. The selection of filters and crystals are done by DC signals from the rig's centre off toggle band switch. The other aspects of the transmitter are as in the single band Isle description. The Isle plus Dual LPF kit shown below and costs GBP 30. Band crystals are GBP 3 each if wanted but see below for VFO operation!.


Three Band VFO schemes

To avoid problems of chirp and poor frequency stability on the higher bands, you can use the Mini Mix kit with a slightly altered VFO of the Mk 2 Yeo, to provide the necessary Local Oscillator (LO) signal for the RX (and the TX); the mixer kit can then also easily provide outputs for 20, 40 and 80m simultaneously, so that three band reception and transmission with VFO control is possible. A simple centre off toggle switch can select the wanted LO output with another pole controlling the filter relays. For SSB, the Yeo's Fine control provides a plain band-spread action, whereas for CW, it provides RIT under control from the Isle.

If you have the Mini Mix kit with the Yeo as above (producing the LO signals for all three of 20, 40 and 80m), it is only necessary to add the receiver's input RF input filters for the missing bands to provide three band reception! The Yeo PCB is drilled for these extra parts as shown below. The Mini mixer kit has been fitted on the side here to keep the footprint small for ease of demonstration and compactness. These extra 3 band filter parts cost GBP 10.

Three Band VFO Controlled Isle & Yeo

The next step is to make the Yeo able to transmit CW on all three bands 20, 40 and 80m! Just feed the Mini Mix's LO signal also to the Isle which has to be fitted with the Dual LPF kit for the extra bands. This combination provides full VFO CW transceiver operation on 20, 40 and 80m as shown below! It comprises a Yeo with 3 band extras, Mini Mix kit, Isle and Dual LPF. The discounted price is GBP 76.


Site Navigation

Home Page, List, Simple, Advanced, Accessories, Ordering

Walford Electronics Ltd.