The Ilford MK 2 CW TX
The Ilford CW transmitter is probably the simplest transmitter that you can make and operate legally when suitably licensed! It has been improved to make it easier to operate with the Shipham or Stathe RXs – see Simple page. The frequency is controlled by a 3.58 MHz ceramic resonator on 80m in the CW part of the band with a few 10 KHz of tuning range which is adjusted by the trimmer when you activate the netting push button; this causes just the oscillator stage to work and be heard on your RX to you check that you have adjusted the TX to the other station’s frequency. (The Ilford can work on higher bands up to 20m but it has then to be crystal controlled – please consult me before ordering for other than 80m.)
The transmitter produces 1.5W of RF using a 13.8 volt supply and includes an output low pass filter to get rid of unwanted harmonics. It also includes a transmit receive relay for switching of your aerial between RX and TX, this is activated automatically when you press the key and has a delay before reverting to reception to cater for the gaps between Morse characters. Closing the key also activates an electronic switch which can mute the RX before/after the relay operates to prevent unwanted thumps in the audio output caused by supply transients. Key action also activates the 725 Hz sidetone oscillator which is normally fed to your phones/LS through the spare TR relay contacts. I have also added a small knobbed preset (blue in photo) in the feed to the RX aerial which is very useful as an RF gain control for very simple RXs like the Shipham. The Ilford PCB is easily attached to the RX by two small pcb joining strips. The Ilford Mk 2 costs £25.
The Sheppy
This is the simplest CW transceiver that I offer – the ‘single’ knob tuning is a big step up in convenience from separate RX and TXs because it avoids having to adjust the RX and TX to the same frequency. It uses a ceramic resonator which can be tuned over a few 10 of KHz in the 80m band down from about 3.6 MHz. The resonator has a high enough Q to prevent chirp but without the restriction of effectively being limited to a single crystal frequency. Unfortunately, resonators for higher frequencies are prone to drift as they warm up, so the Sheppy is limited to only 80m. The PCB is single sided for ease of construction and lower cost! The RX is direct conversion with a double tuned RF filter feeding into the SA602 product detector, followed by audio filtering for CW in the audio pre-amp which feeds the AFG pot and the output LM386 output stage for either phones or a small speaker. The VFO is actually digital but is controlled by the ceramic resonator with both main tuning by the PolyVaricon, and an incremental fine tuning control to set the beat note offset tone; this frequency offset is automatically removed when transmitting so that you transmit on the other station’s frequency. The driver stage does the RF keying and feeds a pair of BS170 MOSFETs for 1.5W on a 13.8v supply. This is passed through a double pi harmonic filter to the TR relay which has semi-break in TR control to cover gaps between Morse characters. The relay also switches the audio output to the adjustable level sidetone oscillator so you can hear your own key action! The price of the Sheppy TCVR is £45.
The Somer
The special feature of this TCVR design is that it is tunable and can do any of the bands 20, 40 or 80m – so goodbye to the limited range of ceramic resonators or crystals! It has a new LO scheme using frequency multiplication up and division down from the VFO to avoid chirp (without using any form of crystal mixing). The RX is direct conversion with a PolyVaricon for the main tuning and a voltage controlled diode for the Fine tuning and beat note offset; the latter being automatically cancelled when you go to transmit. The RX has a double tuned RF filter feeding into a SA602 mixer, with a conventional audio pre-amp, humped low pass CW filter and main audio output for phones or a small loud speaker. For transmission, the LO chain 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). The transmitter output has twin pi low pass filtering with TR control circuits that provide click and thump-free full break-in operation! There is also a 725 Hz sidetone oscillator, with adjustable level, that feeds into the RX audio amp. Compared to the Sheppy, it has proper TCVR tuning for any of its three bands, and quiet full break in TR switching. The Somer price is £55.
Walford Electronics Ltd. 