Intermediate

The Ivel plus Ilford CW TX

The Ilford transmitter (on the left above) allows you to send Morse code. It is normally coupled to a simple receiver like the Ivel or Shipham receivers described on the Simple page. The Ilford transmitter can work on any one of the 20 to 80m bands and is ‘crystal’ controlled – this means that it uses either a crystal or a ceramic resonator to determine the transmitted frequency. For 80m, there is a suitable 3.58 MHz resonator whose operating frequency can be pulled down by a tuning capacitor to give a tuning range of typically a few 10s of KHz in the CW section of the band. Unfortunately, higher frequency resonators are not sufficiently stable and cannot be used above 80m, so you may have to use an actual crystal for 20, 30 or 40m – the consequence is that the tuning range on these bands is very limited – a KHz or so! This means that 80m is often a good band to experiment and learn CW skills. 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. Pressing the key also activates the RX muting electronic switch which prevents unwanted crashing sounds from the RX when transmitting, while still allowing the keyed 725 Hz sidetone oscillator to run and produce audio output through the RX’s audio output amplifier. I have recently improved the facilities in the Mk 2 Ilford to make it easier to use as a ‘sperate’ with simple RXs such as the Shipham – it now has a push button for netting, a trimmer for ceramic resonator frequency adjustment, and the sidetone oscillator can now alternatively drive a small speaker (which is useful when muting is done by the spare contact of the TR relay).

When used with the Ivel RX, the Ilford can be arranged for transceiver operation (or essentially single knob tuning) by fitting the resonator in the RX. The RX’s Fine tuning control is used to offset the LO slightly to create a beat note which is automatically removed by the Ilford when actually transmitting. This arrangement is a little more electrically complicated than separate RX and TX, but it does make operation very much easier! The kits in the picture above are wired this way for 80m. The standard Ilford kit includes the 3.58 MHz resonator but if you want crystals for the higher bands you need to tell me what is wanted. The standard Ilford Mk 2 kit costs £23. If ordered together, the Ivel and Ilford are discounted to £49.

The Sheppy

This is another project in its very early stages. It is a simple 80m only low power CW TCVR.

The Bradney AM Transmitter

This is an AM transmitter that goes well with Regenerative RXs like the Shipham. It uses a ceramic resonator (3.69 or 2.0 MHz) to control the frequency and avoid pulling from the output stage, with a tuning range of about 50 KHz down from nominal, under the control of a trimmer and the push button to activate the oscillator stage while the RX is still active. The speech amplifier is designed for common dynamic type of microphone with PTT control of the oscillator, TX output stage, RX muting and TR relay. Peak output power is 5W on 13.8v supplies so that for normal AM use, the carrier level is set for 1.25W allowing full modulation to rise to peak power. (With a few alterations it can also be used for full output CW!) There is the usual double pi harmonic filter for either band. The TX price is £23.

The Somer

This is a new small CW TCVR for any one of 20, 40 or 80m. It has a new LO scheme using frequency multiplication up and division down from the VFO to avoid chirp without using a crystal or ceramic resonator! So goodbye to rockbound transmitters! The arrangement can provide whole band coverage but this is seldom actually desired to keep the Main tuning rate reasonable. 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 is direct conversion using 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 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 main differences between the Somer, compared to the Ivel/Ilford combination, is that it is ‘half’ the size, with VFO coverage for your chosen band and has full break in operation. The price is £52.

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