by Colin Chidgey G3YHV
I enjoy collecting and restoring vintage communication receivers and have the following in working order. RCA AR88D and AR88LF, National HRO, Marconi B28, Murphy B40 etc etc. Many of these receivers have an historic past, having been used by Bletchley Park during WW2 or on Navy ships. Finding the transmitters used with these sets is difficult, so I set about making something using mainly vintage parts. The Transmitter must be suitable to use on todays busy amateur bands.
The first attempt used a 6V6 valve crystal oscillator driving an EL37 Pentode. This worked rather well but I soon tired of the fixed frequencies from my stock of vintage crystals. The Mark 2 displayed here uses a KT88 power amplifier
driven by a 6V6 and an EF80. The VFO signal is supplied from a direct digital synthesis oscillator (DDS) controlled by a 18F1320 pic chip. The transmitter has the following amazing features:
- Output power is 25 watts.
- The VFO covers 7.0 to 7.05MHz.
- It has a green “magic eye” to assist tuning.
- It has an excellent keying waveform, better than some modern radios.
I will probably take it apart and build an even better one!