Pye PF8 Handheld UHF Transceiver

Back in the 1970s when I was part of the design team at Pye Telecom, I was involved in a project called the PF8. The PF8 was an attempt to produce a radically different UHF hand portable for use by the police and similar PMR users. One thing we learned was that it was the electro-mechanical items which tended to fail: switches, antennas, plugs and sockets. So, this design was to be different - no external connectors, no external antennas, and powered by just two 1.2V batteries. In its day, this was a very radical design and it looked more like a mobile phone (although these were still 15 years in the future) than a traditional PMR handheld.

The receiver was also novel: a dual phase locked loop receiver which helped to overcome frequency stability issues. This was designed by Stephen Watkinson, a brilliant engineer who some years earlier had been involved with the Home Office on a project looking at double sideband supressed carrier systems for PMR use. The transmitter produced about 500mW on a single crystal controlled channel. Another novel feature was the DC-DC converter which efficiently converted 2.4V from two series connected rechargeable batteries to a much higher voltage needed to run the RX and TX. The efficiency was well over 80% but it took Tino Renni, the project leader, and myself some 18 months to overcome the issues resulting from the huge transcient spikes generated by the DC-DC circuitry. It was, frankly, a nightmare. So much so that Tino came in one morning to say he'd had a dream: he'd been digging up potatoes in his garden in his dream and instead of finding potatoes all he dug up was PF8 transceivers! Remember this was years before ICs became available to do the job simply and cleanly.

The antenna was "my" baby. It was the last part of the product to be designed and when there was virtually no space left to fit it! The design is essentially a plate antenna i.e. a plate above another plate with radiation off the edges. In essence it was a dipole with capacitive end loading. but no real dipole wire. Instead this was just a hairpin loop inductor tuned with a small 1-5pF trimmer. As the capacitance would have been too high with a solid "top" plate I replaced this with a skeleton plate using a wire defining just the outside of the plate. The tuning was very sharp (indicating low losses for a very small antenna) and indeed the antenna did perform very well indeed. I have often wondered about scaling this up for VHF or HF.

Another part of the circuit I was responsible for was the transmitter audio. This is a neat little circuit which I used subsequently for other designs. By increasing the pre-emphasis and gain, the same circuit was used for a very effective and truly punchy AM modulator for a 100mW 2m AM rig years later.

Although the PF8 was not a big seller, it did find fame on the TV in the series with Bodie and Doyle called "The Professionals". I did get quite a thrill every time I saw my baby on the TV back in the late 1970s!

See also

Roger Lapthorn,
6 Sep 2017, 06:46