Re: Plessey PR155G

Michael O'Beirne

I have the PR155G and the later PR1553 version.
The radios are beautifully built and very stable.  The trouble lies in the analogue synthesiser.  It’s essentially a one PL loop job and combines a very stable VFO with a selected harmonic of  a IMHz crystal oscillator using a very clever image rejection mixer.  Sadly, the phase noise is quite bad and sometimes the VCO looses lock.  That said,  a sparks friend used them on board ship and encountered no problems.  I sometimes think we make far too much fuss over phase noise.
There is a complete manual on the net via Google search for the PR155B.  This is the version using a very high quality Kokusai mechanical filter at the 3rd IF of 100kHz.  These are vastly superior to the cheapo cylindrical 455kHz ones used in much old ham gear.
The PR155G does not have the mechanical filter and hence uses only one conversion oscillator on 10.6MHz.  I don’t think it has the USB crystal oscillator.  It uses a 3kHz LC filter and is not offset into the LSB, as is the mechanical filter.  USB is obtained by using the same mechanical filter but with mixing on the high side with the 10.8MHz oscillator.
In the PR1553 those oscillators are derived from the synthesiser by selecting the right harmonic and dividing down by 5  I think.
Email me direct if you need further info.

From: Allan via Groups.Io
Sent: Monday, December 23, 2019 12:36 PM
Subject: [wireless-set-no19] Plessey PR155G
I noticed recently that there was a comment about the PR155 receiver.
I've just "invested" in a G version  (I worked for Plessey Electronics at the time these were made in the 60s).
I now have a document which describes the set including a statement that only the 10.6MHz oscillator (LSB) is used and not the 10.8MHz (USB) in the G variant.
Is there a document describing how to use the 10.8MHz oscillator in one of the unused settings of the mode switch (I'm assuming both xtals are fitted)?
It'll save me a lot of trouble if there is such a thing, and I'm really pleased to see the circuitry is pre-microprocessor era.
I expected the thing to be lightweight but it's as heavy as a 19 set plus its power supply and cables etc.
Allan G3PIY

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