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Old 16th Feb 2021, 9:33 pm   #21
G0HZU_JMR
Dekatron
 
Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
Posts: 3,077
Default Re: PIN diode band switching yaesu ft-767

Quote:
Originally Posted by Steve G4WCS View Post
Ive some hp 5082-2800 and 2810 diodes I can send over if they are suitable for your testing
Thanks for the offer of those classic diodes, however I've got quite a few of them here already. They aren't that well suited to this application but I'll do a few tests on one to show why they shouldn't be used here.

I dug out my old >1995 Technical Topics book and there are several articles in it about diode switches in HF radios. There were lots of people contributing test results but there was not much agreement. Some people recommended 1N4148 diodes and others referred to them as catastrophically poor for example. I suspect that the people who recommended the 1N4148 did so as a result of a listening test (for sensitivity?) with the diodes fitted to a radio. The people who didn't like the 1N4148 based their conclusions on distortion tests taken in a 50 ohm test fixture. I do think the 1N4148 will perform poorly in a 50 ohm test fixture but it might be OK to use these diodes when switching a suite of 450 ohm filters as in the Yaesu FT767. Even so I think I'd rather use something else.

Because I work from home my work bench kind of belongs to the company most of the time so I don't have any free space to do testing until the weekend. However, over the next few days I could post up some general diode info and show why fast switching diodes like the 1N4148 are not an ideal choice for this type of application.
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Regards, Jeremy G0HZU
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