Saturday, 11 June 2016

Down the one way street

Anyone who learnt electronics as a kid back in the '80s might remember the works of people like R.A. Penfold and Forrest M. Mims III - and will remember being told that diodes are the electronic equivalent of a one way street,

Well, after testing the Testbed RT-320 on 5MHz for receive and transmit, and finding that it still works, ive moved onto adding the necessary diodes to the decade switches to prevent data contention issues with the Remote projects controller. This aspect of the project, really is a one way street! There are about twenty diodes to fit!

This is what makes this a difficult project! There is very little space between the decade switches and the radios modules, and getting access to the wiring loom requires quite substantial dismantling of the radio.

Once access is gained, it doesnt get any easier! Each of the wires to be worked is wrapped around the terminal pin, careful and occasionally forceful desoldering is needed to free them. Then, the diodes, in this case BAT85 schottky types to minimise forward voltage drop, must be soldered in. It is almost essential to pre-form the leads of the diodes. 

If anyone decides to follow this project and do these modifications, then a few words of advice - do one at a time! Never unsolder more than one wire at once, and make sure you know where the cut leads of the diodes have gone! Test every diode immediately prior to fitting as well, and then immediately after!

Some of the wires cross over adjacent switches in a way that would risk short circuits once the diodes are in place, so be prepared also to use a lot of heatshrink!

Thats the first three anti-data-contention diodes installed, in other words - the 10MHz, first and easiest, switch!

Whilst I have this set apart, it makes sense to do all and any mods I might want, so once these are done, the -2kHz offset mod, the CW(W) to LSB switch mod (even though this one has no LSB mod yet!) and even the S-meter, will all be done.

At this stage, the potential to fuck it up is enormous! All I can do is work slowly and methodically, taking photos and making notes at each stage.

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