[R-390] Thermal Stability and Top and Bottom Covers?

[Tisha Hayes]

Eight or nine years ago I went through the exercise of measuring internal
temperatures with thermocouples on the chassis with the covers on, covers
removed, no tube shields, shiny tube shields and IERC tube shields.

I kept the radio in a room with no airflow at a steady 22 C with the doors
closed and nobody in there moving air around. It is amazing how something
as simple as walking past the radio and creating a draft would lower the
temperature a few degrees.

For temperature, the best combo was IERC tube shields and no covers. The
heat would rise through convection and radiation off of the tube shields.

The covers did bottle up the heat and then the only thermal exchange was
through the air flow over the chassis. The radio did run hotter by 6-8 C.

While the chassis with covers is in no way a perfect Faraday cage to keep
interference out (or in), it does make a difference in providing some level
of EMI shielding.

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On my "golden" radio I modded and added beryllium-copper fingerstock on the
base chassis between the IF deck and the chassis and between the RF deck
and the chassis. There "may" have been a difference but it was below the
level of detection (maybe a dB or two of SNR). I had better luck with
conductive elastomer U shaped gasket material along the edges of the
modules.

I even went a little crazy and patched up chassis holes with adhesive
copper foil (I have a 50 meter spool of the stuff) and it too did not make
that much of a difference.

At the end I pulled off the fingerstock as it changed the spacing dimension
between the chassis and the modules, removed the copper foil as it blocked
up air flow but I left the elastomer U shaped gaskets as they made the
modules a bit snugger fitting when bolted down with the green screws.

What you really cannot improve upon is the radiated RF coming off of the
tubes. The IERC covers help some but to make it any better you would need
to defeat the cooling advantage of the shield by covering the top of the
shield with a circle of copper foil. I did not go that route.

Somewhere in my collection of USB storage sticks I have the test
information and numbers/ methodology that came from this boondoggle. (I am
sure it is hidden with my other set of car keys).  At one time I did post
it on the forum so it may be in the archives.

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I have not made any further improvements or mods on my R-390A's for a few
years. I took them about as far as I wanted to go and now spend most of my
time working with Harris RF-590's. The R-390A is still a fun radio to use
but is lacking in some of the refinements like integrated SSB capability.

*Ms. Tisha Hayes, AA4HA*
*"*There are many who live in the mountains and behave as if they were in **the
town; they are wasting their time.*
* It is possible to be a solitary in one's mind while living in a crowd;
and it is possible for those who are **solitary to live in the crowd of
their own thoughts.*"*
**-Amma Syncletica of Alexandria**