[R-390] Covers & Cabinet

[Roy Morgan]

At 04:08 PM 9/26/03 -0500, you wrote:
>When the R-390/URR is installed in the cabinet does it normally have the 
>top and bottom covers attached?

Ron,

I read your post that you get no/few replies..here is one:

The covers should be removed when installing the receiver in a cabinet, 
especially in the military desktop cabinet.

>  Is there a cooling issue with both?

Yes. AND. the radio will not fit into the military cabinet with the covers 
in place.

(Question about sidetone with the T-368.)
I have no idea about the T-369/R-390A installation.  I suggest you join the 
T-368_BC-610 list below and ask those guys who have them. It is a Yahoo 
group and you need to be a member of Yahoo to get it:

>Yahoo! Groups Links
>To visit your group on the web, go to:
>  http://groups.yahoo.com/group/T-368_BC-610/

>On my R-390 someone removed the twinaxial socket on the balanced input and
>replaced it with an SO-239. The center conductor of the new connector passes
>thru to the high side of the transformer while the other side is now
>grounded. Was this a common mod?

Somewhat common, but it it means removing or butchering the antenna 
relay.  This mod was probably not done by the military or other government 
agency. The twinax connector is part of the antenna relay. It is not clear 
from your post whether or not the antenna relay is present in your radio.

>why wouldn't you just replace the connector
>on the unbalanced input with the SO-239?

Because *** without the field change that re-arranges the coax connections 
to the antenna relay***, the unbalanced input goes to a spot in the circuit 
AFTER the antenna coils and results in reduced selectivity of the front 
end, and also reduced sensitivity.

>Comments? Issues?

Comments:
The field change involving re-connecting the coax connections is detailed 
on Chuck Rippel's site, (and possibly in the Y2K manual).  The circuit 
connections of the antenna relay and the points in the circuit at which the 
two antenna connectors are connected to are shown in the radio schematic.

Issues:
Use of the UN-balanced antenna connector without re-configuring the relay's 
connections will reduce both front end selectivity and receiver 
sensitivity.  (This assumes the antenna relay is present.)    If the field 
change is accomplished, these things are not true.The normal unbalanced 
antenna coax connector requires an adapter to use normal connectors (BNC or 
"UHF"), or a mating coax connector.  Both are available at RF Connections 
(www.therfc.com) among many other places.

Roy

- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
7130 Panorama Drive, Derwood MD 20855
Home: 301-330-8828 Work: Voice: 301-975-3254,  Fax: 301-948-6213
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