[R-390] Muting the R-390A to use it with a Collins 310B1

Ed Tanton n4xy at ATT.NET
Thu Dec 13 18:22:35 EST 2001

Hi Derek... 1) don't switch it to STANDBY; 2) Why not use another relay
to either: a) open the audio line (for SSB); or, b) somewhat reduce the
audio for CW.

It's not like there aren't a plethora of appropriate relays available
surplus; and all you have to do is get a DPDT relay having the same
voltage as the Dow Key, and you're in business. The Dow Key can switch
the RF for you, and the 2nd relay operates on the audio out.

A simple SPST switch can be wired in series with the audio dropping
resistor which is in series with the audio SPDT audio TX contacts. If
the switch is closed, it allows the switched-in-on-TX contacts to take
the rcvr audio output and effectively place the closed switch and the
resistor in series with the (rcvr audio) output-to-speaker line. This
has the effect of allowing you to hear a somewhat muted audio on TX.
Opening the switch means that when the contacts switch, there is an open
circuit to the speaker.

When TX is 'ON', both relays activate. The normally closed contacts (TX
= OFF) are used to simply take the rcvr audio output to the speaker.
Those contacts open up when you transmit (TX = ON).

If you use a DPDT relay you can use that TX = ON closure of the second
set of contacts to operate your amplifier/whatever.

I am building my own dual line (one for HF/etc. & one for
VHF/UHF/scanning/etc.) 8 channel per line, audio controller. It allows
(on each line): 1) several filters to be inserted-including an NIR-12
per line); 2) selection of one or all channels into a mixer/amplifier;
3) DC-only switching on all channels-using relays straight to the
connectors involved-except the rotary output selection; 4) line-level
pickoffs for RTTY/etc. w/VU monitoring; 5) wire-wrap programmability of
function-to-relay/connector set (in case of faults in any of the
components related to a particular relay/connector set [for later repair
during contests/etc]); 6) state indicators for all switches and relays;
and 7) switch selection of dual Phillips DCC recorders on both lines. I
am further along with this than my website page really indicates, but
you can see much of the designs (and some need changing) on my Homebrew
website page: <http://www.qsl.net/n4xy/hmbw1.html>. Near the bottom of
the page. Please feel free to browse around elsewhere while you're at

73  Ed Tanton  N4XY  <n4xy at arrl.net>

Ed Tanton  N4XY
189 Pioneer Trail
Marietta, GA  30068-3466

website:   http://www.n4xy.com

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