[R-390] Break In Operation of R-390 & CV-591 Converter

[roy.morgan at nist.gov]

Quoting "David C. Hallam" <dhallam at rapidsys.com>:

> Has anyone had any experience operating break in with the R-390 and & CV-591
> converter.  My set is not fully muting when the break in relay is activated.

David,

I have not done break-in with an R-390, but I can tell you a bit about the
break-in relay and how it works:

The R-390A break-in relay is a 6.3 volt AC coil device and draws about 40 mA of
current to operate. Grounding the rear terminal strip connection by an external
relay or switch (with the radio function switch in the Break In position) makes
the connection. The 6.3 volts is drawn from the internal filament supply.  You
cannot use a solid state switch or logic line to do the job.

The break in relay does two things:
 - it causes the antenna relay to operate. (I think it is energized to pull the
relay in.) This unhooks the antenna connector from the RF input coil(s) and
grounds the antenna input jack.
 - it grounds the audio in the radio at the output of the detector - input to
the common audio preamp stage.  Thus both line and local audio are supposed to
go away.

The rusult is that the radio is still completely operating at whatever gain you
had set (changed by the AVC when the antenna signal goes away partly or
completely) but the audio signal is or should be muted by being grounded.  Note
that with the CV-591, any signals from the IF strip will be processed by the
CV-591 as normal. The AGC in the 591 may operate also, incresing gain when the
IF signal goes down.  I can't remember if the CV-591 has any provision for
external control of its audio or gain.

This whole system is meant to operate with push to talk type
transmitter/receiver control.  It is not capable of QSK type CW break-in where
you hear the receiver between the CW dots and dashes being sent.

In expectation of one day setting up a station for full break-in CW operation, I
 have collected the experience and advice of folks on mail lists about full CW
QSK operation. It takes a number of elements that the R-390A was not designed
to have. Some of these elements are:
 - very fast switching of the transmitter from on to off, with CW waveshape
under control
 - fast and very reliable switching of the antenna from transmitter to receiver:
 this usually involves vacuum RF high voltage relays, or in modern radios, PIN
diode switch arrangements
 - possibly a second antenna for the receiver only
 - very stiff control of receiver gain - access to the receiver AGC circuits,
and modificaiton of attack and decay times may be involved.
 - possibly reduced and controllable receiver gain during tranmit times to
provide a monitor function.

I have seen the R-390A operated in push to talk break in operation with an AM
transmiter, and it works just fine. (Presumably, it will work just as well with
T/R control for RTTY) CW QSK break in is another matter, and will take a more
complicated system.

Roy


Roy Morgan
7130 Panorama Dr.
Derwood MD 20855