[ARC5] Backwave

[AKLDGUY .]

The ARC-5 transmitters were not operated in CW by keying the relays in
the transmitter.
Both of those relays are selector relays WHICH ARE ON CONTINUOUSLY
while that transmitter is selected, even during reception. The relays in the
other transmitters, if present in the rack, are off because those
transmitters
are not selected.

To send CW, the B+ line was keyed via the keying relay in the modulator.
The B+ line (and modulation) is common to all transmitters that may be
present in the rack, but only the selected transmitter (whose cathodes were
grounded, whose oscillator B+ path was prepared, and whose antenna was
connected) would produce output.

Circuit time constants (decoupling C and R in the oscillator B+ line) have
been optimized for this configuration, although it's a bit of a compromise
as
CW was a secondary consideration. You can key the transmitter the same
way by operating both relays continuously or jamming the relay contacts
closed, and keying the B+ directly. Use a keying relay for safety's sake.

73 de Neil ZL1ANM


On Monday, October 26, 2015, Rich Post <kb8tad at gmail.com> wrote:

> Hi ARC-5ers,
> A friend and I have been experimenting with getting a BC-696A back on the
> air.  The transmitter had already been modified per standard QST design,
> with the oscillator running at all times, the cathodes keyed and, of
> course, the relays removed, so no break-in.  With good band conditions, we
> experienced  backwave.  What have you done to limit or solve backwave from
> an ARC-5 or SCR-274N transmitter on CW?
>
> Has anyone tried keying the oscillator with, say, a solid state switch such
> as a high-voltage NPN or FET along with a mechanical relay for the cathodes
> under the theory that the solid state switch would power the oscillator
> just slightly ahead of the PA?  (Assuming that the difference would be
> enough to avoid chirp)
>
> Let us know your voice of experience.
>
> Tnx de Rich KB8TAD
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