Topband: Loud clicks

[Tod -MN]

A number of years ago I fabricated a very simple circuit to "delay" the "Key
Down" signal sent to the transceiver slightly while allowing that signal to
be sent to the amplifier to change the amplifier relays from receive to
transmit during that slight delay. The delay was 20 milliseconds which
allowed the amplifier relays to change and stop bouncing before the
transceiver began the keying process. 

When the "Key Down" signal changed to "Key Up" the transceiver "Key Down"
line remained "Key Down" for an additional 20 milliseconds so the actual
length of the RF envelope sent out from the transceiver was exactly the same
as if there was no special circuit in the line to the transceiver.

In addition, the "Key Down" line to the transceiver was sensed and for 30
milliseconds after the transceiver "Key Down" line changed to "Key Up" the
amplifier change relays were held in the transmit state before being allowed
to change to the receive state. This 30 millisecond delay allowed the RF
envelope to drop to zero before the amplifier relays started their change
over. 

In principle this meant that the amplifier relays were switched to transmit
and when they were in the transmit state the transceiver was keyed and sent
out an RF envelope. About 10 milliseconds after the RF output had ended the
amplifier relays were returned to the receive state. The relays were 'cold'
switched and there was no possibility of "clicks" due to amplifier relays.
If clicks were generated in the transceiver, however, they continued to be
amplified as 'clicks'.

When I used this circuit I did not need to adjust the keying on the
transceiver from its normal setting for use without the amplifier. The
amplifier I first used this on was a Collins 30S1 which did NOT have QSK as
a feature. 

The circuit used low cost, easily available components to achieve the time
delays. It was external to the transceiver and the amplifier so there was no
equipment modification. If there is no QSK built into the amplifier it may
be necessary to add one high speed relay [ preferably a vacuum relay like an
RF1D or similar ]. Since the relay does not have to handle the possibility
of switching while significant RF current is flowing through the contacts,
the specifications for the relay will not be as demanding.

 

Tod, K0TO