The idea behind this project is a
protection brick, that can be added anywhere, that will provide RF
Over-Voltage /Over-Current protection to whateveris
attached to the output side. It is possible I will add some lightning
protection in the form of your typical gas-discharge cartridge-BUT
I think that is better done by an
Alpha-Delta device closest to where the
antenna comes into the facility. So it is presumed that such protection
precedes
this device, as a general principle.
This
can be done with
expensive vacuum relays-such as the RJ1-A,
but the idea here is to provide just protective switching, fast enough to be
useful (< 20ms), activated by either RF or DC switching, that doesn't have
to carry significant RF, but can standoff just about anything to be
encountered in normal ham radio conditions.
Design specifications
for the particular (over the counter) reed switch I'm using are: 1000V
standoff voltage; 2A carry current, non-switching; 20W carry power (which
for a receiver protection device is more than sufficient.)
The principle idea here
is stated in the block in the lower left corner of the drawing. Basically,
if ANY of several conditions exist, the 'brick' will be OPEN, and not pass
RF any further. Those conditions include: 1) No Power; 2) 'EVENT' detection
at any of its several inputs: a) Significant (e.g. transmitter-and possibly
nearby lightning) RF at the RF-Input; or, b) An 'EVENT' at any of the
operating inputs, e.g. key, PTT, or the passed-through EVENT-Detect line
going active from some other unit (for example a footswitch intended to
switch to transmit, a similar panel switch for TUNE, etc.)
All of these EVENTs are
active-LOW, and set the unit into its BYPASS mode, protecting the connected
device (receiver or, in my case, a receiver distribution unit.) I have
included opto-isolation for EVERY data line, both incoming and outgoing.
There is also included a specific line to input the primary station keying,
and an output line to pass it along. I will probably change the output
keying to another reed relay, to simplify POS and NEG keying in changing
from a modern transistorized rig to one of my BoatAnchor rigs. I MAY keep it
solid state, and use different POS and NEG outputs.
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