[amsat-bb] DC on Coax

["Stan,WA1ECF" <stanwa1ecf@xxxxxxxxxxx>]

Hello Cedar Ryan,

Many radios do not publish the DC power capability of the DC injected
onto the coaxial cable. The ones that do, only allow 0.1A or less.
 If you exceed this limit, you may blow out the switching transistor and
you know that it will be a very small surface mount type buried in the 
depths of the radio.
Difficult to repair, if available.

I avoid using the radio to inject DC onto the output coaxial cable.
 Instead, I use a sequencer and a separate DC injector to put the DC 
onto the coax.

Mic PTT is grabbed before it goes to the radio, and it is routed to the 
sequencer.
The sequencer transceiver PTT out is routed to the
transceiver. The sequencer preamp power output is routed to the
DC injector. The sequencer outputs are dry relay contacts that can 
handle 0.5 amps or more.
Only in RX mode will DC be injected onto the coax cable.

Once TX/PTT is energized the DC to the preamp is turned OFF,
then the IPA, PA, then transceiver are TX enabled.

Going back to RX from TX, the preamp power is reapplied and the 
IPA/PA/transceiver
PTTs are disabled.

Down East Microwave, Advanced Receiver Research, LNA Tech, JBM Eng
SSB electronics, all offer sequencers.

Stan, W1LE  LM-496    FN41sr




ZZZZZ
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