18-08-2017, 01:24 PM
@ Peter,
Interested to learn why you would never use DC up the coax Peter? Apologies to Rick for hijacking the discussion.
Not telling you how to suck eggs but I'll give you my take on how DC up the coax should work.
Sometimes as in Rick's case we go with what has already been prepared for us. I think DC up the coax works as long as it is configured to "fail to safe".
This means the DC should be available only when the RX is active AND the DC should energize the relays. It follows that the preamp should be wired to the N.O. contacts. A failure of the DC means the relays are de-energized and the preamp is protected as it is out of circuit. As a bonus the antenna is still usable albeit without the preamp.
You could do a similar thing with two coax feeds (TX & RX) should you be be dealing with high power. DC up the RX cable (N.O. contact) and a nice beefy CX-520D relay to handle the power and further protect the front end of the preamp by virtue of grounding the inactive contact.
Of course, there's nothing wrong with using a separate DC supply but I feel the same rules for relay wiring should hold. Failure of the supply should always protect the preamp and if possible allow the antenna to still be used.
Posted in the interest of learning from others experiences.
Interested to learn why you would never use DC up the coax Peter? Apologies to Rick for hijacking the discussion.
Not telling you how to suck eggs but I'll give you my take on how DC up the coax should work.
Sometimes as in Rick's case we go with what has already been prepared for us. I think DC up the coax works as long as it is configured to "fail to safe".
This means the DC should be available only when the RX is active AND the DC should energize the relays. It follows that the preamp should be wired to the N.O. contacts. A failure of the DC means the relays are de-energized and the preamp is protected as it is out of circuit. As a bonus the antenna is still usable albeit without the preamp.
You could do a similar thing with two coax feeds (TX & RX) should you be be dealing with high power. DC up the RX cable (N.O. contact) and a nice beefy CX-520D relay to handle the power and further protect the front end of the preamp by virtue of grounding the inactive contact.
Of course, there's nothing wrong with using a separate DC supply but I feel the same rules for relay wiring should hold. Failure of the supply should always protect the preamp and if possible allow the antenna to still be used.
Posted in the interest of learning from others experiences.