18-08-2017, 01:50 PM
Lou,
The reason that I don't like DC up the coax is that you can never be sure that the RF is completely isolated from DC under all conditions (such as transient high SWR) , sufficient to affect the proper operation of the DC applied to the preamp, especially if the preamp requires a bias supply to function correctly.
I totally agree that if possible, the switching should be "fail to safe" provided other factors don't impinge on the operation of the relays.
Of course the controversial question of whether you should leave the DC "on" to the preamp on transmit or not, is another factor to consider.
Cheers
Peter
The reason that I don't like DC up the coax is that you can never be sure that the RF is completely isolated from DC under all conditions (such as transient high SWR) , sufficient to affect the proper operation of the DC applied to the preamp, especially if the preamp requires a bias supply to function correctly.
I totally agree that if possible, the switching should be "fail to safe" provided other factors don't impinge on the operation of the relays.
Of course the controversial question of whether you should leave the DC "on" to the preamp on transmit or not, is another factor to consider.
Cheers
Peter