[TenTec] Omni D odd behavior
dukeshifi at comcast.net
Fri Sep 29 20:24:31 EDT 2017
There are two types of “old Ten Tec Guys”. The first is an old guy (sorta like myself) who has some expertise in Ten Tec gear, and the second is any person who has knowledge of old Ten ten radios. I seek the later…
I have an Omni D on which I had done the PTO rebuild, replaced the receiver antenna switching relay and a few minor things. All seemed well, it would receive well, resonate well and so on. It would transmit on all bands EXCEPT the one to which the receiver was resonated. After a lot of digging it became obvious that the receiver was not being fully turned off in transmit.
Measurement of the T and R voltages confirmed this - the R voltage only went down to about 5.5 volts in transmit. Thus any tiny stray RF could still couple through the receiver with predictable and unfavorable results.
Of course I first checked out the control board and found all was well. However, as I removed the blue/white wires (the R voltage lines) I did not lose the residual 5.5 volts until I unhooked the wire going to the RF amplifier stage. At this point the R voltage properly dropped to a few mV in transmit.
Now there is no source for voltage from that RF amplifier board other than the “R” voltage, which should go to near zero in transmit. However, even when I lift this wire from the R line, I still measure about 9 volts on the line (high impedance, obviously, since this loads to 5.5 volts when reconnected to the R line).
That RF stage is impossible to remove so I opted to put a steering diode in the R voltage line going to it, thereby allowing the RF stage to be powered in receive and then do whatever it pleased in transmit with no ill effects.
Now the radio works perfectly.
However, I am still curious as to whether or not anyone else has seen this and what did you do to correct it? My fix works but my curiosity still rages.
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