Been mulling over how to drive my transverter.
From what has been posted about the FT-817, it sounds like a great I.F. rig, but the extra expense is out of the question at this stage.
(Will probably get an 817, if I build more transverters in the future.)
The VK3XDK transverters need 7dBm (5mW) of drive.
I already have an Icom IC-910. Specified at 75W o/p @ 70cm.
Before I go any further, driving the transverter needs to be idiot proof!
I can't rely on myself remembering to turn the power down.
The original plan was to design everything so that the IC910 always ran full power o/p. (Nothing to turn down!)
However, this seems like a waste of power, and would require a higher powered (read as: bigger, more expensive) relay that would split off the TX and RX paths inside the transverter.
How's this for an untested concept;
I don't plan on having an external 70cm preamp, so why not use that "feature" (on/off in SET mode) to activate an relay that kills the 13V feed to the UHF PA transistors Q151 and Q512.
See attached diagram.
I wonder how much "leakage" of the TX signal would end up at the antenna connector?
We only need 5mW here don't forget, and the RX path in the IC-910 remains unaffected.
Only one 10A 12V relay + 1N4001 diode required.
I would also use that 12V preamp power appearing on the UHF antenna connector to activate the transverter.
ie; DC sense inside the transverter, which would be the master 12V switch to the rest of the transverter.
No power switch on xverter required... a bit like having it in a STDBY state.
So, the [SET mode] PRE-440 setting would;
1) Reduce the 910 UHF power output to bugger all, by killing the 13V to the PA stage
2) Activate the transverter
This idea totally relies on having enough RF drive pass through the Q151/152 base-collector junctions.
A bit like, bugger all output, when you've blown your finals. :wink:
How dumb is this idea?