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TX inhibit



Doug Faunt wrote:

Transceivers should have a "TX inhibit" input, so if it's held low, no TX would take place.

Wayne replies:

This is the approach I plan to take with my FT-847.  It should be easy to remotely disable the "key" line of the 144 MHz PA with the same signal that I use to power a 2400 MHz down converter and coaxial relay.  At most, it should only require a NPN transistor to hold the 144 MHz PA "key" line low using the 12V that is applied to the downconverter and coaxial relay.

I glanced at the schematic and it was NOT immediately obvious which signal enables the 144 MHz PA.  If I can't figure it out after studying the schematic for 5 minutes, I will have to either buy the service manual or find the data sheet for the 144 MHz PA module.

I don't have a 2400 MHz downconverter or antenna yet, so it's not a high priority for me.  I wouldn't be upset if somebody beat me to this and published "FT-847 144 MHz TX inhibit" instructions on a WWW site.      ; )


Howard Long wrote:

You could use the ALC input of the FT-847.
Rick VE3CVG did some tests on using the ALC input for a DEMI Transverter...
Check out http://207.206.11.2/ft-847/page2.htm#alccontrol <http://207.206.11.2/ft-847/page2.htm#alccontrol>  for more details.
Problem is as always is that it requires intervention to STOP the RF rather than intervention to ALLOW the RF.

Wayne replies:

I think the FT-847 have only one ALC input.  If so, this technique would disable transmit power on the desired TX band as well as the band used for the RX downconverter.  


Wayne Estes
Mundelein, IL, USA
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