Brian,
Page 19 of K3 manual near bottom of second column tells what you
need to know. Using TX INH set to HI=inh you apply about 5v to keep
radio inhibited from transmitting. To active TX you take line 7 = LO
(ground). Elecraft shows how you can wire +12V thru a 2.2k to 10K
resistor to provide 5v to pin 7 (6.6K probably will be fine to do
this). You need to ground pin 7 to enable RF OUT IN TX.
Or provide 5v to pin 7 thru a 1K resistor and ground pin 7 to
TX. The resistor limits current when the line is grounded;
See: http://www.kl7uw.com/TX-INHIBIT.htm
pin 7 needs to be HI=5v or LO=grounded. Leaving pin 7 unterminated
(floating) will result in erratic operation.
73, Ed - KL7UW
------------------------------------------
From: Brian Moran <[email protected]>
To: Elecraft Reflector <[email protected]>
Subject: [Elecraft] TX_INH input (pin 7 on ACC) behavior
With my early K3, I'm attempting to control the TX_INH line on the
ACC Connector, and am finding this odd (to me) behavior.
Starting with the radio off, I'm driving the pin with either 0 or 5v
through a 6.6K resistor per the Elecraft manual. I set the TX_INH
mode to HI in the config screen, and even with the line NOT driven,
TX_INH is indicated by the flashing TX in the display.
If I get out my Fluke VOM, I see that there's around 0.2v measured at
pin 7... BUT THEN THE TX INHIBIT goes off (that is, it starts working
as described in the manual)?? Is the TX_INH line floated in the radio?
?Do I need to also "pull down" this line to ground through a suitable
high-value resistor?
Adding a 470K ohm to ground seems to make everything happy. If this
is expected behavior (requiring pull down as well as pull up),
perhaps this could be mentioned in the manual in the future (maybe it
only matters to my era of K3 radio -- #512)
What makes this a little more difficult to debug is that after the
line has been measured with the meter, causing it to work, TX_INH
sometimes continues to work (High=inhibit, LO=tx). Until I power
cycle the radio.
Anyone who has done this before have any insight?thanks,-Brian N9ADG
73, Ed - KL7UW
http://www.kl7uw.com
Dubus-NA Business mail:
[email protected]
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