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Re: pin 3 on the ICOM 910H ACC socket

At 03:43 PM 1/5/2003 -0800, you wrote:
>Has anyone tried the SEND on transmit option associated with the ACC socket
>of the ICOM 910H? Not sure why they call it that, I am hoping it is a simple
>ground on transmit. ICOM radios don't give per band ground on transmit
>options like Yaesu does, but they do allow the user to disable the bands
>that shouldn't be keying an external amplifier. In my case, I have a 23cm
>amplifier that needs a ground on transmit signal. So, I have configured the
>910H to use pin 3 of the ACC socket for the 23cm band, disabling the SEND
>option for the other bands. This works just fine on SSB and CW modes but has
>a really annoying side affect on FM. When I key the mic in FM mode, the 910H
>and the linear switch to transmit mode, when I un-key the mic, both the 910H
>and the linear remain on. I have to power the 910H off in order to stop
>Does anyone know what is wrong or what is happening? Apparently, pin 3 of
>the ACC socket can be an input as well, perhaps when used as an output the
>input is still active, creating this lockup condition? This can't be by
>design, can it?

Yes, it's by design. The purpose is to allow an external TNC to key the 
radio for
packet and other data modes using external hardware.

The likely cause of your problem is rf getting back into the keying circuit via
the PTT lead. If you don't have that shielded, it should be. If that 
doesn't work,
then you might have to try some additional isolation.

You might try a diode on the output (with the cathode pointed to the radio).
Or bypass the PTT line with a .01 cap right at the output of the radio, or 
It's not a totally uncommon problem, it can happen if you have enough RF 
around, but the only place you'd notice it is on FM or data where you are 
a constant carrier.

Hope this helps.

John - K9IJ


John Rice  K9IJ
Webmaster, Network Admin, Janitor

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