Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/5/84; site ky2d-2.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxn!ihnp4!drutx!mtuxo!mtunh!ky2d-2!ai2q
From: ai2q@ky2d-2.UUCP (Alex)
Newsgroups: net.ham-radio.packet
Subject: Re: Icom 2AT PTT
Message-ID: <53@ky2d-2.UUCP>
Date: Fri, 15-Nov-85 00:50:15 EST
Article-I.D.: ky2d-2.53
Posted: Fri Nov 15 00:50:15 1985
Date-Received: Sat, 16-Nov-85 08:48:14 EST
References: <370@mit-eddie.UUCP>
Organization: KY2D-2 Packet Radio Gateway, Little Silver, NJ
Lines: 26

> From: Richard Gillmann <GILLMANN@USC-ISIB.ARPA>
> I'm just finishing construction of my TNC2 and I'm trying to figure
> out how to interface it to an Icom 2AT handheld.  The 2AT doesn't seem
> to have a separate PTT line as the TAPR documentation assumes.  From
> reading the 2AT schematic I see that the PTT switch merely interrupts
> the ground return side of the mike.  Has anyone had any experience
> hooking up a 2AT to a TNC2 (or for that matter to any kind of
> packet controller)?  I'd sure appreciate any advice.
> 
> 73,
> Richard N6MPP
> -------

*** REPLACE THIS LINE WITH YOUR MESSAGE ***
Dear Richard:
I've found the easiest way to connect either my GLB TNC (which uses a 
bipolar keying xstr) or my TAPR TNC1 (which uses a FET) is via small
audio xfmr. I've used junkbox specials with roughly 1:1 turns ratio as
well as two xfmrs back-to-back to establish an approximate 1:1 ratio.
The Z is abt 600 to 1000 ohms. Simply feed the AFSK from the TNC ouput
into the primary (grounding one end). At the secondary, pick off the afsk
at the xfmr "top" and ffed it to the combined PTT/mic line. Pull the "cold"
end of the secondary to ground with the keying xstr. That's all there is to
it; it works FB here. I've also seen a schematoc where the afsk is fed via small cap and a resistor is used to pull the line low. I've never tried it but
I see no reason why such a network shouldn't work, and it'll be cheaper.
Good luck es 73 de Alex, AI2Q, Freeport, Long Island, New York >>AR>>