GILLMANN@USC-ISIB.ARPA (11/09/85)
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 -------
ai2q@ky2d-2.UUCP (Alex) (11/15/85)
> 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>>
john@anasazi.UUCP (John Moore) (11/15/85)
In article <370@mit-eddie.UUCP> GILLMANN@USC-ISIB.ARPA writes: >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 I have made a (crude) remote base using the 2AT. It turns out that if you provide a high impedance path from mic audio to ground when you want PTT, and leave it open otherwise, it will work. I think about 10K will do it. To find out, just connect a test resistor from the hot mic lead to ground. Warning: I found out that if you have it "key down" with this method, and you power it off and on, it will come up in a wierd state from which it cannot recover without powering it off, opening the mic lead, and powering it back on. -- John Moore (NJ7E/XE1HDO) {decvax|ihnp4|hao}!noao!terak!anasazi!john {hao!noao|decvax|ihnp4|seismo}!terak!anasazi!john (602) 952-8205 (day or evening) 5302 E. Lafayette Blvd, Phoenix, Az, 85018 (home address)
GILLMANN@USC-ISIB.ARPA (11/18/85)
From: Richard Gillmann <GILLMANN@USC-ISIB.ARPA> Thanks for replying to my request for help. I finally figured out a circuit that works (with a little help from my friends). To connect an Icom 2AT to a TNC2 I just used a 33K ohm resistor between the PTT line and the TX audio line. It seems to work fine. The TNC2 uses an FET to key the PTT line and it already has a blocking capacitor on the TX audio output. I'm glad to hear that you approve of the resistor approach, which I can say after two days of use seems to work just fine. 73, Richard N6MPP -------