[FADCA] Re: Help needed from all TNC-2 Experts

[Dan Babilla]

I agree with Chuck.....

I have 3 MFJs with the G3RUH 9600 baud modems in them. 2 of them are wired
direct into the channel element of a Mitrek and there is plenty of audio.

The other one I use as a TNC 2 wired direct to my Yaesu FT-736 modulator
which I use to work the PCSATs.

Dan


-----Original Message-----
From: fadca-bounces at mailman.qth.net [mailto:fadca-bounces at mailman.qth.net]
On Behalf Of Chuck Hast
Sent: Sunday, October 15, 2006 11:36 AM
To: bud Thompson
Cc: Charlie N3PPC; fadca at mailman.qth.net; k4gbb at earthlink.net
Subject: [FADCA] Re: Help needed from all TNC-2 Experts

On 10/15/06, bud Thompson <budt at cfl.rr.com> wrote:
> (How  many are there out there?)
>
> We have run across several MFJ TNC-2 clones (i.e. 1270c, etc, etc.) that
> have zilch TX audio output at the 5-pin din to the radio.  Circuit tracing
> indicates plenty of TX audio from the modem clear out to a 0.33 capacitor
> coupling to Pin 1 of the 5-pin din.
>
>  circuit looks like this:
>
> TXA generator ---> 0.0047mfd->-7.5k resistor-> 0.33mfd->Pin1 5pin din.
>                                                                         |
>                                                                         |
>                                                                   560 ohm
>                                                                         |
>                                                                      GND
>
> That 560 ohm (swamping?) resistor to ground is really swamping the
circuit.
> Lift if off ground and there is plenty of TX audio.
>
I wonder if the .0047 is bad and passing less audio, or the load on the
TNC is higher than expected? Is there any audio with no load on pin1 of
the din?


-- 
Chuck Hast  -- KP4DJT --
To paraphrase my flight instructor;
"the only dumb question is the one you DID NOT ask resulting in my going
out and having to identify your bits and pieces in the midst of torn
and twisted metal."
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