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QRZ! Ham Radio 18
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QRZ Ham Radio Callsign Database - Volume 18.iso
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tc2duplx.txt
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2001-11-01
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34 lines
Subject: TNC2 Duplex Mod
I thought I would pass along a fix for a problem that has been cropping up
more and more across the country with packet on full duplex machines.
It would appear that a lot of synthesized radios wander in transmit
frequency when the first key up. If your located in a crowded repeater area
there is a very good chance your keying up a repeater that might be within
50Khz of your transmitting frequency, on the input of repeaters. Especially
bad is the ICOM 2AT. We have spoken with ICOM about this problem and they are
working on it.
There is a simple fix for folks running MFJ TNC's or TNC2 hardware clones.
This does not include the Pac-Comm Tiny 2's or their latest TNC's on the
market. It must be a TNC2 hardware compatible clone, such as the MFJ TNC's.
The fix involves soldering a 4.7uf tantalum cap across R44 with the positive
side towards Q8, or the junction of R44 and R45. This will give you around
500ms delay of audio on the XR2206 chip, while allowing your radio to key up
immediately, without tones for 500ms. After you make the mod, you will need to
increase your Txdelay anywhere between 10-20 over what your using as a default
now. Some experimenting with the Txdelay is require to get things adjusted
correctly.
Hope this mod will help users out there, and I'd appreciate a note back to
anyone trying this and finds it fixing this problem. It has cured our problem
in this area. You may wish to post this as a bulletin for users to try out and
circulate it to other BBS's.
73, Steve N7HFZ @ N7HFZ
NAPRA Technical V.P
Copied from the QRZ! Windows Ham Radio CDROM