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hamradioversion3.0examsandprograms1992.iso
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tnc2.5
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1990-08-26
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2KB
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31 lines
TNC2.5
Hello,
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