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David/All,<br>
<br>
I'm not suggesting your problem is tone level related but failure to
grasp the following is arguably responsible for more TNC decode issues
than any other cause.<br>
<br>
The need for "twist" adjustment depends on the radio hardware involved
so a brief discussion is probably in order.<br>
<br>
The "norm" for an FM/PM radio is to apply 6dB (x2) per octave of
preemphasis in the transmitter. For packet, this results in the high
tone (2200Hz) having twice (near enough) the deviation as the low tone
(1200). In the receiver deemphasis is applied which restores the audio
to a "flat" condition, i.e. both tones going to the TNC have the same
level.<br>
<br>
If TNC audio is fed into the microphone socket you can depend on 6dB
per octave preemphasis. However, if the TNC audio is fed in further
down the tx audio chain, such as the audio injection point for tone
signalling, preemphasis will not be applied in the tx and should be
applied externally - with twist, in the case of the TT4.<br>
<br>
Going to the receiver again, if it receives a signal without
preemphasis, it will still apply deemphasis (assuming audio is taken
after deemphasis), resulting in the high tone being just half the level
of the low tone when fed to the TNC. FSK demodulators based on the the
exar pair 2206/2211 will not decode if the high tone is lower in
amplitude than the low tone, by even a very small amount.<br>
<br>
If rx audio is taken from the demodulator in the radio, i.e. before
deemphasis, the preceding is not a problem because audio that is
transmitted "flat" will be decoded "flat".<br>
<br>
The exar chip set (found in genuine TNC2 TNC's) is not disturbed by
high tone being considerably higher in amplitude than the low tone.<br>
<br>
In summary, every tx should employ preemphasis, regardless of it being
generated internally, or externally. That will eliminate any decode
problems in TNC's with finicky chip sets because high tone will always
be the same level as, or higher than, the low tone coming out of the rx.<br>
<br>
David, is TXD 60 60mS or 600mS? Although TXD provides time for your tx
to stabilise before valid data is sent, it can also have an impact on
the remote rx in cases where muted audio is being used for the TNC.
There are some very sluggish receivers kicking about and TXD needs to
be long enough for that rx to unmute. My Icon handheld scanner is
pathetic in this regard, with the mute being so slow that I can miss at
least half of the digi beacon, even when I'm at the digi site.<br>
<br>
Get that CRO working and save your hair, lest you should end up like me
<span class="moz-smiley-s1"><span> :-) </span></span><br>
<br>
Ray vk2tv<br>
<br>
<br>
<br>
David and Justine Olsen wrote:
<blockquote
cite="mid:9B237126-EE07-4BDE-BC8A-AFA14D998086@bigpond.net.au"
type="cite">I am presently running TxD of 60 and TXTWIST of 50. I've
tried a range of TXTWIST but none sound too different
<div>David</div>
<div><br>
<div>
<div>On 18 Feb 2010, at 00:36, Scott Evans wrote:</div>
<br class="Apple-interchange-newline">
<blockquote type="cite"> <br>
ABAUD is just the speed set for serial port 1 ... what TXDELAY are you
running? because depending on how quick you radio is you may need to
lengthen the delay a little, also check the TXTWIST setting too, this
controls the level between the 1200Hz & 2200Hz tones.<br>
<br>
On Wed, 2010-02-17 at 21:51 +1000, David and Justine Olsen wrote:
<blockquote type="CITE">
<pre>ABAUD is set to 19200
On 17 Feb 2010, at 21:37, Norm, VK3XCI wrote:
> Sort of like 9600 baud?
>
>
>
>
>
>
>
> 73 de Norm, VK3XCI
> Mildura, Australia
> The Wintersun City
> QF15bt.
>
> David and Justine Olsen wrote:
>> I've gone through all of the TT4 audio adjustments as explained in
>> the help docs by listening on another set, but still no success being
>> received by any digis.
>>
>> One thing that has me curious, is the the squak from my Tx sounds
>> nothing like those from others. The others are a deehdaaah kind of
>> sound with two distinctly different tones ate the beginning and end
>> tone, whereas mine is a sqaaaark :-) of mixed tones at the same time.
>>
>> David
>>
>> VK4MDX
>>
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<td> -- <br>
Scott Evans <<a moz-do-not-send="true"
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