I'm suprised that 'eye diagrams' are mentioned at all for 2100baud Bell202 as
the two tones are not harmonically related so hence unlikely (with random data)
to produce a display thats useful - I've not looked at the soundcard stuff to
see what qualifications are made using this diagnostic tool.
A very common cause of bad decode is unmatched pre-emphasis/de-emphasis.
Standard voice radios filter audio with a passband from 300 to 3400Hz and that
region has a 6dB/octave rising characteristic for pre-emphasis and similar on
the receive. If at all possible, look at both transmitters on a radio that has
access to the discriminator (as used for 9k6) and check the relative levels of
the two tones on a 'scope.
Despite a mixture of radios on the channel, I've found that a 'flat' response
seems to work best on both transmit (for others to decode) and receive (when
I'm looking at a variety of others).
On Mon, 13 Dec 1999, you wrote:
> My station's performance on 1200 packet seems to be appalling; some
> packets simply don't seem to get decoded properly. The biggest problem
> is that my transmitted packets don't get decoded properly on the other end.
>
> I've tried increasing the txdelay and it doesn't seem to make
> a significant difference. The station I've been testing with is
> just a standalone TNC digipeater. I think the power output here should
> be good enough over this path (25W into a vertical).
>
> Receive decoding is fairly reliable although not 100%.
> I'm using the soundmodem with an SBPro card. The eye diagram in
> smdiag looks OK (although as the manual page notes, the diagram
> is distorted for 1200 mode). Can anyone with a reliable setup post
> a screen grab of the eye diagram? I'd like to see how mine compares.
>
> I mainly use APRS here, so poor performance is not going to fill
> the channel with retries. It'd still be nice if it worked a bit better
> though. Any ideas where I might be going wrong? The rig is a Yaesu
> handheld. I'll try an ex-commercial set once I make up the cables.
>
>
> thanks
> Hamish VK3SB
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