Re: problems with soundmodem (userspace)

[Jochen Schaeuble <psionic@psionic.de>]

Hi,
thanks for your reply. I've found the problem. As you suggested it had 
something to do with the audio level. The soundcard-interface I use here 
seems to have some problems. If I directly connect the audio output of 
the soundcard to the data input of the TX everything works.

Thanks for your help.

vy 73 de Jochen DG1PSI

Dave Platt wrote:
> Jochen Schaeuble <psionic@psionic.de> wrote:
> 
>>Hi,
>>I have several problems setting up the userspace version of soundmodem 
>>with 9k6. Everything works perfect if I only send a small set of 
>>characters (like c or m) - but sometimes a bit slow. If I enter a larger 
>>amount of text (like a message) the connection is lost after about 10 
>>minutes of retries. Any hints what I'm doing wrong? I use a Yaesu FT-817 
>>with Debian testing (Kernel 2.4.22, ALSA). The parameters of soundmodem 
>>are as follows:
>>
>>txdelay="150" slottime="30" ppersist="30" fulldup="0" txtail="25"
>>
>>As terminal I use xcall.
>>
>>Is it better to use the kernelspace driver?
> 
> 
> From what I've seen, problems with the user-mode soundmodem driver
> can fall into the following categories:
> 
> -  Incorrect audio levels.  A receiver whose audio output is too
>    "hot" can overdrive a PC's sound card input, clipping the
>    waveforms and distorting the signal.  Similarly, a PC whose
>    audio output level is set too high can overdrive the rig's
>    microphone or accessory audio input, clipping the signal or
>    overdeviating.
> 
>    The 9k6 FSK modulation is, I understand, quite "touchy" in
>    terms of the transmit audio level.  Since you're driving the
>    modulator directly, too high an audio output level can
>    easily over-deviate your signal, and you might drive the
>    signal out past the receiving radio's discriminator lock
>    range.
> 
>    See if you can find someone in your area who has a
>    deviation/modulation meter, and see whether you're pushing the
>    transmit deviation too hard.
> 
> -  Incorrect setting of the radio.  For 9k6 FSK, you can't use
>    the mic and speaker jacks.  You must use an audio interface
>    which bypasses the transmit equalization circuitry, and which
>    gives you access to the receiver's discriminator output without
>    re-equalization.  Some radios with auxiliary audio jacks have
>    a menu setting e.g. "1200" or "9600" - if the FT-817 has such
>    a menu, make sure you've selected 9600.
> 
> -  Sound-card resampling problems.  Many modern PCs use sound
>    interfaces based on the AC97 codecs, which have only a couple
>    of hardware sampling rates.  The soundmodem driver may be expecting
>    to use a different sampling rate.  If the soundmodem sample rate
>    and the codec sample rates don't overlap, then somebody has to
>    re-sample the audio data - some chipsets do this in hardware, while
>    others have no such ability and require the CPU and drivers to do
>    the resampling.  ALSA's OSS-compatibility driver will try to do
>    resampling, but some reports on this group seem to indicate that the
>    resampling code has bugs in it and can result in bad samples being
>    transmitted or received.
> 
> Also, packet transmissions in general and (I think) 9k6 in particular
> are often quite sensitive to RF signal quality.  In particular,
> multipath reflections can result in enough inter-symbol interference
> to render the signal unreadable.  Use of directional beam antennas,
> mounted high up in the clear, may clean up the signal enough to make
> the channel usable.
> 
> Another thing to check is to make sure that your radio isn't set
> in a power-saving mode, which leaves the receiver turned off much
> of the time.  These modes play merry hell with packet, as the SYNC
> bursts are often lost.
> 
> My guess is that the kernel soundmodem driver is probably not going
> to be the cure for your problem... the fault lies elsewhere.