[1000mp] Sound Card Digital/Ritty Modes - Filters/Rx Performance

[WD8ARZ]

If your working a weak signal and sending that to a sound card for
processing, and a stronger signal near the edge of the filter bandwidth in
your receiver your using comes on (even though outside the bandwidth of the
digital program mode) and reduces the RF gain due to AGC action, there will
be a negative impact to the sound card program, both due to reduced signal,
but also due to interference in the audio stream.

My expectation is that receiver performance issues are as much a factor with
a sound card interfacing, especially bandwidth considerations, as not using
a sound card. Keep in mind that filters are in the I.F chain, and critical
to performance for bandwidth, and what signals will affect the agc system.
Programs using Dsp at audio levels are no better than the crud that comes
its way from earlier stages in the receiver. There is no substitute for good
filters for the mode in use in early I.F. stages.

I see several problems in sound card programs, even though I do use them.
Many sound cards dont use crystal control in their oscillator systems, thus
some sound cards are virtually worthless in some digital modes, especially
Ale and PCHFDL Acars modes. Some will work, even with some drift. Many do
not work at all ..... There are few crystal controlled sound cards out there
I have heard, but much worth having .... no I dont know which ones those
are, it is a future research project for me on this on ...  hi hi

Sound Card gain control and mixing issues are easy to manage in some
systems, and very poor in others. Makes the interface a challenge at times,
especially in a transmitting environment.

Crystal controlled Tnc/Modems tend to be designed for transmitting and not
just receiving, making it a much better performer for digital modes than
sound cards .

Hf/Vhf/Uhf radios with built in tnc/modems are a must for some of the better
performing digital modes these days, and we will see more of this in future
ham products. Ale in particular is popular for this kind of radio hybrid.

Would appreciate anyone else's insight.

73 from Bill - WD8ARZ
wd8arz@ix.netcom.com