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

Sun, 2 Jun 2002 09:57:52 +0200

Hello Bill,

Good filters in early IF-stages are very important for receiver performance;
without any doubt! This is one of the benefits of rigs like the
1000MP/MarkV.

I use a SCS PTC-IIpro for digital modes. You may consider this as a high-end
TNC which is very advanced.

PACTOR-III requires a bandwidth of 2.2 kHz on the HF band, which means that
it requires more space than PACTOR-II (with 500 Hz) did. That's why a speed
advantage of factor 3..5 compared with PACTOR-II is achievable, with NO
degradation of robustness. The transceivers must be set to the 2400 Hz
IF-filters, 500 Hz filters do not work any more.

73, Hans Remeeus PA1HR.

e-mail: [email protected]
site: www.remeeus.nl
Ham Radio call: PA1HR

----- Original Message -----
From: "WD8ARZ" <[email protected]>
To: <[email protected]>
Sent: Saturday, June 01, 2002 11:25 PM
Subject: [1000mp] Sound Card Digital/Ritty Modes - Filters/Rx Performance

> 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
> [email protected]
>
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