[hfsig] Performance of 24/192 soundcards? USB Soundcards

[Anthony.N.Martin at marconiselenia.com]

> Bad idea (to use the standard mic connector). Been there, done that.
> The problems are:

> * most mic connectors are followed by an AGC/limiting circuit, which
> introduces nonlinear distortion

A bigger problem I've just thought of is the hard audio bandwidth
limits applied by filters in many of the CTCSS chips; 300Hz to 3kHz.

> * some (most?) handhelds do not disconnect the internal microphone when
> you connect an external one, so any ambient noise gets transmitted along
> your modulation signal

Well that's just broken. You couldn't even use that with a headset
in your car. I've seen some very cheap PMR446 and CB handhelds and
I've not seen this. Return to supplier. Problem solved. Next.

> The best I could get was about 4.8kBit/s, and that was pretty fragile.

What did you try?

I suppose that if we want to develop higher-BW more spectrum-efficient
modulations for V/UHF 12kHz channels we have to design our own digital
I/Q transceiver.

Another subject:
Have you seen this digital HF transmitter-on-an-FPGA?
http://www.microtelecom.it/digimit/

Ant M1FDE

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