The SSM2165 is a good speech compressor and not expensive. I'm assuming it
will work on data....? to bring up the level as required.
You can get a complete kit from www.box73.com DYC-817 (Code 734980)
External dynamic compressor kit for FT-817.
Or from OK1CDJ, but I can't find the link at the moment.
This will incur some extra noise, but there are components to adjust to
optimise compression etc.
David
G3UNA
----- Original Message -----
From: "Joe Subich, W4TV" <[EMAIL PROTECTED]>
To: "'Michael Keane K1MK'" <[EMAIL PROTECTED]>; "'Elecraft Reflector'"
<elecraft@mailman.qth.net>
Sent: Thursday, August 16, 2007 5:50 PM
Subject: RE: [Elecraft] external soundcards for digimodes
Obviously, the performance specs for a 24-bit sound card should be
better than for a 16-bit card.
Does anyone know which software apps actually do make use of the
extra bits and the higher performance of a 24-bit sound card?
There is not much that can be done in the application to take
advantage of the 24 bit sound cards. All of the devices are
limited on the "strong signal" end of the spectrum by their power
supply (typically 5 volt) which limits the signal to the ADC to
about 4.5 volts p-p. On the low signal end, the digital software
is limited by the noise level from a "quiet band" (receiver IF
noise, atmospheric noise, etc.) at the receiver output. From memory,
most receivers I've seen show composite noise floors about 80 dB
below their peak output (peak output is generally around 200 mV
average or somewhat less than 1 volt p-p) with no antenna and
"quiet band" noise around 70 dB below maximum output.
Even if the DSP algorithms in the digital software could get 10
dB below the noise, the 16 bit sound cards with their 95 to 97
dB theoretical dynamic range would be more than enough for most
amateur work at HF.
They key to getting everything you can with soundcard modes on
HF is having a very low noise audio amplifier between the
receiver and ADC (it may be in the soundcard) and minimizing
any power supply and logic noise in the sound card. If you
will be using AGC and narrow filters in the receiver (one
key to maximum weak signal effectiveness), the receiver AGC will
limit the dynamic range into the sound card to well less than
40 dB (the difference between MDS and AGC threshold) in any case.
You want the peak audio to be as close to the 4 V p-p point
as possible to make maximum use of the sound card's available
dynamic range as you can. If the maximum signal to the ADC is
only one volt p-p you have already given away 12 dB of DR!
73,
... Joe, W4TV
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of
Michael Keane K1MK
Sent: Thursday, August 16, 2007 11:49 AM
To: Elecraft Reflector
Subject: Re: [Elecraft] external soundcards for digimodes
At 09:08 AM 8/16/2007, Don Wilhelm wrote:
>Typically, the more bits in the Soundcard A-D conversion, the better
>the dynamic range. There is also the noise floor of the
soundcard to consider.
>
>Most internal soundcards are 16 bit while the upgrades are typically
>24 bits for the A-D.
Obviously, the performance specs for a 24-bit sound card should be
better than for a 16-bit card.
However, in his review of sound cards for Amateur Radio that appeared
in the May 2007 QST, Jonathan Taylor, K1RFD wrote that very few
digital-mode apps are designed to take advantage of the higher
precision when it is available.
Does anyone know which software apps actually do make use of the
extra bits and the higher performance of a 24-bit sound card?
73,
Mike K1MK
Michael Keane K1MK
[EMAIL PROTECTED]
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