[Elecraft] external soundcards for digimodes

[David Cutter]

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" <w4tv at subich.com>
To: "'Michael Keane K1MK'" <k1mk at alum.mit.edu>; "'Elecraft Reflector'" 
<elecraft at 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: elecraft-bounces at mailman.qth.net
>> [mailto:elecraft-bounces at mailman.qth.net] 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
>> k1mk at alum.mit.edu
>>
>> _______________________________________________
>> Elecraft mailing list
>> Post to: Elecraft at mailman.qth.net
>> You must be a subscriber to post to the list.
>> Subscriber Info (Addr. Change, sub, unsub etc.):
>>  http://mailman.qth.net/mailman/listinfo/elecraft
>>
>> Help: http://mailman.qth.net/subscribers.htm
>> Elecraft web page: http://www.elecraft.com
>>
>>
>
> _______________________________________________
> Elecraft mailing list
> Post to: Elecraft at mailman.qth.net
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com