> 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 don't want compression on data modes. Better to use a good low noise, single rail op amp with a low noise reference as a preamplifier to bring the maximum receive level up to 4 V P-P. Compression effects the characteristics of some data modulation modes (one reason for the suggestions to not run any transmit ALC with data modes other than FSK). 73, ... Joe, W4TV > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of David Cutter > Sent: Thursday, August 16, 2007 1:19 PM > To: Joe Subich, W4TV; 'Michael Keane K1MK'; 'Elecraft Reflector' > Subject: Re: [Elecraft] external soundcards for digimodes > > > 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'" > <[email protected]> > 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] > >> > >> _______________________________________________ > >> Elecraft mailing list > >> Post to: [email protected] > >> 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: [email protected] > > 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: [email protected] > 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: [email protected] 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
