[CW] OT DSP Speakers/Aftermarket products

[David J. Ring, Jr.]

Hello Mike,

DSP "only" works when there is a wide bandwidth (either of which ever type - 
audio or radio frequency).  There is an advantage of having r.f. DSP in the 
intermediate frequency (i.f.) amplifiers of the radio.  This is done usually 
around 15 kHz or so.  The advantage is that the noise that is eliminated 
doesn't trigger the automatic gain control (AGC) which controls (usually) 
the i.f. and r.f. amplifier gain.  So if the noise is QRM/QRN and is 
eliminated with DSP your receiver is fully sensitive to signals and isn't 
blocked by the AGC turning down the gain.

Audio DSP suffers from desensing of the receiver - since the QRM is already 
in the i.f. strip, it pumps the AGC and turns down the sensitivity of the 
receiver - unless the receiver uses audio derived AGC.

However when used on CW with very narrow filters, the DSP doesn't have a 
chance to work because the signal to noise ratio is very high with such 
filtering - not much noise gets through.

My ICOM IC756PRO has i.f. DSP and it is quite useful at 3 kHz SSB, somewhat 
useful at 1.2 kHz CW and not useful at all at 50 Hz CW selectivity.  (Yes 
that isn't a typo!  The '750PRO family can go down as narrow as 50 Hz.)

Put another way the narrower the filtering, the less effect the DSP has.

I think a 250 Hz filter for your radio would be a much better use of your 
money.  You won't be bothered by nearby signals and you'll have much less 
noise in your ears.

73

David Ring, N1EA

----- Original Message ----- 
From: "Mike Besemer (WM4B)" <mwbesemer at cox.net>
To: <cw at mailman.qth.net>
Sent: Monday, January 16, 2006 10:44 AM
Subject: [CW] OT DSP Speakers/Aftermarket products


Please pardon the off-topic post, but I was wondering if anybody on the list
has any experience with any of the DSP speakers or other aftermarket DSP
products currently available.



I really can't afford (or justify, anyway) a new rig, but would like to have
SOME sort of DSP.  I see that a lot of the new rigs only have AF DSP anyway,
as opposed to IF DSP, therefore it occurred to me that an aftermarket
product might not be too bad a deal.



I'm running a TS-440SAT and operate primarily PSK-31 and CW.



Any thoughts?



-- de WM4B

Mike

Kathleen, GA

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