DSP Capable Transceivers

[W0LC]

Thought that it might be nice to get some real user perspective on the "benefits of IF DSP" in actual on the air radios.

My opinion(s).

I have used a good many radios in the past years, many touting IF DSP and some that stated IF DSP when in fact it was AF DSP.

I have found that IF DSP equipped radios never pulled that "weak, in the mud, near ESP signal" into arm chair copy, or for that matter, made the signal that much more audible.

In the CW mode, however, I did note some improvement, but when a signal is weak, it is weak. Period. In the SSB mode, I found DSP to do little to improve the audibility of the signal. I found DSP didn't help in improving the individual's voice quality, annunciation of phonetics, etc. All in all, I found that DSP took some of the "harsh" edges off the noise on the signal but never really "pulled that weak signal" up out of the noise.

When a receiver has just so much signal strength to work with that is about it. Selectivity, signal to noise ratio, blocking dynamic range to me meant more the the ability to apply DSP to "improve" the signal.

I have found over the years that a good receiver with a number of optional filters installed made more difference in taming the bandwidth, rejecting adjacent channel interference, etc. then any DSP could offer.

CW is much more easier to copy in bad band conditions, something the NCT's will never appreciate. SSB signals are very dependent upon the individuals mic gain, compression level, speech frequency range, annunication, etc. DSP would help but with some many variables, it has to do more variables to deal with then I honestly feel the DSP can improve in the signal.

All in all, from the $12K priced radios down to the used TS-830s, etc., I have found that many radios hear just as well as the highest priced radios. More bells and whistles do very little to help the weak signal.

To me, optional crystal filters help a great deal more then DSP, DSP makes the copy more "pleasant" for the ears, CW is much more likely to get through then SSB under rough conditions (DSP or not), and outboard DSP filters may be nice but take too long to tune in the signal before the transmission ceases.

Thoughts? Comments? Experience?

Be interesting to see some of your comments on DSP equipped radios and how well they work/don't work.

...-.-

[K0RGR]

I can't speak to IF DSP, but I've had three flavors of AF DSP, and the answers are YES, NO , and MAYBE. YES, it definitely seems to help CW. I can pull weak CW signals out of the mud and make them armchair copy. But NO, I can't do the same with SSB. And MAYBE it has some effect on digital modes, which may or may not be helpful - in some cases it seems to be a negative impact on them.

[K7FE]

I have DSP on two transceivers. It works to some degree, however have much better results with my DSP speaker, so I do not use the ones in the radios.

[KC9ECI]

I have DSP on my 703 and I almost never use it.

[WB2WIK]

Design and implementation are very important, not just "DSP." There are huge differences in rigs in this regard, I've found.

If you read my comment re: the IC-756PROIII on this matter at the attached site, I summed up what I found with that particular rig (which I don't own, though I'd like to).

http://www.eham.net/forums/Elmers/95210

The noise reduction system, on SSB, was demonstrably awesome compared with everything else I was able to compare it to -- and it's DSP. Obviously very well implemented. I believe the IC-7800 uses the same system, although I didn't have one to test that day.

WB2WIK/6

[kf6rdn]

Quote[/b] (K0RGR @ July 21 2005,12:49)]I can't speak to IF DSP, but I've had three flavors of AF DSP, and the answers are YES, NO , and MAYBE. #YES, it definitely seems to help CW. I can pull weak CW signals out of the mud and make them armchair copy. But NO, I can't do the same with SSB. And MAYBE it has some effect on digital modes, which may or may not be helpful - in some cases it seems to be a negative impact on them.
Probably not helpfull on the digi modes. The computer IS the dsp anyway. Definatley not the AF dsp,s if the if ones can clean the signal at all without processing it.. Maybe.

[W3MIV]

Quote[/b] (kf6rdn @ July 21 2005,17:46)]Probably not helpfull on the digi modes. #
Wrong. The IF DSP in my ICOM IC-746Pro (basically the same system that is in the IC-756ProII) is very helpful in any mode, and especially so in the digital modes.

ICOM has a very versatile system that employs a special digital SSB mode (both DUSB and DLSB are available) which takes the audio only from the rear ACC connector (cuts out the mic input) and lets me select any bandwidth from 3kHz or so down to a mere 50Hz. In addition, I can shift the passband radically to eliminate QRM and concentrate on a tiny slice of passband that can be centered on a very narrow signal, such as CW or PSK.

Similarly, in other digital modes (RTTY has a nice dual filter system in the DSP) and in SSB, you have a great deal of control over what you want to hear. Notch, either full auto or manual, works superbly and quickly. I should add (edit) that the Noise Reduction works fairly well, too, but at its most extreme settings can make folks sound more like Donald Duck than anyone else. Still, it lets you understand what is being said.

I wouldn't give you a plug nickel for most of the AF DSP iterations I have auditioned, but the IF systems, at least those from ICOM, work well.