It is interesting to note that Tom and others share exactly the same
experience as I have. There is a certain 'flavour' to DSP audio that is not
making it easier to copy weak signals in the noise. I find that using an
(old) analog system actually makes it much easier to copy signals hidden
deep down in the noise.
I have long experience from listening to extremely weak signals in the
noise (CW EME on VHF/UHF and some while Topband DX'ing) and I am still
waiting for a DSP radio that outperforms my old analog radios and my
homebrew LM13600 audiofilter. The filter was published in QST in October
1983.
For EME, my TS2000X with it's filter combinations is just not as
comfortable to listen to as the old FT736R and my vintage LM13600
audiofilter. I plain words, I copy much better on the old system. And DSP
in the low end Yaesu radios (FT817/897) is not performing anywhere near the
old analog systems. The same goes for the SDR's that I use.
Granted, tuning in a very weak steady carrier in a narrow DSP filter (a few
tenths of Hz wide) can give you the impression that DSP is magic stuff. But
as soon as the carrier is chopped up into CW there is a 'mushiness" to the
DSP processed white noise that affects copyability. For me, this can often
be verified when doing an A/B check on a very weak beacon that sends a long
carrier between it's CW ID's.
In my view, even static crashes when listening to weak signals on Topband
are easier to deal with when using analog filters.
But the whole audio chain is important. The choice of headphones is
certainly a key to success when it comes to copying weak CW in the noise.
Each one of course has his/her own preference when choosing headphones. My
best ever are a pair of very old Radio Shack "Nova 10". They are badly
beaten and patched up with tape and glue, but I still use them every day
and they are the best headphones for copying weak CW that I've ever tried.
And beleive me, I have tried many headphones.
Some good tests for copying weak signals in the noise can be found at
http://sm2cew.com/wavefiles.html
There might be one or two broken links on that page after a transfer to a
new server but try the plaintext59_17.wav it is a real challenge. There is
a genuine 59 character CW message in the noise and it is possible to copy
and decode it 100% by ear when using a good filter. Good luck!
73
Peter SM2CEW
At 12:58 2015-08-07 , Tom W8JI wrote:
>> I'd like to know whether it's ever been established that some very
>> talented
>> hams can out-hear the best SDRs and/or DSP available. Can a skilled
>> ear-brain combo (such as some highly-skilled and talented 160 meter
>> contesters) beat state-of-the art digital signal processing when it comes
>> to copying the very weakest of signals buried in the noise?
>
>Excluding time-synchronized signal processing methods, I've never found any
>DSP system do better or do more than an analog system in signal
>readabilitly.
>
>They are really just different methods of doing the same thing analog
>systems can do.
>
>I actually find DSP detector systems inhibit my ability to "hear" or copy
>noise floor signals in rough noise. I'm not sure why that is, but it is more
>difficult for me to piece together a signal that is in the noise when it has
>been detected in a DSP system.
>
>I normally set my K3's so DSP filtering is wider than the analog filter at
>filter switch in, so I can change the DSP bandwidth from wider than any
>analog filter down to the DSP being narrower, but I still think analog
>detection is much better for signals below the level of rough noise.
>
>73 Tom
>
>_________________
>Topband Reflector Archives - http://www.contesting.com/_topband
>
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|