[Fwd: LF: Comparison of FFTDSP4 and Specrogram 5.09 on QRS]

Andre' Kesteloot akestelo@bellatlantic.net
Mon, 23 Aug 1999 08:56:32 -0400

Alan Melia wrote:

>                           with some comments on HAMVIEW
> Having installed what I think is probably the latest of the Spectrogram
> upgrades, 5.09, I have arranged the two aux. audio outputs from my receiver
> to go to the sound cards in 2 separate PCs. One runs FFTDSP4 under DOS 5,
> the other runs Windows 95 and Spectrogram. Both use genuine Creative Labs
> SB16 cards. I had an opportunity a few days ago to watch the effect of
> severe QRN as I monitored Geri DK8KW through a local thunder storm. On that
> occasion Geri would have been copiable on either system, but the effects of
> the lightening crashes chopped him up very badly on FFTDSP4. It is possible
> that a different setting of the colour scale would have improved things, but
> unfortunately either the version I have has a small bug or there is an
> incompatibility with my hardware. If I select a manual colour scale and an
> integration time of greater than 1, the screen does not scroll when it
> reaches the bottom. It does work well on AUTO. Geri would have been 'M'
> verging on 'T' on FFTDSP4, but was a perfectly readable 'O' on 'gram with
> the 4096 point display (similar resultion). For some reason Geri's morse
> elements were readable right through the crashes (from strikes with 2000m!)
> This exercise was they first real use of 'gram in anger and it showed up
> well. I determined to leave the connection (10m of RG-58 allong the passage
> from the rx to the main room!) to the Windows 95 machine and compare the
> ultimate performance on a weak QRS signal.
> On Saturday morning early, Mike G3XDV called Gerd DJ5BV , no trouble reading
> Mike of course, but I had not heard a signal from Gerd before. FFTDSP4
> showed a signal, the noise level was low and there were no static crashes,
> but the signal was hardly readable. It was bobbing in and out of the noise.
> I would not have been sure of the call if I hadn't heard Mike calling.
> Spectrogram was set up for 16K points 60dB range and an averaging of
> 4....and there was a beautiful solid signal from Gerd at a full 'O' with no
> compromise.  Later in the morning after Mike had called QRZ I went snuffling
> around in the noise looking for the signal and realised that some weak lines
> I could see at about 7Hz spacing were the dreaded Loran sidebands (abt 2-3dB
> above the noise) I'd heard so much about. It is the first time I have seen
> them, they are not visible on FFTDSP4, even with the 500Hz filter in the rx
> and the highest resolution. ( It looks as thought the rx hardware is working
> well, what I need to do now is put the same amount of effort into sorting
> the aerial out and getting better sensitivity!)
> In conclusion, I still like FFTDSP4 as an operating aid. I find that on a
> full scan 200-2500Hz I can quickly locate a new station calling and
> concentrate the hardware on it. I have a paper template stuck to the bottom
> edge of the monior screen as there is no offset capability allowing the
> display to indicate the correct frequency (like there is on 'gram). I can
> see stations on hand keyed speeds that I cannot hear in the phones. I can
> see where the QRM is and shift the filter away to to listen to a weak
> station. Ok, a good CW operator could do this without the aid but it is nice
> to see what is happening ( and I am not a real morse operator!). I leave my
> RX tuned to 138.10 kHz LSB and use the pass-band tuning to 'isolate' the
> signal and BFO shift on the AOR 7030 to adjust to a listenable tone. It is
> posible to have 3 pre-programmed filter 'positions' for the 500Hz filter
> within the 2.5kHz view by using the filter select, and the CW and DATA
> modes.
> I would normally use Spectrogram on the 4096 point resolution set to cover
> the top 300Hz of the band, switching to a 16K point resolution and adjusting
> the position of the display to catch the required signal for weak signals I
> find averaging between 2 and 10 useful. With a timing of 400mS for 3 sec
> dots. Sampling is left at 5K and range at 60dB with the standard colour
> palate. I have not found ,personally, that changing the colour range of the
> display makes any difference to the visibility of signals on the edge of the
> noise. It would seem as though Spectrogram has up to about a 10dB advantage
> over FFTDSP4, this is probably accounted for by the increased resolution of
> Spectrogram 0.3Hz against 2Hz for FFTDSP4.
> I also have a copy of Hamview, which I have used for a time. Hamview has the
> interesting possibility of being able to drop a very narrow filter, or a
> bandpass filter defined by clicking the mouse, over a signal and listen in
> the computer speakers to the (delayed) filtered signal (It is essential to
> turn the rx speaker down or it gets VERY confusing.) It produces a dispay
> that wraps horizontally around the screen rather than scrolling and will
> display about 7 minutes of signal in the highest resolution mode. The
> program does not run well on my system, crashing with a variety of
> breakpoint numbers, after anything from 2 mins to half an hour. I have run
> FFTDSP4 for 12 hours using the longtem logging (25Mbyte file) on many
> occasions. Hamview does enable a display file to be logged and a WAV file
> (these are enormous after a few hours) to be stored for replay and
> filtering. Its major disadvantage for QRS work is that the highest
> resolution (about 2Hz I think) produces a scan of 4kHz and there is no
> facility to be able to tune the averaging to suit the signal. It is about
> the same as FFTDSP4 on sensitivity. I might use it more if I had a version
> that didn't crash on my hardware. It has taught me that audio filters, no
> matter how good, will not put a weak signal out of the noise and make it
> more readable! Narrow IF filters do help but not as much as I used to
> believe. Audio filters are good for reducing the effect of nearby qrm on
> signals that are otherwise readable. I have found the notch of an external
> Daiwa filter ,most useful for removing the fatigue of listening to the
> screech of the Greek RTTY station at night.
> On the use of filters I have found that putting the required signal near the
> edge of my 500Hz IF filter, sometimes makes the tone of a weak signal stand
> out more from the sound of the
> filtered noise. Is this a normal technique known to morse men?
> Alan Melia G3NYK
> Alan.Melia@btinternet.com