[Lowfer] Argo Working

[Lyle Koehler]

I think the AGC in Argo works fairly well, which is another way of saying
that the incoming audio level is not very critical when you're in AGC mode.
As for the smearing, dropouts and all of the other effects that make valid
QRSS signals unreadable and turn spurious signals into something that looks
like it might be a LowFER beacon, that's a fundamental limitation of QRSS.
Other modes like Jason and WOLF provide more certain results. Unfortunately
Jason requires better signal-to-noise ratios than QRSS30. WOLF offers about
the same sensitivity as QRSS but involves post-processing of wave files in a
DOS window, and for best results WOLF also requires precise knowledge of the
signal frequency and other parameters such as the sound card sampling rate.

When conditions are fairly stable and the QRN levels are low, it is possible
to clean up the Argo display by turning off the AGC and tweaking the manual
settings for audio input level, sensitivity and contrast. Using the
"magnitude squared" spectral estimator also helps to make the signal stand
out from the background. It's a pretty slow process to optimize the settings
manually for these slow-speed modes. Another problem is that without AGC, if
the QRN levels build up after you've gone to bed, you will find that the
overnight screen captures are nothing but snow!

An example of an Argo capture of VD, WA and MP with manual adjustments (on a
good quiet night last month) is at http://www.qsl.net/k0lr/VD-WA-MP.jpg  MP
was just beginning to build in strength during the last part of the capture.
The traces at 1.0 and 1.5 Hz are spurious signals of unknown origin, and if
I had cranked up the gain a little more, there would be another spur at 0.5
Hz that looks like a LowFER QRSS signal but isn't...

Lyle, K0LR