Hi group,
mni tnx to Ko NL9222, who has sent a pair of Argograms of my Slow-Hell
transmissions, allowing a direct comparison of 5 Hz and 10 Hz bandwidths. As
expected, the readability of the narrower version was better, but the amount
of difference was surprising: barely readable T to M in 10 Hz versus
comfortable O in 5 Hz, certainly more than 3 dB's worth.
The 10 Hz Hell mode is based on 1.35 Hz x 0.74 s pixels. Accounting for a
factor of 2 due to the receiver's Hanning window, this is optimally matched
to a FFT bin width of 0.67 Hz (8192 bins at 5512.5 Hz samplerate). However,
the generally preferred resolution for 3s-QRSS is 0.34 Hz bins (as in Argo),
rather suited for 5 Hz MT-Hell.
To send chirped Hell at half speed in a 5 Hz, you can to modify "Hell1g8.bas"
to produce a new set of audio files. In the 4th line of code, simply replace
"samplespercol = 4096& * 2" by "samplespercol = 4096& * 4" and run it (F5
key). On my computer, I keep seperate sets of files in different directories.
Today, after a nice QRSS/Hell QSO with Fabian, Geri and I had a long contact
in the afternoon using PSK and Hell. We successfully tried QRP (4 W PEP) in
both modes, also indicating that very slow PSK might indeed be an excellent
choice for weak-signal work. - A few minutes later, Cesare's Hell from
Firenze showed up again around 137690, just on the fringe of readibility due
to QSB and local QRN. It certainly is fun...
73 and happy experimenting
Markus, DF6NM
|
