Hello Dave,
I just had a play with the IZ8BLY program and it looks to me like the FM
Hell 105 Baud is the only one that would be useable on a crowded band. The
rest of them seem to fill half the band with sidebands.....
I would be very interested to see which one proves most effective though.
I'll look out for you in Hell, but which one??<
... I am not so sure about the bandwidth. Of what I have seen, the
bandwidth of each sideband of the standard FELDHELL (using an on/off keying
of one single frequency with 122.5 Bd) is around 62 Hz, so the total
bandwidth should be around 125 Hz, centering this on 137.400 Hz I do not
think that there is a considerable QRM on either side of the signal,
neither in the CW segment nor in the QRSS section of the band.
I know that standard FELDHELL is not the optimum for LF but I would like to
test this first, as a kind of "reference", before going to other HELL
modes. The main reason I like to use FELDHELL first is because this is the
original HELL mode that was developed some 70 years ago and is the father
of all FAX and RTTY systems.
If you have a look in IZ8BLY's program, you will find a menu "Meteor
Scatter" (under "Transmit Options I believe". Here you can choose "1/8
speed" which should give us a bandwidth of only 30 Hz or so. This migh be
suitable for LF operations under noisy conditions (probably). Also the PSK
Hell based on phase shif keying similar to PSK31 might be an option, here I
would choose the 105 bd option.
The beauty of HELL is simply that it is a system that is not designed to be
machine readable (such as RTTY and PSK31) but reabable by the human eyes
and brain. Each letter is kind of transmitted as a small "fax", you can use
different fonts to give best readability. This allows to compensate for QRM
and missing parts of letters etc.
Although people do claim that machines can detect and read signals burried
in noise better than the human senses, I have not yet seen this really
happening (despite, probably, WOLF, but this also works only if a human eye
looks through the garbled text received and immediately finds those
sequences that make sense). People claiming that for example PSK31 works
better than CW either have not tried this on LF or are not sufficently
trained to listen to weak CW signals ...
What I will do is to call cq in standard FELDHELL on 137.400 kHz this
evening from time to time, and listen out for replies. If anyone feels
disturbed by wide sidebands or other effects, please let me know
immediately.
Best 73
Geri, DK8KW (W1KW)
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