Stefan,
technically this is an intruiging experiment.
Doubling the frequency from 8.3 to around 17 kHz would allow you to bring the
same antenna to 16-fold radiated power. An intercontinental detection of a 20
mW signal on that QRG seems quite feasible.
But I have my doubt that transmitting a low-level
"fundamental" along with the signal would render it legal. You argue that in
theory you might radiate arbitrary power on 1f, thus allowing you some
moderate output at 3f. Then how would one measure harmonic suppression -
presumably with a calibrated receive antenna somewhere in the radiation field.
So you'd really (and not only hypothetically) have to physically radiate 60 dB
more on 5.75 kHz, or not?
But wait a minute, who says 60 dB? Formally there
are no rules for transmitters below 8.3 kHz, neither for output power nor for
spectral properties. So you can claim the harmonic may be allowed to radiate
even stronger than the fundamental. The catch may be transmitters below 8.3
are not licensed radio transmitters. One could argue that they are thus not
elegible to produce any specified amount of harmonics (at least not beyond
what general EMC limits for electrical equipment would
prescribe).
There may be another pitfall regarding the
"wanted" signal versus the "undesired" harmonics. By the context of the
experiments, it is quite obvious that the 3f signal is the intended
transmission, and the 1f subharmonic is no more than an alibi. Taking it
further, one could claim to transmit legally anywhere on HF, just because his
TX contains a switched mode power supply which happens to leak some low-level
junk below 8 kHz.
Stafan, don't get me wrong, I'm in no way against
you or anyone conducting this kind of experiment. I find it novel and
interesting, and I don't believe anyone else will have a good reason to
complain about interference. I just dont believe that someone would really buy
the legal cover story.
73, Markus (DF6NM)
----- Original Message -----
Sent: Sunday, February 02, 2014 9:05 PM
Subject: Re: LF: DX VLF experiments in 3HD
VLF,
That 3rd harmonic is on the 17 km band. Do we have any
experiences about local diurnal propagation?
Sooner or later there will
be misunderstandings and some will say i am transmitting on 17.265 kHz
although the TX runs on 5.755 kHz!
I had a thought about that. 3rd
harmonics are generated by all HF amateurs, but we all ignore them. We
actually can ignore them if they are well attenuated but that doesn't mean
that they do not exist! BTW has someone ever tried to decode a 3HD signal
(that name, 3HD, is just for fun, like the Dreamers band, a shortcut for 3rd
harmonic detection, reminds on HD quality movies or 3D glasses ;-) ) in OPERA
mode?
Example: When someone transmits a legal (!) QRO signal of
750W (in DL) on the 160m band using a typical lambda/4 vertical (which is
radiating the 3HD signal because there it is lambda 3/4 and thus low impedant
too), using a 60 dB attenuating low pass filter, which is quite a good
supression, then there should be a 750uW signal on the 53m band, which could
be detected in some distance, probably several 10km when using slow modes like
OPERA-4 (WSPR will not work so easily here). Receiving this 3HD signal is
certainly not absolutely strictly forbidden :-) So actually the amateurs can
do legal QRPP tests in slow modes on 53m, can't they? Would you think that it
is ethical unjustifiable to try to receive such a signal if it is there anyway
and legally generated?
Example2: PA0WMR is often TXing OP8 on
478.x kHz, making 2000km distance. If someone in say 30 km distance can
receive him on 1434 kHz (if there would be no AM BCD stn), close to the decode
limit, would something be wrong with this test?
I know from WSPR QRP
transmissions from DL to VK on 15m with 0.1 W TX power!! So i assume a 3HD
signal could be detected in a few 100 km, maybe?
Below 8.3 kHz there is
no TX power limitation and we can certainly assume that no interference is
caused to anyone at 3HD, just like in the above example (53m band ( i never
tried it)).So why not trying to do tests like these today? The noise floor is
much lower there which improves the situation :-)
73,
Stefan/DK7FC
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