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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