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Date: Sun, 02 Feb 2014 22:50:04 +0200
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From: phl@netikka.fi
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Subject: Re: LF: DX VLF experiments in 3HD
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Well, well Stefan,

I was playing with the thought of "leaky" power line or cable  
transmissions back in the days when 600 m opened up to a few select  
countries (but not here in "Kekkoslovakia" despite the pressure from  
me and some others). Since all kinds of "ethernet over mains" devices  
etc. are legally free to spew out part of their output in the ether as  
a "by-product" of their normal operation and so on it was kind of  
logical reasoning. You get the point...

My message is: If you choose this path, why settle for just "legal  
harmonics" when the whole RF spectrum may be yours to use? Just run it  
into leaky cables and claim you are inventing a new mode of bringing  
high-speed internet cheaply to every home. Even better, get some  
generous EU-funding for it while you're at it :)

Could be easier to claim to be doing the above than getting a NOV  
these days...


The above is purely meant as "food for thought", not as critisism  
against the original idea.


Paul-Henrik, OH1LSQ


Quoting Stefan Sch=E4fer <Stefan.Schaefer@iup.uni-heidelberg.de>:

> 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
>
> Am 02.02.2014 18:15, schrieb Markus Vester:
>> Stefan,
>> your third harmonic is clearly visible in Holland
>> http://www.qsl.net/pa1sdb/
>> and here
>> http://www.df6nm.de/vlf/vlfgrabber.htm
>> Started spot-on 17265 Hz, now another peak is coming up 15 mHz up.
>> Good luck,
>> Markus (DF6NM)
>>
>> *From:* Stefan Sch=E4fer <mailto:Stefan.Schaefer@iup.uni-heidelberg.de>
>> *Sent:* Sunday, February 02, 2014 3:27 PM
>> *To:* rsgb_lf_group@blacksheep.org <mailto:rsgb_lf_group@blacksheep.org>
>> *Subject:* Re: LF: DX VLF experiments in 3HD
>>
>> Markus,
>>
>> I am 16 dB stronger now!
>>
>>
>> Am 02.02.2014 14:52, schrieb Markus Vester:
>>> So what should be expected here? Scaling the fieldstrength from 1  
>>> km to 180 km (1/r^3 to lambda/2/pi, 1/r thereafter), the signal  
>>> should be 82 dB weaker here on 5.755, and 63 dB weaker on 17.265  
>>> kHz. Neglecting ionospheric contributions (not really correct),  
>>> and assuming similar noise levels (though 5.5 kHz is much affected  
>>> by railway QRM here), my SNR in 0.47mHz should theoretically have  
>>> been
>>> 35 - 82 + 10 dB =3D -37 dB on 5 kHz and
>>> 50 - 63 + 10 dB =3D -3 dB on 17 kHz.
>>> So while a detection on the fundamental seems pretty hopeless, the  
>>> third harmonic should already be getting close.
>> Yes, the QRN and QRM is much lower in 3HD :-) Why didn't we get  
>> this idea earlier???
>>
>>> What is the inductance of the loading coil?
>> Ehm , i didn't really measured it, it's just trial and error.
>>
>>> Would be interesting to see a picture of the scope trace picked up  
>>> near the antenna ;-)
>> Looks quite good but could cause misunderstandings...
>>
>> The amperemeter in the coil shows 350 mA now! There is some kind of  
>> selfoscillations, audible. Thus i do not rise the power even more.  
>> Have to search, find and fix this problem later. The AC voltage  
>> from the vari-transformer is 110V now, so there is room for at  
>> least another 6 dB. Power is in the range of 100W now.
>>
>> I'm going to measure the strength at home now. Hopefully the signal  
>> is audible :-) Yesterday it was still weaker than the mains hum, so  
>> far away from any interferences!
>>
>> 73, Stefan
>>
>>> Best 73,
>>> Markus (DF6NM)
>>>
>>> *From:* Stefan Sch=E4fer <mailto:Stefan.Schaefer@iup.uni-heidelberg.de>
>>> *Sent:* Sunday, February 02, 2014 2:06 PM
>>> *To:* rsgb_lf_group@blacksheep.org <mailto:rsgb_lf_group@blacksheep.org=
>
>>> *Subject:* Re: LF: DX VLF experiments in 3HD
>>>
>>> Markus, VLF,
>>>
>>> Am 01.02.2014 20:34, schrieb Markus Vester:
>>>> Stefan,
>>>> running two 478 =B5Hz "6000" windows centered on 5755 Hz (on the  
>>>> grabber, but much QRM here) and also 17265 Hz (offline) which  
>>>> seems more quiet. So hoping for a long carrier...
>>> Well, i hope that 16 hours key down were long enough ;-)
>>>
>>>> On which of the two frequencies would you expect to radiate more power=
?
>>> I don't know. But the harmonic signal is very weak and cannot  
>>> cause interferences for JXN or HWU or SAQ or GBZ...
>>>
>>> I've done measurements at home, 950m distance, of that _5.755 kHz_  
>>> transmission and saw that the signal was very weak, see  
>>> attachment. Just 50 dB SNR in 4.5 mHz at 3HD. The TX power was  
>>> just 15W at the end. Also the frequency response of the active  
>>> antenna + soundcard is attached.
>>>
>>> The experiments are very interesting here and i like to do the  
>>> measurements. Despite rain the coil was on the top of the building  
>>> and on air. It was just covered by a trash bag. The voltages are  
>>> very small...
>>> I just hang out a 30cm long wire connected to a probe of the  
>>> oscilloscope and so the voltage waveform of the antenna wire. It  
>>> nearly looks as expected :-)
>>>
>>> Now i got another idea. There is a 2.2 uF WIMA MKP-10 capacitor in  
>>> series to the output of the H bridge, just to protect it against  
>>> damage in case of a DC output. Now i've disconnected the antenna  
>>> and tuned for the series resonance of this C and the L of the  
>>> primary winding of the loading coil. The resonance is at 1.77 kHz.  
>>> This allowed me to calculate a much smaller additional series C  
>>> which helps to attenuate unwanted frequency components, i.e. makes  
>>> the spectrum cleaner and provides a lower impedance on the wanted  
>>> frequency :-)
>>>
>>> There is really no alternative to that H bride PA which works from  
>>> 10 Hz to 100 kHz :-)
>>>
>>> in a few minutes i will be on air again for a longer time,  
>>> hopefully with a much stronger signal.
>>>
>>> Maybe you can detect something of that 5.755 kHz transmission.
>>>
>>> 73,GL, Stefan/DK7FC
>>>
>>>
>>>> BTW Today I have updated SpecLab from version 2.79 b08 to b10  
>>>> (Jan 26), and it seems that GPS 1-pps sync is finally working  
>>>> well now, even with 42 =B5Hz resolution.
>>>> Good luck for the test!
>>>> 73, Markus (DF6NM)
>>>>
>>>> *From:* Stefan Sch=E4fer <mailto:Stefan.Schaefer@iup.uni-heidelberg.de=
>
>>>> *Sent:* Saturday, February 01, 2014 5:46 PM
>>>> *To:* rsgb_lf_group@blacksheep.org <mailto:rsgb_lf_group@blacksheep.or=
g>
>>>> *Subject:* LF: DXl VLF experiments in 3HD
>>>>
>>>> VLF,
>>>>
>>>> This evening and night i'm planning to transmit on _*5.755 kHz*_,  
>>>> using the large antenna, the large coil and the large PA :-)
>>>> I don't know what can be expected and how the system works at  
>>>> that frequency. Actually it is just _a first test for playing  
>>>> arround and doing some measurements_ :-)
>>>> If some nearby stations want to give it a try, maybe even in  
>>>> *3HD*, then don't hesitate :-)
>>>>
>>>> 73, Stefan/DK7FC