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Date: Mon, 11 Mar 2019 13:29:43 +0100
From: DK7FC <selberdenken@posteo.de>
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References: <alpine.DEB.2.11.1903021056370.22616@mailn.lipkowski.org> <alpine.DEB.2.11.1903021853290.22616@mailn.lipkowski.org> <5C7AD93E.8010402@posteo.de> <alpine.DEB.2.11.1903031913120.22616@mailn.lipkowski.org> <5C7CEF81.5080302@posteo.de> <000201d4d2ce$4aa091c0$dfe1b540$@go2.pl> <5C7EC39A.5070903@posteo.de> <6DB8451D7F3D3947A5918808A59621EA315303E3@servigilant.vigilant.local> <044601d4d43e$749bb790$5dd326b0$@comcast.net> <5C803777.8070401@posteo.de> <alpine.DEB.2.11.1903091117390.22616@mailn.lipkowski.org> <435595266.2127766.1552155007472@mail.yahoo.com> <5C8430BD.9030002@posteo.de> <alpine.DEB.2.11.1903100945390.22616@mailn.lipkowski.org> <5C84DE49.6080503@posteo.de> <01c201d4d776$0afecad0$20fc6070$@comcast.net>
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Subject: Re: LF: Re: Re Loomis?  & ... 12.47 Hz
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Hello Jim,

Yes, indeed.
I'm now preparing the circuit and want to set it up in the evening. 
Found an IRF820 in the 'junk box', a good choice. Or, maybe even a BS170 
will work. It handles 60V only but i had the following thought:

The ERP at a constant voltage across the antenna (say 50 V rms at the 
fundamental frequency) will rise with the sqare of the frequency (for 
electrically short antennas). But that voltage will not be constant in 
practice. It will drop linearly with the frequency ( ~ 1/f) because the 
sky-current is assumed to be constant and the charge up time is T/2. 
And, doubling the voltage at the antenna will also rise the ERP by a 
factor of 4. All in all it means the the ERP is constant, or independend 
of the frequency!?
That means, it would be wise to select a band where many RX stations are 
watching and propagation is promising. The number of RX stations is 
higher at MF but (groundwave) propagation is better at LF.
Since the peak voltage will be lower at MF (shorter charge-up time), MF 
is less critical.

And which mode?! I think the best choice is a 100% duty cycle WSPR 
beacon. It also has the advantage that one can check the results in the 
database. And there are many RX stations, even in the groundwave 
distance and even in less than 100 km here. And i have my tree which can 
detect small differences at very low levels.
At MF, the BS170 is a good choice i think. And it can be driven by a 
Raspi directly, maybe with a ferrite transformer in the gate-source 
path, to decouple the shack from the antenna...

If that works, one could try LF.

73, Stefan


Am 10.03.2019 20:18, schrieb hvanesce@comcast.net:
> All great ideas in the preceding messages.
>
> A steady signal from the 136 kHz sky-current transmitter could indicate that a data bit might be available later from the 10 Hz sky-current transmitter.
>
> Agreed, the triggered gap sounds better than an HV vacuum relay (for jitter and reliability).
>
> Sounds like the voltage divider doesn't need to be more than a gigohm, but perhaps for future reference: a reliable 50kV 1 terohm divider can be made very easily: encapsulate ten 100 gigohm resistors in hard epoxy, being sure not to touch them during assembly. A single linearity calibration after curing will be remain valid +/- 10% for years in varying humidity and temperature.
>
> 73,
>
> Jim AA5BW
>
>
> -----Original Message-----
> From: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of DK7FC
> Sent: Sunday, March 10, 2019 5:52 AM
> To: rsgb_lf_group@blacksheep.org
> Subject: Re: LF: Re: Re Loomis?&  ... 12.47 Hz
>
> Hi Jacek, DC,
>
> Yes yes, i already see a new project for summer :-)
>
> A floating antenna will charge up to a voltage where the E field strength is high enough to start partial discharges, something like 20 kV maybe, depending on the wire diameters and homogenity of the arrangement, also on pressure and humidity. So there will be a voltage limit given by the arrangement. But a higher field strength in summer will help to charge up the antenna faster, so higher switching frequencies are possible.
>
> One could build/use a triggered spark gap, https://en.wikipedia.org/wiki/Trigatron, this will hold higher voltages and you can connect the trigger directly to a ublox GPS module running e.g. at 3 Hz :-) I think this will give a lower jitter than when using a vacuum relay.
> Could this work over my 3.5 km path if i use my inv-L? I don't think so.
> The time to integrate will be to short and there will be much QRN during such an experiment, so the SNR will be very low. Currently (at 12.47 Hz) i already have 15 kV DC available...
>
> Anyway, interesting questions, there is something interesting to learn.
> Maybe i will do a few experiments in summer. Building a HV divider and measurement should be no problem...
>
> 73, Stefan
>
> PS: Assuming 100 uA constant current 'coming from the sky', my 470 pF antenna would charge up with 213 kV/s, so it would be possible to switch at 10 Hz and get a 21 kV 'square wave'. Maybe the harmonics could be detected easier than the fundamental frequency.
> At 137 kHz it would be 1.5 V only (0.53 V rms). This can be switched with a normal FET! Imagine we would switch the antenna permanently at, say 136.172 kHz, using a FET and a ublox GPS module. Then, as soon as the field strength is high enough, we would see a carrier on the grabbers? We need to try that out! Amazing! What a great hobby we have!?!
> PPS: For this experiment, the antenna can be series resonated, which would help to concentrate the energy to the wanted spectrum...
>
>
>
> Am 10.03.2019 09:58, schrieb Jacek Lipkowski:
>    
>> I haven't tried this with 300m kites, but even ordinary low-band
>> dipoles can charge quite quickly if they are high enough, so 100uA
>> seems to be a good approximation. This is already comparable with the
>> 170uA you're getting at 12.71Hz now (and which will be lower at lower
>> frequencies).
>>
>> The only problem is the switch, but a high voltage vacuum relay (or a
>> few in series with a piece of fiberoptic for controlling each of them)
>> should be sufficient upto a few Hz.
>>
>> Also note that the more charge in the atmosphere, the more ERP you
>> get. But it also gets more dangerous. No risk no fun on the "loomis
>> band" :)
>>
>> VY 73
>>
>> Jacek / SQ5BPF
>>
>>
>>
>> On Sat, 9 Mar 2019, DK7FC wrote:
>>
>>      
>>> Date: Sat, 09 Mar 2019 22:31:41 +0100
>>> From: DK7FC<selberdenken@posteo.de>
>>> Reply-To: rsgb_lf_group@blacksheep.org
>>> To: "rsgb_lf_group@blacksheep.org"<rsgb_lf_group@blacksheep.org>
>>> Subject: LF: Re: Re Loomis?&  ... 12.47 Hz
>>>
>>> Hi Jim,
>>>
>>> I hope you don't mind that i'd like to share the email with the
>>> reflector, because i've a thought that might be interesting.
>>>
>>> In my view, the Loomis experiment it is rather the detection of a
>>> changing current (charge per time) on the RX site. The changing
>>> current is coming from a change in the static electric field, caused
>>> by the shortcutted 'TX' antenna. Something like a current divider.
>>>
>>> In 2010/2011 i've done VLF transmissions on my own, using a 300m
>>> vertical kite antenna (having a special licence for that altitude).
>>> The antenna capacity was about 1.5 nF. During an experiment in the
>>> summer time there was a short moment when the vertical wire was
>>> floating. It quickly charged up to some kV, which was quite noticable
>>> when i catched and touched the wire then!! Since that time i
>>> carefully kept the wire grounded during such experiments.
>>> So, it means that the wire charged up, so there must be some
>>> continuous charge flowing onto the wire and, if the wire would be
>>> grounded permanently, you could probably measure a more or less
>>> stable current, i guess it would be some 100 uA.
>>> Now imagine someone else would rise a grounded kite in a few meters
>>> distance. This would certainly affect the current flowing in my kite
>>> wire.
>>> The farer both 'antennas', the lower expressed the effect will be and
>>> the higher the antennas, the stronger it will be expressed.
>>>
>>> I think the effect would be much better expressed by measuring the
>>> voltage across a 1 MOhm resistor instead, which could be done by
>>> using a scope and some overvoltage protection!
>>> Actually an interesting question: In the summer time, which DC
>>> voltage could be measured over a 1 MOhm resistor when connecting to a
>>> large E field antenna and ground?
>>> And, a next step: If i let my antenna charge up (floating) and then
>>> discharge it in exact time intervals, say each second, then i should
>>> see something at 1 Hz on a suitable receiver. This would already come
>>> close to the experiment i'v done. I'm just replacing the 'natural
>>> charge source' by a high voltage power supply and modulate that
>>> voltage (with a sine wave, not rectangular).
>>>
>>> So, to answer your question, i think that Loomis experiment was not
>>> dedicated ELF, it was rather a broad-band spectrum that was radiated,
>>> since the charged antenna was discharged immediately. For a real ELF
>>> transmission i would say that the carrier frequency has to be at ELF,
>>> not the modulating frequency. OK here you might say the carrier
>>> frequency is
>>> 0 and it is AM modulated...
>>>
>>> Try to repeat the experiment! Use smaller antennas and shorter
>>> distances. Could be interesting :-) Rise two 10m high wires in 10m
>>> distance in an open field. Connect one of them to a scope (1 MOhm
>>> input resistance), protect the input with a glow lamp. Keep the other
>>> wire floating.
>>> Select 1 second/div. If there is a thunderstorm coming and you can
>>> see a rising DC level on the scope, then do a shortcircuit on the
>>> other wire. I bet you will see the voltage dropping on the scope.
>>>
>>> 73, Stefan
>>>
>>>
>>>
>>> Am 09.03.2019 19:10, schrieb James Hollander:
>>>        Hi Jacek and Stefan,     I?d like to suggest that while I can?t
>>> say for sure there weren't ELF frequencies received in the Loomis
>>>        experiment of 1866, I?m hesitant to reach the conclusion ELF
>>> was used by Loomis because of the following questions.
>>>        1) If the transient current that flowed when Loomis?
>>> transmitter circuit was closed probably lasted only a few
>>> milliseconds, wouldn?t the modulation frequency content exceed at
>>> least the upper ELF boundary 30Hz as impressed on the ?carrier??
>>>        2)  With a 600? long TX antenna and only a galvanometer fed by
>>> similar height RX antenna, wouldn?t any radio waves that might have
>>> been received be shorter than 10x the wavelength for which a 600? TX
>>> antenna is a quarter wavelength?    10x(600?x4)=24000? or about
>>> 8km.   If the
>>> wavelength is less than about 8km, wouldn?t the ?carrier? frequency
>>> content exceed about  37 KHz?
>>>        3)  Nevertheless, one might say, if galvanometer deflected
>>> temporarily in Loomis? system, it must have detected some near-DC
>>> content
>>> unless some nonlinear element were in the receiving circuit.   If I
>>> Fourier Transform a damped DC transient, what is the frequency
>>> content?
>>>        4) If there were DC transfer, wouldn't we say it's in the
>>> nature of a current charging an atmosphere-ground capacitance through
>>> the ground resistance, not radio in near field ELF?  Or should we say
>>> the meaning of ?frequency? in this case becomes so fuzzy that Loomis
>>> both did and didn?t use ELF?
>>>        5)  If indeed Loomis communicated any ELF, can?t one still
>>> radically distinguish the 12.67 Hz experiment at DK7FC as involving a
>>> very narrow band  continuous wave with 227 hours integration of this
>>> continuous wave to detect it and make it separable from other waves
>>> that could be generated in the ELF band?
>>>        I?m new to the subject of ELF, and would appreciate any words
>>> of wisdom you?d like to give.
>>> Vy 73, Jim Hollander W5EST
>>>
>>>
>>> -----Original Message-----
>>> From: Jacek Lipkowski<sq5bpf@lipkowski.org>
>>> To: rsgb_lf_group<rsgb_lf_group@blacksheep.org>
>>> Sent: Sat, Mar 9, 2019 4:28 am
>>> Subject: Re: LF: RE: RE: Almost touching the ground... | 12.47 Hz
>>>
>>> Actually a similar experiment to Stefan's has been done already, and
>>> at much lower frequencies (almost 0Hz :):
>>>
>>> http://aerohistory.org/Wireless/loomis.html
>>>
>>> In this case the power supply is from the cloud electric field and
>>> probably had quite a few more kV than Stefan's.
>>>
>>> Please note the DX distance.
>>>
>>> VY 73
>>>
>>> Jacek / SQ5BPF
>>>
>>> From: DK7FC<selberdenken@posteo.de>      To: rsgb_lf_group
>>> <rsgb_lf_group@blacksheep.org>
>>> Sent: Tue, Mar 5, 2019 12:50 pm    Subject: ELF: Almost touching the
>>> ground... | 12.47 Hz
>>> Hi ELF friends,        During the last 2 weeks i've done another
>>> experiment on ELF, this time
>>> on 12.47 Hz, the 24 Mm band (wavelength 24057 km). Again i've crossed
>>> the local distance of 3.5 km. That's the lowest frequency i've ever
>>> been and it feels like i can see the ground already :-)    The
>>> dimensions of everything down there are extreme. I've integrated 227
>>> hours of a carrier transmission into one spectrum peak, it is shown
>>> in the attachment in 1.25 uHz. This carrier could have transferred an
>>> EbNaut message of nearly 100 characters.
>>>
>>> The ERP was 50 attowatt or -163 dBW and the antenna current was 170
>>> uA only, despite about 5 kV antenna voltage.
>>>
>>> I'm now trying to put a step below 10 Hz but the RX antenna becomes
>>> less efficient with each Hz. 73, Stefan
>>>
>>>
>>>
>>>
>>>        
>
>