Message-ID: <5B6050DA.60905@posteo.de>
Date: Tue, 31 Jul 2018 14:06:50 +0200
From: DK7FC <selberdenken@posteo.de>
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; de; rv:1.9.1.8) Gecko/20100227 Thunderbird/3.0.3
MIME-Version: 1.0
To: rsgb_lf_group@blacksheep.org
References: <CA+GfORvAA10STf3zWSQ-dRFwk5BBS25Ht0x8cDZ3cYTa09dYbw@mail.gmail.com> <5B54CCCB.6060903@posteo.de> <5B59E687.5030805@posteo.de> <5B5C3ABF.3030809@posteo.de> <5B5C4A63.3040504@posteo.de> <5B5C5446.30105@posteo.de> <14080281532786049@iva8-6be7d23653d9.qloud-c.yandex.net> <5B5CD03F.40602@posteo.de> <14811811532865577@myt4-415a3339794b.qloud-c.yandex.net> <5B5DC8BC.9030601@posteo.de> <5B5E2D7D.6050908@posteo.de> <5B5F678B.7000506@posteo.de> <6dc15e3e-a325-4be2-55e3-44413e814f8a@web.de>
In-Reply-To: <6dc15e3e-a325-4be2-55e3-44413e814f8a@web.de>
Subject: Re: VLF: Earth antenna transmissions on a guide rail?!?? 2nd day...
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org

Hello Eike,

Thanks for your ideas. That Alu-wire is good for normal E-field antennas 
carrying some kV. A good source, thanks!

BUT, here i need an isolated wire because it is laying on the ground 
directly. OK, one could say that the wire would have only a very bad 
contact to the ground, anyway when laying on dry grass. But over a 
length of 900 m i expect the losses will be significant.
It could be worth a test to compare both solutions but the isolated 
cable will work for sure.
My wire is already ordered and payed anyway ( 
https://www.pollin.de/p/lautsprecherkabel-2x0-75-mm2-100m-transparent-cca-562602 
)

73, Stefan

Am 31.07.2018 13:19, schrieb Eike DL3IKE:
> Hi Stefan,
>
> instead of expensive and heavy copper-wire take a look at this 
> fence-wire: 
> https://www.weidezaun.info/voss-farming-aludraht-alu-draht-400-m-2-0-mm.html# 
>
> 400m of 2mm diameter aluminium wire for aprox 30eur has a dc 
> resistance of 4 Ohm an a weight of only 3,5kg.
> You´ll find also other usefull things like these: 
> https://www.weidezaun.info/weidezaun/verbinder-spanner.html and more 
> for buildig long antennas.
> A lot of those things are sold much mor expensive on ham-radio-markets...
>
> 73 de Eike DL3IKE
>
>
>
>
> Am 30.07.2018 um 21:31 schrieb DK7FC:
>> Hi VLF and ULF friends,
>>
>> In the attachment you can find 3 spectrograms from transmission of 
>> the last weekend. For the 8270 Hz and 2970 Hz transmission i took the 
>> data of the 900m ground loop, 5170 Hz is from the 450m ground loop.
>> The 8270 Hz signal was very strong even in 3.8 mHz ('DFCW-600'). Some 
>> real QRSS-60 would have been possible!
>> The spectrograms also show that there was no trace on the frequency 
>> of interest before and after the transmission (no traces from the 
>> right channel ( 1 PPS) ).
>>
>> A few minutes ago i built the switchable network for resonating the 
>> antenna properly. And i actually ordered 1000 m of that 0.75 mm^2 
>> loudspeaker cable. Thus, in the next experiment i think the Q of the 
>> antenna will be much higher and it will be possible to tune it 
>> accurately. Then, the tuning capacitance will tell us what the ground 
>> loop inductance is! And then, we can calculate the depth where the 
>> current is flowing backwards in the ground, asuming a simple model in 
>> first steps.
>> Next, we can see whether the inductance or depth stays constant at 
>> lower frequencies (hopefully it will increase!) by resonating the 
>> antenna at 2.97 kHz for example.
>>
>> BTW i measured the DC resistance of the wire i used last weekend, it 
>> is 116 Ohm, so it agrees well with the calculated 120 Ohm...
>> The new wire should have 21.4 Ohm only.
>>
>> The big advantage of this antenna is that no high voltage and large 
>> coils are needed. Usually the voltage is the limiting factor for a 
>> VLF or ULF TX antenna. But not here. Here it is the power of the PA. 
>> The antenna could easily handle 2 kW, which means 5.16 A, no problem 
>> for the wire. And it would be a 20 dB stronger signal than last 
>> weekend...
>>
>> 73, Stefan
>>
>>
>>
>> Am 29.07.2018 23:11, schrieb DK7FC:
>>> As a next result from today's experiment, here is a spectrum peak of 
>>> the 2970.005 Hz transmission. I reached 20 dB SNR in 180 uHz! This 
>>> far more than expected, in July anyway.
>>> It is the first ULF transmission (by amateurs) from an earth 
>>> electrode TX antenna, detected in the far field.
>>> Spectrograms will be produced soon...
>>>
>>> 73, Stefan
>>>
>>>
>>> Am 29.07.2018 16:01, schrieb DK7FC:
>>>> Hello Roman, VLF,
>>>>
>>>> I transmitted pure carriers each time. It was just a first test.
>>>>
>>>> Today i've done a second experiment, this time using a 900m long 
>>>> wire! So the wire should have about 125 Ohm DC resistance. I 
>>>> measured 220 mA DC at 38.4 V, so the overall loss is 175 Ohm. Very 
>>>> interesting; the ground loss resistance stays at 50 Ohm although 
>>>> the distance between the electrodes has doubled!
>>>> If i would use the 0.75 mm loudspeaker cable then i can reduce the 
>>>> losses by 100 Ohm which is more than 50 %, so i will gain 3 dB at 
>>>> the same output power! Then with a switch mode PA having nearly 
>>>> 100% efficiency i may gain 2 dB more (mmy lonear mode PA was not 
>>>> well matched today and quite warm). So maybe i can reach 1 A 
>>>> antenna current with just 75 watts??!!!
>>>> Today i tuned to 550 mA antenna current again, at 8270 Hz. With the 
>>>> scope, i measured the phas, it was more inductive than yesterday. I 
>>>> actually found a 1 uF MKP-10 cap in my car and switched it in 
>>>> series to the antenna. This improved the phase slightly. Then i 
>>>> also found a low pass filter for 137 kHz, the pypical pi 
>>>> configuration, i.e. it acts as 4*22 nF in parallel here on this 
>>>> frequency. Switching this in series leads to a low current, so the 
>>>> C is to small. So for the next experiment i'm preraring a 
>>>> switchable C network (47n, 100n, 220n, 470n, 1u, 2.2u, 4.7u). It 
>>>> will be even more necessary when i lower the wire resistance 
>>>> (higher Q).
>>>> Well, today the QRN was much lower, especially for the 2970.005 Hz 
>>>> transmission period. Yesterday this was totally buried in the noise 
>>>> on my RX on the tree. But today! I transmitted another 90 minutes 
>>>> with much lower QRN background. I already have a clear spectrum 
>>>> peak but i like to try to improve it a bit more before presenting 
>>>> it here.
>>>> Todays carrier transmissions:
>>>> 8270.000 Hz : 08:12...09:33 UTC
>>>> 2970.005 Hz : 09:42...11:15 UTC
>>>>
>>>> Sorry for the confusing email ;-)
>>>>
>>>> 73, Stefan
>
>
>