Re: LF: VLF Small magnetic antenna for Tx

[DK7FC <selberdenken@posteo.de>]

Hi Juan,

Good luck with your tests. Do you have/need a special license for transmitting on that frequency or is it free for everyone unless you stay below a certain ERP level?

Oh, i have another question: Did you try to receive on VLF from underground with your loop? Actually 38 kHz is still LF but it is the same equipment i think.
I would be interested in a spectrogram generated from a loop RX operated under ground. A non-resonated loop.
Right now i am transmitting on 970 Hz. That frequency will pass the soil and would reach an underground loop! But the power levels are not high enough here to pass the distance over to EA :-)

I would expect there is no 'gain' from such a site, only some kind of low pass filter. This should not improve the SNR. But it would be interesting :-)

73, Stefan

Am 05.02.2018 20:30, schrieb Juan Leandro Ronda:

Hi Stefan, 

    

   A piece is better. I have mixed copper and brass union nuts. The reason is for the space it occupies when passing through underground cavities, there are very narrow passages. I have not observed losses in the inductance, but the MKP / FKP capacitors are heated and I have a drift in the tuning. They have to go through them the 100A. In just one turn, 85Vp is already produced. Now I am using capacitors NP0 in SMD, it is incredible the behavior before the great tension and amperage, they have the disadvantage of having limit of high values ​​of capacity. I want to perform a test with Luis orienting the loop to his antenna, we are 49 km away, but he always has a lot of noise at 38KHz.

Regards

Juan Leandro

El 5 feb. 2018 19:33, "DK7FC" <selberdenken@posteo.de> escribió:

Interesting.
I built a similar loop and transmitted on MF. The maximum power was about 30 W RF because the resonating Cs (WIMA-FKP-1, 2kV) became warm and the resonance drifted away. But i managed up to 450 km distance with that compact antenna.

You loop may become more effective when using a single piece of copper. Don't you have such 'endless' tubes available? Like this one: https://www.hornbach.de/shop/Kupferrohr-weich-22-mm-Wandstaerke-1-mm-Meterware/3308518/artikel.html

73, Stefan


Am 05.02.2018 15:13, schrieb Juan Leandro Ronda:

    I have to say that I am also lacking in theory, but the tests carried out on airborne and core coils have been successful and are working.

The most relevant loop antenna has been an octagon-shaped loop, formed by 22mm diameter copper pipe of 1mm thickness, equivalent to 66mm square, forming a surface of 1m square. As seen in the attached diagram, I put in resonance by LC series (38400Hz) giving close to 100A, which in turn gives a magnetic moment of 100A per square meter. I verify that in the center of the octagon I am condensing enough the magnetic flux, knowing that it is very difficult to saturate the air. In summer I get to notice heating of the pipe. If I bring a euro coin to the pipe, it heats up and diverts the antenna's resonance.

Then I was forced to reduce the volume of the antenna for comfortable use in underground cavities. I had to resort to using cores to keep an effective area as large as possible. I tried what I had at hand, the coils of the TV deflection coils and I observed good operation, I also circulated a large amperage for it, giving rise to the development of a new transmitter for radiolocation, it is the Summer, published in the CREG JOURNAL nº99 " of the BCRA.

I have always wanted to use the power through low voltage and a lot of amperage, which will translate into great magnetic moment. It is necessary to use few loops in the loop, with a large section of the conductor and a high magnetic permeability core to increase the effective area. I also intend to minimize the tensions in the resonant circuit, there are partners who can suffer electrocution risk, since the equipment works at one hundred percent humidity and other times submerged.

So far I have changed the cores of the air antennas for ferrites, and now I would like to use mu-metal that has very high magnetic permeability. I see hard to get that material. I have seen that they manufacture rods of several cm in diameter. It would be interesting to contact the manufacturer and ask for samples, if someone sees it feasible to say something about it.

I have always worked in the near field for the use of radiolocation, and speaking with Luis EA5DOM, we discussed the effectiveness of using the electric field or the magnetic field with air, knowing that it is the magnetic that crosses the rocky pack more easily . I appreciate the comments on this part by this group.

https://drive.google.com/folderview?id=1V4K2T2e3ActVqPaHr1xXLcjBkD16NtGB

Regards

Juan Leandro

El 4 feb. 2018 8:35 p. m., "Juan Leandro Ronda" <juanleronda@gmail.com> escribió:

    I have to say that I am also lacking in theory, but the tests carried out on airborne and core coils have been successful and are working.

The most relevant loop antenna has been an octagon-shaped loop, formed by 22mm diameter copper pipe of 1mm thickness, equivalent to 66mm square, forming a surface of 1m square. As seen in the attached diagram, I put in resonance by LC series (38400Hz) giving close to 100A, which in turn gives a magnetic moment of 100A per square meter. I verify that in the center of the octagon I am condensing enough the magnetic flux, knowing that it is very difficult to saturate the air. In summer I get to notice heating of the pipe. If I bring a euro coin to the pipe, it heats up and diverts the antenna's resonance.

Then I was forced to reduce the volume of the antenna for comfortable use in underground cavities. I had to resort to using cores to keep an effective area as large as possible. I tried what I had at hand, the coils of the TV deflection coils and I observed good operation, I also circulated a large amperage for it, giving rise to the development of a new transmitter for radiolocation, it is the Summer, published in the CREG JOURNAL nº99 " of the BCRA.

I have always wanted to use the power through low voltage and a lot of amperage, which will translate into great magnetic moment. It is necessary to use few loops in the loop, with a large section of the conductor and a high magnetic permeability core to increase the effective area. I also intend to minimize the tensions in the resonant circuit, there are partners who can suffer electrocution risk, since the equipment works at one hundred percent humidity and other times submerged.

So far I have changed the cores of the air antennas for ferrites, and now I would like to use mu-metal that has very high magnetic permeability. I see hard to get that material. I have seen that they manufacture rods of several cm in diameter. It would be interesting to contact the manufacturer and ask for samples, if someone sees it feasible to say something about it.

I have always worked in the near field for the use of radiolocation, and speaking with Luis EA5DOM, we discussed the effectiveness of using the electric field or the magnetic field with air, knowing that it is the magnetic that crosses the rocky pack more easily . I appreciate the comments on this part by this group.

Regards

Juan Leandro

El 3 feb. 2018 21:35, "Jacek Lipkowski" <sq5bpf@lipkowski.org> escribió:

On Sat, 3 Feb 2018, VIGILANT Luis Fernández wrote:

Jacek, you mentioned what I was midnight oiling here
" If you want some semi-DX in the H-field, then try coupling into some long
conductors (pipes, power lines, railway tracks etc)"

And i forgot phone lines :)

Actually there has been a 700m phone line, that was well grounded at the phone exchange (old exchange, no local modules were used, so the wire went all the way there). This makes a nice ground dipole when a transmitter is placed between the local ground and the grounded wire from the phone line. Putting abt.  30mA at 8.97kHz (this was when 9kHz was the ITU limit) gave a very nice signal 600-700m from the phone line.

What about coupling the loop to my 90m vertical ?
Adding another transformer from loop to vertical or just winding some coils of the vertical over the
small loop ring would work ?

No, because the amount of current induced in the mast would be very small.

BTW i wish i had a 90m vertical.

VY 73

Jacek / SQ5BPF