Автор Тема: Широкополосный трансформатор  (Прочитано 1346 раз)

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Широкополосный трансформатор
« : 20 Февраль 2019, 22:32:12 »
Широкополосный трансформатор 8.27 кГц-136 кГц-472 кГц 1:1, 1:4, 1:9, 1:16 и 1:25. 1:36

UPD - на всякий случай дискуссия по сему поводу из рсгб:

Hi All
Transformer is ready.
73! Marcin SQ2BXI

-----Original Message-----
Sent: Friday, February 15, 2019 5:56 AM
To: rsgb_lf_group@blacksheep.org
Subject: RE: R: Re: VLF: in VK?

Hello VLF!
The primary coil of the transformer is ready. 10 turns (diameter 2mm) give 9.62mH which gives about xl=500Ohms at 8.27kHz. It is a good idea!

73! Marcin SQ2BXI

-----Original Message-----
Sent: Monday, February 11, 2019 4:55 PM
To: rsgb_lf_group@blacksheep.org
Subject: RE: R: Re: VLF: in VK?

Hello Stefan!

Today, the ferrite cores B64290L82X830 came to me. I'm building a transformer 1:1/1:4/1:9/1:16 and 1/25 on the VLF. I'll check if it works soon.
73! Marcin SQ2BXI

-----Original Message-----
Sent: Monday, February 11, 2019 2:50 PM
To: rsgb_lf_group@blacksheep.org
Subject: Re: R: Re: VLF: in VK?

Hi Dimitris, VLF,

Am 11.02.2019 01:07, schrieb Dimitrios

     I have an idea about impedance transformation and that is to use high
     power 70V/100V audio distribution transformers at both ends. I don't
     have to go to 50 ohm as I don't use the coaxial cable as a
     transmission line (it's only a tiny percentage of the wavelength!), so
     I could use a 4 ohm to 400 ohm transformer or similar. I think in
     general the impedance transformation ratio goes down as the power
     rating goes up and we can live with that. THe audio transformer should
     work fine on the higher frequency but that will have to be tested.
     Perhaps something like this but not at that price!!


     Another option is to get a PA amplifier of suitable power output that
     has a 70V or 100V output. You only need one transformer at the antenna
     end to get down to 4 ohm to reduce losses. I have a 50 W amp with such
     output but that's not enough power.

These high power audio transformers are interesting. I wonder how well they work below 1 kHz. But they are to expensive, as you say. You don't need them. For any impedance transformation above 1 kHz i use ordinary
N30 ferrite toroids. There may be slightly better core materials but i'm getting very good results and they are not expensive and you can find them at many distributors (min quantity = 1, not 50000000000000000000000000). Especially at VLF they are well suitable and not expensive.
One of my preferred cores is that one:
It works easily for a few hundret watts on all VLF frequencies.

Yes you don't need to match the cable impedance but the losses on your cable are caused by the current and resistance of the wire and so, if you transform from 4 Ohm to 50 Ohm, then your losses drop by 92 %, regardless if it is necessary to match the cable impedance.

     I can easily try the ground loop on the 120m long antenna as I do have
     ground rods at both ends. It would be interesting to compare the
     signal strength in both cases. THat's why I am building a network of
     VLF stations by giving away the large ferrite rods to interested
     amateurs! They can help doing comparisons like this.

Yes, sure. Good luck in getting people motivated to build up a permanent VLF RX station. It would also be good to have someone building up a grabber site or maybe even providing a stream. Your activity can cause a world wide motivation for people who are principally interested in VLF reception and/or transmission, even if they won't be able to receive you from so far away.

     The ground is very rocky and there is almost no soil at the top.
     Typical Australian native vegetation is the only thing that can
     survive on it. I have thought about the dipole on the ground and I
     have the perfect spot for it which is putting the feed point at the
     top of the hill therefore making an inverted-V :-) Only concern with
     that is the high voltage at the end of the dipole wires and the
     possibility of a bush fire ignition. Definitely a project for winter!
     I have tried to tune my ~120 metre wire to VLF in the past with mixed
     results. Worth revisiting this. The wire basically starts at my house
     and follows the hill resulting in the top of the wire being maybe 20
     metres higher than the bottom.

I'm taking part in your experiments by imagining that i would be in your position :-) My latest thought is that a few (wooden?) poles of 10m height or so would be ideal. One is close to the house, and then two more in 100m distance from the house, e.g. here:
The 2x 100m dipole could be connected using a good HF ladder line down to the shack.
Aluminium wire is light weight and cheap and the lower conductivity could be compensated by using a higher diameter, something like this,
This antenna would have the advantage that you can use it from MF to DC and the kangaroos would not be able to destroy the antenna.
For VLF experiments, the ends of the wire can be grounded, just by adding another 100m of wire at the ends and let them slope down, maybe with another pole at 4m height.

73, Stefan
« Последнее редактирование: 20 Февраль 2019, 22:42:20 от rw3adb »
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Re: Широкополосный трансформатор
« Ответ #1 : 22 Февраль 2019, 08:22:32 »
Ба-а!! Да у меня тоже есть кусок провода развешанный на деревьях длиной примерно в 100 метров. Сегодня еду на дачу и переключу на него свою ДВ"аппаратуру". 
P.S/ Толи  R7NT,  толи UT7GH, уже и не помню,  давно мне это предлагали
UB1APE (exRA1ADF) Сергей. Самодельный приёмник прямого преобразования. Т-образная ант  высотой 10 метров