Inductor question for vlf receiver

[Myrmidon]

Greetings.

I'm currently making a vlf receiver for listening to 'natural radio' (see attached)
I have all the parts, however, the 200mH inductor is causing me hassle.

I can't seem to find inductors anywhere this size, no problem, wind my own.

But the size of a wound air core inductor has me doing 3000 odd turns and would be pretty large.

edit: I have some ferrite rings lying around but they are unmarked so i can't finish the equation to find the turns for a torroidal.

The maker of the receiver uses a 1k to 8ohm audio transformer using the centre tap and one of the ends to make the inductor, however i can't find one of these either.

So, i was wondering if i could omit some parts and stick in an oscillator of some kind tuned to the freqs i would be looking for around 12-25khz, but i'm not that far into my electronics course and not sure how i would go about it, or even if it could be done. I think it could though.

Any radio heads able to advise me?

Cheers.

 

[Nigel Goodwin]

The transformer sounds like a standard audio transformer (as used in 1960's radios), these are still fairly available, but you may need to search a bit.

 

[Myrmidon]

Hmm, i'll dig around. I have a few transformers lying about but not sure of there properties.

 

[Mikebits]

You have some huge impedance on your input, I would suspect it will be a noisy bugger.

 

[Nigel Goodwin]

You have some huge impedance on your input, I would suspect it will be a noisy bugger.

I think you've missed the point?, that's what he's trying to receive.

 

[k7elp60]

The Radio Shack part number 273-1380 meets the description of the transformer.

 

[Nigel Goodwin]

The Radio Shack part number 273-1380 meets the description of the transformer.

That looks spot-on to me!

Well done.

 

[Myrmidon]

Thanks very much!

 

[stevez]

I can tell you that I've seen descriptions of the inductors for VLF receivers - made by hobbyists. I wish I could tell you where. Keep searching. There are SWL groups who focus on VLF and they've published a lot of stuff.

If I had ferrite cores of unknown characteristics I might wind some turns then measure the impedance. I'd do it with a signal generator (audio), resistor or two and a DMM - just to get crude approximation. Then you know about how many more turns you need - again crude but might be what you need.