Author Topic: Can I use an FM variable cap for a magnetic loop antenna for RX?  (Read 946 times)

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Offline azigta

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Can I use an FM variable cap for a magnetic loop antenna for RX?
« on: September 04, 2016, 04:24:42 pm »
Hi, In the next few weeks I'm going to recieve my very first non commercial radio, a chinese rtl sdr that can go from 100khz to 1.7ghz. So I decided to make an antenna, since I want to recieve hf for swl.

I saw this video and I decided to make that antenna. I know how many meters of copper tubbing I have to buy and everything , but I have a little problem.

In the video, the guy uses an air variable capacitor. And from what I've read on some forums, that is an essential piece of the project. I also read that it is important to put a capacitor that has a great gap between plates if you're going to transmit. But since I'm not going to transmit at all, I was thinking if I could use a regular FM radio variable capacitor that I desoldered time ago from an FM radio.

I took some pictures of the capacitor so you guys can see how is it. I've seen similar capacitors but with different pins, so I thought It would be a better idea to take some pictures.

Here they are:

Picture 1, picture 2, picture 3

As you can see, is the kind of capacitor that you find on an analog fm radio.

In the third picture you can see that 2 tabs are located one on the top of the other, so if you look at the second picture it might be hard to tell if there's one or two tabs there.

One of the tabs was already cutted when I desoldered it, but is not too short, I can solder on that (I'm describing the left top tab that you can see in the first image)

Also, I have a multimeter that can measure capacitors but I can't measure this one. Not a slight change on the meter when I turn the screws or the "big" shaft (in the center of the box, you can see it in the third image, that's the "shaft")

When I turn the trimmers they don't have a limit. The big shaft does have a minimum and a maximum limit.

So, Can I use this for a magnetic loop antenna if I'm only going to recieve with it? if so, where would I connect the loop? I don't know how to measure this thing so I don't know where do I have to connect it.

Maybe someone here knows about this stuff and can help me


Edit: After a lot of searching, it turns out that I can! here's a link to a good tutorial on how to make a magnetic loop antenna for SWL with an fm capacitor
« Last Edit: September 05, 2016, 01:25:46 am by azigta »

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