Making tunable loop antenna

[Chernobyl2]

Hi,

Instead of buying a ready-made loop antenna, I'd like to build one. From reading around the required wire length (in feet) is approx. 234 / f (where f is in MHz). What kind of tuning capacitor do I need? It seems people are using 350 μF or so.

Anyone know how to build extremely low power repeaters? Some people are building loops that can receive sub 150 kHz then re-broadcasting at very low power so their radio can pick it up around 1 MHz or so.

Best regards,
Chernobyl2.

 

[Wire Weasel]

I think you need to do some more reading C2. The Loop measurement formula is 1005/freq.

What exactly is it you are wanting to do with a loop? Where do you want to transmit/receive?

I have much experience with loops and there are the only type of wire antenna I will use on the HF ham bands.

Loops are full-wave antennas and are the only type of antenna I know of that works at a full wavelength on the fundamental, or bottom-most frequency.

If you make the length of a big HF Loop where it is resonant within the boundaries of the bottom band, say 80 meters for example, then it will have a natural resonant area there and in or very near every major HF band above 80 up to 6 meters. So it will have a resonant area in or near 40,20,15,10 and 6 meters.

Tuning will be required to spread the resonant transmitting ability out to the edges of these bands. This is usually accomplished by using a typical antenna tuner. A modern HF rig with an internal tuner may take such a loop most places but they have SWR maximum limitations, most such internal tuners being only able to correct a 2:1 mismatch or less. Outboard tuners can correct greater mismatches and usually can extend the range of a loop over much wider areas within each ham band.

 

[Chernobyl2]

I think you need to do some more reading C2. The Loop measurement formula is 1005/freq.

Ooops. I was confusing it with long wire aerials.

What exactly is it you are wanting to do with a loop?

Primarily enhance reception of frequencies between 150 kHz and 10 MHz, though anything that can enhance the general range 150 kHz to 30 MHz (if I need to build multiple aerials to achieve this, so be it). I'm wanting to enhance what I already have before I dive in and buy a desktop rig, get a license, etc..

For now I'm only looking at making a small loop - one that is portable, but can be reasonable size (e.g. 6 ft diameter). I see people are having good results with loops made from hoola-hoops and other similar sized loops.

I'm pretty useless with math and electronics so please excuse my ignorance. Despite much trying I consistently fail to "get it"; even though I can remember most of what I read it doesn't make sense. I can't make it work in my mind. I can only liken it to reading a foreign book without knowing the translation - I could remember most of it but not tell you what it means. I find it quite infuriating to be honest. Apparently it is a formal condition now, called "discalculia". On the flip side, tell me what I need to do to get a job done and I can do it, though I don't usually like doing things by rote.

Thanks for the info so far! I do research what people write to learn as much as possible, even if I may not understand all of it.

If you have any recommended reading on the basics of aerials in general, radio etc.. it would be greatly appreciated. I'd like to at least try and understand the basics of how it all works.

Best regards,
Chernobyl2.

 

[Wire Weasel]

Okay then, What you have seen is an indoor Active Loop. It consists of some sort of frame, like the hula hoop you suggest, and it is then would with many turns of insulated wire. Also in the circuit is some kind of tuning network and may or may not be amplified.

These are for receiving only. Absolutely not for transmitting. So if you are wanting to eventually get a ham license and wish to be talking on the lower bands, then we are talking about a long outdoor loop also called a Loop Skywire if you care to do internet searches on them. A loop for say 80 meters, will be in the neighborhood of 250 feet long and is usually erected horizontally and in a square pattern. Square shapes work very well and will only require 4 tie off points. Other shapes are possible. Square gives a good omni-directional pattern though. An 80 meter loop will work well for receiving much lower frequencies too. There's nothing much down there but aeronautical (airport) beacons...which isn't very exciting....but folks get interested in listening to different things and it's all good.

There's much info on the internet regarding Indoor Active Loops and outdoor Loop Skywires. Just google

Good luck !