Build a loop antenna for medium wave reception - Page 1
Forum section: electronics / rf-microwave

author: prabhatkarpe4
author_rank: Contributor
timestamp: September 23, 2024, 12:27:16 pm
content: I need to know one thing about making a small loop antenna using the LC and coil inductance formula.The solenoid inductance formula is shown in the attached file.Where, l is the length of the coil and N is the number of turns. So, does that mean that the turns of a loop can't be overlapped?If I need to use 20 meter long wire to wrap around a square plastic frame of 20 cm each side with a width of 2 cm, and if the wire is 1 mm thick and doesn't fit after a few turns then can I wrap the wire over the previous turns?I need one more clarification:A perfect resonant antenna is the one that has 1/4 of the wavelength. So, if I need to receive the 850 kHz using a loop antenna, then as per the formula, I will need a (300/0.85 = 356/4 = 88 meter) long wire.Instead of using it as a long wire antenna, if I wrap it around a plastic square frame of any size, then will it work as a loop antenna?

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: September 23, 2024, 01:02:33 pm
content: A small loop is NOT 1/4 wavelength but is just a tuned LC circuit.The multi turn antennas I have seen have the turns spaced apart from one another on a frame. or next to one another on a ferrite rod.

author: radiolistener
author_rank: Super Contributor
timestamp: September 23, 2024, 04:11:23 pm
content: Quote from: prabhatkarpe4 on September 23, 2024, 12:27:16 pmNo, the turns should not be wound in different directions. You can wind in two or more layers, but when transitioning from one layer to another, you need to make only one turn in the opposite direction, and then wind the next layer in the same direction as the other layers. And it needs to be carefully phased. All turns should be wound in the same direction because turns wound in the opposite direction will weaken the signal instead.In short, just don't overlap and keep all winding in one direction, it will be more easy.

author: A.Z.
author_rank: Super Contributor
timestamp: September 25, 2024, 07:36:32 am
content: Willing to simplify things, one may just go for this build ideahttps://www.instructables.com/Medium-Wave-AM-broadcast-band-resonant-loop-antenn/which eases the build and offers decent result

author: prabhatkarpe4
author_rank: Contributor
timestamp: September 27, 2024, 02:47:16 pm
content: But why the first turn needs to be in opposite direction while changing layers?How the loop will stay on the frame if I wind it in the opposite direction?

author: shabaz
author_rank: Frequent Contributor
timestamp: September 27, 2024, 04:43:57 pm
content: Hi,You don't need to make a U-bend in the wire if that's what you mean, and then wind that wire back, and, as you say, that wouldn't support the end of the first layer.Let's say your first layer started at the left, and as you wound it, it gradually ran to the right side.For your second layer, you can just continue to wind the way you did for the first layer but just let the layer form from the right side, running gradually to the left side. Imagine a machine winding layers of cotton thread onto a bobbin; it's the same thing. Or, you can let a kind of "mezzanine" partial layer form after your first layer, where you rapidly move to the left side over the space of (say) a turn or two. But all the time, imagine if your coil former is on a spindle, that it continues to rotate in the same direction, just like with a cotton reel/bobbin.However, either way, that formula you have in your original post, won't apply to multiple layers. Although formulas do exist for multiple layers (one is called Wheeler's formula), it's likely you'll need to just try it, and gradually remove windings if you overshoot your desired inductance.

author: A.Z.
author_rank: Super Contributor
timestamp: September 27, 2024, 07:02:39 pm
content: but the OP didn't yet understand, or it serms so, how a forum works; he keeps REPOSTING the very same questions, and opening new discussions; now... I'm not a moderator or whatever, but sincerely, I believe someone should enforce the rules, otherwise in a while we'll see a bunch of topics, from the same OP, dealing with the SAME matter; how would you like that ?Maybe he's just trying to train an AI LLM, who knows?

author: shabaz
author_rank: Frequent Contributor
timestamp: September 27, 2024, 07:31:54 pm
content: Thanks for the info. I would not have wasted any time on a response if I'd noticed : (

author: prabhatkarpe4
author_rank: Contributor
timestamp: September 28, 2024, 10:53:37 am
content: Yes, I got it this time. I should wind it from left to right (1st layer) and then from right to left (2nd layer). But without using formula it would be experimental and wastage of time and money.Could you please describe the wheeler's formula for the loop antenna?

author: tggzzz
author_rank: Super Contributor
timestamp: September 28, 2024, 11:33:06 am
content: Quote from: prabhatkarpe4 on September 28, 2024, 10:53:37 amThere are good explanations for thathereandhere.

author: prabhatkarpe4
author_rank: Contributor
timestamp: September 30, 2024, 11:48:21 am
content: These are phishing links. You should be reported.

author: A.Z.
author_rank: Super Contributor
timestamp: September 30, 2024, 01:06:49 pm
content: Quote from: prabhatkarpe4 on September 30, 2024, 11:48:21 amROTFL !!Come on, report his post, do it !

author: tggzzz
author_rank: Super Contributor
timestamp: September 30, 2024, 02:22:50 pm
content: Quote from: A.Z. on September 30, 2024, 01:06:49 pmI'd provide links so he can find out what "phishing" actually means, but he might report me for those

author: A.Z.
author_rank: Super Contributor
timestamp: October 03, 2024, 07:01:50 pm
content: strange, no reply, maybe he's busy studying some books or, at least, let's hope so