Antenna winding questions

[Perrold]

Anything being "transmitted" over 5 meters shouldn't require the same level of care and effort as an actual receiving loop. Just do it. It'll all be boring near field stuff.

[Amish_Fighter_Pilot]

So I have been playing around tonight and came up with an antenna design I haven't seen before that incorporates some aspects of basketweave, loopstick, and simple loop into one antenna. It is made from approximately 25'(7.62 meters) of 18ga bell wire. The idea is to put loading coils directly into the loop while barely affecting it's on-axis profile. I haven't had much time to play with it yet but the reception from it is surprisingly good in the at 17.3KHz(I have a metal detector pinpointer and was watching the antenna on my oscilloscope). I will try to get pictures when I can. I didn't expect this antenna to work so well and just really made it for fun. The design gets best reception in parallel to the transmitter, but the off-angle reception is significant. I would estimate it to be 30% signal at 90*. For what I am doing that isn't great, but it was surprising to me anyway.

[Amish_Fighter_Pilot]

Here's my new antenna. I call this design a "Loaded Basket Loop". I wanted to try and add loading coils directly to a loop antenna. The off-angle gain of it is better than anticipated(or wanted). I wish I had a VNA to check it with, but it seems to pick up the best clean signal at 2.3Mhz so it might be resonant at or near that. I can see it plain as day on my oscilloscope. I was seeing a modulated signal at that frequency.

[TimFox]

If it’s self-resonant at 2.3 MHz, you can easily tune down to the AM band (550 to 1600 kHz) with a good air variable capacitor.  If you measure the inductance at 100 kHz or below, what do you get?

[Amish_Fighter_Pilot]

I am saving up to buy a NanoVNA. Hopefully within the next couple of weeks I can get one. I am not sure what it's inductance at specific frequencies is, but I was able to do a bit of a trick with my DSO-TC3. It can't measure inductors under 50uH, but if I put them in series with a known inductor that is big enough to read; I get the combined inductance of both inductors. I tried a few known transformers and it consistently was showing it to be 30uH and the DC resistance is less clear at somewhere between 1-2 ohms in the various readings.

I found the coil below on a web search and it is rated at 30uH, but I don't know a lot else about it aside from it being a similar diameter to mine(mine has 13 turns and that one has maybe 20). It leads me to believe that number is at least roughly accurate.

[coppercone2]

what material is the frame of that coil lol, it looks just like steel/iron

[iMo]

Here's my new antenna. I call this design a "Loaded Basket Loop".

Nice basket, indeed..
Do not forget to include those 104 small inductive loops into your L calculation ..

[Amish_Fighter_Pilot]

what material is the frame of that coil lol, it looks just like steel/iron

Yeah they're just nails lol

I thought about using ferrite but I didn't have a matching set

[radiolistener]

Do you understand that these nails and windings around them significantly affecting your coil properties and increasing energy loss?

[coppercone2]

Oh I meant the commercial coil frame, is that dark bakelite? I never saw it like that before


For your own antenna you want plastic hardware or ceramic if you have the money ideally.
https://www.mcmaster.com/products/bolts/material~plastic-1/


But your design with ferrite in the antenna is some weird LF hybrid.

[coppercone2]

What you did seems most similar to this

https://www.eevblog.com/forum/rf-microwave/ferrite-sleeve-antennas/

Read the document it has something conceptually similar and you see the result is like potential material savings but it seems difficult to engineer.

if you scroll down page 100 or so, you will see actual pictures of what they built. But it does not have individual loops (series inductance  in the antenna). What you did probobly does something but no one is gonna know what IMO


Keep in mind the point of ferrite sleeve antennas is low frequenciers, like longwave and VLF and stuff. Your idea is HF so IDK how relevant  any math or analysis in there is related to distributed cores.

The only simple one that most people know is adding a small coil to a monopole antenna to change the electrical length (I.E. wifi antenna). I never saw inductance in series with a loop before


At least you can do a simple experiment to tune something and remove nails to see what they do, then retune and see how the signal strength is

[Amish_Fighter_Pilot]

The ferrite sleeve antenna is interesting. I had to look around a little to find pictures of it.

https://swling.com/blog/tag/ferrite-sleeve-loop/

The nails are necessary structurally, but I do intend to try a version without them when I can find something strong enough. At this point it isn't intended to be anything serious. I just made it on whim and was surprised by how good the reception is from a couple of different transmissions.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         

[TimFox]

To avoid iron nails, etc. when holding down wires for high-Q coils, I have used polypropylene (not nylon) "ty-wraps" into holes on a low-loss substrate (e.g., polyethylene or polystyrene).
Do not use black polypropylene (sold for UV resistance), which is stabilized with carbon.  The good stuff for this purpose is green.

[coppercone2]

usually what they seem to say in general is that conductive objects near the antenna cause loss. I don't know anything about using them on purpose

[Amish_Fighter_Pilot]

usually what they seem to say in general is that conductive objects near the antenna cause loss. I don't know anything about using them on purpose

It kind of reminds me of a tiny version of this:

https://commons.wikimedia.org/wiki/Category:Circularly_Disposed_Antenna_Array

[TimFox]

In the "near field" region, close to the antenna, conductive objects will have currents induced in them (not radiation) and absorb energy from that field (which is oscillating, not radiating, and storing energy).
For example, putting an antenna close to a tree will increase loss (lower Q).
Similarly, ferromagnetic objects in the near field will dissipate power:  each traversal around the hysteresis loop dissipates an amount of energy equal to the area of the B-H curve enclosed by the loop.

[Amish_Fighter_Pilot]

That must make radio towers a real pain to design. There's tons of steel in them. I'm guessing there's tricks to deal with it or we wouldn't be having this conversation because I'd have no hotspot

[TimFox]

One trick is using “egg” insulators along the guy wires that stabilize the tower to break up the conductor.
Properly installed, should the insulator fail, the guy wire is still mechanically sound to avoid catastrophe.