Antennas for experimentation - Page 1
Forum section: electronics / rf-microwave

author: Grandchuck
author_rank: Super Contributor
timestamp: November 16, 2022, 08:31:48 pm
content: These antennas are interesting and are available for $2.39 plus shipping. Amazon USA has them listed for $9.00 (Prime).https://www.aliexpress.us/item/2255800677446691.html?spm=a2g0o.productlist.main.7.6b5c6fc9fzQ0K9&algo_pvid=1cd35da7-2dbc-44b4-bb5a-c45ec30cd8d4&algo_exp_id=1cd35da7-2dbc-44b4-bb5a-c45ec30cd8d4-3&pdp_ext_f=%7B%22sku_id%22%3A%2210000009701039767%22%7D&pdp_npi=2%40dis%21USD%212.5%212.37%21%21%21%21%21%402122457116686255270284599d0732%2110000009701039767%21sea&curPageLogUid=IdcTy0e3axNIThe first shot is the test setup using a nanoVNA V2+4. The next one shows both sides of the pc board and the size. Last, the Smith Chart and the SWR are shown.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 17, 2022, 12:55:27 am
content: Quote from: Grandchuck on November 16, 2022, 08:31:48 pmThat is pretty interesting. I'll throw my ring into the hat with one I call Child's Toy. For completeness, also shown are the Smith Chart and SWR. Mine also make free energy from the Ether using what I call flower power.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 17, 2022, 04:26:33 am
content: Radiation pattern for Child's Toy. While the SWR looks good it sure makes a poor radiator. Who would have thunk.

author: Geoff-AU
author_rank: Frequent Contributor
timestamp: November 17, 2022, 08:30:29 am
content: I think the planar disc antenna is an unusual beast.My first attempt was here:https://thenack.com/2016/11/planar-disk-antenna/I also made a little version from a 15x8cm protoboard (see attachments) that works above 600MHzThe pattern is like a dipole (imagine two very fat elements) at low frequencies and eventually becomes endfire-ish (imagine a bidirectional vivaldi) at high frequencies. The lobes are a bit all over the place, so it's a matter of wiggling the antenna around to optimise the signal at the frequency you're trying for.

author: aweatherguy
author_rank: Contributor
timestamp: November 17, 2022, 05:52:43 pm
content: The antenna posted by Grandchuck appears to be a variation on the well known bazooka dipole.

author: Bud
author_rank: Super Contributor
timestamp: November 17, 2022, 06:01:38 pm
content: Quote from: joeqsmith on November 17, 2022, 12:55:27 amFor our amuzement could you also make some fun of the modern cell phone antennas ?

author: joeqsmith
author_rank: Super Contributor
timestamp: November 17, 2022, 09:20:22 pm
content: Quote from: Bud on November 17, 2022, 06:01:38 pmThis has been a serious discussion on experimental antennas. I have never owned or had any desire to own a cell phone. That said, I am working on a new design you may be interested in. This is a transverse axial parallaxer, or TAP for short. You can remember the acronym by Terrance and Phillip.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 18, 2022, 01:27:45 am
content: The transverse axial parallaxer required a little bit of tuning.Maple1 Smith Chart while adjustments were madeMaple2 SWR after adjustmentsMaple3 Matching stubMaple4 2D radiation pattern of the TAPMaple5 3D radiation pattern " " "Shows some directivity but doesn't radiate very well.

author: Geoff-AU
author_rank: Frequent Contributor
timestamp: November 18, 2022, 04:01:00 am
content: I think the TAP is the first example of "antenna looks like its radiation pattern" that I've seenGreat job

author: joeqsmith
author_rank: Super Contributor
timestamp: November 20, 2022, 07:41:38 pm
content: Quote from: Geoff-AU on November 18, 2022, 04:01:00 amCountless hours of simulation and several layouts to get that just right....

author: tautech
author_rank: Super Contributor
timestamp: November 21, 2022, 05:12:16 am
content: A J Pole is one of the simplest to make if you have some lengths of conductive rod in the workshop.https://m0ukd.com/calculators/slim-jim-and-j-pole-calculator/

author: joeqsmith
author_rank: Super Contributor
timestamp: November 21, 2022, 01:40:24 pm
content: Maybe just some wire would be even more simple?

author: tautech
author_rank: Super Contributor
timestamp: November 21, 2022, 07:19:46 pm
content: Quote from: joeqsmith on November 21, 2022, 01:40:24 pmMaybe but with lesser gain.I did a 315 MHz J Pole a few years back and tuned it to better that 1.1 SWR which replaced a piece of wire jammed into the center conductor of a BNC socket.I needed a keyfob transmitter to work reliably over 500 yds and that was achieved no problem.The last adjustments to the J Pole to account for installation proximity effects was made while installing and measured from the end of the Coax feeder.Wrote it up here:https://www.eevblog.com/forum/rf-microwave/antenna-project-log/

author: aweatherguy
author_rank: Contributor
timestamp: November 22, 2022, 12:55:02 am
content: That's 315MHz, not 3.5MHz....right? Or did I miss something (I do that on occasion)?

author: joeqsmith
author_rank: Super Contributor
timestamp: November 22, 2022, 01:14:43 am
content: Another highly experimental antenna based on the "Slim Jim" called "Fat Bird". Red traces showing the final result.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 22, 2022, 01:54:45 am
content: Flying the bird upside down, it's more directional that I would have guessed.

author: tautech
author_rank: Super Contributor
timestamp: November 22, 2022, 02:00:01 am
content: Quote from: joeqsmith on November 22, 2022, 01:54:45 amThat's still a good directional node just at 90 to the bird.A buddy that helped me on the J Pole journey instead simulated this for it as I needed omnidirectional sensitivity.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 22, 2022, 04:37:41 am
content: Fat Bird 3D sweep.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 23, 2022, 01:20:26 am
content: In an attempt to replicate the nice torus shape, I recycled Fat Bird and built a real Slim Jim. Nothing I would consider experimental as it seems well documented. To keep the size down, I target the 900MHz IMS band. Using calipers and carefully measuring the lengths, when it was all done I had constructed a pile of crap. Note my patent pending slide turning stubs used to overcome the problems. The SWR is decent enough.I started out running a 4 X 4 sweep (4 azimuth 4 elevations). Antenna was mounted vertical and view is looking down towards the top of the antenna. So we end up with a box with the lid sunk in. Seems like a sort of doughnut.Next, crank up the resolution....

author: tautech
author_rank: Super Contributor
timestamp: November 23, 2022, 01:29:39 am
content: Quote from: joeqsmith on November 23, 2022, 01:20:26 amNo, close up please.I used double screw inners from electrical chocolate blocks (snap off joiners) with one fixing the feed point in position and the other screw shortened a little and a washer added to secure the feedline.With patience this method allowed for quite fine tuning with a VNA although installation tuning is still required.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 23, 2022, 02:26:06 am
content: No problem... Shown mounted to the mast. Adding a few more data points, it does start to look like a doughnut.

author: tautech
author_rank: Super Contributor
timestamp: November 23, 2022, 02:51:56 am
content: Quote from: joeqsmith on November 23, 2022, 02:26:06 amAh OK you fixed the feed points and modified the Slim Jim gap. Fair enough.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 23, 2022, 07:50:27 pm
content: Shown are my latest experimental slip joints for easy tuning. Also shown are the new high tech materials used for spacers.

author: tautech
author_rank: Super Contributor
timestamp: November 23, 2022, 08:02:22 pm
content: Looking good Joe.I used 1/8" brazing rod so to be able to fit 2 screw cable joiner inners for the feed points whereas I could've used 1/4" solid copper rod but needed to manufacture adjustable feed points which really wouldn't be a problem on the lathe but as the J Pole was quite small so the the 1/8" brazing rod was quite adequate.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 23, 2022, 08:45:04 pm
content: Maybe some hobby brass tubing and make everything adjustable. Come up with something you like, solder it up. This one can be tuned over a fairly wide range but may not radiate very well.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 25, 2022, 01:26:02 am
content: Second Slim Jim.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 25, 2022, 04:04:03 am
content: The Vivaldi is a bit more directional.These last two antennas were taken with a 5deg resolution, or 36 elevation and 72 azimuth. Taking 2592 data points by hand would be a nightmare. Added one more zoomed in a bit on the backside.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 25, 2022, 10:03:44 pm
content: Taking the same Vivaldi and moving to a half meter away from the reference antenna does have an effect on the pattern. Considering that I am testing these in my home lab it's actually closer than I would have expected. Shown from two different viewing angles along with a low res 2D plot of the same setup. Where the SlimJimII was tested a bit over 900MHz, this Vivaldi is being tested at 2.4GHz.The low cost VNAs don't have very good noise specs and moving it further away could be a problem. My Signal Hound would do a better job making these measurements but it's fun playing with this $120 unit. The LiteVNA's firmware limits measurements to 9.3GHz. I have included data comparing it's noise floor against my old Agilent PNA, both using a 1k IF and again with the PNA set to 100Hz. Also shown is the SA with nothing but a 10dB attenuator attached to it, using the realtime mode with a 2.4GHz center. Note it still picks up interference from my router.Article using a drone to map the radiation pattern.https://signalhound.com/news/antenna-measurement-and-characterization-with-uavs/

author: Thedrunkenflea
author_rank: Contributor
timestamp: December 18, 2022, 03:43:46 pm
content: Very interesting stuff - i might have found my next project or two!