DIY Antenna Design

Discuss commercial and home made antennas.
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iScan
Posts: 13
Joined: Wed Sep 09, 2015 10:11 pm

DIY Antenna Design

Post by iScan » Thu Sep 10, 2015 1:10 am

My first post will be long-winded, hopefully to start something. I'd like to hear other stories, designs and attempts, reports of success.

I got off on a bad foot with home-built antennas. My experience with antenna making started about 51 years ago with a simple long wire aerial that I hung with stealth from a tree across the alley to an electric pole also across the alley. We had no space at all for what I knew at the time. I used magnet wire from transformers and so of course it lasted for maybe three hours before breaking. It worked and I was determined. I strung it again and again.

We moved and then there was room for my creations. I put up a proper version of the same. Knowing it was finally my best effort, I bored myself to tears using it. I left home and next had dorm rooms for years. Yeah, there were a few folded dipoles made from 300-ohm TV transmission line. Again rules and space constraints were death to my thinking.

I married and bought a house in a suburb. There was room on the roof for two rhombic antennas. These do have gain in a directional pattern. I made them each with transmission line, 90 degrees to one another. That rhombic design requires a terminal resistance at the corner opposite the feed point. I switched each of the resistors and feed points to their opposite direction. They may have worked well had any broadcasts originated in any of those four directions. But all four changes turned out to be totally wasted efforts.

Citizens Band radio was big then for awhile. I tried making a Coaxial wire antenna (Vertical wire dipole. I slit the outer jacket for tuning a central channel on the band and pulled the end of the braid backward over the jacket and taped it down. I hooked the end of the center wire and hung it with an insulator.) That work was worthwhile and there I was -- a portable base station transmitting, receiving and all totally legal. Of course I bought a manufactured CB antenna for best results. For fun I could still move around and hook up that vertical too. With transmitting there's that standing wave ratio thing that so rips you off and with already low power. I quickly learned to make the most of the situation. Tuning helps the equipment. A steel crowbar can be tuned. Getting it right in the first place helps the equipment and the power of the radiated signal.

Most of my efforts have been for reception. I was stationed in Turkey and took a nice short wave radio along. It had an antenna input tuner, dual intermediate frequencies and I was spoiled -- anything I tried for an antenna worked. I had learned to calculate great circle headings and distance. In HF bands there's skip and multiple skips, so the distance is roughly translated like -- "Who really cares?" But since longitudes and latitudes of broadcast locations and my own were known, my interest turned back to directional reception and those antennas. And I lived across the street from one of my rich uncle's antenna farms. I first saw a discone there, so big it had to be HF. It was inverted from these you see like the commercial VHF/UHF discones we are using. This one was strung with a wire each sloped down from many telephone poles in a circle down to the center, and then a radial wire to form the disk also from each pole to meet parallel with others and earth at the bottom. Everything was done right just as though lives might depend upon it. Yes, I was there generally too long but in a few ways, not long enough. Pac Man bloomed from nothing in those two years and a different world awaited my return back into it.

Computers, Cable TV, then cable TV bills occurred. I started to rent movies and put in a TV antenna in the attic because of the high cable fees and of course also because that pleased my uncle more than antennas mounted on his roofs. I totally nailed the directional stuff and practice re-aiming it just proved I was the ace. I was thinking about making helical antennas. Not that I really minded whether some satellite was rolling around and changing polarization modes constantly that needed to be dealt with... I just wanted to try one. I made a three turn helix. It worked somewhat though it was without any doubt the most intense structure I will attempt. I never got around to aiming it so seriously as I had thought I would. Computers as a hobby took over.

Things circle around, lo and behold, here we are now with SDR!

I got one for little more than twenty bucks. What to do? WAIT FOR SOME manufactured antenna? One that I will have to figure out how THEY assembled it? Then, PAY for one that will cost three or more times what I started into this with? or I could have it just as inexpensively in a few hours once I have had a blast figuring how I want to make it? Well? Oh so definitely so!

It was suggested to make a planar disk antenna with two pizza pans. Interesting that here's an antenna that is not directional, is broadband, and aren't 18" pizza pans everywhere? Hmm. No, not here, they are not. NOT in the largest US metropolis on a labor day weekend. Instead I head for big box building supply store thinking what do they have like that. They have 20" aluminum flashing. Stuff is so thin it cuts with scissors. 3/4" PVC to assemble on. A pack each of long screws, of matching thumbscrews, of crimp ring terminals, a drill bit for the screws to pass into the PVC and a paddle drill to widen the hole opposite the screw for the PVC and aluminum, a roll of vinyl electrical tape, large cable ties, roll of coax cable and a bit of shazam--my newest, a Planar disk antenna. Now, 18"-pizza pans are each about the cost of my SDR dongle. I did better than that and mine are aluminum, not steel! In the meanwhile, I had read a paper they tested rectangular elements to replace the discs and had very similar results. They tried to angle the upper element from the middle feed point to the nearest two corners--again similar results. I decided it was easier to leave them straight. Now they liked 18" pans. And I have this 20" flashing, so why not try it, then if needed I can always trim two inches off the top and an inch off the sides/or/even more at my will. IF you make this there are sharp edges all around the panels! Same warning came with the manufactured TV antenna I put up in that other attic thirty years ago-- "CAUTION! Edges are sharp on some antenna elements."

Dang, this is a beauty! What a crying shame that wind would catch it, it would have been so awesome on my chimney! Oh yeah, turns out the thing works as well as it looks. The guy (a licensed HAM operator) with the 18" pizza pans who said he put his in his attic nearly two decades ago, he still uses the thing he made.

This is a three-D vertical dipole. Next I am thinking about what is going on and how this could be working so well... Broadside there are many bandwidths available due to angles at each corner. From the end, panels are broad elements even though the material is hardly more than foil-thin and broad elements also promote more bandwidth than expected from a similar vertical wire dipole.

I am planning maybe next to try another, substituting two ~18" diameter rings made with 3" or 4"aluminum dryer duct for each panel. Toying also with an alternate idea of not joining the rings at each end though I really don't expect this to work as well. Okay, yes I went back for some flexible aluminum dryer ducts PVC unions and stuff. Have to get back about that...

So, what have you been doing?

trevatxtal
Posts: 6
Joined: Sat Sep 05, 2015 6:27 am

Re: DIY Antenna Design

Post by trevatxtal » Thu Sep 10, 2015 7:01 am

Hello iScan
I am a new'by to on this forum. I have just the one post a query on modifications to active antennas.
I like your post very much so like my own antenna making history, I will be following you closely.
Thank you for your input.
I live in South Devon UK.
I mention this as there is a Radio Rally on the 13th at Newton Abbot Race Course,
Absolutely nothing to do with me but I find it useful to attend and see the trend in radio communications.
Trev

iScan
Posts: 13
Joined: Wed Sep 09, 2015 10:11 pm

Re: DIY Antenna Design

Post by iScan » Thu Sep 10, 2015 3:49 pm

Hi Trev,

What's available from SDR is what caught my attention in the first place: Defcon 21 - All Your RFz Are Belong to Me - Hacking the Wireless World with Software Defined Radio /or/ https://www.youtube.com/watch?v=ZuNOD3XWp4A

So much has been done on one hand. Yet on the other, I haven't scratched the surface, myself.

Software is in it's infancy, reminiscent of hardware moving from cat whiskers on crystals to vacuum tubes. It's our turn now!

trevatxtal
Posts: 6
Joined: Sat Sep 05, 2015 6:27 am

Re: DIY Antenna Design

Post by trevatxtal » Fri Sep 11, 2015 9:51 am

Thank you iScan for the link a very informative presentation even if it started slow.
I will be back in time with some of my observations.
I now have two of the sdr blocks one a rtl-sdr 5mhz to 2000mhz and a DVB+DAB+FM+SDR range unknown so far, both partly working but lots more to explore.
I hope to have them fully working in time with Linux and win ???
Trev

SholomPei
Posts: 1
Joined: Mon Dec 14, 2015 3:16 pm

Re: DIY Antenna Design

Post by SholomPei » Mon Dec 14, 2015 3:37 pm

Can you please help me to understand the Antenna designing?
I also want to design some antennas for some applications?
Where i should learn about this? Is there any simulation software available for it?
What are the basic components for it?

iScan
Posts: 13
Joined: Wed Sep 09, 2015 10:11 pm

Re: DIY Antenna Design

Post by iScan » Tue Jan 12, 2016 5:57 pm

Hello SholomPei,

So much, or maybe all of this is about trade-offs. Design of an antenna itself makes the final decisions by what you're trying to receive and what you have to work with (E.G. available acreage or owner association rules, bandwidth or tuned, directional or omnidirectional, construction expense and relative signal gain.) Simulation amounts to yet another trade-off--without construction cost, mechanical effort or expensive testing you get decent simulations. Then regardless whether you estimate or simulate when you build real, it's real.

My short answer is that I don't have a great short answer. Mountainous heaps of antenna design and construction publications are more available and seem to be far more useful to estimate outcomes for me. Antenna simulation programs exist that handle published antenna concepts for any very specific plan. Things I've wanted to try seem to be out of my reach for simulation.

Looking into this issue myself, I am disappointed in multiple ways. The antenna drafting portion of this kind of software has been too tedious. I've spent enormous spare time redoing my Windows OS efforts with Linux-based packages. (Similar results there so far.) Icing the cake is how much I've learned in computer management keeping Windows 10 boots healthy during multiple Linux distributions and each of their multiple boot options. Nevertheless, I've actually accomplished what would amount to not making the cake. Maybe sexy, maybe not, I'm back to building these rather than simulating them.

My trade-off is getting to be whether I want my RTL-SDR hobby to be more about listening, more about making antennas, more about software and OS, or more about reworking the hardware. What I have the most of is too much interest in too many facets. My most insurmountable limit is time.

GabrielOl
Posts: 2
Joined: Tue Apr 12, 2016 5:16 pm
Location: Estonia
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DIY Antenna Design

Post by GabrielOl » Sat Apr 16, 2016 10:47 am

Do you offer any isotropic antenna or how to make a isotropic 3D measurement?

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