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Built some Hovermans

The technical side of broadcasting. Think IBOC is a sham? Talk about it here! How about HDTV? Post DX reports here as well.
km1125
Posts: 3570
Joined: Thu Mar 14, 2019 3:09 pm

Built some Hovermans

Post by km1125 » Mon Oct 26, 2020 1:59 pm

I've been meaning to build a couple DIY antennas to use in the attic. I was going to use an antenna design that seems to be pretty popular that's made with a 4' 2x4 and 8 "V" sections of copper. Not sure what it's called, but seemed pretty easy.

Instead I built a couple Hoverman's based pretty closely on his original patent. I'm using a #10 copper wire, just because I had some #10 romex laying around. I also put a screen behind it for a bit of directionality. I'm thinking if that knocks down any interference from behind that would make a more reliable signal.

I also wanted to make something that was collapse-able so I could fit it through the hatch to get it into the attic. I ended up taking a few 1x4 boards and making a sideways "H" structure to hold the wire. It's just over 30 inches tall and each "H" leg is 12" long. I shaped the Hoverman elements and connected them on the front and staples some metal mesh on the back. Tried them and they are MUCH better than the cheap commercial UHF antennas I had been using. They appear to have somewhere between 10-15 dB of directionality to them. They work great for picking up all the UHFs and some of the high VHFs but don't get down enough to pick up WHNE (RF3). That's OK though, because I had built a folded dipole for the VHFs and combine that with a UHF/VHF combiner.

******...******
........ *...*..........
........ *...*..........
........ *...*..........
........ *...*..........
........ *...*..........
****** ******
(ignore the periods... I had to put them in for the spacing. The * are where the boards are)

If I can figure out how to post pics on here I'll add a couple of the finished product.

In doing some research, I found out the original Hoverman patented antenna was not commercially successful because it really only worked good on 1/2 of the UHF band. About a dozen years ago some folks dusted off the original design and recalculated the dimensions and were able to stretch the UHF performance so it could reach up near the 700MHz range and pick up a lot of the stations that were going there with the original digital transition.

However, in the years since when the FCC started trimming off the UHF band for other uses, we now have a UHF band that almost mirrors exactly what Hoverman's original antenna was perfect for - the lower half of the UHF band!! Scrap the mods that were made a dozen years ago and use the original!!



CK-722
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Joined: Sun Dec 16, 2018 3:53 pm

Re: Built some Hovermans

Post by CK-722 » Mon Oct 26, 2020 8:18 pm

I wonder if a Hoverman designed for 155-216 MHz would work well at the third harmonic, 465-648 MHz, which would cover Channels all channels from 7-36. Granted, it would be better with a reflector screen, and would be somewhat unwieldy and heavy, like nine times heavier. It would be somewhat similar to a bedspring antenna, and those faded out quickly due to such issues.

Image


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Same (x, y, z), different (t)

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k8jd
Posts: 603
Joined: Fri Jun 28, 2013 3:35 pm
Location: Commerce, MI

Re: Built some Hovermans

Post by k8jd » Mon Oct 26, 2020 10:33 pm

Placing a reflector screen may really Lower the feedpoint Z !
I recall a multi element colinear ant that was slightly popular for 2 M SSB/AM/CW horiz polarized work.
(It looked a lot like that Finco in the picture) Can't recall the catchy name they gave it.
Don't think the Finco design needs a screen, it already has a reflector parasitic element behind each bay of dipoles (4) !



CK-722
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Re: Built some Hovermans

Post by CK-722 » Mon Oct 26, 2020 11:23 pm

The ARRL Book on VHF UHF and Repeaters had some plans. There were graphs that showed how it changed the impedance with distance to the reflector. But you could really just do it empirically by maximizing signal at least for receivers. I experimented with an oven rack and a UHF bowtie, and received WEYI-TV 25 55 miles away over the ridge at ground level!

John Kraus, who had the callsign W8JK, which reminds me of K8JD, invented the corner reflector. They had that design in the ARRL Book, and a graph showing impedance vs. reflector distance.


Is THAT where they got the idea for the 486-SX?

Same (x, y, z), different (t)

Your bullet missed my trial balloon.

RTN Price. Not guaranteed. As of 12:30, 157.71 Down 0.22.

Artificial Intelligence is a Child that needs a Parent to guide it through.

CK-722
Posts: 1284
Joined: Sun Dec 16, 2018 3:53 pm

Re: Built some Hovermans

Post by CK-722 » Tue Oct 27, 2020 12:17 am

A better picture of a Finco Bedspring and CM-4251 UHF Parabolic Dish.

Image


Is THAT where they got the idea for the 486-SX?

Same (x, y, z), different (t)

Your bullet missed my trial balloon.

RTN Price. Not guaranteed. As of 12:30, 157.71 Down 0.22.

Artificial Intelligence is a Child that needs a Parent to guide it through.

km1125
Posts: 3570
Joined: Thu Mar 14, 2019 3:09 pm

Re: Built some Hovermans

Post by km1125 » Tue Oct 27, 2020 11:29 am

I don't have a way to measure the feedoint impedence, or I haven't figured one out yet with the equipment I have available. How would you do it and what would you use, other than lab-grade stuff? If I could tune it and get it around 150 Ohms that would be ideal because then I could combine two parallel antennas directly to feed into a 75 Ohm combiner. Right now I'm assuming it's closer to 300 and using a 300:75 transformer.

There are several designs out there for Hovermans using reflector elements, but they get pretty complicated and need a more complicated structure to support them, as there over 10 elements in typical ones. My only concern with using the screen was if 3.5" spacing (the 1x4s) was going to be appropriate. It seems to work well but it probably could be tuned better with some experimenting and the board cut or bought to the appropriate width.

For the Detroit stations, I wasn't interested in trying to extend down to VHF, as I knew I likely would need another antenna anyways to get to VHF_LO for WNHE. For Toledo stations that might be an advantage but I already have a diplexer and a simple dipole picks up 11 and 13 pretty good.



k8jd
Posts: 603
Joined: Fri Jun 28, 2013 3:35 pm
Location: Commerce, MI

Re: Built some Hovermans

Post by k8jd » Tue Oct 27, 2020 4:08 pm

Most antennas I build are aimed at 50 Ohms feedpoint to use coax feedline, I just use a low power calibrated osc/swr bridge device that came from MFJ. for 1.5 to 30 MHz.
I suppose if you were looking at 300 Ohm twin lead feed you could use a 4:1 wide band Bal;Un or "Q section" coax trasformer for a single freq band. measurement.



k8jd
Posts: 603
Joined: Fri Jun 28, 2013 3:35 pm
Location: Commerce, MI

Re: Built some Hovermans

Post by k8jd » Tue Oct 27, 2020 4:11 pm

Neat antenna , I can see the phasing stubs part way out each dipole element.



km1125
Posts: 3570
Joined: Thu Mar 14, 2019 3:09 pm

Re: Built some Hovermans

Post by km1125 » Tue Oct 27, 2020 4:44 pm

Can you imagine trying to put one of those "bedspring" antennas in your attic?



CK-722
Posts: 1284
Joined: Sun Dec 16, 2018 3:53 pm

Re: Built some Hovermans

Post by CK-722 » Tue Oct 27, 2020 4:53 pm

Supposedly, from a performance standpoint, it was the best antenna ever made up to that time.

Looks like it would be kind of high end in wind loading.

The last I saw a bedspring antenna, it was on a house about 2 blocks East of US 31 in Pellston. I watched in time lapse sightings over the years how it slowly disintegrated. The mast still stands. They might have been able to get WPBN-TV 7 on it, before WTOM-TV 4 signed on. Maybe WWTV 9 on tropo.


Is THAT where they got the idea for the 486-SX?

Same (x, y, z), different (t)

Your bullet missed my trial balloon.

RTN Price. Not guaranteed. As of 12:30, 157.71 Down 0.22.

Artificial Intelligence is a Child that needs a Parent to guide it through.

km1125
Posts: 3570
Joined: Thu Mar 14, 2019 3:09 pm

Re: Built some Hovermans

Post by km1125 » Tue Nov 17, 2020 8:21 pm

I was able to run some tests of the Hovermans I built to his original patent. I built the first ones using just screens for the reflector, but his original patent had a couple different designs for reflector elements. The one he suggested had the best performance had one vertical center piece and four pairs of horizontal elements.

With the screen reflector I could remove two screws from the frame and bend the antenna in half so it would fit through the hatch to the attic. Using the separate elements, you could just uncouple both halves of the antenna with two screws.

Running some tests, I compared the gain vs a dipole at about 500Mhz. I measured about 12dB better than the dipole. I also measured about 16-18dB of front-to-back directionality. I was pleasantly surprised with that. Very simple antennas to build, just some 1x4s, a handful of some screws and some 10 ga. copper wire.

Here's some pics:
Image

Image

Image

Image



CK-722
Posts: 1284
Joined: Sun Dec 16, 2018 3:53 pm

Re: Built some Hovermans

Post by CK-722 » Wed Nov 18, 2020 10:24 am

So is the last picture another Hoverman? Looks like you took two wires out of some Romex and left the insulation on.


Is THAT where they got the idea for the 486-SX?

Same (x, y, z), different (t)

Your bullet missed my trial balloon.

RTN Price. Not guaranteed. As of 12:30, 157.71 Down 0.22.

Artificial Intelligence is a Child that needs a Parent to guide it through.

km1125
Posts: 3570
Joined: Thu Mar 14, 2019 3:09 pm

Re: Built some Hovermans

Post by km1125 » Wed Nov 18, 2020 11:08 am

CK-722 wrote:
Wed Nov 18, 2020 10:24 am
So is the last picture another Hoverman? Looks like you took two wires out of some Romex and left the insulation on.
Yes, that's exactly what I did. That was the earlier one I made with the screen as the reflector.

I thought about stripping it, but wondered if it would really make a difference. If I was trying to tune it to a specific frequency, I could see that making a difference and having to cut segments ~3-5% shorter but since I was looking for a broadband antenna I really didn't think it would matter much.

Overall I'm pretty happy with them. Very inexpensive, very simple to build, very compact and pretty good performance. I can pick up 15 UHF transmitters (and 5 more VHF with the folded dipoles). The only one I can't get (yet) is WNWO and I think I'll get that when I move the antennas to the house attic.,



CK-722
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Joined: Sun Dec 16, 2018 3:53 pm

Re: Built some Hovermans

Post by CK-722 » Wed Nov 18, 2020 11:40 am

Could you build the supports out of PVC Pipe and Elbows to make it lighter? So the insulation having a dielectric constant of about 2-2.5 would change the capacitance effect vs. air?


Is THAT where they got the idea for the 486-SX?

Same (x, y, z), different (t)

Your bullet missed my trial balloon.

RTN Price. Not guaranteed. As of 12:30, 157.71 Down 0.22.

Artificial Intelligence is a Child that needs a Parent to guide it through.

km1125
Posts: 3570
Joined: Thu Mar 14, 2019 3:09 pm

Re: Built some Hovermans

Post by km1125 » Wed Nov 18, 2020 3:41 pm

I did see some examples on the web somewhere that were built out of PVC pipe. I'd be surprised if it's much lighter, if any.

The nice thing about 1x4s is that they are approximately the right width for the spacing from the active elements to the reflector, if you're using one. I had planned for reflectors all along, so that was advantageous to me.



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