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post #1 of 35 Old 03-15-2008, 12:25 AM - Thread Starter
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http://www.digitalhome.ca/ota/superantenna/design.htm

Slashdot linked to this (please, don't hit me). It's a GPL'ed version of a Gray-Hoverman design. Seems similar to the CM-4221 and CM-4228, but claims quite a bit better results in the post-2009 UHF bands.

I was curious what the hardcore engineers thought of this design?
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post #2 of 35 Old 03-15-2008, 04:13 AM
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I'm not an engineer, but from a DIY perspective the Hoverman seems a little easier to fabricate. Bending up 2 long wires is less work than forming and placing 8 separate V's that are then tied together with 2 wires that crossover twice.

BTW, can someone explain to me why the polar plots from this NEC2 modeler are often asymetric? One would presume the geometry input for the antenna was idealized, so getting oddball lobes on side of the axis that aren't reflected on the other side is disconcerting.
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post #3 of 35 Old 03-15-2008, 08:21 AM
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Quote:
Originally Posted by vman41 View Post

BTW, can someone explain to me why the polar plots from this NEC2 modeler are often asymetric? One would presume the geometry input for the antenna was idealized, so getting oddball lobes on side of the axis that aren't reflected on the other side is disconcerting.

vman41,

Good question..

The polar plots that I made showed results at 500 Mhz and 660Mhz.
For the SBGH (4 Bay), you can see that the 500Mhz is symmetrical, the 660MHz is not for collinear rod reflectors and split-screen.
The DBGH (8 bay) does not exhibit this asymmetric behaviour.

I looked further into this on the SBGH 6 pair rod reflectors and found that the asymmetric polar plots occur over the frequency range of 600 to 700 Mhz. Below 600 Mhz the polar plots are symmetrical.

I'm just the modeling nerd and I don't have any explanation for this.
In terms of the SBGH antenna's gain performance, this is really not significant.

I will have to leave any explanations up to the experts.

In the meantime, why not build it and give it a spin.
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post #4 of 35 Old 03-15-2008, 12:46 PM - Thread Starter
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Quote:
Originally Posted by autofils View Post

In the meantime, why not build it and give it a spin.

I'm more inclined to try this one than some others I have seen. I gotta move the antenna to the peak of the roof this spring anyhow.

One question: is there a real difference in choice of materials for the actual elements? Is copper, aluminum, etc any difference?
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post #5 of 35 Old 03-15-2008, 01:13 PM
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Quote:
Originally Posted by autofils View Post

In the meantime, why not build it and give it a spin.

I built one some time ago, but all I had to go on was the description and illustration in the 1982 article. The 7 inch characteristic dimmension was easy to figure out, but I placed the gap between the elements much closer. I don't use a reflector because I've got towers in 2 directions that I wan't to see (I figured the 4-bay size would match a 2-bay with reflector). Nonetheless, I was happy with the result. I'm pretty close to the towers, so I don't need a lot.

Note that the graphic in the 1982 article doesn't have the horizontal extensions at the ends. Doyt's patent left me the impression that he thought extensions were for the VHF band.
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post #6 of 35 Old 03-15-2008, 01:36 PM
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Um, what are these weird measurements?

...where is a metric ruler, tape measure, etc. when you need it?

18" Stonehenge, anyone?

Looks like an interesting design. I may give this one a try.
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post #7 of 35 Old 03-15-2008, 01:56 PM
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Originally Posted by vman41 View Post


Note that the graphic in the 1982 article doesn't have the horizontal extensions at the ends. Doyt's patent left me the impression that he thought extensions were for the VHF band.

Hoverman's first patent 2918672 (Array-Only) did give the impression that the horizontal stubs were for VHF, however the EZNEC modeling results clearly show that those horizontal stubs are quite important for shaping the UHF frequency response and have absolutely no effect on VHF. In fact the modeling did not show any positive net gain for the VHF bands (2-6) and (7-13).

Hoverman's second patent 3148371, included the rod reflecors, and he made no mention of VHF performance in that patent.

Regarding the asymmetrical minor lobe at 660Mhz, I ran the polar plot on the array-only (ie no reflectors) and the 660 MHz asymmetrical minor lobe is present in the two main loops of this bi-directional array.

So this is the characteristic of the array, assuming that the EZNEC v3 modeling program that I use, is correct, and I have high confidence in this modeling program.

Perhaps there are experts that could model the array on other modeling programs and examine and report on the polar plot at 660Mhz.

Full details of the array dimensions, as well as other relevant information are available at the link in post #1 "New DIY antenna design from Slashdot"

Hope this helps...
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post #8 of 35 Old 03-15-2008, 02:01 PM
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Good point about the non-symmetrical results. I'm not familiar with the CAD software used, but I can only assume that the results are calculated with numerical methods - a solution is "converged" on rather than solving a specific equation. You may get some discrepancies depending on how the software "breaks up" the problem and how sensitive the simulated system behaves.

Another interesting point is that autofils' modeling for the 4221/8 shows the VSWR peaking near the upper end of the UHF band. This shows that the double bowtie design can likely be re-tuned for the post 2009 UHF band. Who knows, maybe it would even match this modified Hoverman design?
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post #9 of 35 Old 03-15-2008, 07:20 PM
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Has anyone tried to adapt a 4228 to get better high VHF reception, especially channel 12. Analog 12 is my weakest station (analog 8 from similar distance and direction is solid), and after transition it will be in use.
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post #10 of 35 Old 03-16-2008, 01:20 PM
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I've been playing with the nec2dxs program (Arie Voors 4nec2 program), and it seems very finicky. For example, changing the radius of the 'feedpoint' wire segment from 1.5 mm to 3 mm adds around .5 DB to the peak gain. I get the feeling you need something besides an EX card to really model what is happening at the feed point.
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post #11 of 35 Old 03-17-2008, 04:58 AM
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Vman41,

I sought a second opinion from Old Sparks, another member of our digitalhome.ca forum, regarding the asymmetrical lobe that shows up in the 600-700 Mhz range of the Single Bay Gray-Hoverman (SBGH) polar plots, and he has identified the problem in my model files of the SBGH.

"The voltage source was not placed directly in the middle of
the wire tag that defined the voltage source for the SBGH files."

Hence the SBGH polar plots exhibited this asymmetrical behavior.

For the DBGH polar plots, which do not show any asymmetrical behavior, the voltage source was located correctly in the middle.

It's nice to have the explanation, even though I have a bright red face

Thank you for raising this discrepancy and my thanks to old sparks for identifying the cause.

I will post corrected polar plots for the SBGH on our digitalhome.ca forum and ensure they are added to the Gray-Hoverman GPL web page.

Regards
...Autofils
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post #12 of 35 Old 03-17-2008, 06:16 AM
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Quote:
Originally Posted by autofils View Post

"The voltage source was not placed directly in the middle of
the wire tag that defined the voltage source for the SBGH files."

So generally you want to ensure those wires have an odd nmber of segments.

BTW, it looks like you can model a solid reflective screen with a multiple surface patch (SM) card.
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post #13 of 35 Old 03-17-2008, 07:17 AM
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Quote:
Originally Posted by vman41 View Post

So generally you want to ensure those wires have an odd nmber of segments.

BTW, it looks like you can model a solid reflective screen with a multiple surface patch (SM) card.


Yes indeeed. I started with 4nec2 and then switched to EZNEC v3, so I think I messed up when I took my SBGH nec file into EZNEC.
My DBGH files were made on EZNEC and they were fine.

The SBGH file used in EZNEC had 5 segments for the voltage source tag, so I'm not sure how I messed it up, but I now know to double check that source entry.

Again, my thanks for pointing out that discrepancy.
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post #14 of 35 Old 03-17-2008, 10:40 AM - Thread Starter
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Quote:
Originally Posted by DrBri99 View Post

Has anyone tried to adapt a 4228 to get better high VHF reception, especially channel 12. Analog 12 is my weakest station (analog 8 from similar distance and direction is solid), and after transition it will be in use.

The only adaptation you need is to use some plastic ties to make sure the two screens are tight together. It works well enough, but it isn't better than running a VHF antenna.
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post #15 of 35 Old 03-17-2008, 11:11 AM
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Originally Posted by dbc View Post

... This shows that the double bowtie design can likely be re-tuned for the post 2009 UHF band. Who knows, maybe it would even match this modified Hoverman design?

Apparently, Ken Nist has projected what an optimized CM4221 might do.
http://www.digitalhome.ca/forum/show...9&postcount=32

"Kq6qv also pointed out that the CM-4221 was designed for the UHF Ch 14-69 range and if it's gain characteristic was maximized for the new UHF Ch14-52 range, it would be better than the SingleBay Gray-Hoverman."

We can discuss what "better" means, but I think you get the point.
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post #16 of 35 Old 03-17-2008, 11:18 AM
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Quote:
Originally Posted by DrBri99 View Post

Has anyone tried to adapt a 4228 to get better high VHF reception, especially channel 12. Analog 12 is my weakest station (analog 8 from similar distance and direction is solid), and after transition it will be in use.

I'm experimenting with an oversize 4228, which I've shown has more gain at lower UHF-band frequencies. In theory, it should shift some of the Ch 13 gain down, but without some understanding what causes the sharp dips in 4228 VHF response, I don't know how well my 112% clone will react. I need Ch 10 and 13, post-transition, and an oversized 4221 does the job today.
Frank
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post #17 of 35 Old 03-17-2008, 11:57 AM
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Wow, this looks awesome and I want to give it a try building one.

It looks like the "splitscr" version has the highest gain. If I'm reading the pictures and diagrams right, you can eliminate the reflector rods if you use something like chicken wire as a wire screen 10cm behind the driven elements.

I'm guessing split screen means the wire mesh should be cut down the middle. and it looks like 20cm should separate the two screens. Is that right?

Two questions on materials... copper wire seems like it would be easiest to work with, should 12 gauge solid copper wire do the job or would anyone recommend something else?

What is the best way to get the signal from the antenna, RG-6 coax or something else?

Check out my Cozy Room within a Room Theater Build... in progress and closing in on completion.
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post #18 of 35 Old 03-17-2008, 12:00 PM
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Quote:
Originally Posted by vman41 View Post

I'm not an engineer, but from a DIY perspective the Hoverman seems a little easier to fabricate. Bending up 2 long wires is less work than forming and placing 8 separate V's that are then tied together with 2 wires that crossover twice.

I've built both with the same low skill level and inattention to detail ie. the wires I made are roughly straight, but not exact and some of the bends are not the 90deg I would have hoped for.

The 8 V's was easier (IMO) just b/c you are dealing with a shorter (overall) length of wire to keep straight and to bend in the same plane.

Both gave me roughly the same reception (mounted 30' up in my attic), altho the 8 V version (coat-hangers), gave me a 100% signal on ch 28, whereas the Hoverman close and all other channels are in the upper 60's-mid 70's (tuner is Dish 622 OTA DVR)

I'm a EE, but a digital guy, so all the RF is greek to me
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post #19 of 35 Old 03-17-2008, 12:58 PM
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Quote:
Originally Posted by fbov View Post

Apparently, Ken Nist modeled an optimized CM4221.
http://www.digitalhome.ca/forum/show...9&postcount=32

"Kq6qv also pointed out that the CM-4221 was designed for the UHF Ch 14-69 range and if it's gain characteristic was maximized for the new UHF Ch14-52 range, it would be better than the SingleBay Gray-Hoverman."

We can discuss what "better" means, but I think you get the point.


I would first like to express my thanks to Ken Nist for his helpful comments and assistance on my modeling journey of the Gray-Hoverman project and then add some further clarification to the comparison with CM4221 ...

The model results of the CM-4221 in the above link is Ken's modeling results of the current commercially available Channel Master CM-4221, along with the SBGH 6pair collinear rod reflector version, as well as some other commercially available antennas (Dat75 and PR4400)

I have not seen any modeling results for down-shifting the CM-4221's frequency response to the post 2009 UHF bandwidth, and I am a bit surprised that Channel Master has not made any announcement about producing a new version of their popular bow ties (CM4221 and CM4228) to maximize the gain characteristic for this UHF bandwidth revision.(it's less than a year away)


Also note that Ken uses the nec4 engine, whereas my EZNEC v3 uses the public domain nec2 engine, so there will be some differences due to different nec engines used.
This particular link is a net gain comparison that Ken provided to me and was run on his nec4 engine.
All of my net gain plots of the Gray-Hoverman are run with the nec2 engine, and the plots of CM4211 and CM4228 are from Ken's nec4 modeling results, contained in his spreadsheet and available from his website hdtvprimer.com.
http://www.hdtvprimer.com/ANTENNAS/comparing.html
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post #20 of 35 Old 03-17-2008, 01:10 PM
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I saw this "easier to fabricate" claim, too. Fewer parts, perhaps, but it's much harder to make a complex wireform with critical bend locations and angles than to make a u-band. The result is more robust, given the element ends are supported, but easier? No way!

It goes with the mindset - what's "better" must be better in every way! Of course, this thing isn't actually "better" it's just different.
Frank
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post #21 of 35 Old 03-17-2008, 01:29 PM - Thread Starter
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Originally Posted by fbov View Post

It goes with the mindset - what's "better" must be better in every way! Of course, this thing isn't actually "better" it's just different.

True. But, it is still interesting.

I'd like to see a little more advice for the non-engineer. I'm kinda baffled that a GPL'ed project somehow isn't inclined to try to be a little more user-friendly.

I've never heard a definitive answer on materials. Is copper superior to other materials for the elements? Or is it just that copper is cheap?
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post #22 of 35 Old 03-17-2008, 01:32 PM
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Quote:
Originally Posted by autofils View Post

... I have not seen any modeling results for down-shifting the CM-4221's frequency response to the post 2009 UHF bandwidth, ...

Ken Nist's work on HDTV Primer has not received the praise it deserves in my reading. It's become one of my most often referred sites.

Earlier today, I sent him a note asking if some work I did based on his antenna modeling was valid. It specifically addressed modeling I'd done asking how one might re-optimize gain response of a 4221-type design, shown here.
http://www.avsforum.com/avs-vb/showt...8#post13338498

My modeling was crude - frequency shifting the curves based on dimensional relationships rather than RF modeling - but empirical results indicate the predicted trends are true. I'm always hesitant to request things of personal rather than univeral interest, but I'd love to see what happens to antenna response when a design is scaled.

If nothing else, it would give people like me a rational basis for modifying antenna designs.

And it would make comparisons among multi-bay design approaches valid by allowing comparisons when optimized against the same performance targets. What approach has got the most potential?

Frank
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post #23 of 35 Old 03-17-2008, 02:28 PM
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Originally Posted by fbov View Post

Ken Nist's work on HDTV Primer has not received the praise it deserves in my reading. It's become one of my most often referred sites.

Frank

Frank,

You are absolutely right.!!! Ken's hdtvprimer.com web site has an enormous amount of excellent detail information on all aspects of OTA (Over the Air) HDTV reception, in additional to all his modeling results of many commercial antennas. And from my journey on modeling just one fairly simple antenna, Ken has modeled 20+ commercial antennas, of which many are very complex to model.

For anyone , even slightly interested in OTA HDTV reception, this is a MUST READ site.
Here is the link to the home page. I highly recommend this site to all.

http://hdtvprimer.com/
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post #24 of 35 Old 03-17-2008, 03:11 PM
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Quote:
Originally Posted by fbov View Post

I saw this "easier to fabricate" claim, too. Fewer parts, perhaps, but it's much harder to make a complex wireform with critical bend locations and angles than to make a u-band.

Are you sure? This would be only my 3rd attempt at building an antenna, but it looked pretty straight forward to me.

I was thinking of measuring out all the angles on a piece of plywood, when just using screws at the angle points and pulling a rigid wire taught and making all the bends. At the top, I might even leave a little extra to fix it tight during bending then cut it to length when the angles were finished. Seems a jig like this would make it pretty simple to make two accurately angled elements.

I'd still like to know if copper wire is a reasonable material or if there is something better suited to the project.

Awesome work to the folks who researched, modeled, and released this. I may finally be able to cut the cable!

Check out my Cozy Room within a Room Theater Build... in progress and closing in on completion.
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post #25 of 35 Old 03-17-2008, 03:39 PM
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I'd still like to know if copper wire is a reasonable material or if there is something better suited to the project.

bmcent1,

When I made my first prototype, I made a jig like you described. It worked out quite well.

Regarding materials for the array and rod reflectors, there are lots of choices which will work quite well. The original Hoverman patents used #9 solid aluminum wire, but you could also use copper wire, as small as #14, wire coat-hangers, (although they are harder to bend), fencing wire, etc.
You can use the same material for the rod reflectors, or if you have any old antenna parts, then re-use the 3/8" Al tubing.
If it's a matter of cost, go for the least expensive material.
If you are considering an outdoor installation, I'd recommend the #9 Al wire, because its quite light, but very rigid for the lengths used, is easily bent and with good mechanical connections at the feed-point, it will be somewhat corrosive resistant.

If it's for the attic, then go for the split screen reflector, using tin-foil.

Have a look at our forum, and you'll see a number of examples of builds.
Your also welcome to join and participate in our forum, as well as this great AVS forum.
http://www.digitalhome.ca/forum/showthread.php?t=81982

Hope this helps..
...Autofils
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post #26 of 35 Old 03-18-2008, 09:47 AM
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The type of wire used should slightly change the ideal dimensions. What sort of wire was modeled for the Hoverman?

The CM4221 uses galvanized steel wire, about #9 gauge I think. The hdtvprimer site models it as zinc, because of the skin effect presumably.
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post #27 of 35 Old 03-18-2008, 01:16 PM
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Originally Posted by nybbler View Post

The type of wire used should slightly change the ideal dimensions. What sort of wire was modeled for the Hoverman?

The CM4221 uses galvanized steel wire, about #9 gauge I think. The hdtvprimer site models it as zinc, because of the skin effect presumably.

I hope you guys are not offended by my following comments, but you will at least understand my position.

I am the modeling nerd that designed this "new Hoverman" for UHF Ch 14-51, and I am very active on the Gray-Hoverman thread on the DigitalHome.ca forum.

I have made a few postings on this AVS forum regarding the Gray-Hoverman project, but I am finding that since our Gray-Hoverman GPL site was launched, I am now getting a bit swamped, so it's becoming more and more difficult to find the time to keep up with your forum. (You'll find the Gray-Hoverman GPL site here http://www.digitalhome.ca/ota/superantenna)

I find that quite a lot of queries on building this antenna and some other queries raised on this forum, have already been answered on our forum and I can better spend my time on other things, rather than simply re-post summarized answers here on this forum.

I trust you can understand and appreciate my position.

I would encourage you to keep an eye on our forum to keep up with our latest info at his link.
http://www.digitalhome.ca/forum/showthread.php?t=81982

Your are more than welcome to join and participate on our forum.

Regards
...Autofils
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post #28 of 35 Old 03-18-2008, 05:12 PM
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Makes sense! No use duplicating efforts and best to keep all the information in one place. Thanks for visiting here and providing the links. Also for your efforts modeling this and releasing the results under a beneficial license like the GPL!

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post #29 of 35 Old 04-22-2008, 08:56 AM
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Quote:
Originally Posted by fbov View Post

I saw this "easier to fabricate" claim, too. Fewer parts, perhaps, but it's much harder to make a complex wireform with critical bend locations and angles than to make a u-band. The result is more robust, given the element ends are supported, but easier? No way!

It goes with the mindset - what's "better" must be better in every way! Of course, this thing isn't actually "better" it's just different.
Frank

I just made one of these on Sunday, and found it quite easy to fabricate!

Using some household 14 gauge electrical wire, I clipped it to the overall length. Then I took a purple sharpie and marked ALL the bend locations before I started working.

A standard pair of pliers placed just to the side of the bend made for easy right-angling all the way down the line.

Was using rabbit ears before and getting signals between 17 and 40 % (DTX9900), now with SBGH and a 3.99 phillips balun from K-mart, i'm now in 60 to 85 % - indoors!
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post #30 of 35 Old 04-22-2008, 09:13 AM
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Quote:
Originally Posted by aethyrmaster View Post

I just made one of these on Sunday, and found it quite easy to fabricate!

Using some household 14 gauge electrical wire, I clipped it to the overall length. Then I took a purple sharpie and marked ALL the bend locations before I started working.

A standard pair of pliers placed just to the side of the bend made for easy right-angling all the way down the line.

Was using rabbit ears before and getting signals between 17 and 40 % (DTX9900), now with SBGH and a 3.99 phillips balun from K-mart, i'm now in 60 to 85 % - indoors!

Shoot! And I was waiting for stories about your search for a free second-hand antenna . Sounds like you are doing great with this homebrew model. 80% at 20+ miles with an indoor antenna sounds great to me.
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