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FYI, I own a little (140") Winegard VHF antenna, a DIY APS-13 FM antenna clone, and a bunch of miscellaneous antenna parts which will hopefully be a 16 bay Gary-Hooverman soon. I just need to figure out how to most efficiently combine the four 4-bays, etc.

The rig will hopefully be going up this summer.

I'm interested in building different antennas. When I get the time, I really want to get into antenna modeling. Just for the heck of it.
 

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FYI, I own a .... DIY APS-13 FM antenna clone...
rochmndx,

I can see that you are into really big antennas.
I found some info for the APS-13 FM antenna and it's big - 200" boom or 16.7 ft
Do you have the dimensions of your clone? I'd be interested in having a closer look at this Lpda-Yagi with 6 driven elements....thanks

APS-13

* Frequency Range: 88.1 - 107.9 MHz
* Impedance: 300 Ohms
* Average Gain: 10 dBd
* Avg. F/B Ratio: 30 dB
* Boom Length: 200"
* Turning Radius: 127.5"
* Elements: 13 (6 driven)

 

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rochmndx,
Check out Ken Nist's work on ganging multi-bay arrays at HDTVPrimer.com. He used 8-bay 4228's to make 16- and 32-bay arrays, with varying results due to his location. In LOS applications, signal field intensity is relatively uniform perpendicular to the LOS. Ken has severe diffraction at his site that results in poor performance with the 32-bay due to signal strength variations across the antenna aperture. He stuck with the 16-bay, analogous to the DBGH in aperture size and orientation, because it could be located away from signal nulls.
Frank
 

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Resources for Antenna Design Newcomers?

Are there any articles out there like 'Antenna design for Dummies' or explanations on the theory of antenna design? I'm curious why the 'zig-zag' and 'bow-tie' designs work well for UHF, and possibly tuning a home-made antenna for slightly lower freq. (ch 14-40).
 

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If a person doesn't have the basics of electronics down then it all might seem a bit like voodoo, so I'd say an intro course on electronics would be good. Maybe night school, that sort of thing.

If there is already a basis of electronics knowledge then a good purchase would be the ARRL Handbook, which is packed full of antenna design info amongst other things. Here's their home page: http://www.arrl.org/ They offer beginners courses and books too. Here's a good one: http://www.arrl.org/catalog/?item=9078#top
 

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Hello all - 16 bay clone of CM4228

Hi all,

A quick note of introduction. I've been browsing the web for a few months looking for information on how to improve my reception of Boston tv station in Ayer, MA (25-30 mi). Coming across you all is a blessing, and I've reviewed most, if not all of your thread on "Channel Master Model 4228 Antennas."

I ended up building a clone of sorts of two CM 4228 ganged (still trying to connect wires appropriately). The difference between my antenna and the real thing is that mine is made of 8 gauge copper bowties 7" V legs spaced roughly 7" apart, galvanized steel 1/2" gridded reflector, twin lead, and the rest are plastic and duct tape. It is an indoor antenna of about 10 lbs. and receives most Boston stations (GBH, GBX, ABC, NBC, CBS, CW, but not Fox, LVI, and Ion) at 90% or greater strength. The SAD thing is that my cloned 8 bay works just as well and built the exact same way. I've TRIED to gang the pair of 8's parrellel/series as well as parrellel with shared CM 7777 pre-amp, but not with splitter and dual pre-amps. But results aren't any better than 8 bay. I'll keep trying but would LOVE SOME HELP. Can't want to see results from the fella experimenting with connections for ganging 4228's. Thanks for your time.

I also have two questions on my mind:

1) Why aren't directors ever used on CM bowtie antennas?

2) How can I get better results than an 8 bay, fudge?!?
 

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d'Avalonia,
I'm one of the guys stampeder is talking about cloning 4228's, but my jury is still out. I made two 4221s, but haven't tested the combo for want of a reasonable signal field at home and a sub-200 lb. tuner.

A quick scan of Boston MA at TVFool.com shows you're all UHF for your locals so these are the right kinds of antenna. Without knowing more about the signal field at your location, I can't comment on why some come in and others don't. I can offer a resource for ganging 4228's; scroll down to 16-bay and 32-bay links, or better yet, read it all!
http://www.hdtvprimer.com/ISSUES/erecting_antenna.html

His conclusion was that diffraction effects caused signal strength variations across the antenna aperture when he went side-by-side with the 32-bay, while the vertically-stacked 16-bay was small enough to fit in a signal maximum. The DBGH is a similar form factor and so should perform well for the same reasons the 16-bay did.

An added issue is that 7" centers and wiskers in your clone moves the peak gain of the bowties up to channel 83; any chance you were inspired by YouTube or the Blogspot DIYs? Channel Master's 422x products are based on an 8" spacing and the 4-bay peaks at Ch 63; the smaller scale is hurting your 14-52 performance compared with the CM version. I went with 9" spacings, to peak at Ch 52. YMMV.

Frank
==================
PS Your questions:
- I've seen directors on bowties, but not from reputable sources. Directors and reflectors on a Yagi are there to increase the antenna aperture. Arrays by their nature have large apertures, so there's little benefit.
- try stacking your 4-bay sections vertically (separate feeds and baluns into a combiner), or try a vertical array like the DBGH.
=============
PPS: twinlead for the feedlines? Did you put in the twist? It's not optional.
 

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Stampeder,

Thanks for the comments. I've checked out the DBGH superantenna. It's an interesting read, and I'm sure that I'll keep updated.

fbov,

Your analysis of the dimensions on my attempt at a 16 bay clone is very valuable. What program(s) did you use, or did you do it all long hand? I'm a designer by training so I would much rather "model" things out before hacking away like I have. Do you or anyone else have recommendations for programs/books with noncalculus formulars for calculating shapes of radiating elements, spacing, and the likes?

I've checked out the hdtvprimer instructions earlier, and have already tried both their suggested serial/parrellel with 4:1 balum and the parrellel only gains for my four 4 bays. I did not see improvements of the 16 bays (8 bays vertically stack) to just one 8 bay (4 bays side-side). In fact, I had better reception when I built an 8 bay all out of twin lead. And yes, I included the twists at the top and bottom of each 4 bays for "phasing" reasons, but I'd like to know more about calculating phasing.

Tvfools is great. I'm inserting their reading of my specific location for your review -- the name of my area is Nasoba VALLEY. Love to hear additional comments from you about my stuff and about your own successes. Thanks again for your time.

 

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d'Avalonia,
I started with the idea to duplicate the conductor geometry of an existing commercial antenna. A UHF bowtie had given me my first OTA signals and the 4-bay design intrigued me.

I did a little photogrametry on a picture of a Channel Master CM4221 antenna, but got the vertical dimension wrong. I subsequently found that the HDTVPrimer site had a link to the dimensional images used for the antenna modeling. I've since verified that the dimensions I got from that were correct. The rest was a little math; what are the resonant frequencies of these sized elements; how might one change the elements to alter the frequency response?

The phasing goes something like this. The wiskers and the element spacings are each 1/2 wave resonances near the peak gain frequency. The twist inserts a 1/2 wave phase difference and the transmission line length (element spacing) adds another 1/2 wave so the outer element signals arrive in-phase with the inner elements.

The reflector is 1/4 wave away, again so the reflected wave (1/2 wave phave change) travels another 1/2 wave to and from the reflector and arrives in phase. Electrically, dipoles are nominally 300 ohm, and this arrangement combines them in a series/parallel circuit that preserves the individual dipole impedence.

By shear luck, I'd made an error that resulted in a 1/8x scale shift that shifted the peak gain to channel 52. Scaling antenna designs over short ranges yields predictable results, and that's all I'm doing - scaling dimensions and thus frequency response.

As a test, I made a series of antennas, using spacings of 10, 9, 8 (4221), and 7" aimed at channels 40, 52, 66 (4221), and 83 respectively. Sure enough, they had different gains at the range of channels (16-59) that I receive, so I think there's something real going on here.

Up to 4-bays, I can make sense of this. Ganging into an 8-bay is tough to predict. Ken Nist talks about feedline issues in the CM4228 and there is a shift to lower frequencies compared with a 4-bay. I want to try my pair in several configurations, and recently found a good signal field for testing (like you have). I'm just waiting on my coupon so I can get a 12v ATSC/NTSC box to go with my AC/DC analog TV.

FWIW, my weakest station here is -77 dBm, and a 4-bay clone in my attic gives me 90%+ signal. You're going to get a ton of stations! In fact, your biggest problem may be pre-amp overload due to WUNI when trying to get the fringe stations. If you use one, make sure any pre-amp is a high-overload design.

Frank
 

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CM bowties and digression to Archimedian Spiral

Frank,

Thanks for your explanations of antenna dimensions, phasing, scaling, and pre amp overload. Now I know to check my dimensions and scale it to the right frequency. Also you may be right about pre amp overload. Channel UNI is quite strong and my Channel Master 7777 gives an additional 28 db boost. I'll have to adjust my reflector or shorten the side lobes somehow to get rid of that station completely. The only thing I watch on it is soccer anyway. Gooooooaaaaaal!

You seem like someone with whom I can have a good discussion about an antenna design that I found in a book called Modern Antenna Design by Thomas Milligan. Under the Self-Scaling Antennas chapter, the Archimedian Spiral Antenna appears as a quasi-self-scaling piece. It radiates over a large frequency band! One can designate the lowest frequency by making the distance of the spiral's circular perimeter 1.25 times the wavelength. In other words, the circumference of the antenna is 1.25 times the lowest frequency's wavelength. From the outer edge and opposite of each other in position, two elements spiral inwards leaving only their width as the spacing between the already turned outer spiral and themselves. The turning must progress to at least 0.25 wavelength and continue to as high a frequency as space allows. My guestimate suggests that the spiral will have less than a half meter diameter when set for UHF levels. Can you or anyone "model" it for it's properties such as gain, possibilities of using a reflector, and making an array perhaps? Awaiting anyone's response. Thanks.

Lee
 

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I just had a revelation!

In the 4228s and other antennas, there are issues with the feed line connecting multiple bays acting as an antenna. I was thinking about twinlead and the like, when I remembered that they once made shielded twinlead. If used properly, this stuff might be able to get rid of those issues (if you can find it).
 

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NEC2 Modeling Links

I've seen a few postings asking "how to get started" with antenna modeling.
For those that want to explore NEC2 modeling, here are a few links.
You will need a basic understanding about antennas and be prepared to spend some time learning how to model.
If that's you...then here is a simple guide on how to get started.

Step1.
Visit Arie Voors site. http://home.ict.nl/~arivoors/
Download the 4nec2 program and "NEC Beginners Guide- (a 4 part pdf set)" [link to the guide is at the bottom of his main page.]

You'll find the 4nec2 program's General help file accessible via F1 key to be very complete.
If you get stuck, you'll find most answers in the General help file.

Step 2.
Start with the ReadMe-First file and then once you are setup with a running 4nec2 program,
then read the Get_started file and follow through the examples.

Step3.
Explore 4nec2 features. The 4nec2 package has many, many antenna examples that you can examine.

Once our NerdClub gets a core-base, you will find this forum to be a source of modeling projects, complete with the .nec files.

Additional Info Links
Here are some ARRL links.

http://www2.arrl.org/cce/sample-lesson/

http://www.arrl.org/tis/info/HTML/antenna-modeling/index.html

And finally there is a wealth of more advanced info on the web pages of L. B. Cebik [W4RNL] that deals with Radio Amateurs and Modeling.

http://www.cebik.com/amod/modeling.html
 

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I'm just waiting on my coupon so I can get a 12v ATSC/NTSC box to go with my AC/DC analog TV.
If you have a laptop, you may want to consider a usb tuner based on the latest XCV5000 tuner chip. It claims a 5 dB noise figure, and generally out performs my 1991 era Panasonic Gaoo analog TV. My Elgato EyeTV hybrid tunes both NTSC and ATSC over the air, as well as ClearQAM cable channels. I believe Hauppauge has recently released their 950C model USB tuner based on the same chip. You should be able to get one for under $90. A small laptop with a usb tuner makes a handy portable TV. (Previous versions claimed a 6dB NF, which is still pretty good for a consumer tuner.)

TVl
no connection with Elgato, Hauppauge, or XCeive.
 

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rochmndx,
I plan to gang my 4221 clones with a pair of baluns and a combiner. I want to avoid any additional elements, like the linking feedlines, and hopefully get a 3-4 dB gain increase across the spectrum, without losing high channel response.

An alternative is taking twinlead straight back, through the reflector, and then combining signals. Without shielding, you'd have to be careful about routing, and you'll have a 150 ohm impedence at the junction unless you're making a 16-bay ...

Frank
 

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d'Avalonia,
Autofils has posted the modeling software links if you're interested. I'm dabbling with the modeling s/w at this point for lack of time, and want to understand what I've got before moving on. You never know what will work ...
Frank
 
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