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I'll raise my hand as another person who has downloaded 4nec2 and been able to run basic analysis of the G-H that fits with the expected results. I'm a physicist by training, but software inept so I expect a bit of a learning curve with the modeling programs.

I look forward to contributing ... eventually.
Frank
 

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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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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
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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.
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PPS: twinlead for the feedlines? Did you put in the twist? It's not optional.
 

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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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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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