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RESIZE THE REFLECTOR GRID WIDTH:
The next thing that will need some adjustment is the width of the 24” wide reflector grid. The new CM4221HD reflector grid is 24” wide and the old CM4221 is only 20” wide. To do this, just carefully remove the plastic side retainers from all of those grid rods. Then cut exactly 2” off each of the aluminium grid rods and then reinstall the plastic side retainers.
That one I wouldnt do. Instead I would increase its width to 32 to 44 or so inches to pick up vhf-hi.
 

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The old 4221 design was more multi-directional for those who desired to receive from various broadcast tower locations without the use of a rotor.
I think thats going to depend on which channels.

As far as VHF-Hi, I have found that the old CM4221 design was already pretty good at picking up analog channels VHF-5 through UHF-66. I suppose the new wider reflector design was intended to improve the VHF-Hi at the expense of losing some of the multi-directional qualities and the higher freqs above UHF-50.
Channel 5 ?? You must have very strong vhf signals. Post your TVFool. The 4 bay bowtie doesnt really kick in with really good vhf-hi gain until the reflector width is above 28-32 inches or so.
The difference in vhf hi between the old 20 inch width and the new 24 inch width is pretty small.
 

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There should be soon. Ken Nist has been modeling the new CM stuff, so Im sure he'll post them soon. I stopped doing mine because, #1 I dont have the antenna in front of me and trying to get exact measurements etc for the model over the internet can be trying, heh.
 

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Seeing a model of the modified antennas performance would assure us that this would work in other locations as well where a wider coverage area is desired.
Yep. Since you have the antennas in front of you, simply download 4nec2 for free and get busy, heh.
 

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The proof is not always proven by theory, but it is always proven by the tweeks of practical results.
Keep in mind the bowtie was invented in 1898 (and was re-invented 3 or 4 times since then, heh) and youre observing a very very old theory at work. Which is, when you reduce the forward gain of an antenna (by making the reflector smaller, for example) you increase the beamwidth of the radiation pattern. Which in the DTV age, can make aiming the antenna less critical and gives wider coverage. With digital, unlike analog, once youre comfortably past a certain threshold level, more gain can become irrelevant.

On the flip side, by reducing the width of the reflectors on the bowtie instead of increasing them to around 32 inches or more, you also give up vhf-hi performance, which in a lot of cases will be needed.
 

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flip the balun instead of flattening the two rails to gain more clearance from the boom.
Ken Nist, who has the exact dimensions of the new CM4221HD, should model this. Wouldnt it be funny if it turned out that was the way it was engineered originally, but due to some misunderstanding with the production dept, they screwed up and got it backwards ? Heh. :p
 

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Hopefully Ken Nist will post his model of the CM4221HD soon. Ive found that not having the actual antenna in front of me makes modeling very hard and could be unreliable, heh.
 

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I believe the stacking will widen the horizontal beam + add some gains + can overcome airplane flutter. So, the latter could be my best solution.
You want vertical stacking for airplane flutter.

Stacking two identical antennas on a common vertical mast significantly narrows the vertical beam-width angle. That is, vertically stacked antennas more effectively reject those interfering signals arriving from above or below their horizontal plane than does a single antenna. It’s as though they were looking through a horizontal venetian blind. Because there’s nothing mounted to the side of either antenna, their side-to-side vision is virtually uneffected. In the process, gain increases about 2.5 dB over that of a single antenna.

Vertical stacking improves both gain and vertical directivity. This helps reduce airplane flutter and attendant picture roll, and certain types of ground noise and ground reflections.
http://www.kyes.com/antenna/stackluge.html

I believe the stacking will widen the horizontal beam
Nope, with stacking you increase gain, narrowing the beamwidth.
 

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would simply joining the two CM4221HDs' feed points with shielded foam core twinlead be a suitable co-phasing line for running into a preamp?
Ken Nist on it :
(Warning: Too much plastic will change the velocity factor. Using larger gauge wire would require a larger spacing, increasing crosstalk with both the screen and the dipoles. Building the feed harness out of commercially available 300-ohm twinlead does not work because of the velocity factor. I looked for a good compromise based on that but did not find one.)
http://www.hdtvprimer.com/ANTENNAS/TemporaryPage.html

He has a design of the 8 bay phasing harness as it should be for the 4228.

For a horizontal harness, I think I would put in one or two twists to it.
 

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disagree with the quote from Ken Nist, I think 300 ohm twin lead will work
But you see the technique hes using, dividing each phasing line into approx 1/4 wavelength sections. That should also be doable with open wire twin lead or even regular twin lead by splitting the wire (cutting the plastic standoffs on open wire) and using new wire separators for new distances. Of course for regular twin lead, you have to look up the velocity factor for that particular twin lead, which should be around .82. (open wire around .95)
 

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The single antenna was more sensitive to drop-outs.

Overall- the stack is more reliable.
Yep, thats one of the side benefits of a stack over a single antenna with the same gain as the stack, in an article I read. Theres only speculation as to why.
 

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Speculation???? How about some basic Physics.....
Well, the author used the term "speculation" because you cant actually see the signal bouncing all over the place, and hence cant prove it in every situation. But yeah, the gist of the article was about signals bouncing everywhere with multipath, fading characteristics rapidly varying in all 3-dimensions, and how the stack performs better/more consistantly under typical conditions than a single antenna of equal dbi.

So this would suggest that a vertical stack is generally better than a horizontal stack above your average home?
The vertical stack has the advantage of reducing overhead airplane induced flutter better than a horizontal stack. And I would think vertical stack is better for fading in general (the ground heating up during the day). But of course, there can be situations where the signals cancel each other out, so its location, location, location, determined by experimentation over time.
The horizontal stack should be better for a many types of multipath.
 

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You have a basic problem of a copper to aluminum connection. That will have fairly quick galvanic corrosion over time. Youll have to redo it next year, I would say. Tinning the copper with solder will lessen the effect a lot.
 

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trying to build a Wide-Band Hoverman as per jedsoft site. Could I just build the elements on some pvc and screw it on the cm4221 reflector?
Nope. JEDs models are highly optimized with his specific reflectors. Using the CM4221 reflector will produce completely different results.
 

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The original CM4221 reflector screen of 1" X 2" mesh, 36" high by 20" wide is a bit too narrow for use as a good GH reflector screen. :( It will still work, just not at its full potential.
 

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I certainly wouldnt throw it away. I would probably repair it as is. (Maybe make the whiskers 9.5 inches instead of the original 7 inches.)

But building a GH frame from gray electrical pvc is more likely to be quicker and easier than drilling out the standoffs etc and moving them around to accomodate.
 

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i was sweeping it 10degrees forward based
so i definately lost some forward gain
Sweeping it forward a bit makes it more directive, so you should have had a hair more forward gain.
Sweeping it back makes the beamwidth wider at the expense of some forward gain.
So, you have to pick your poison, heh.
 

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One way is to upload your pictures to a site like imageshack. Copy and paste the direct link into the picture icon dialog box. (the icon looks like two mountains and the sun)

Another way :
http://www.digitalhome.ca/forum/showthread.php?t=92167


Thats impressive, over 30 NM at over 136 miles LOS.

There appears to be very little difference between them as far as transmitting power and location goes. My results are similar to neighbors', however, so the reception problems are not limited to just my specific spot.
Hmm, at that distance, the signal may just be fading in spots. Since the transmitters are grouped closely, you dont need much beamwidth. I would try a higher gain, taller antenna, like the DBGH.

Are you using a quality preamp ?
 
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