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Again, astonished how this simple mod completely opened up my setup.
Yep, it really makes one wonder about the engineering staff at that plant.

Oh wait, here he is now :




The concave face explains it all. It all looks good to him, so no problemo :)

(Im making fun of the antenna, not the poor soul pictured, so dont anyone get their panties in a bunch, heh)
 

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So, does trimming the reflector in the 4221HD make its performance closer to the original 4221?

I am considering doing this to broaden the beam width of mine, but I have a concern: The gain of the 4221HD is reported as being ~ 2.5dB higher on channel 14 than the 4221. Channel 14 (Fox 29.1 out of buffalo) is one of my weaker stations. 2.5dB less might kill it.

Would trimming the reflectors drop the gain on channel 14?
 

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Specific CM4221HD questions

I've been on the forum for a few months now, read LOTS, including FAQ, area-specific posts, etc, but still have some questions after installing and using my CM4221 for a bit. Please help!

NE Burlington, Appleby/Dundas, antenna mounted on peak of two story roof, pointed between Buffalo and Toronto.

I'm happy with the number of stations I'm pulling, but would like greater strength/stability of some stations, specifically Global and NBC.

I've read the post on hacking the CM4221, and have pulled off the black boxes, but do not understand the 2nd point about baluns and booms. I've tried Googling these terms, but still don't really know what they are! I think the balun is the little black box stuck on two flat rails. It says to pull this away from something, but it seems pretty immovable to me? Like it will break if I try to pull it away from main antenna.

The second question is that I've read in other places that I should have the antenna mounted vertically for best performance? But couldn't find anything here about that? When I mounted it on J pole, it seemed horizontally was the only option? Confused!

This forum has been a great resource, thanks so much!
 

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CM4221HD Hack

Ota_Canuck,

Have you done this reflector distance mod on a 4221HD?
I don't have a CM4221HD but I've made many 4 bays and did experiment reflector distances with them.
Do you have results that you could share?
I do have results but they would be useless to others because my location and TV channels are different. Remember, location, location, location . . .
Moving the reflector back just 1" doesn't seem like a big modification
That mod would help getting channel 14, that you cannot deny.
but I suspect that moving a reflector forward or backward may change more than just the beam-width.
I suspect it would also change the gain and impedance. It's not any worst than your proposal of shortening the reflector at the begining of this thread to get a wider coverage area but lose gain and VHF HI reception.

What else now ?
-
 

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Discussion Starter · #270 ·
BOUVAL,

I do have results but they would be useless to others because my location and TV channels are different. Remember, location, location, location . . .
As far as we have determined, shortening the 4221HD reflector width only changes the beamwidth and possibly reduce a little forward gain[distance]. I don't believe that the 4221HD reflector mod has ever been modeled.

I realize that your own location reception results would not mean much to people in other locations. I wasn't asking about your personal reception results, I was refering to measurable changes in the antennas reception characteristics other than beamwidth.

To my knowledge from my past experiments with the 4221HD mods,.. narrowing the 4221HD reflector width increases the antenna's beamwidth, but no other changes in reception have been documented. Whereas, changing the spacing of the reflector can have many other pros/cons on UHF bandwidth centering, forward gain, impedance, beamwidth, etc..

Moving the reflector back just 1" doesn't seem like a big modification, but I suspect that moving a reflector forward or backward may change more than just the beam-width.
How does adding 1" reflector spacing improve the antenna for channel 14RF?
Does it shift the UHF bandwidth lower?
What other antenna reception characteristics would be changed?

It's not any worst than your proposal of shortening the reflector at the begining of this thread to get a wider coverage area but lose gain and VHF HI reception.
Worst vs better than what I had proposed in the OP is irrelevant.

What else now ?
This is not a forum geared to debate/argument,.. this forum is about discovery, sharing, discussion.
All I was asking: "Do you have results that you could share?"
 

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Speaking for myself at my location, this hack(including trimming back the reflectors) improved my reception immensely. I have my antenna point half way between Toronto and Grand Island to try and catch some Buffalo without sacrificing my Toronto stations. Not looking at getting a separate antenna just for Buffalo or a rotor. Before the hack, i couldn't pull in any Buffalo, except for 23.1 and only at night...maybe. After the hack, I got WNED, WLNO, WUTV no issues in the same position, along with my Toronto stations.

I for one am completely sold on the effectiveness of this hack, but as mentioned before, location, location, location!
 

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A thorough reading of this thread answered my one question, but still can't find and answer to this one;

I should have the antenna mounted vertically for best performance? But couldn't find anything here about that? When I mounted it on J pole, it seemed horizontally was the only option? Confused!

Please help! Thanks!
 

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A thorough reading of this thread answered my one question, but still can't find and answer to this one;

I should have the antenna mounted vertically for best performance? But couldn't find anything here about that? When I mounted it on J pole, it seemed horizontally was the only option? Confused!

Please help! Thanks!
the correct orientation mounting will be when the "whiskers" (V shaped elements) and the reflector rods are horizontal. I believe the channel master install instruction show this...if you look at any of the adverts. for a 4221HD the photos will reflect this......you can alos find some photos of installs in the "pimp my gear" thread on this forum...

regards,
 

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here in thorold i sit between bufflo and cn tower so the removing those caps and flattening the phase line and swap out the original CM balun (cause i lost 9 & 11 after the transition) with a $ 3 one from nutech and now i get everything including channel 7 :D
 

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CM4221HD (New) 4-Bay Bowtie with Balun Hack Modifications:

I posted 4nec2 simulation results at fol. webpage (incl. 4nec2 source file):
http://imageevent.com/holl_ands/multibay/4bayrefl/uhfnewcm4221hd
Measurements were from information posted by <smpowell55> and Balun Hack details
derived from a photo posted by <rabbit73> (see results webpage for thread references).

UHF Raw Gain=12.2-15.3 dBi. UHF SWR(300) under 2.1.
UHF F/B Ratio=19-33 dB and UHF F/R Ratio=15-18 dB.

Hi-VHF Raw Gain=3-6.6 dBi (FORWARD), but HIGHER Hi-VHF Raw Gain=7.7-5.0 dBi
(TOWARDS REAR!). Hi-VHF SWR(300)=EXCESSIVE, esp. on lower Hi-VHF channels.

UHF Raw Gain:


UHF SWR (300-ohms):
]

Hi-VHF Raw Gain - Higher towards the REAR (Azi. = 270-deg):
]

Hi-VHF SWR (300-ohms) - EXCESSIVE, esp. on lower channels:
http://photos.imageevent.com/holl_a...ds_4_25_Hacked - Hi-VHF SWR_300 EXCESSIVE.jpg]

Although NEW, CM4221HD is still optimized for OLD UHF Band (up thru Ch69),
wasting Max Gain peak on channels that are no longer available for DTV.
UHF Raw Gain is about same as older CM4221 with improved UHF SWR on
lower channels....and Hi-VHF Raw Gain & SWR, such as it is, has been degraded....

Super-Sized-4-Bays have better Gain on New UHF Band (up thru Ch51) and
don't have a Hi-VHF Gain Reversal problem.

BTW: I don't think the NEC2 Engine has sufficient accuracy to model the
capacitive coupling problem caused by the Balun Feedlines being too close to
the vertical support beam in the "as-shipped" CM4221HD configuration.
 
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