CM 4221HD & 4228HD engineering data - Page 2 - AVS Forum
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post #31 of 46 Old 01-28-2009, 02:39 PM
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Thanks for the tip. Quizzed him and they are as pictured the old style American made. Picked one up.

Vizio VP322 Plasma / Vizio GV42LF LCD / Denon 2200 Silicon Image DVD / Panasonic S97 Faroudja Genesis DVD / Oppo 970HD Mediatek DVD / Oppo 983H Anchor Bay DVD / Panasonic LX-600 Laserdisc / Aiwa MX100 Multi-region VCR / JVC S7600 S-VHS / PS2 / Sega Genesis / Nintendo SNES / Roku 2 XS & HD-XR / Realistic STA-90 Reciever / Realistic Minimus 7 / Antennacraft G1483 Hoverman / Belden 7915A RG6 / Channel Master 7777 Titan 2 UHF/VHF / Panasonic AX-200u / Optoma Graywolf 92" / Draper Luma 92"
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post #32 of 46 Old 02-20-2009, 09:05 AM
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I have an original 4228 on the roof with a 777 pre-amp. Metro Atlanta area. We have two high VHF stations, one on 8 and one on 10. The 4228 does OK on 10, but does not seem to do well on 8. I have significant attentuation due to Kennesaw Mountain being close by and in my line of site to all Atlanta stations.

So, I see two options to improve my hi-VHF reception.

1) Get a seperate hi-VHF antenna (1713 - very long...or... HD-1080 - enough gain??) and use seperate VHF and UHF feeds to the pre-amp
2) get the 4228-HD to replace existing 4228.

My concern with 2 is losing a touch of gain on UHF. I am thinking the 1713 is the best option. 9 or 10 dB of VHF gain versus about 5 dB with the 4228HD

Thoughts?
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post #33 of 46 Old 02-20-2009, 07:01 PM
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I just wanted to let everyone know that I purchased a 4228HD for my parents house and installed it. I was concerned because most of their stations, 1 VHF and about 5 UHF stations, are located at 300 degrees but one VHF station is located at 70 degrees from their house. I was afraid that I might need to point the 4228HD at 300 degrees and buy a VHF only antenna to get the station at 70 degrees due to the directionality of the 4228HD. However, by pointing the 4228HD to about 340 degrees, we are able to pick up all of the stations with strong signals.

Jeff Burleson
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post #34 of 46 Old 03-09-2009, 01:08 PM
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HDTV Primer has a new (temporary) page up about the 4228HD and the new DB8.

http://www.hdtvprimer.com/ANTENNAS/TemporaryPage.html

In short:

Quote:


The bad news is that the new 4228HD and DB-8 are both wrecks. The good news is that the 4228HD can easily be turned into the best UHF antenna presently available.

Quote:


As delivered, the 4228HD is a good antenna below channel 30, but above channel 40 it is no better than a 4-bay.

Fortunately fixing it is trivial: You just replace the phasing harness with two baluns and a combiner. Those plus two short cables will cost you another $25, but a nut-driver is the only tool you need. If the loss in the baluns and combiner is 0.5 dB then the performance will be 0.5 dB less than the B3 plot above.



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post #35 of 46 Old 04-14-2014, 01:41 PM
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Was somebody able to verify or correct these engineering specs? Some of the numbers don't look correct. The curves that show gain variation with respect to frequency "make sense" for the old antennas (4221 and 4228); but look really odd for the new ones (4221HD and 4228HD).

 

 

Such variations (going up and down across the band) are very unusual for properly designed antennas. I think these are either typos or incorrect data.

 

Also, does anyone know if these numbers reflect raw (theoretical / simulated) gain, or net (measured) gain; and what the reference is (dBd or dBi)?

 

Thank you.

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post #36 of 46 Old 04-14-2014, 01:58 PM
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After awakening a 5 year old thread...
If you can find a "real" Channel Master 4228 or 4221, you will probably be better off.
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post #37 of 46 Old 04-14-2014, 02:55 PM
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Where did those so-called "specs" come from???? They don't always agree with modeled results (esp CM4221).
Is Vertical Scale in dBi or dBd (probably the latter where dBi=dBd + 2.15).

Here are 4nec2 results that I believe are correct....except for ANOMALOUS Gain results I documented on the lower channels, wherein the ACTUAL Gain may be higher than modeled results, depending on choice of parameters:
http://imageevent.com/holl_ands/multibay/4bayrefl/cm4221
http://imageevent.com/holl_ands/multibay/4bayrefl/uhfnewcm4221hd
http://imageevent.com/holl_ands/multibay/8bayrefl/oldcm4228wrefl
http://imageevent.com/holl_ands/multibay/8bayrefl/cm4228hd

Here are some comparison charts:


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post #38 of 46 Old 04-14-2014, 03:15 PM
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Note that I found ANOMALOUS Gain vs Tine Separation results on lower UHF channels, illustrated here for CM4221HD, CM4228 and CM4228HD 4nec2 models on worst cast 470 MHz (CM4221 model did not have this Anomaly). I believe that this is inherent in the 4nec2 models (or modeling program), rather than REAL behavior:
CM4221HD_16RR_Hacked%20GainVsWideTS%20470.jpg
CM4228_RH_GainVsTS%20NG.jpg
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post #39 of 46 Old 04-17-2014, 08:07 AM
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Sorry for "waking up" the thread. :)  In my searches, came across the data referenced by videobruce more than once.  Reportedly it has been provided by the manufacturer, but the numbers for the 422XHD don't seem to make sense. CM won't provide any clarification (called them, emailed them, nothing!); and you are right, the data available out there (thanks to enthusiasts who took it upon themselves to do time consuming simulations) looks very different. I was wondering if the antennas themselves are "iffy" or just the data in the tables is "fat-fingered". Based on the reviews (and the simulations referenced above), the 4221HD seems to be a pretty good antenna.

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post #40 of 46 Old 04-17-2014, 11:58 AM
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Channel Master is no more... they sold out years ago.

The 422xHD models are now made in China and differ from the original.

If you can find the "original" CM models (new, in the box), it is probably worth the price/premium IMO.

Other than that... good luck. tongue.gif
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post #41 of 46 Old 04-17-2014, 06:54 PM
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I did some tests to compare the original stock 4221 with the stock 4221HD. The 4221 did quite well compared to the 4221HD, but with a few simple modifications, the 4221HD did much better:



Here is the post with more information:
http://www.digitalhome.ca/forum/showpost.php?p=1167870&postcount=221

In order to see all of the photos (like the balun position and the two antennas on my car) in that post, it is necessary to login and refresh(F5).

If you can not measure it, you can not improve it.
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post #42 of 46 Old 04-17-2014, 09:18 PM
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When looking at old CM4221 specs, bear in mind that the actual DIMENSIONS have varied over time.....

"Hacked CM4221HD" 4nec2 results charts I posted above correspond to fol. picture, wherein entire Balun and Feedline Assembly has been "Flipped Over" [YELLOW in Chart above] so that Feedlines are much further away from the Vertical Reflector Supports, which was apparently perturbing the performance of the Antenna:
http://www.digitalhome.ca/forum/showpost.php?p=952715&postcount=95
As modeled here:
http://imageevent.com/holl_ands/multibay/4bayrefl/uhfnewcm4221hd

Although I modeled the short length of metal from the Feedlines to the Coax Connection Point, there is no way in 4nec2 to model the plastic in the Balun "Box" and "Caps" [ BLUE in Chart above].

I'm not sure what "CM4221HD Spacers" [CYAN in Chart above] would look like....can anyone cite a link with a picture????
Perhaps it refers to fol. picture, which is a GOLD (vice) SILVER color and hence might ALSO have different Dimensions:
http://www.digitalhome.ca/forum/showthread.php?t=104837&page=2


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post #43 of 46 Old 04-17-2014, 09:37 PM
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Also note that there are TWO versions of the A-D DB-8, as described by Ken Nist in HDTVprimer:
http://www.hdtvprimer.com/antennas/temporarypage.html

And in 2012, A-D announced a THIRD version, the A-D DB-8e, where the two side-by-side 4-Bay Sections can be splayed in different directions to widen the overall Beamwidth until there are two separated Beam Directions:
http://forums.solidsignal.com/content.php/834-CEDIA-Expo-Report-Antennas-Direct-DB8
http://www.antennasdirect.com/cmss_files/attachmentlibrary/Technical%20Data%20PDF%27s/DB8E-TDS.pdf
Note that Gain numbers in the Technical Data Sheet DO NOT INCLUDE LOSSES in the RF Combiner.

Although A-D did NOT provide Loss Data for the RF Combiner, AntennaHacks measured several commercial RF Splitter/Combiners, finding a SIGNIFICANT amount of Loss, which had wide variation with Frequency (divide pictured scope value by TWO, cuz tested back-to-back):
www.antennashacks.com


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post #44 of 46 Old 04-18-2014, 07:13 PM
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Quote:
Originally Posted by holl_ands View Post

I'm not sure what "CM4221HD Spacers" [CYAN in Chart above] would look like....can anyone cite a link with a picture????
Perhaps it refers to fol. picture, which is a GOLD (vice) SILVER color and hence might ALSO have different Dimensions:
http://www.digitalhome.ca/forum/showthread.php?t=104837&page=2
Your link takes me to page 2 of that thread; you must mean post #18. His photos do indeed show aluminum as a gold color. It must be a problem with the color balance of his camera. His 3rd photo shows the phasing line strips flattened to move the balun away from the square support tube. CM bent the strips down so that the antenna would fit in the box, but it makes the coupling between the strips and the support tube bad enough to harm the performance of the antenna. His photos do not show the spacers. I suggested the spacers in my post #221 because I noticed that while the balun was mounted at the midpoint between the two inner bays, its electrical connection was NOT at the midpoint, which meant that the two inner bays were not being fed in phase.

The link that I gave above takes you to my post #221, but you must login to that forum and hit Refresh (F5) to see all of the photos, including the balun, which I find to be a troublesome quirk of that forum.
http://www.digitalhome.ca/forum/showpost.php?p=1167870&postcount=221
Quote:
I examined how the balun box was attached to the strips and noticed that although the rivets that attach the balun to the strips were centered between the two inner bays (point A), the effective electrical connection was not centered (point B). This meant that the two inner bays were not being fed in phase, and therefore all four bays were out of phase, which would reduce the gain.

4221HDbalun_1_zps9ad34af0.jpg
Quote:
I added nylon spacers between the strips and the lugs on the balun box using the 8-32 hardware that I had, moving the balun to the front. To duplicate the mfg method, you could use metal spacers and long aluminum pop rivets. If you decide to use the spacers, flat strips would probably be OK, but I haven't made measurements. I left the strips in their bent form and just turned them over for the tests so that I could return the antenna to it stock condition for further tests, but the balun sticks out too far to suit me. Inserting a thin insulating strip between the balun tabs and the feedlines WOULD NOT work, because it would act like a coupling capacitor at UHF:

4221HDspacers_1_zps74910f97.jpg

TEST CONDITIONS:
Quote:
OTA signals are constantly changing in strength, so I knew that I wouldn't get reliable readings if I made measurements before and after modifications. And, I don't have a constant level output signal generator to make antenna range tests like mclapp, so I decided to make rapid A/B comparisons between my 4221 as a standard antenna and the 4221HD as the test antenna.

2ANTSoncar_1_zpsea7dd688.jpg

Recently, I made some quick comparisons between the 4221HD and the DB4e. The modified 4221HD and the DB4e have about the same gain, but further testing would be needed for better accuracy.

If you can not measure it, you can not improve it.
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post #45 of 46 Old 04-19-2014, 12:30 PM
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In my "CM4221HD Hacked" 4nec2 model, I included the Nylon Spacers between the Feedlines and the Balun, where i presumed a length of 0.5-inch (and shouldn't make any significant difference if 3/4 or 1-inch long)....as shown in SECOND picture you posted above.

So "CM4221HD Flip Balun" (YELLOW) has the insulating tape installed between the Balun and the FLIPPED Feedlines, whereas 'CCM4221HD Spacers" (CYAN) uses a (0.5-inch??) Nylon Spacer instead and appears to be the (PREFERRED) configuration I modeled, rather than "CM4221HD Flipped Balu"n (CYAN).

Only remaining confusion I have is the FIRST picture above shows some insulating tape between the Feedlines and the Balun....which appears to have been applied to an UNMODIFIED CM4221HD. Am i correct in presuming that this prototype configuration was NOT included in the reported OTA test???

And what configuration does the "CM4221HD no caps" (BLUE) correspond to.....the "Gold" colored CM4221HD with FLAT Feedlines....or the "Flipped Balun"....or the UNMODIFIED CM4221HD???


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post #46 of 46 Old 04-19-2014, 04:07 PM
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Quote:
In my "CM4221HD Hacked" 4nec2 model, I included the Nylon Spacers between the Feedlines and the Balun, where i presumed a length of 0.5-inch (and shouldn't make any significant difference if 3/4 or 1-inch long)....as shown in SECOND picture you posted above.
That's correct.
Quote:
So "CM4221HD Flip Balun" (YELLOW) has the insulating tape installed between the Balun and the FLIPPED Feedlines, whereas 'CCM4221HD Spacers" (CYAN) uses a (0.5-inch??) Nylon Spacer instead and appears to be the (PREFERRED) configuration I modeled, rather than "CM4221HD Flipped Balu"n (CYAN).
"Flip balun" is like shown in post #95 on that thread. The bent feedlines are now bowed out, but the balun is now inside the lines. I did each of the modifications as suggested by the OP, one-at-a-time, to see what difference each modification made. I did not make the reflector smaller; I didn't think that was a good idea, and it would make it impossible to restore the antenna to it original stock condition.

There is NO insulating tape between the balun and the feedlines; it wasn't suggested by the OP to my knowledge. It wouldn't do any good because you would have capacitive coupling between the metal tabs on the bottom of the balun box and the feedlines, which would still maintain the off-center feed at point B.

The purpose of the spacers is to get the balun away from the feedlines so that the capacitive coupling would be minimized and the feed point would be at point A. Using the spacers is my idea that I added to the OP's mods to feed the two inner bays in phase, so I feel that it is a preferred additional mod, not an alternative to the mods suggested by the OP. "Flip balun" is probably an ambiguous misnomer; better to call it "flip feedlines" so that they are moved away from the square support tube. After that mod, I decided to move the balun out to the front to make it easier to connect the coax, and finally I added the spacers.

If you can not measure it, you can not improve it.
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