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post #1 of 14 Old 09-19-2019, 04:41 PM - Thread Starter
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Question about CM 4251 parabolic

A friend just gave me one.. It was hit by a falling tree, and got a few elements bent and the aluminum boom that extends from the reflector broke.. Looks like maybe an hour of easy work, probably a lot less actually, and it will be up and running good as new.. He opted to put up a smaller cheaper Stellar labs 91 X copy, and is happy with it.. Just wanted the massive 4251 out of his yard. I came to his rescue!

anyway, many years ago I had a CM 4251.. Bought it at a dealer and put it up myself.. however, it looks different than this one.. My old one had more elements in the parabolic grid, and they were smaller in diameter.. Same element size as most antennas..They were made more rigid with small aluminum wire snaps that clipped all the elements together.. It worked well..
| however this 4251 my friend gave me has huge thick elements as big around as a grown mans thumb,, It also kind of 'folds up when taken down,, which my old one did not.. My old one was not the smaller 6 foot 4250, I remember it very well.. I bought my first 4251 around 1975... My friend said his was up on his tower for 30 years, which would mean his was made in the late 80's... Were these units redesigned/changed at any points during their production?... bob
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post #2 of 14 Old 09-19-2019, 06:35 PM
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Channel Master Parabolic UHF Antennas



Antennacraft Parabolic UHF Antennas

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post #3 of 14 Old 09-19-2019, 07:03 PM
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Quote:
Originally Posted by steel guitar guy View Post
... many years ago I had a CM 4251.. Bought it at a dealer and put it up myself.. however, it looks different than this one.. My old one had more elements in the parabolic grid, and they were smaller in diameter.. Same element size as most antennas..They were made more rigid with small aluminum wire snaps that clipped all the elements together.. It worked well..
| however this 4251 my friend gave me has huge thick elements as big around as a grown mans thumb,, It also kind of 'folds up when taken down,, which my old one did not.. My old one was not the smaller 6 foot 4250, I remember it very well.. I bought my first 4251 around 1975... My friend said his was up on his tower for 30 years, which would mean his was made in the late 80's... Were these units redesigned/changed at any points during their production?... bob

Are you sure you actually had a CM 4251? "Small aluminum wire snaps that clipped all the elements together" does not sound like Channel Master. Finco, one of their chief competitors, put out a parabolic dish for UHF that was their answer to Channel Master's 4251, and had the kind of clips you describe. IIRC, the CM 7-foot dish did not.

When I was in college in the late '70's, I worked summers with an electrical contractor who branched out his business into TV antenna installs, and we put up a few of them in the Irondequoit area near Lake Ontario, where the UHFs were relatively few and far between. Nothing else at the time had the kind of gain that the parabolics offered, except for some of the better 8-bay bowties, or maybe the 12-bay that TACO/Jerrold put out in the mid-1960s.

Those UHF parabolics were the "White Elephants" of the TV antenna industry. That's why Channel Master discontinued them. The sales guy at Crosstown Electronics in Buffalo told us that no other antenna got so frequently returned as the CM 7-foot dish. They eventually refused to carry them, and it was a shame, because Channel Master had the best quality back in those days before everything started to get made in Mexico and China. Problem was that the screwdriver jockeys and D-I-Y'ers who tried to put them up themselves would use regular TV masts that bent in the wind (HUGE wind load on those puppies, and a completely crazy center of gravity) and regular rotors would fail soon if you tried to use one to aim those monsters at a weak signal. They really were meant to be mounted in towers with at nothing less than ham radio-grade rotors, and guys were stickin' 'em up on roofs with in "El Cheapo" Archer Radio Shack tripods.

The irony is that those parabolics did work well if you installed them carefully, and had plenty of forward gain as advertised, plus some really insane nulls and front-to-back ratios. I don't think they were ever re-designed; no reason to do that, everything about 'em, from the feed section design to the roll grade of the aluminum, was close to perfect.

In case you don't already know about it, here's a site that might interest you:

http://www.rocketroberts.com/cm4251/cm4251.htm
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post #4 of 14 Old 09-19-2019, 08:53 PM - Thread Starter
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well, I suppose it was NOT a CM model.. i would have sworn it was, but every pic i see of the CM 4251, shows the larger diameter aluminum tubing, and a lack of clips.. It was 45 years ago, and I had not thought a lot about it until just a few years ago, when i started playing around with OTA tv reception, and antennas and amplifiers. Was Antennacraft in existence in 1975, making the 7 foot parabolic?... If not, I suppose it could have been a finco.. The only thing i recall 100%, was the clips, the smaller diameter tubing, and the fact that most of the CM parabolic antennas I have seen look more like plain old silver color aluminum. The 7 foot parabolic I had so long ago, was more of a brass/gold anodized looking color.. My mistake, and thanks for the clarification.. I plan on getting the "real"4251 back up to snuff shortly, and just fooling around with it for a bit.. Its too big for me to put up, and the 91 X knock off w/ RCA amplifier I have up now does very nicely indeed for whats available in this area.. If anyone would like it , can use and appreciate it , and can come get it, I would sell it for almost nothing, and just hand the money over to the guy that gave it to me...bob
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post #5 of 14 Old 09-20-2019, 04:57 AM
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Quote:
Originally Posted by steel guitar guy View Post
well, I suppose it was NOT a CM model.. i would have sworn it was, but every pic i see of the CM 4251, shows the larger diameter aluminum tubing, and a lack of clips.. It was 45 years ago, and I had not thought a lot about it until just a few years ago, when i started playing around with OTA tv reception, and antennas and amplifiers. Was Antennacraft in existence in 1975, making the 7 foot parabolic?... If not, I suppose it could have been a finco.. The only thing i recall 100%, was the clips, the smaller diameter tubing, and the fact that most of the CM parabolic antennas I have seen look more like plain old silver color aluminum. The 7 foot parabolic I had so long ago, was more of a brass/gold anodized looking color.. My mistake, and thanks for the clarification.. I plan on getting the "real"4251 back up to snuff shortly, and just fooling around with it for a bit.. Its too big for me to put up, and the 91 X knock off w/ RCA amplifier I have up now does very nicely indeed for whats available in this area.. If anyone would like it , can use and appreciate it , and can come get it, I would sell it for almost nothing, and just hand the money over to the guy that gave it to me...bob
Wish somebody would still make a parabolic antenna. I would like to have one.
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post #6 of 14 Old 09-20-2019, 01:26 PM
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Originally Posted by steel guitar guy View Post
...was Antennacraft in existence in 1975, making the 7 foot parabolic?... If not, I suppose it could have been a finco...
Antennacraft had an "OEM" relationship with Winegard and started as a joint venture with them in 1970 by genius TV antenna designer Doyt Hoverman, the guy who designed the G-1483, one of the best UHF antennas ever made (a collinear variation on the "stacked bay" approach which can actually offer gain that exceeds that of the best 7-foot dishes.) They made their antennas in the same Iowa factory where Winegard was based. The Antennacraft "brand" and proprietary designs were eventually sold to Tandy, which owned RadioShack; RS ended up having Antennacraft manufacture all their TV antennas.

Finco, OTOH, was bought out by a Dutch company called Sonim, who then sold off the design of the P-7. their version of a 7-foot dish, to Antennacraft. That particular version of the P-7 came out sometime in the early 1980's.

When it came down to comparing the CM4251 to the P-7, my understanding was that the P-7 design was hotter in the old channel 70 to 83 "translator range" near the very top of the UHF TV band (which was RF channel 83 at 890 Mhz in those days--for all intents and purposes, the edge of the microwave region) and of course those channels are long gone. There are a bunch of other differences, such as the 4251 having a better 300-ohm feed section allowing it to perform better on RF channels 14 thru 20, while the P-7 has a denser reflector that gave it slightly better front-to-back and nulls.

I'm in agreement with tylerSC above. I would love to see these antennas made again, but unfortunately no-one seemed to be able to make a profit on them. There were other antenna makers such as Jerrold who offered UHF parabolics for a short time, but their version was a joke, nothing like any of those Finco and Channel Master designs.
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post #7 of 14 Old 09-20-2019, 03:33 PM - Thread Starter
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Originally Posted by Al_the_xmtr_tech View Post
Antennacraft had an "OEM" relationship with Winegard and started as a joint venture with them in 1970 by genius TV antenna designer Doyt Hoverman, the guy who designed the G-1483, one of the best UHF antennas ever made (a collinear variation on the "stacked bay" approach which can actually offer gain that exceeds that of the best 7-foot dishes.) They made their antennas in the same Iowa factory where Winegard was based. The Antennacraft "brand" and proprietary designs were eventually sold to Tandy, which owned RadioShack; RS ended up having Antennacraft manufacture all their TV antennas.

Finco, OTOH, was bought out by a Dutch company called Sonim, who then sold off the design of the P-7. their version of a 7-foot dish, to Antennacraft. That particular version of the P-7 came out sometime in the early 1980's.

When it came down to comparing the CM4251 to the P-7, my understanding was that the P-7 design was hotter in the old channel 70 to 83 "translator range" near the very top of the UHF TV band (which was RF channel 83 at 890 Mhz in those days--for all intents and purposes, the edge of the microwave region) and of course those channels are long gone. There are a bunch of other differences, such as the 4251 having a better 300-ohm feed section allowing it to perform better on RF channels 14 thru 20, while the P-7 has a denser reflector that gave it slightly better front-to-back and nulls.

I'm in agreement with tylerSC above. I would love to see these antennas made again, but unfortunately no-one seemed to be able to make a profit on them. There were other antenna makers such as Jerrold who offered UHF parabolics for a short time, but their version was a joke, nothing like any of those Finco and Channel Master designs.
So because my old parabolic was purchased new in 1975, and had those clips to stabilize it, should I assume it was most likely a finco?...
I was 21 when i put it up, and am 65 now, so there's been a lot of time to forget specifics!... bob
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post #8 of 14 Old 09-20-2019, 04:31 PM
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So because my old parabolic was purchased new in 1975, and had those clips to stabilize it, should I assume it was most likely a finco?... bob
Definitely! If it was bought new in '75, it's definitely a Finco. I used to get all the antenna catalogs way back then, and I don't think I saw the Antennacraft version of the P-7 appear until well into the 1980s.

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post #9 of 14 Old 09-20-2019, 04:52 PM
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Photo of Finco P-5
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post #10 of 14 Old 09-20-2019, 06:14 PM
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Photo of Finco P-5
Sweet! Gotta admit, that P-5 is a lot prettier-looking than most UHF antennas!

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post #11 of 14 Old 09-20-2019, 10:10 PM - Thread Starter
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thanks to all... I might get that 4251 repaired in the next few days and try it out.. Then try and find someone to get it OUT of here.. Massive antenna!.. If I can pick up Rochester [90 miles] even sporadically, I might consider putting it up permanently, but it would have to absolutely blow my doors off with its performance to justify the effort it will take.... bob
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post #12 of 14 Old 09-23-2019, 08:13 AM - Thread Starter
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ok, listed this in the classifieds here, for the vast sum of $20.. No response.. So that means its not worth much. correct?.. If anyone can use this CM 4251 that was up running,and delivering great reception a few weeks ago, simply come and get it, no charge... I am in NY state, but from the rarity, and the sheer number of guys screaming for one of these, I would think this would be a no brainer.. I just no longer have the energy to install something this big myself.. If you do, its yours.. Any minor repairs it needs can be done with a hacksaw, and about 4 inches of 1 inch aluminum tubing.. the mast clamps are gone as well.. they were rusty so my friend discarded them before he gave it to me.. Anyway, its a CM 4251, its here, its intact, and its free... bob

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post #13 of 14 Old 09-23-2019, 05:31 PM
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Originally Posted by steel guitar guy View Post
ok, listed this in the classifieds here, for the vast sum of $20.. No response.. So that means its not worth much. correct?.. If anyone can use this CM 4251 that was up running,and delivering great reception a few weeks ago, simply come and get it, no charge... I am in NY state, but from the rarity, and the sheer number of guys screaming for one of these, I would think this would be a no brainer.. I just no longer have the energy to install something this big myself.. If you do, its yours.. Any minor repairs it needs can be done with a hacksaw, and about 4 inches of 1 inch aluminum tubing.. the mast clamps are gone as well.. they were rusty so my friend discarded them before he gave it to me.. Anyway, its a CM 4251, its here, its intact, and its free... bob

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New York is a big state - If you post your general location, you may get more response. Someone from Mass. would notice Albany, someone from Ontario would notice Buffalo, etc....
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post #14 of 14 Old 09-30-2019, 12:39 AM
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I would not waste much time with a parabolic uhf HDTV antenna. Stick with the 91XG. I wasted considerable time and money building my own parabolic uhf antenna. The big problem is the high gain dish's extremely narrow signal reception angle. Aiming the dish for reliable reception is nearly impossible, especially for weak signals. Constantly changing weather conditions keep changing both the signal path's vertical and horizontal angles. An antenna with lower gain and a broader signal reception angle gives more reliable reception. And if the broadcast signal is cut-off due to a temperature inversion or simply if the broadcast vertical beam is too narrow and tilted too low to reach places like the Sierra foothills, no antenna, no matter how much gain it has, will receive the signal! See:


https://www.avsforum.com/forum/25-hd...a-project.html
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