Got this today for $50

[Kraven]

Went and asked about this antenna that I had been watching. The guy said he did not use it and it had been there a long time.

He asked $50 and I said sold. I pick it up next Saturday.

It is either a Channel Master 4250 or 4251 - - - I'm sure which yet as I could not measure it.

Chap... if you're not satisfied w/ the antenna, I'll give you 60$ for it.

 

[boba]

Come on Sat. so we can get rid of these jealous posts and find out if it was a good buy or not.

 

[chapelrun]

I want to compare the antenna's head to head

I've been doing alot of reading about the CM-4251 since I found this antenna.

I don't have the new antenna yet but my current antenna is a Antenna Direct 91XG. I would like to compare them for UHF gain head-to-head. Based on what i've learned from published sources the 91XG might very well be the better antenna.

Attached is a very old gain chart for the CM-4251 and the hyperlink is the gain chart for the 91XG. (see pg 4 of pdf).

http://www.antennasdirect.com/cmss_files/attachmentlibrary/Technical Data PDF's/91XG-TDS.pdf

 

[chapelrun]

Chap... if you're not satisfied w/ the antenna, I'll give you 60$ for it.

How would I get it to you?? It is mighty big!

 

[navychop]

How would I get it to you?? It is mighty big!

I'm closer. $61.50!

 

[primestar31]

I've been doing alot of reading about the CM-4251 since I found this antenna.

I don't have the new antenna yet but my current antenna is a Antenna Direct 91XG. I would like to compare them for UHF gain head-to-head. Based on what i've learned from published sources the 91XG might very well be the better antenna.

Attached is a very old gain chart for the CM-4251 and the hyperlink is the gain chart for the 91XG. (see pg 4 of pdf).

http://www.antennasdirect.com/cmss_files/attachmentlibrary/Technical Data PDF's/91XG-TDS.pdf

I had a 91xg back in the late '80's, on about a 58' tall pole with guy wires and a rotor, rg-6 cable, and a Winegard super-low noise lnb. This was in Bridgeport Michigan, and I could pick up UHF stations in Toledo Ohio (135 miles) with ease, and all the time. At frequent times I picked up Pennsylvania stations, and one time I even picked up a Florida station on skip!

I always wanted, but never bought one of the parabolic antennas, as they were just too large. So, I can't directly compare them, but the 91xg worked very well, and had a very tight beam.

 

[Stargazer]

I see the 91XG for $50 new online. So it beats the CM-4251?

Here is another one similar to the CM-4251 but it has also been discontinued ...

http://tvfmantennas.a.wiki-site.com/index.php/Image:AntennacraftParabolicUHFAntennas.jpg

Some more discussion comparing the two and a new HD 4251 is at the following link:

http://www.dtvusaforum.com/dtv-hdtv...a-really-best-deep-fringe-91xg-cm-4228-a.html

 

[Bob2011]

I've been doing alot of reading about the CM-4251 since I found this antenna.

I don't have the new antenna yet but my current antenna is a Antenna Direct 91XG. I would like to compare them for UHF gain head-to-head. Based on what i've learned from published sources the 91XG might very well be the better antenna.

Attached is a very old gain chart for the CM-4251 and the hyperlink is the gain chart for the 91XG. (see pg 4 of pdf).

http://www.antennasdirect.com/cmss_files/attachmentlibrary/Technical Data PDF's/91XG-TDS.pdf

If the numbers for the CM-4251 really are in dBd then it crushes the 91XG on the lower channels and is on par with it in the last few upper channels in the current band. If you're adventurous you could replace the bowtie antenna in front of the dish with one fine tuned for todays UHF band. You probably could get a real 16 to 18 dB of gain across the band.

 

[chapelrun]

If you're adventurous you could replace the bowtie antenna in front of the dish with one fine tuned for todays UHF band. You probably could get a real 16 to 18 dB of gain across the band.

Could you possible give additional detail about this. One question I've been trying to figure out is the best balun for the CM-4251??

I'm also trying to figure out how to get this antenna higher in the air.

 

[boba]

Could you possible give additional detail about this. One question I've been trying to figure out is the best balun for the CM-4251??

I'm also trying to figure out how to get this antenna higher in the air.

Hire Superman to fly it up there.

How about renting a lift truck?

 

[pamajestic]

One question I've been trying to figure out is the best balun for the CM-4251??

I prefer the Channel Master CM3075 because it has two solid wires going into the balun. Most of the other manufacturers crimp a U blade on the ends creating a future fail point.

 

[Bob2011]

Could you possible give additional detail about this. One question I've been trying to figure out is the best balun for the CM-4251??

I'm also trying to figure out how to get this antenna higher in the air.

At the focal point of the dish is just a 2 bay bowtie antenna with reflector. Looking at your pictures that antenna has small bowtie elements and is likely designed to cover up to channel 83. New bowtie antennas today have larger elements because the last channel is 51. If you replace that bowtie antenna with a new one you should be able to bring up the gain on all channels at least a dB or two.

 

[Stargazer]

If the numbers for the CM-4251 really are in dBd then it crushes the 91XG on the lower channels and is on par with it in the last few upper channels in the current band. If you're adventurous you could replace the bowtie antenna in front of the dish with one fine tuned for todays UHF band. You probably could get a real 16 to 18 dB of gain across the band.

Each channel, running on a specific frequency, can have an antenna designed to pull in that particular frequency.

What I am curious is if anybody has ever tried making adjustable antennas, by having the elements being able to pull in and out like the antenna's on rabbit ears or radio's. You could then make adjustments for that particular frequency (channnel) that you are trying to tune in.

 

[chapelrun]

Just picked it up

My son and I just picked up the CM4251. The man I bought it from said he is 91 years old and it was there when he bought the house.

It was a little scary to get down - - - very steep roof - - - I was glad my son helped me.

I have not done any cleaning on it yet (and may only do a little). This will make a cool project.

Some Pix.

 

[Blindowl1234]

Nice find! There is one close to me sitting in a guys yard on a short pole. I don't know if it's hooked up since it appears to be pointed in the wrong direction. It's missing a few of the lower elements. I think I read there's a few Db gain over the good version of the CM4228. Still wish they made the 4251 though

 

[boba]

Well it's Sunday evening what have you learned, yeah I know it was the wife's day but you have us interested.

 

[chapelrun]

She's Up and Running!

OK, I already love this antenna. Install was not too bad - - took down the XG-91 and installed the CM-4251 in its place. Wanted to go higher but to put it above the VHF would have required to put up a different mast. Both VHF and UHF antennas are amplified by a CM-7777.

Anyway took reading from the XG-91 before using a Tivo HD and recorded the Peak signal for each UHF channel. Then after the CM-4251 did the same thing for each channel. In almost all cases the CM-4251 pulled in more signal. See the attached excel - - - also the graph on the second tab.

The weird thing is that for the 4 VHF channels I have the signals were lower for VHF 7, 9, 11 and 13. I'm only concerned about two though 7 and 9. I think maybe the the big Channel Master is conflicting with the VHF antenna. My have to try moving a different VHF antenna over by the chimney.

Here are some pix and the excel.

 

[SatelliteAV]

Definitely way too close to the VHF. The metal will become passive elements and degrade performance on both bands.

Try to separate by over a wave length and experimentation will provide the optimal distance so not to interfere with key channels.

 

[No Static At All]

Do you have the FM trap engaged? The full band antenna is getting a huge dose of FM from 105.5 whose 2nd harmonic falls right on top of channel 13.

The antennas being so close is likely not helping either. If in your shoes, I would replace the RCA combo antenna with the lightweight/low windload VHF-Hi Antennacraft Y10-7-13 & mount it at least 1 foot above or below the 4251. This will really help improve the dynamic range of the 7777 which is likely suffering from some signal clipping due to the strong local FM's in the valley.

 

[chapelrun]

Thanks for the suggestion - - - question first. I wonder if the CM antenna has any ability to pull in VHF channels?

If so I could change the 7777 to combined and see if that makes any difference. No cost option and might be worth a try.

What do you think?