mrvanwinkles, don't assume that the concavity is efficient for an OTA parabolic reflector though! ;)

4 or 4 1/2 feet in diameter isnt going to do much good for the new range of uhf frequencies.

I have thought of tilting my 4251 but it would make an awkward assemby if done at the bottom of the mast/rotor.
Has anyone tried mounting one like Wade does? This could provide tilting easier.
No matter what this could be a real project!
Also, I use a CM7777 amplifier on mine. It has no overload on local channels and helps pick up the ones about 90 miles away and further.

Has anyone tried mounting one like Wade does? This could provide tilting easier.

Look at post #30 in this thread.

I also have a P-5 parabolic. It may be a good antenna for tilting as it is very light weight and smaller than the 4251.
Not as much gain though.
Post #30 looks like a "fun" tower to climb.

http://www.digitalhome.ca/forum/picture.php?albumid=301&pictureid=1378

What I meant about post 30 was that by shortening the top horizontal mounting pipe distance to the tower and increasing the bottom one, you can tilt the CM4251. :p

Got some time to play this weekend with my unknown parabolic. Currently it is installed in my attic. Did a pass with my DTVPal and picked up all the boston/providence stations. Antenna is pointed northeast towards the boston towers. To my surprise i also pulled in WMTW in Portland, Maine. About 165 miles away and i had a good 70 on the meter.

Tried the scan again with my tivax stb-t8 and got nothing. Also with the tivax quite a few local channels fade in any out while most of the others are at 100%. My guess is the signal is too strong for the Tivax?

In any case i am real impressed with my clam-shell antenna.

Interesting parabolic mount:

http://img19.imageshack.us/img19/2121/gridantennamastmount.jpg

well heres my CM4251 mounted, later dismounted, and disassembled, this was a HUGE disappointment, by far the worst reception on my tricky 2nd edges, and rather weakish on the most stable ones...:mad:

the M4, M8 easily outperformed it at this location, almost consistently... so i guess as we have seen before, BIGGER is NOT always better

I thought the interfering co-channels were coming in from behind the large parabol, so i tried covering the whole thing with 1" chicken mesh, and actually reception became worse


http://www.digitalhome.ca/forum/picture.php?albumid=355&pictureid=3215

I thought the interfering co-channels were coming in from behind the large parabol,
Theres actually more to learn from failed experiments than from successful ones. So, it sounds like the signals are not coming in like you thought they were. The CM4251 has a very narrow lobe, so that doesnt seem to be what you need.

I have both a silver sensor (great for its size) and a winegard solid 39inch satellite dish that neighbour relations currently won't allow me to install outside.

Anyone ever try to put a silver sensor at the focal point of a large(ish) satellite dish? Kind of like a smaller CM4250?

I would think that positioning would be critical for the SS, and could probably be tuned to maximize one frequency. But I am worried reflections might make this multi-path hell. Is it worth a shot?

Balm.... since the cm4251 did not perform for you do you have any plans on selling it? I have a nice long southern view straight down Lake Simcoe towards Toronto and Buffalo NY ... hmmmmm..... wondering how it might perform at my location : )

Is it worth a shot?


At 39 inches, that dish will act more or less like a regular flat reflector. Parabolas dont really start kicking in until more than about 6 times the wavelength, which with the new uhf channel range, is about a minimum of 72 inches.

Thanks 300ohm, not worth the effort then.

I guess am just itching to install that dish. I have clear view of FTA sats and everything. Sad to see a 200$ piece of equipment gathering dust in the basement.

A popular non-Channel Master parabolic (we think it's a Jerrold or Wade) in my area, recently taken down from a DMX tower. This one is about 5' in height. The active element is grounded out to the frame (per it's design). Despite it's age, it looks like it could work for another couple of decades. A few fasteners are rusted and will require replacement; but otherwise a solid antenna.


http://img691.imageshack.us/img691/6979/img3063lv.th.jpg (http://img691.imageshack.us/i/img3063lv.jpg/)


http://img375.imageshack.us/img375/7493/img3062f.th.jpg (http://img375.imageshack.us/i/img3062f.jpg/)


http://img808.imageshack.us/img808/5139/img3061q.th.jpg (http://img808.imageshack.us/i/img3061q.jpg/)

Post some detailed measurements, especially of the driven element.

The active element is grounded out to the frame (per it's design).
It looks like there is a couple of resistors on the back going to the frame.

Those aren't resistors. The back (inside) of the active element simply has two nuts for the twin lead attachment. There's some twin lead coiled up around the wire nuts.

The vertical length of the parabola is 4'9" from the top of the uppermost element to the bottom of the lowest element.

The length of the driven element is 12" from the wire nuts to the front. It's made up of four folds with the widest "wave" at the outside or front of the antenna. These are 9", 14", 16" and 17" each in width from side to side.

The horizontal mast--holding the active element--extends 34" from the back of the parabola. There is an additional 5" of active element extending beyond the end of the wave folds. These two extensions are straight and coated with a black plastic or rubber material.

Below is a bottom view up of the active element. Followed by a close up of the front section of the active element, where it is grounded off to the horizontal mast pipe.

http://img72.imageshack.us/img72/3305/img3071v.th.jpg (http://img72.imageshack.us/i/img3071v.jpg/)
http://img828.imageshack.us/img828/3063/img3064l.th.jpg (http://img828.imageshack.us/i/img3064l.jpg/)

That's a Finco. The smaller version is the P-5:

http://www.digitalhome.ca/forum/showpost.php?p=869383&postcount=13

and the bigger version is the P-7:

http://www.digitalhome.ca/forum/showpost.php?p=1067044&postcount=98

The smallest Wade, the D-1338-BB, looks like this:

http://www.digitalhome.ca/forum/picture.php?albumid=260&pictureid=3340

Ahhh. Thanks, Stampeder! Mystery solved. I see a lot of these in our area, so there must have been a dealer around here some 30 years ago.

When I look at the focal point on the other Fincos in those posts I can't make out if they have the wavy-loopy feed element that yours does.

Finco was selling their parabolics under other brand names too. I'm thinking Antennacraft for some reason, and I think as Lafayette models in the U.S. (300ohm and others would know better than me about that).