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Towerdude

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Reply with quote  #31 
Here is a professional VHF high band.  This company makes great antennas.. log periodic.jpg 

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Wayne Johnson
Comptech

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Reply with quote  #32 
50 ohm impedance, made for comms not TV. It would still work as receive only for TV though. Did not look it up would guess the price is high, being able to transmit 2Kw.
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12 foot Unimesh, with Chapperal ortho C-Band feed with Norsat 5150's, 10 foot perforated Unimesh with a Pansat DP4 Feed with four Norsat Pll LNB's.Octagon 4K, Micro HD, Wetek Play and a TBS 6903 PCIe card.Modded WNC 4x8 switch for power.
majortom

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Reply with quote  #33 
Obviously does not qualify as a consumer TV antenna
One would have a difficult time finding a 7/16 DIN adapter to an F connector used on RG-6 coax.
Only 7.15 dBi gain.


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Perfect 10 7.5' mesh Chapparal C/Ku Co-Rotor feed, Norsat 8115 CBAND, Norsat 4106A Ku Thomson Saginaw Actuator, Vbox positioner,
Home Brew Polarotor683 Servo circuit. Openbox S9, Prof7500, v4l-updatelee linux drivers installed.
ricardo's geo-orbit archive: https://web.archive.org/web/20071202191450/http://www.geo-orbit.org:80/sizepgs/tuningp2.html
Comptech

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Reply with quote  #34 
Oh, come on, you could use the hardline as a wall mount also!
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12 foot Unimesh, with Chapperal ortho C-Band feed with Norsat 5150's, 10 foot perforated Unimesh with a Pansat DP4 Feed with four Norsat Pll LNB's.Octagon 4K, Micro HD, Wetek Play and a TBS 6903 PCIe card.Modded WNC 4x8 switch for power.
majortom

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Reply with quote  #35 
hehe, I still haven't tested the Y10-7-13 a friend gave me.
At 120", it is twice the boom length of my existing VHF Hi yagi.


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Perfect 10 7.5' mesh Chapparal C/Ku Co-Rotor feed, Norsat 8115 CBAND, Norsat 4106A Ku Thomson Saginaw Actuator, Vbox positioner,
Home Brew Polarotor683 Servo circuit. Openbox S9, Prof7500, v4l-updatelee linux drivers installed.
ricardo's geo-orbit archive: https://web.archive.org/web/20071202191450/http://www.geo-orbit.org:80/sizepgs/tuningp2.html
rikoski

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Reply with quote  #36 
My personal pick would be an 8 dipole with reflector. Channel master makes one. Higher gain than a log periodic and broad beam width so it can receive stations coming from slightly different directions. Has some gain on the high VHF band (not all HD stations transmit on UHF.) Higher gain than a log periodic. I also like a simple corner reflector because of its very high gain and the reliability that comes with simplicity.

Direct Link removed by Mod. Please refer to the rules of the forum.


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Rick W9ZD
Currently:10' Winegard Pinacle with AJAk 180; RayDx 10.5; Orbitron Spinclination 8'; Sadoun 6' Steel. Manhattan receivers migrating to Icecrypt. In 1961did video design for the ITT Transportable Earth Station. First home dish was a 10' fiberglass; Boman receiver and a 120 degree lnb.
Captain_Kurtz

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Reply with quote  #37 
There is a "Channel Master 4250" parabolic reflector UHF antenna currently on ebay for $500 OBO,
local pick up only in Toledo, OH.
CWDM

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Reply with quote  #38 
That is a beast which out perform anything on the market today, if that was closer to me I would take a road trip. 
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John 3:16
1.2-meter motorized,2 1.2-meter 103w, 72W. Manhattan 1933.Quali.AZ Prem.
Captain_Kurtz

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Reply with quote  #39 
Note that he has it listed as a 4250 and 6' diameter, not a 4251, so was that a little brother to the 4251?
(Isn't the 4251 an 7' reflector?)
Or is it a typo?
majortom

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Reply with quote  #40 
After looking around, I do believe there was a smaller CM-4250, so not a typo.
It is before my time... Don't recall ever seeing any UHF parabolic antennas installed anywhere around here. When I was a kid, I always "looked up" at envy of any outdoor TV antennas so I think I would have noticed. There was only one UHF station around here at the time worth pulling in, and it was local, so something like that wasn't necessary.
A simple UHF loop on the back of your TV was good enough, even for some DX from neighboring markets, especially in the summer months.

Aside from the obvious size challenges, around  that time they were in the process of moving 800 MHz spectrum from television to the new Cellular service which never existed prior. Certainly the change in spectrum allocation at the time would have played some role in antenna designs changing too. Given it rolls off so much at the low end (typical for any broadband UHF antenna), not sure how much benefit you would get
vs the conventional designs ya see today that are designed for today's spectrum usage / scattered transmitter locations.
The more they keep carving spectrum away from UHF TV, the easier it becomes to design suitable broadband UHF antennas.

http://www.digitalhome.ca/forum/186-antenna-research-development/96216-building-uhf-parabolic-reflector-like-cm4251.html

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Perfect 10 7.5' mesh Chapparal C/Ku Co-Rotor feed, Norsat 8115 CBAND, Norsat 4106A Ku Thomson Saginaw Actuator, Vbox positioner,
Home Brew Polarotor683 Servo circuit. Openbox S9, Prof7500, v4l-updatelee linux drivers installed.
ricardo's geo-orbit archive: https://web.archive.org/web/20071202191450/http://www.geo-orbit.org:80/sizepgs/tuningp2.html
boblop

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Reply with quote  #41 
Keep in mind here that Rick sells some OTA antennas.

I have had these two OTAs up now for getting close to two years. They are standing up to ice and high winds very well, so far. I would like to put a motor on one of them some day. My near by transmitters I pickup from the back side of the bowtie machine. I often get from the front side signals more than 70 miles away.

I would like to try out for blocking and possible gain increases a large C band dish mounted behind a few UHF antennas to perhaps improve signals from selective transmission locations. The Avcom PSA 37XP will cover those freqs so I have a way to "see" what is happening to my signals.

Still two more months of too cold weather outside to mess with any thing for now. If not for risk from high voltage strikes I would try the old Birdview dish with holes up on the 60 foot tower and a motor to spin it around like it was a radar dish. Rather I should say point the dish. But at issue is the fact that I can get all the OTA networks now so little would be gained by getting signals from farther away.
 XZQeII3PC6F4MFQi-pic-jpg.jpg


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Captain_Kurtz

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Reply with quote  #42 
@majortom:

The FCC has basically ruined UHF DXing, and "broadband UHF" has become an oxymoron.
I read over the first page of that thread that you linked, about newer designs being as good or better than the CM-4251, and I think that they are forgetting that gain isn't everything when evaluating an antenna. Close, but not quite. I believe I read that in addition to its high gain, another advantage of the CM-4251's 7' diameter was the ability to "hold" a weak signal. For distant and weak signals, there are going to be "hot spots" in the electromagnetic field where the signal is stronger, next to weak areas - maybe a few feet apart and the difference between getting a lock or not. As the electric field fluctuates and these areas move about, an antenna with a smaller cross sectional area like the CM4228 would repeatedly lose lock on the signal, whereas the much larger signal collection area of the CM-4251 allows it to stay locked on the signal.

@boblop

Yes, Rick sells antennas, and I certainly wouldn't recommend a CM4251 to someone who just wants to watch TV, and also usually the better solution to a weak signal is to mount the antenna higher to get a clear line of sight, before you go with a bigger antenna.
Keep us posted if you use a C-band dish as a reflector for UHF TV, but you better calculate the wind load first and have an extremely strong mount. [wink]

The CM4251 would be fun to try out, and might be the right solution for someone in a fringe area, but $500 isn't cheap.

rikoski

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Reply with quote  #43 
Long, long time ago (1975) I was living in the south side of Chicago and wanted to watch South Bend television (16, 22, 28, 34), 70 miles away, to get to watch the network news an hour early. So I bought and put up a CM-4251 in my 3rd floor attic. It worked well but then I rediscovered satellites in the '80's and sold off the CM-4251. I still do TV DX from Beverly Shores, not to South Bend (35 miles) which gets covered with an 8 dipole bedspring but places like Milwaukee, Grand Rapids, and Madison when tropo comes up, usually in the early fall. My antenna of choice for that is the Create log periodic CLP-5130. I bought mine out of Japan but it can be found in the US now.

The Create does not have the gain of the CM-4251 at about 7 dBd but having frequency coverage from 50MHz to 1.3 GHz; on a rotor is my go-to VHF, UHF antenna.

If I wanted something with higher gain for UHF television, I would build a UHF antenna by repurposing a mesh reflector from an 8', 10' or 12' big ugly dish with a stacked dipole and a secondary reflector.

Really, you can make these things.

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Rick W9ZD
Currently:10' Winegard Pinacle with AJAk 180; RayDx 10.5; Orbitron Spinclination 8'; Sadoun 6' Steel. Manhattan receivers migrating to Icecrypt. In 1961did video design for the ITT Transportable Earth Station. First home dish was a 10' fiberglass; Boman receiver and a 120 degree lnb.
kd4moj

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Reply with quote  #44 

Quote:
Originally Posted by WellerTip
Never buy an antenna based on a distance it claims..the laws of physics don't bend due to fancy marketing hype nor pretty plastic casings.

Plot your address here: http://www.tvfool.com

It takes into account your terrain and distance from the transmitters.

As kurtz says, the 4251 if you can find or handle it. The Channel Master 1160 was also a V/U beast back in the day. But that was when
channelmaster was made in smithfield nc.


Interesting.... TVFOOL doesn't include the oldest TV station here.

...DOUG
KD4MOJ

 

rikoski

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Reply with quote  #45 
I found a Katherin log periodic at the Dayton hamfest for 20 bucks. It is now my house antenna for Chicago television 35 miles line of sight over Lake Michigan. Built like a "brick outhouse." 

A few years ago, I went to the Friedrichshafen hamfest in Southern Germany. An incredible collection of well built VHF and UHF antennas. Not available here.


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Rick W9ZD
Currently:10' Winegard Pinacle with AJAk 180; RayDx 10.5; Orbitron Spinclination 8'; Sadoun 6' Steel. Manhattan receivers migrating to Icecrypt. In 1961did video design for the ITT Transportable Earth Station. First home dish was a 10' fiberglass; Boman receiver and a 120 degree lnb.
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