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Discussion Starter · #1 ·
I am trying to pick up a signal that is broadcast about 10 miles away. There are some mountain ridges that prevent a straight shot to transmitter. I had a 3017 with no amp and could tune in to most analog channels. The channel came in pretty good for a med. size antenna. By aiming the 3017, I was able to reduce ghosting but it will not lock onto digital channels.


I want to order a antenna but I can't find any good description on what conditions the 4251, 4228, and 4248 are good for. I belive the 4248 has a more narrow range than the 4228, but what about the 4251, is it only for picking up real far away signals, or can it be fine tuned to lock in a close signal with bad multipath problems?


Thanks,

Glenn
 

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Please check out the specifications on the attached URL.

http://www.starkelectronic.com/cmg5.htm


The CM4251 has the most gain (distance/weak signal and narrow beamwidth (multi-path). It also excels in the higher UHF frequencies. Because of its size it, is more expensive to ship and is more difficult to put a rotor on it, but this is clearly the best UHF antenna on the market right now for problem locations ~ whether distance or multi-path. Tom Harms


[This message has been edited by Tom Harms (edited 04-02-2001).]
 

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You will probably need an attenuator though. Using the 4521 to get a station only 10 miles away, holy smokes.


BTW, word is that they no longer make/sell the 4521 so if you want one you better act quick.
 

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Discussion Starter · #4 ·
The 4251 has a gain of 15.6, I read that the ideal db at the receiver is 15db or less. So with some loss in the cable and a weak signal, it should work out just right. I should not need an amp.


The station is 10 miles away, but I think I will have to pick up a reflected signal, so the distance could be twice as far or more. I want an antenna that will allow me to pin point the strongest reflected signal while rejecting the weaker ones, is the 4251 the best for this? If I can't find one locally, would the 4248 with a amp be the best second choice?


Thanks,

Glenn
 

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Quote:
Originally posted by Glenn_L:

The 4251 has a gain of 15.6, I read that the ideal db at the receiver is 15db or less
Glenn,


You're mixing up two different things. The 15.6 dB for the 4251 is "antenna gain", i.e., how well the antenna is at capturing a signal. For the same field strength at a given location, the 4251 will output a signal at its terminals that is 15.6 dB stronger than a simple antenna would.


A dB number is always a ratio between two values.


The 15 dB number for the receiver refers to how much higher the signal needs to be above the noise floor in order to decode the digital signal. For 8VSB, the signal needs to be at least 15 dB stronger than the noise, or the bits in the digital bitstream cannot be reliably received. The noise includes all noise sources such as thermal background noise, the noise generated in the receiver circuitry itself, any interfering signals, etc.


For multipath, with current technology the best you can do is get an antenna with a narrow beamwidth and high front/back ratio. The best you can do is probably the 4251 with the dish section covered with chicken wire, although it sure sounds like overkill for your situation. Whatever you do, do NOT use a preamp; signal strength isn't your problem.


Note the different receivers vary in how well they handle multipath. Perhaps a different receiver might work better.
 

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Discussion Starter · #6 ·
Barry,


Do you know what db range the noise floor can be? best to worst case? I have a dish 6000.


Do you have any more details on the chicken wire? What exactly does it improve? Does it increase the front/back ratio? Is that applied to the back side of the entire dish section? What mesh size for the wire?


If the 4251 is overkill, what would be second best?


Thanks,

Glenn
 

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I doubt the signal to noise ratio is the problem in your area, so don't worry about it. How do the UHF analog signals from Mt. Wilson come in? They aren't snowy, are they? If not, you're getting plenty of signal.


There's someone on this forum that ueses a 4251 with chicken wire for DX'ing (pulling in occasional long-distance TV signals). Yes, the chicken is put on the back of the dish, and improves the front/back ratio. Standard, garden store type chicken wire would help. Without it, the F/B ratio is worse than the 4248 or 4228.


I said "overkill" because it just sounds ridiculous that you'd need a 7' dish antenna to get a signal only 10 miles away. But maybe even it wouldn't work from your location. I haven't gotten my 4248/6000 combination to work yet, either.


The 4228 is a great antenna that isn't very big, but it's not UPSable. The 4248 is almost as good, but is UPSable. But with FedEX shipping just about anything that's not as big a deal (I just got a 500 lb. tablesaw via FedEx frieght from amazon.com!). Either should work better than the UHF portion of the 3017.


Some here have suggested trying the big UHF-only antenna from Radio Shack; they claim with the RS return policy you can always bring it back if it donesn't do the job.
 

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Discussion Starter · #8 ·
Barry,


All 3 of these antenna are available locally. Some UHF channels have snow, most are grainy with ghosts. In VHF, CBS has bad snow on channel 2, but NBC on 4 is only a little grainy with a few wide spaced ghosts.


I'm not so concerned about the price or size of the antenna. I just want to get the one that is going to work best for this location. These 3 antenna have very different shapes and should handle the signals in a different way.


Mt. Wilson is 15.5 miles away. I trig'd the elevation and Mt. Wilson is located 4 degrees vertically from me. I made a adjustable bracket to allow me to tilt the antenna upward, maybe that will help. I can't lock-on to any digital channels now, the signal only goes up to 55% then drops off. I don't think the 3017 is pulling in a strong enough signal.

www.antennaweb.org recommends a large directional with pre-amp. I may call a few installers to see what they say.


What problems are you having with the 4248 in your area?


Glenn
 

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Any idea how these Channel Master antennas compare to the Winegard CA-9095. The 9095 is Winegard's top of the line yagi UHF antenna. I have a Winegard 8200 VHF/UHF antenna (their top of the line VHF/UHF antenna) and CBS is good but not 100% reliable and I am considering what to do. I am 35 miles from Mt Wilson but have 2500' hills 3 miles from me in the way.


Rick
 

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Discussion Starter · #10 ·
After a lot of research, I am going to get the CM 4228 with the 7775 pre-amp. The screen type (4228, 4251) seem to reject multipath better at extreme angles than the yagi's. If that is not enough, then I will get a 4251. One advantage the 4251 has over the others, is that you can probably skip the pre-amp. This will give you a little less noise in signal.


Rick,

The Winegard CA-9095 looks a lot like the CM 4248, I would guess they are about the same specs. Since you are farther away than me, maybe the multipath angles are not as extreme and the 4248 or 9095 might work better for you.


Glenn



[This message has been edited by Glenn_L (edited 04-04-2001).]
 

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Glenn I also live here in Burbank above Glenoaks around Jefferson Elementary School. I've tried a the 9095, 4248, and the 4251. None of them will receive all the digital stations in our location. The best was the 4251, but only slightly better than 9095. I finally settled on the 9095 with a 4800 preamp. If you want to try the 4251, I have one you can test out. They do make fabulous cloths hangers.
 

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Discussion Starter · #12 ·
Mike,


I just tried a Winegard PR-8800 and a CM7775 pre-amp. The 8800 is a 8-bay bowtie that is supposed to be the equivalent to a CM-4228. The 8800 has horizontal reflector elements, where the 4228 has a screen. Unfortunately it did not do any good, with or without the amp. Now I wonder if it really is as good as a 4228? The CM 3017 VHF/UHF antenna that I have picks up better analog UHF channels than the 8800. I can't get digital at all.


I'm located near Buena Vista, above Kenneth. I would like to give your 4251 a try. That was going to be the next antenna to try before giving up. I might try to get a pro antenna installer out here to check out the signal with a spectrum analyzer. Do you get any digital channels? I'd be happy to just get a few at this point.


Glenn
 

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Hi Glenn, Please check your Avscience mailbox. You are only about a 1/2 mile from my place. I'm using a Winegard 9095, 4800 preamp. and channelmaster rotor. I can receive NBC, PBS, and KTLA just fine. I get CBS and ABC with many dropouts. When CBS and ABC in LA are really bad I swing the antenna toward San Diego. Quite often I can't get the station 15 miles away, but the station 120 miles away comes in. I do find that my DST 3000 does bring in the signal better than my DTC-100. I do believe that because of where we live we will never be 100 percent successful with receiving ota signals. Again please check your mailbox or send me your email address.
 

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Hey Mike55:

We spoke a couple of months ago. Unfortunately, I've had a tougher time with my situation than I thought I would, given that I'm I'm only 10 miles from Mt. Wilson! If you recall I'm up in hills of East Glendale. I'm currently using a CM4248 with an AP4800 that I got at Pace per your suggestion. Not having much luck. I'm only receiving channel 43(at 55% strength), but I can't get a steady/locked signal on anything else?!! Analog channel 28 (kcet) comes in without snow but heavily ghosted. Looks like major multipath problem. No luck on KCET-D,or KCBS-D or anything else for that matter. I'm about to give up. So close and yet so far! I'm open to suggestions from anybody.
 

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Discussion Starter · #15 ·
mlabrinos,


I tried the PR-8800, which is Winegards version of the CM-4228. It performed worse than the CM-3017. The 3017 is a vhf/uhf antenna that has a med. range yagi (like the 4248) for uhf. I can not pick up any channels from Mt. Wilson, but I can get ABC ch. 25 and CBS ch. 55 from San Diego. The 3017 has only a 35 mile uhf range but it picks up Mt. Soledad 113 miles away. I am going to give Mike's 4251 a try, if that does not get me any Mt. Wilson channels then I'm going to get a 4248 for the San Diego channels.


Glenn
 

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Glenn,


If you're getting snow on channels from Mt. Wilson, you must be in a very bad spot. If I remmeber there are hills NE of Burbank between you and Mt. Wilson?


'sounds like you're in a similar situation to me. Some folks out alot farther than me have no problem, but I'm too close to a big hill. And I get an analog UHF station 60 miles away better than any of the local stations.


The ironic thing is that it's theoretically possible for a 8VSB receivers to handle just about any amount of multipath, especially the mostly static type that you get from a fixed location. But the receiver needs to be designed for it. This is especially in non-LOS the case where you are, where you may be getting alot of pre-echo; even the 2nd generation chips like those in the 6000 only handle a limited amount.


Fortunately the recievers seem to be getting incrementally better. I've heard of testing with the latest Broadcom chip that are prety impressive. I don't know if any STBs are using this chip yet. But at least there is hope that future designs and Moore's Law will make this issue easier to handle.


BTW, this is different than OFDM, where the modulation itself has a built-in tolerance to multipath, but only for a specific amount. It basically uses up a percentage of the bandwidth for a "guard interval". For short-duration multipath of less than the guard interval time, it's very easy to design a receiver that's immune to it. But if there's signicant multipath outside the guard interval time, you're basically toast - it would be very difficult to squeeze long duration multipath cancellation into the architecture for a OFDM receiver.

 

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To my fellow hill people here in the Verdugo Hills (GlennL and Mlabrinos). I have gone thru using 4248s,4251s, 9095s, 4700. 4800, and the Silversensor. I believe that antennas are not that inportant. The bigger issue is mast height and a rotor to point the antenna properly. I really believe you can take a coat hanger and if you can can get it high enough, and point it in the right direction it would work just fine as an antenna. I took my silversensor, dtc 100, and small monitor up on the roof and went snooping for signal. I tried placing the sensor on top of a 20 pole and went around my roof. What it did for me was it told me there was some signal up that I could receive and some that I couldn't. The antenna's elevation was the most inportant factor. With PBS at 3 feet above the roof the signal strength 3 to 6, at 20 feet if was 65. It was the same antenna, same dtc 100, the only difference was the elevation.
 
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