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Discussion Starter · #1 ·
I live in Bloomington IN which is 60 miles from Indianapolis towers and 60 miles from Louisville towers. I just bought a CM4228 and CM7777 in hopes of being able to get HD from either of the two cities. Surprise! - I get pretty darn good reception from both. So, rather than choosing which way to point the antenna, I'm considering a system to get both.


I've had rotors in the past, they're slow and somewhat prone to failure.


I know I could buy another CM4228 / CM777 and run two sets of coax down the mast, then switch between the two.


Since the stations are 60 miles and 100 degrees apart, is there any chance I could put a second CM4228 on the mast at a 100 degree offset and simply connect the two antennas with twin lead, then run one coax to the preamp and down the mast? I know, it sounds like a multipath nightmare, but I'm hoping the separation and distance will minimize the problems.


Thought? Thanks.


Jerry
 

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Another solution would be to use a STB with two antenna inputs. I have a MIT MDR-200 OTA STB which has two antenna inputs. It allows you to scan each antenna separately. The MIT MDR-200 also has a firewire connection which allows hookup to a HD VCR, which is why I got it. I do not use the second antenna input but I have heard from others that do and like it. It is available at digitalconnection.com.


Rick R
 

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Jerry,


Combining the two CM4228 antennas should work. I would suggest using 12 gauge solid copper wire to connect the two antennas together and not a twin lead wire. Be sure to attach grounding clamps and another 12 gauge wire to the antenna screens and then run a ground wire from the lower antenna to a grounding post.


If you have a newer 3rd generation or higher digital receiver you shouldn't have a problem with multipath. If you are planning to receive analog signals, then multipath would be a problem.


Good luck,


Joel
 

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"If you have a newer 3rd generation or higher digital receiver you shouldn't have a problem with multipath. "


Since when wasn't multipath a problem for digital receivers? I'm sure quite a few of the OTA using members here would beg to differ on that opinion.
 

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I live about 50 miles from two towers in opposite directions (Greensboro and Raleigh, NC). I've got two UHF only radio shack $21.95 antennas pointed in opposite directions on a 40' mast. I use Twin Lead from both antennas with equal distance leads into a channel master amp. I'm using HD tivo and 3 other HDTV tuner's throughout my house that get perfect reception from both antennas.

I hooked up a friend of mine with the same hookup and he's got about a 25' mast. Gets just about perfect reception also.
 

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Jfath


Your bigger issue might be co-channel interference. For instance, there's an analog 8 in Indy and a digital 8 in Louisville. And the opposite with channel 21 (if I read the charts correctly). Add in skip from adjacent markets and the line loss of the splitter, itself, and you could find that you don't do well with either market on all channels as you would with a rotor. Fortunatley, swapping a combiner with a simple A/B switch isn't terribly expensive and works faster than a rotor.


Doc
 

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Discussion Starter · #7 ·
Thanks for all the help and information.


Very good point regarding fequencies occupied in both markets.


About using an A/B switch - my (limited) understanding is that it's much better to have the pre-amp mounted as close to the antenna as possible without splitters in the path. Since I'm 60 miles out, this is probably especially true in my case. If so, this leaves me with the choice of either a rotor, or another antenna/pre-amp/downlead. Since a rotor would allow me to do some fine tuning and give better analog results, that solution starts to sound more appealing.


Thanks again.


Jerry
 

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To effectively couple two highly directional antennas pointed 100 degrees apart without fortuitous technical parameters takes luck. That doesn't mean it can't be done. It just means there is little point in pontificating over it. You try it, using a simple hybrid antenna combiner (cheap part) but if it gets you unreliable performance on any important channel, then you go with two seperate antenna leads instead.


Ground only the antenna masts, according to NEC "code", if possible, which means with 10 gauge copper, 8 gauge aluminum or 17 gauge copper clad steel wire, and ground the coax outer conductors at the point at which they enter the building. That grounding is for safety, not for technical performance.
 

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AntAltMike


If he's stacking on the same mast, how far apart should they be? (I figure you know and I'd have to dig out my ARRL Antenna Book)


Doc
 

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At 100 degrees, there should be no discernible interaction between the antennas, so calculating minimum spacing is not necessary. Also, since they are UHF, you probably couldn't mount them close enough together to mess each other up because the wavelengths are so short. I don't think the reflector screens would even let the active elements get too close to one another.
 

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Quote:
Originally Posted by AntAltMike
To effectively couple two highly directional antennas pointed 100 degrees apart without fortuitous technical parameters takes luck. That doesn't mean it can't be done. It just means there is little point in pontificating over it. You try it, using a simple hybrid antenna combiner (cheap part) but if it gets you unreliable performance on any important channel, then you go with two seperate antenna leads instead.

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I have a CM 4228 and was picking up 2 stations that I wanted off the back of the antenna – transmitter was 10 miles away. The front was facing towards the main stations I wanted and was 30 miles away. However using the back of the antenna was proving unreliable as the signal would come and go. So I bought a cheap Radio Shack UHF antenna and used a combiner up by the mast to join both cables (inside an upside down water bottle BTW). It didn’t help at all. The Radio Shack on its own was fine when I disconnected the cable from the CM 4228.


So I added a 6db attenuator to the CM 4228 cable to reduce that bad backside signal, without hopefully killing the main signal, and it worked great!


Guess I got lucky ‘cos people told me that I needed another A-B box (I already have one to switch between cable and OTA)


Peter
 
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