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Jointennas

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Old 01-24-2007, 08:06 AM   #1
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Default Jointennas

What can you guys tell me about Jointennas? I'm thinking about getting one for my setup since the station where I work will begin multi-casting this summer.

My setup: Winegard 9032 in attic
Radio Shack pre-amp
100 ft. run of RG-6 to preamp from antenna
40 ft. run each of RG-6 from preamp to Samsung and Sony HDTV's (2Ghz splitter between pre-amp and TV's).
2nd antenna would be Radio Shack U-75R
ZipCode 55060
I need to get KEYC-DT on UHF Channel 38. Given the fact that I NEED a preamp to get the stations that I do (I get all but one of the major Twin Cities stations - tpt-dt 16), will adding a 2nd antenna and jointenna weaken or swallow the TC stations I currently get? If a jointenna doesn't work for me, do they typically take those back, or are you stuck with them since they basically have to be customized?

Thanks!

Dan
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Old 01-24-2007, 08:29 AM   #2
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have been experimenting alot with jointennas lately.

you would order the jointenna for ch 38. the ch 38 jointenna will attenuate ch 35 some. the bandwidth of the unit attenuates 5 channels either side of center channel.

KARE-DT 11.1 NBC MINNEAPOLIS MN 2° 68.7 ch35

amplifying both antennas equally seems to lessen the attenuation affect from my experiences.

the jointenna is a special order with about a 3 week leadtime. cm0582-2 ch 38.

http://www.warrenelectronics.com/ant...Jointennas.htm

doubt they will take back a special ordered item.

are you sure a Radio Shack U-75R will be adequate ...would rather try an antennas direct 43xg instead...you are using a cm 9032 for the others.
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Old 01-24-2007, 08:40 PM   #3
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Well, the U-75R is what I have right now in my possession. I used it to get the Twin Cities stations, but it didn't handle multipath that well, so I got the Winegard 9032, and I've been happy with the stability of the signals since then, although I lost a few channels because it was more directional than the u-75r. Basically, I'm thinking about putting a splitter between the mast-mounted portion of the preamp and the antenna. I get the impression from your post that you're thinking this setup should have two preamps - one for each antenna. Am I correct in thinking that? I'd prefer just one pre-amp since this project's cost seems to keep creeping up.
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Old 01-24-2007, 09:49 PM   #4
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Quote:
Basically, I'm thinking about putting a splitter between the mast-mounted portion of the preamp and the antenna. I get the impression from your post that you're thinking this setup should have two preamps - one for each antenna.
What are you trying to accomplish here???

you need to order the ch 38 jointenna to properly combine the 2 antennas.

the ch 38 antenna goes into the "ch 38 input" of the jointenna

the cm 9032 into the all channel input of the jointenna

amplify the "to tv" output coming out of the jointenna.

if this setup attenuates ch 35 more than your liking, amplifing both antennas before going into the jointenna would improve the situation.
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Old 01-26-2007, 07:52 PM   #5
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Quote:
Originally Posted by Rick0725
If this setup attenuates ch 35 more than your liking, amplifing both antennas before going into the jointenna would improve the situation.
That's the key point!
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Old 01-26-2007, 08:21 PM   #6
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Honestly? Dump the Radio Shack preamp and get a good low-noise preamp like a Channel Master Titan 7777 or a Winegard AP8275. I am going to bet that the station that you are looking for is being buried in the inherent noise of the Radio Shack preamp.
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Old 01-27-2007, 09:59 AM   #7
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Pardon my ignorance, but the Radio Shack boasts a 30db gain, while the CM 7777 maxes out about 5db less than that. Is it possible that I'd get even fewer stations since I'm already in fringe reception territory? The other pain is that there are no local vendors for the CM 7777, so if it gains me nothing, I have to pay to ship it back + restocking... but I really WOULD like to try it out. I have a friend that is an RF engineer, and he uses the same Radio Shack preamp and has the same Winegard 9032 antenna. The only difference is that he lives 10-15 miles farther out from the towers and doesn't get quite the same number of stations.
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Old 01-27-2007, 10:21 AM   #8
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Quote:
Originally Posted by DRuiter
Pardon my ignorance, but the Radio Shack boasts a 30db gain, while the CM 7777 maxes out about 5db less than that. Is it possible that I'd get even fewer stations since I'm already in fringe reception territory? The other pain is that there are no local vendors for the CM 7777, so if it gains me nothing, I have to pay to ship it back + restocking... but I really WOULD like to try it out. I have a friend that is an RF engineer, and he uses the same Radio Shack preamp and has the same Winegard 9032 antenna. The only difference is that he lives 10-15 miles farther out from the towers and doesn't get quite the same number of stations.
If the Radio Shack preamp is nosier, which I believe it is, it will amplify that noise even more. Which is a very bad thing for clean reception. I have listened to Tiger and the others on here and have NEVER bee steered wrong. If I were you, I'd give it a try.

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Old 01-27-2007, 10:47 AM   #9
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Does anyone have noise figures for the Radio Shack preamp? I see the 7777 has 2.0db of noise.
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Old 01-27-2007, 10:51 AM   #10
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If memory serves me correct, that's actually made by Antennas Direct... their 30db gain model says < 4db of noise on UHF... vs. the 7777's claim of 2db
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Old 01-27-2007, 11:01 AM   #11
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Gain is not the issue here: noise floor is, and the Radio Shack amp is noisy as hell. A noisy preamp will bury digital TV stations as surely as an ineffective antenna will. Remember that the quality of a digital signal is measured in signal-to-noise ratio, and your tuner reads that signal-to-noise ratio in order to determine if it has enough quality to reliably display a picture. The Radio Shack amp has better than THREE TIMES as much inherent noise as the Channel Master Titan 7777. Couple that with a weak fringe area signal, and you have effectively buried the signal in the noise of the preamp. With analog signals, we were able to tolerate that noise because the preamp had enough gain to bypass the first stage of a TV set's tuner. With a digital signal, signal strengths are about 8 DB lower than analog, and what passed for an acceptable signal-to-noise ratio in analog becomes a problem in digital. I have proved this one myself on a number of occasions in weak signal areas: noisy preamps are digital signal killers! If you change your preamp, and get your antenna outdoors, I can almost guarantee you a good signal on KARE-DT!
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Old 01-27-2007, 11:01 AM   #12
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The cm7777 preamp is a great performer in the boonies.

simply explained without writing a book

Low noise preamplifiers are designed to improve the signal to noise ratio of your system. This means increasing signal levels, but with minimal noise contribution.

High noise preamplifers also increase signal levels, but they also increase noise, which can degrade picture quality on weak signals. Ideally you would need a high signal to noise ratio (high signal/low noise) in order to improve weak signals. thus the specs of the cm7777.

-Preamp noise figure should be 2dB or less.
-Preamp voltage gain should be around 20dB for most applications. Too much gain (25dB+) can sometimes lead to overload problems.
-Lowish gain (12-14dB) preamps will likely also need another line amp, further down the line to compensate for the signal voltage loss.
-Strong signal handling ability is important.
-Look at the signal handling specification.

The radio shack preamps are in the 5-6 db noise range and to honest 30 db gain is a bit much for most applications.

Buy 2 cm7777's. One for yourself and the other for your RF engineer buddy.

Sorry tigger we were typing at the same time.
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Old 01-27-2007, 11:36 AM   #13
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found this
Attached Images
File Type: gif AmplifierTable (Medium).gif (12.1 KB, 69 views)
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Old 01-27-2007, 11:43 AM   #14
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* measured at channel 30
** +13V=FM trap in, -13V=FM trap out.
*** This is the longest RG-6 cable that satisfies the rule “The gain should equal the cable loss plus an extra 10 dB” at channel 30, assuming the power injector is at the TV.

The “Cable length” from the above table is a telling statistic. It makes clear that there is generally no good reason to buy a Radio Shack amplifier.
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Old 01-27-2007, 11:49 AM   #15
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Rick, I was looking for that same chart that you posted: I couldn't remember where I had seen it. As usual, we are on the same page about this stuff! Now tell him to get his antenna out of the attic! LOL
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