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Discussion Starter · #1 ·
I recently installed a Mits HD SR-5 STB and am using a RS Cat.# 15-2162 Yagi antenna, 75 ft RG6 QS in series with a RS VHF/UHF Adjustable Preamp Cat.# 15-1108 (states it boosts signal by up to 26db) in my attic. Signal lock is great at times and lousy at others. When the signal locking is bad (tiling), the strength meter is at anywhere between 30-50. Also, when I get a good lock, the signal strength meter is anywhere from 72-100. Either way, the signal strength meter bar seems to "bounce" rapidly +/- 10.


Questions:


Is the rapid signal meter bounce normal?


Do weather "disturbances" (rain/storms) impact signal strength?


If it's hardware related, will a better(?) preamp make a difference? I was thinking about trying the CM 7775.



Thanks in advance to all who reply.



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M. Maylock
 

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Rapidly varying signal levels is often a sign of multipath interference. Thats a tough one to fix especially if it is coming from a moving source like an airplane.


I'd try moving the antenna around your attic a bit.


Did you try without the amp first? I don't know your specifics, but try without the amp to make sure you're not overdriving the signal.


As a last resort try on the roof.


As you can see, it's mostly trial and error with this stuff.


Josh
 

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Discussion Starter · #3 ·
Thanx for the quick reply Josh. Your right, trial and error is the process. Funny thing, I pre-cut 75' ft of coax for the run to the attic. After I got it positioned, I removed the excess cable (+/- 20ft.) After that, the signal strength was worse. I put a barrel connector in line and it went back to the better reception level. Go figure.


BTW With the amp off, the signal level is very low (0-15). Definately need it. I just caught the thread on the 7775 vs. 7777 debate. I'm still not sure if a CM 7775 will be better than the RS one.


Back to the dart/drawing board.


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M. Maylock
 

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Discussion Starter · #4 ·
Oops!

Said: "After that, the signal strength was worse. I put a barrel connector in line and it went back to the better reception level."


Meant to say: "After that, the signal strength was worse. I replaced the missing cable length and it went back to the better reception level."


Duh.


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M. Maylock
 

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Quote:
Originally posted by M. Maylock:
I replaced the missing cable length and it went back to the better reception level.
That suggests that the signal is overdriving your receiver's front end. The extra length acted as an attenuator. And, when the tiling is particularly bad, the signal is likely particularly stronger than usual. First remove the pre-amp completely - it might not be necessary. If that makes things worse, then reconnect it and play with the level control on the power inserter - it can attenuate 10 dB, and maybe it's set too high. Also, though it shouldn't make any difference on the UHF band, try changing the switch position of the FM trap in case there's interaction anyway. If the gain's at its lowest, try one of the cheap RatShack variable attenuators (15-578; $6.49) so you can "dial down" the signal level further.
 

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Quote:
Originally posted by M. Maylock:


...............................

Questions:


Is the rapid signal meter bounce normal?


Do weather "disturbances" (rain/storms) impact signal strength?


If it's hardware related, will a better(?) preamp make a difference? I was thinking about trying the CM 7775.

..........................



As already mentioned, the rapid movement is often a sign of multipath.

It might also be due to intermittent overload.


Weather should have negligible effect, unless you are far from the station.

Then the effect can mean the difference between great reception and no reception.


But rain can cause problems even close in with multipath. This problem is present even after rain stops: The wet ground drastically can change the multipath signal strengths and directions, depending on your terrain. I have to reaim my antennas during and after a rain storm.


A better preamp won't likely help with your problem if it is multipath, but

could if you have overload, or very weak signals.
 

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I tried the RS preamps with no luck at all. The CM 7775 (UHF only) did very much better and I am using it now.


Several posters on the forum have said that how NOISY the preamp is can be a very significant factor, and that no preamp can often be better than a noisy one.


 

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Discussion Starter · #8 ·
Thanks to all who offered help or sugeestions. Here's a new twist: Today it's Sunny, Cold (42), and very windy. I was checking signal strength of my digital channels in preparation of tonights PBS broadcast of 'NOVA: Cracking The Code Of Life' and they all are a solid 100. No bounce, just a solid 100. I haven't moved the attenna in days yet the signal variance continues to stump me. The only variables that I'm aware of in my situation are weather or broadcast signal strength. Do stations vary their power levels? If so, why?


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M. Maylock
 

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M Maylock,


Some of your signal variations could be due to weather conditions causing

varying amounts of atmospheric reflections. This can be due to wind, cloud cover etc. This would occur mainly if you are at a good distance and do not have a line of sight signal. I get best reception from my 60 mile away UHF station when there is a solid heavy cloud cover that is not too low, and it is not raining.


Ionosphere bounce, prevalent in the summer, can also cause distant stations to come in and interfere, causing meter fluctuations. Here in the Boston area when channel 30 was at low power, I used to lose it at times due to channel 30 from Connecticut, way over the horizon.


Wind can also affect outdoor antennas, and only a few inches of movement affects signal readings, in multipath areas.


Stations could lose power due to a tube failure, etc, and use a lower power at times till they get it fixed.


Finally, and this is pure speculation on my part, I think things like snow cover at the transmitter could affect the signal tilt angle, and thus the signal levels reaching distant viewers.

 

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Discussion Starter · #10 ·
Thanks jhe. I think your right. I guess as a self-imposed "test pilot" for DTV, I'm beginning to relate to the dilemmas that most are facing with OTA DTV. If it's not an STB problem, it's OTA reception issues. All the expensive gear and now I have to count on the weather! Who knew. Funny, I just heard somewhere that only 1% of the U.S. population is watching DTV. I wonder how many are having reception problems? Does anyone think there will be a change in the way the signal is broadcast or will they just boost the signal transmission strength? Quick question. What's the story with cable companies? Are they subject to the same timeframe?







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M. Maylock
 
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