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Discussion Starter · #1 ·
This (unfortunately) is no joke... here's my story and then a plea for help.


Last month I moved to a new home outside of Sacramento. Shortly after I moved in, I installed a CM 4228, CM 7775 pre-amp, and CM rotator on my roof. The results were excellent - consistent 100% signal strength from my DST-3000 for all 4 Sacramento stations (which are about 40mi. away). I even occasionally was able to receive a signal from some of the SF stations approx. 90mi away! Oh happy days...


This all worked great until about 2 weeks ago when it rained. On that Sunday, I started seeing break-ups for the first time. On Monday, pretty much no reception. It was raining, but it didn't seem like that should totally wipe out my signal. Right?


On Tuesday, in between the raindrops, I decided to go up to my (slippery wood shingle) roof to check things out. Well, when I took the pre-amp off the mast, I noticed it seemed "heavy". Sure enough, it was totally filled with water! The reason: I mounted it upside down, with the connections facing the sky. Needless to say, that was the cause of my problems!


I tried simply hand-drying the pre-amp and re-installing, but reception was flaky (lots of "spiking"). So, for a short-term fix, I removed the pre-amp altogether. For the most part, this has worked - I stiill typically get a 100% reading on all 4 Sac stations.


FYI, I have a 75ft RG-6 coax run to the power supply. And for now I have the 3ft RG-6 cable from the antenna (that used to be connected to the pre-amp) connected to the 75ft coax run with one of those cheap "connectors" that you'd find in a cable TV wall outlet.


Sorry for the long-winded story but I hope it gave some a chuckle!


Unfortunately, the last few days I've noticed some break-ups at certain times of the day (mid-afternoon and early evening). The signal readings on the DST-3000 are still high but they are "spiking" between 72 and 93 or so. I had thought that would still be strong enough to get a perfect signal but I guess not.


What do you think of my reception issue? Does my 40mi distance and 75ft coax run mean I really need a pre-amp? Is it possible the old pre-amp is OK now that it should be fully "dried out" or do I need to buy a new one? Or could the cheap Coax "connector" be hurting things? If I eliminate the 3-ft coax altogether and connect the 75ft run right to the balun would that make a difference?


Thanks for the help!

SteveD (somewhat embarrased to be disclosing this!)
 

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Steve,


Sounds like you need the preamp for more reliable reception.If you decide you need a new one,I have a 7775 I'm not using,and would like to keep the power supply.If you need it,let me know.


Eliminating the barrel connector probably won't make any difference unless you have some moisture in the connection.


Greg B
 

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If you want to keep your soggy preamp you could take it apart and get out the hair drier! (Seriously...that's how TV engineers restore cameras and other field gear that gets wet.)


Then seal it up with GE Silicone II. You should be using waterproof F-connectors. Radio Shack has them along with a crimping tool that's especially for weatherproof ones. It wouldn't hurt to then seal the connectors with silicone once they're installed. That's what I do...it not only keeps out moisture, it also slows-down corrosion if the atmosphere has a lot of saline in it as it does here.


Regarding your reception issues, there are things other than low signal strength that can adversely affect DTV reception that could cause the periodic downward spikes you are observing: multipath reception (which causes ghosting in analog reception), impulse noise interference (which is most noticable on VHF but which can show up on lower UHF channels as well) and even corrupted data being transmitted by the station can cause this phenomenon.


Your so-called "signal strength" meter is actually not measuring signal strength...its really attempting to quantify signal quality by looking at the bit error rate of the data being decoded, and bit error rate, or BER can become excessive due to any combination of low signal strength that therefore fluctuates, severe dynamic multipath interference or impulse noise interference.


While we still have analog NTSC signals you can look at them for some indication of the absence or presence of these conditions if the NTSC and ATSC signals are coming from the same location.


Fluctuating, marginal signal strength might manifest itself as slight to severe bursts of snow in an analog picture. Dynamic multipath looks like ghosts that change in severity and move rather than remaining stationary on an analog image. And impulse noise looks like litlte black and white dots all over an analog picture. You will never see any of this on a digital picture. Instead, you'll see the image pixelate or freeze and the sound may be interupted by chirps and/or silence.
 

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Discussion Starter · #4 ·
Thanks to both Greg and David for your replies... a few comments.


Greg: I would be interested in your pre-amp, and my power supply should still be good... send me an e-mail ([email protected]) so that we can discuss price, mail, etc.


Curious: are you saying I need a pre-amp for a specific reason (the long coax run or just the behavior since I removed it)?


David: good advice regarding "sealing" the connectors. As a matter of fact, I bought a 3ft "gold" RG-6 coax cable from Radio Shack for use from the balun to the pre-amp, and the cable came loose from the connector when I was re-wiring. The silicone and crimping tool sounds like a good idea.


As for other causes of picture loss: well, I have 3 analog stations (31, 40, 58) that I've looked at through my TV tuner with my antenna set-up. All look rock solid with no ghosting or snow. So I don't think I have a big problem with the issues you raise. But who knows.


Thanks again, and if you have any more comments/suggestions I'm all ears!

SteveD
 

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Before you seal it, I good idea is to wash it out with isopropal alcohol to remove any saline and corrosion that may cause shorts or degrading materials.

Then dry it out with the hair dryer.


Now you can seal it with silicone.
 

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Yet another case of someone NOT reading the directions....


Take the case off. Give the board and mounting plate a good soak in distilled water. After that, gently dry it with a hair dryer (not too close, don't get things too hot). After that, leave in a low-humidity location for a couple of days to make sure it really is dried out.


Despite what others have said, I'd advise NOT sealing the case to the mounting plate. The reason is that you won't get a 100% hermetic seal. Thus, some humidity will end up getting inside. This normally has a way of getting out throug the unsealed seam, provided it is mounted correctly.


If you don't re-install the preamp, be sure to cover the barrel connector with waterproofing tape (can get a Radio Shack). You don't want moisture getting into the coax.
 
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