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Old 8-Nov-2017, 4:41 PM   #1
twaw
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Join Date: Oct 2015
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Why is my bearing to towers off so much now?

About a year ago I installed a Winegard HD7697P Hi/UHF 131, 25' height, with a ChannelMaster 30db preamp, and a 120' cable run to my house. Bearing to towers is supposed to be 184 degrees true north, I ended up at about 195 true north... there's a hill in my path.

Going direct to the TV I was fine, but then I got a 4 tuner Tablo which is a noisy signal killer, even though it has a dist amp in it... and I couldn't get good signal out of the Tablo. So I tried an old radio shack 0-18db amp I had, inside the house just before the Tablo, and was getting about 70% signal. I know that's not necessarily the "best" way since it adds noise, but hey... it worked. So all was good... installation was done, and it worked through heavy storms all last winter, high winds, etc.

Then about a month ago I lost signal. Found Ok signal of about 30% at bearing 211 on a clear day. A few days later lost signal on a cloudy day, searched for a signal again and got it at 255 degrees !??? Pretty big difference. Did further trouble shooitng and took the old RS amp out of the path, and bingo... I had OK signal again, about 30%, rain or shine. So the RS amp had died, I guess, which explained my sudden loss of signal. So now my system is working, but lower signal than I had a year ago.

Before I start fooling around with everything again, I thought I'd try to learn exactly what's going on here. Is a bearing change of 70 degrees vs. true bearing to tower an unusually large difference? Is it bouncing off the hill? Leaves are pretty much down here in the Northeast, but that was the case a year ago during installation, too.

Any suggestions as to what to try next? I think I have a few options:
1. Try going back to 195 bearing and search for better signals. Will definitely try that, but I did that a year ago during installation, and don't expect much change.
1. Raise mast up another 4-5'... that's the highest my Rohn 30 will go. I had avoided that during initial installation because I was concerned about high winds, and I have it guyed down at 25'. But I could raise it... I left enough extra cable, and with a year of no wind issues under my belt I'm less concerned about high winds... the guys are doing their job well. But will a mere 4' make a big difference? I doubt it, the hills in my path are pretty high, I can't remember exactly but I think they're several hundred feet high.
2. Replace the old RS amp inside with a better, low noise one... maybe the Skywalker Signature Series SKY38323 25dB Amplifier? Seems like a no brainer... for $25 it should get me back to my 70% signal I had before, I think...? Or is there a better one? I looked a bit at the Solid Signal Televes unit for $80, claims to be 2.5 db S/N... but there are a few things about it I don't like, and I'm not sure that spec is accurate.
3. Replace the channel master 7777 with a higher gain preamp... maybe 50db? Dont' know which models to look at yet, and it's more work to replace, but that's another option.

Here's my report. Many thanks!
http://www.tvfool.com/?option=com_wr...60ed3ad79b6b1c

Last edited by twaw; 8-Nov-2017 at 4:52 PM.
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Old 8-Nov-2017, 8:20 PM   #2
ADTech
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Do NOT go to a higher amount of amplification, you likely have too much as it is. More amplification rarely helps and, more often then not, destroys reception due to overloading.

If you are immediately behind a hill, whatever signals make it to your antenna are going to be some combination of diffraction over or around the hill and reflection off any adjacent hills. Reception in these types of locations is pretty much impossible to predict reliably.
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Old 14-Nov-2017, 6:14 PM   #3
twaw
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Thanks for the reply! It's not working again so I have to go back to the drawing board. Any suggestions appreciated...

I hear you on too much amplification, but if that's the case I don't understand why I have no issues when going direct to the TV, but when I go thru the Tablo I get nothing. Do you mean that my 30db preamp is probably adding too much noise and the Tablo with it's 4 way dist amp is adding even more? If so, any suggestion on the correct amount of amplification, or which unit?

If I simply unplug the power inserter on the CM 7777 preamp on the mast, will that give me an indication of whether I have too much amplification? When I do that, I get nothing even when bypassing the tablo, and re-aiming doesn't help at all. I know it's a better test to take it out of the path completely, but I'm getting on in years and trying to avoid climbing up the 25' ladder again, if I can.

Only other thing I can think of is a bad F connection...? I've checked them all except on the preamp at the top of the mast, they seem good, I used electrical tape and then covered with silicone, I'm using a single run of RG-6 through a conduit out to a single ground block 5' up the mast, then another coax run up to the preamp, then 1' coax to antenna... all those at the top of the mast are booted and siliconed, too. If it wasn't such a PITA I'd try a new cable run. Guess I could maybe test the coax with a voltmeter, but I'm not sure exactly what voltage I shoudl see, given the preamp is still in line at the top of the mast.

Anyway, I re-aimed the antenna back to 195 degrees, going direct to the TV and bypassing the Tablo, it works and I get my channels at 50-70% signal (as measured by the "Signal Meter" on my TV). Still nada on the Tablo... and I suspect the Tablo's not fried because when it's in-line and I re-aim the antenna (255 on clear day, 195 when overcast), I can get it to work usually. But I've also contacted Tablo to see if there's a solution on their end. All I know is it worked great for a year before the old RS var gain amp died... but the fact that it worked at all surprised me too, since it's the "wrong way" to do it.

Thanks for the help... you're awesome!

Last edited by twaw; 14-Nov-2017 at 6:23 PM.
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Old 14-Nov-2017, 7:08 PM   #4
ADTech
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Quote:
Do you mean that my 30db preamp is probably adding too much noise and the Tablo with it's 4 way dist amp is adding even more?
Think about what would happen if you went to a rock concert, sat in the first row, and had a hearing aid turned all the way up...

You have to remove the amp COMPLETELY. Leaving it in circuit without power turns it into a 30 dB attenuator.

Bypass the amp completely, remove it's power inserter and see if the Tablo works. If it does, you have your answer (too much amplification). You have calculated signals that are quite strong and shouldn't be amplified in the first place.

A good rule of thumb is to add up your cumulative insertion losses (coax & splitters) and add -5-8 dB. Pick the preamp that comes closest or just above that number if the use of a pre-amp is actually called for. Do not fall into the "more better" trap.
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Last edited by ADTech; 14-Nov-2017 at 7:10 PM.
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Old 15-Nov-2017, 6:33 PM   #5
twaw
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Great, thanks for the explanation. I really appreciate it!
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Old 21-Nov-2017, 9:17 PM   #6
twaw
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AD Tech, you are right on the money... I just took the preamp out of the signal path, so it's jsut the antenna right into the tablo, and it works great on all channels. And when connected directly to my TV, the stations that were at 50-70% are now all at 100%. It's a clear day now, so I'll measure again when we have a storm.
Thanks!

In case this may help someone later, AD Tech was right not only on all counts, but especially on the point about adding up your losses. That gave me the spefici info I needed... I calculated my losses using this calculator... http://otadtv.com/cables/index.html Remember to calculate your connectors (at .5 db per connector). In my case I had a total of 9.6 db loss. My antenna has 10-12db gain according to the specs. And that worked, although as AD Tech said, I should add a preamp of about 5-8db. I don't have one of that rating right now, so I'll see how it goes, and add one if I need it.
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Old 22-Nov-2017, 12:22 AM   #7
ADTech
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Actually, it's (total estimated insertion loss) + (5 to 8 dB) = approximate desired gain of amp for picking the ideal pre-amp gain. Realistically, just pick one with 15-20 dB gain, unless you have a very extensive distribution network, and make it easy on yourself.
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