One channel issue, high VHF

[MikeBear]

Originally Posted by rabbit73

Which 7777 do you have, the old one with separate inputs for VHF and UHF, or the new 7777 with one antenna input?

Are you talking about signal strength or SNR on the TiVo?

First it was the trees, and now a house?

The trees are 85-90ft tall. I know this for a fact, as I dropped some of them (to clear satellite arc) a few years ago, and measured them once they were on the ground. That way I knew what I'd deal with on all the rest that are left. There's NO WAY I can get my antennas above them. I will not go to the expense and trouble of installing a tower or mast that tall. My wife lets me get away with murder (I also have multiple KU and C-band sat dishes, as I am an FTA person, and post at SatelliteGuys) but she'd never allow a 100ft tower.

I have the NEW CM7777, with a single VHF/UHF input.

Yes, I mean SNR on the Tivo. As luck would have it, I was in such a hurry to swap my CM7777 back in, this time I totally forgot to write down the LG tv's signal and quality numbers just before. They've always been about 5% higher than the Tivo.

Yep, the house next to me has a HIP roof, and I was trying to eye-ball the height of it's peak compared to the height of my VHF antenna. That's not easy to do, due to the thickness of the trees right now. But I am now convinced that the house is at least a couple feet taller at the peak (than my antenna). The antenna actually aims at a bearing that's in front of the peak, but I still think the roof height might be problematical.

The taller mast I will be installing will definitely clear his roof.

I'll bet those Tin Lee pre-amps are real pricy? I sent them and email two weeks ago, and still haven't received any reply at all.

[rabbit73]

There's NO WAY I can get my antennas above them.

Understood. Then what you are left with is small increments of improvement like modifications to your yagi that I see on DHC and clearing the roof.

Stupid question: could a CH 12 antenna be mounted in a tree?

If your CH 12 yagi uses a balun, would reducing the balun loss help? When I was doing a mod on a 4-bay antenna for CH 15, I tried about 20 different baluns and found the difference between the best and the worst was about 5 dB. They were all ferrite core baluns, but I could have made a half-wave coaxial balun with even lower loss.

Have you tried looking at the green signal lines in a satellite view of your location. I was able to make good suggestions to mulliganman for the location of his C2V so that it would clear his neighbor's roof.

The antenna actually aims at a bearing that's in front of the peak, but I still think the roof height might be problematical.

Kevin couldn't get the signals he wanted through the trees with his antenna aimed at the correct azimuth as you see in this photo. But when he aimed the antenna to the left where he is looking, he received some signals that came around the trees by diffraction.



http://www.avsforum.com/forum/25-hdt...l#post17280909

We tried clocking the antenna at as many discrete positions as we had time for, with the rapidly fading light last night. We let Media Center run through the signal strength loop each time we moved the antenna. The best overall reception seemed to be pointing at the only real open spot out of my neighborhood, or about 300°. As a refresher I was expecting to receive the strong RI stations @ 41° and the weaker Boston stations at 28-29° while pointed at ~32°. Well, how about 300?

http://www.avsforum.com/forum/25-hdt...l#post17297708

Cut down two trees and aggressively limbed the big white pine. I played the aim-game again with the laptop on the roof. I ended up at about 50 degrees which is almost exactly where the old antenna was aimed. Seems like the best overall trade off. I get a Boston CBS, ABC and FOX. And I get the off axis RI CW and RI ION. Boston 38 is intermittent but all of this is better than the 300 degree aim I said I was using earlier.

[MikeBear]

Originally Posted by rabbit73

Understood. Then what you are left with is small increments of improvement like modifications of your yagi that I see on DHC and clearing the roof.

Stupid question: could a CH 12 antenna be mounted in a tree?

If your CH 12 yagi uses a balun, would reducing the balun loss help? When I was doing a mod on a 4-bay antenna for CH 15, I tried about 20 different baluns and found the difference between the best and the worst was about 5 dB. They were all ferrite core baluns, but I could have made a half-wave coaxial balun with even lower loss.

Have you tried looking at the green signal lines in a satellite view of your location. I was able to make good suggestions to mulliganman for the location of his C2V so that it would clear his neighbor's roof.

No, the trees aren't large enough to be stable at full height for mounting an antenna, even supposing I had a way to climb up there that didn't cost a fortune. They are tall trees, tight-together, but sway too much up there in the breeze. Even if I managed to do this, there's more trees on the other side of my neighbors lot... Our lots are 250ft wide. I'd also need at least 300' of coax for this option.

Yes, the antenna uses a Winegard TV-2900 balun right now. I'm aware there are many other choices, but I'm not sure which ones would be better. Baring buying a bunch at random and trying them, I'm still limited at the moment in dropping the mast to try balun after balun. That's very hard on my muscles, as I'm 56 years old and have had neck and back surgery. That bringing the mast down issue will change once I get the swivel hinge made and taller mast installed. Then again, the taller mast might be enough to solve the issue.

Yes, I have extensively viewed my property via satellite views to clear trees for my satellite-arc on my FTA dishes. I would have to move my antenna mast about 50' out into the middle of my front yard, and then it would have to be free-standing.

Ok, I'm going to try to post some photos, but it's later here and they might be a bit dark. Let me WARN you now, after seeing these, you may wonder just HOW the heck I'm able to get any OTA as well as I do now... Well, we are in the home-stretch of me tweaking everything over about two months now, off and on...

The VHF antenna points at 160 degrees magnetic. The 3rd photo is a back view of the antennas, and shows a bearing of directly what it's looking at. That photo also shows an open area ("V") of cleared tree branches that my UHF antenna aims through. That was opened up years ago for satellite.

The HDB91x points at about 145 degrees magnetic, which is weighted towards my weaker UHF channels, and slightly away from WNEM 5 (22uhf), and which is by far the strongest station.

[MikeBear]

I wish to gosh I owned a bulldozer, as I'd LOVE to clear out more than 1/2 of those tree's.

I don't think we are going to be living here beyond another 4-5 years at most, as when I retire we are going to move for sure.

Next house I'm going to make sure there's not that many tree's around, I'm tired of so many...

I do have the possibility of dropping some of the tree's that are in the way, but it's fairly tight in there, so I need to plan out some careful logistics. I'd hate to drop a tree on a building.

[rabbit73]

Thanks for the photos Mike. I appreciate the trouble you went to and have a better understanding of your problem. The trees are so close; I thought they would be further away.

Yes, the antenna uses a Winegard TV-2900 balun right now. I'm aware there are many other choices, but I'm not sure which ones would be better. Baring buying a bunch at random and trying them, I'm still limited at the moment in dropping the mast to try balun after balun. That's very hard on my muscles, as I'm 56 years old and have had neck and back surgery. That bringing the mast down issue will change once I get the swivel hinge made and taller mast installed. Then again, the taller mast might be enough to solve the issue.

Yes, that would be very inconvenient, no matter what your age. You could test balun loss before connecting it to the antenna with an A/B switch to make a rapid comparison with the CH 12 OTA signal. A DIY half-wave coaxial balun would have the lowest loss.




Your photos are quite wide. They make all posts wide on this page. I use 125% to read the text and 75% to look at the photos. Do you have a way to resize a little smaller? I try to limit mine to about 800 pixels wide. If not, I could resize for you.

[MikeBear]

I've resized the photos. Thanks for the schematic of the balun "testing machine".

This "swivel hinge" I've mentioned a few times, will allow me to permanently have the antenna mast connected towards the middle top of that larger pipe, and be able to swing it back and down over the peak of that porch roof. That'll take all the leverage off of ME, and put it on the mechanical swing point. The 21' mast I'll install will hang past the middle of the porch roof, and I can easily make changes, and then swing it back up by walking it up to the large pipe. Then U clamp it down in two more places above the bottom swivel point.

That's such an elegant (and in retrospect, obvious) way to do it, I'm amazed I didn't think of it a month ago. I could have saved so much time and effort. Oh well, better late than never!

[rabbit73]

Thanks for the rapid resizing, Mike; much easier to read.

The "swivel hinge" is a clever solution. The Australian hams think the US hams are crazy to maket it so hard to bring the antenna down for adjustments. They use a pivot and counterweight system, for a welded pipe mast, that requires very little winch effort to go from vertical to horizontal and back.

[No static at all]

The 2 antennas seem a bit close & may be interfering with each other.

If in your shoes I would remove the UHF antenna & lower the VHF antenna in 6 inch increments to see if you can find a better sweet spot. Concentrate on finding the best spot for VHF, then add the UHF antenna above or below it depending on where the VHF antenna ends up. Higher is not always better.

Anyone else think this is worth a try?

[rabbit73]

Originally Posted by No static at all

You certainly don't need more amplification. What you do need is more signal AT the antenna.

How close are your antennas to each other? Can you take a pic & post it?

I think your post #18 was on target. The increase in antenna separation, and a little more height might help, but the trees are a big problem. Maybe Mike can have a few critical trees topped without having to remove them completely.
http://www.avsforum.com/forum/25-hdt...-part-1-a.html

Originally Posted by Calaveras

I have a couple of examples of vegetation affecting DTV signal strengths. The spectrum analyzer displays in this post show the difference between my antennas with the tower fully cranked up at 71' and fully cranked down at 36'. The yellow trace is tower up and the magenta trace is tower down. One image is VHF and the other three are spaced across UHF.

Attached is a picture taken from just below the UHF antennas at 69' looking west towards my local stations. (Camera was mounted on the mast and the tower was cranked up.) There is a clear shot to the 2nd edge that the signals pass over. There is vegetation on that hill. When the tower is cranked down much of the foreground vegetation blocks the view to the hill. There is as much as 20dB attenuation from the vegetation. UHF is generally affected more than VHF. Even though the signals look strong enough to receive, only 2 out of 9 stations will decode with the antennas lowered and their SNRs are very low due to severe multipath.

Getting the antennas above the vegetation is the difference between useable OTA and no reception.

[MikeBear]

Originally Posted by No static at all

The 2 antennas seem a bit close & may be interfering with each other.

If in your shoes I would remove the UHF antenna & lower the VHF antenna in 6 inch increments to see if you can find a better sweet spot. Concentrate on finding the best spot for VHF, then add the UHF antenna above or below it depending on where the VHF antenna ends up. Higher is not always better.

Anyone else think this is worth a try?

That's already been tried (lowering). Also, I know the antennas are probably too close, however moving the UHF antenna lower kills it's signal a lot. That UHF antenna also works best BELOW the VHF antenna, and is sitting in it's sweet spot for the coordinate aim of the antenna. It's hard to tell in the photos, but the UHF antenna is also tilted UP about 5 degrees. That gave me more than 5 points jump in signal. That leads me to believe that there's a possible big "signal wave" sitting up above the level of where my antennas are right now. Or at least there is for the UHF antenna.

The VHF antenna loses signal quite badly if it's lowered at all, even a few inches. There is NO "sweet spot" lower on the pole for VHF. It doesn't have a cut or open spot in the trees anywhere towards it's direction.

I'm lucky in that the "V" cut in the tree's towards the left happens to be a sweet spot for the UHF antenna. Even though those tree's have grown higher and started filling that in since others were removed 8 years ago,

The ONLY way to go is UP for VHF.

Or to put it on it's own pole somewhere else, but that's logistically not going to be easy and still stay anywhere on my roof area. Moving it to a tripod at the very end of the porch roof MIGHT work, but even I don't think putting it there would look good. Not to mention I don't want to put holes through my roof for bolts, even with using pitch patches to limit leaks.

I might ultimately just need to settle for what I get, but since I am not quite at the quitting point as of yet (haven't been able to get antennas higher than they are now), I'm not ready to settle as of yet. There's reasons I can't just go out there and "crank it up" and get it over with. Lifting a 10' mast with antennas using my arms is hard enough, lifting a 21' mast with those same antennas is a disaster just waiting. Weather, health, and my 12 hour night-shift schedule at work are fighting me lately. I hope to have it ready to go higher in the next week, now that I thought of the "swivel hinge" idea, and am making that in my garage. That new mast will allow the antennas to go higher by over 10' more.

[rabbit73]

In order to better understand your situation, I looked at some aerial photos of your area and the channel 12 signal has to cross your neighbor's roof and also two other houses. I also did some terrain profiles for the signal path from the CH 12 transmitter to your location. The transmitter is at the left end and your location is at the right.



http://www.tvfool.com/index.php?opti...id=15&Itemid=1

The color code indicates signal strength.

- White is extremely strong. Beware of signal overload on amps.
- Red-yellow-green are all quite strong. You can expect reasonable coverage with an indoor antenna.
- Cyan is where it's advisable to move the antenna up to the second floor or attic.
- Blue is where it's probably necessary to install a good antenna on the roof.
- Purple is quite weak and you really have to work at it for any chance of reception.

If you look carefully you can see it's starting to turn cyan. The same colors are used for the coverage map.

[rabbit73]

Using another terrain profile system:

[MikeBear]

Hummm, so as I suspected, my VHF antenna for WJRT-12 is just BARELY at the very bottom of the 'wave' of signal from this transmitter. It's a wonder at the moment that I get it as well as I do most of the time!

I think that extra 10-12 feet of higher mast, might really be the thing that makes the biggest difference. Short of chopping down, or thinning out some trees.

Thanks for your work so far on this Rabbit, I REALLY appreciate it! I'm sure it'll also help others reading it to understand a bit more about their antenna situations.

[rabbit73]

In the last profile I saw a peak by the lake and wanted to do a closer profile.





WJRT transmitter site:

[MikeBear]

The "Lake" (and I use the word loosely) is the Tittabawassee (yes, it's an American indian word) river, that's dammed up on one end with a hydroelectric dam that's been there since 1925. The dam is on the left side of your terrain pic. The river drops towards it to build up head-pressure.

Us-10 expressway crosses the lake right there, just after the supposed "peak" you show (it flows right to left). There is an outjutting (into the lake) of land there, with a subdivision of very tightly packed houses. The signal passes over that outjutting, and then is clear over the water again all the way to my subdivision.

There is no peak there that I am aware of, or that can be seen by the naked eye, certainly not to the height of what that terrain profile shows. I can't even imagine what that is showing in this case at all. There's just no chance that there's any sort of high ridge on that side of the expressway that's invisible, so I'm at a total loss here as to why it shows one.

[rabbit73]

I think the vertical scale exaggeration is misleading you.

The average peaks on your side are at 680 feet; the tall one is only 15 feet more than that average. It would be difficult to see that difference when standing there, but that peak does project into the signal path, and it can't be ignored.

That extra 15 feet probably isn't any more than the height of the trees.

Also, the resolution of the measurement data probably isn't that precise.

Sorry, didn't mean to mislead you, I was just curious to see what a close-up profile would show.

[MikeBear]

Well, if you think it's only around 15', then I'd agree it wouldn't be easy to see by eye. It then does make sense that the out jutting subdivision, which has lots of trees, could have a slight rise that could explain it.

[rabbit73]

The channel 12 signal reaches landfall on the west side of the "Lake" far above US10, because it crosses at an angle, not straight across. The terrain profile follows the green signal line; it is not an east to west profile.

[MikeBear]

Originally Posted by rabbit73

The channel 12 signal reaches landfall on the west side of the "Lake" far above US10.

Ok, in that subdivision as you drive along the road ( starting at the landfall area of the Wjrt signal), that parallels the lake (UP in your pic) you go UP a hill there that's just past the upper edge of the map photo. I would have to say that hill is at least 15' higher than the normal ground level on the majority of that area.

You are certainly making me see my whole area in a different way now, lol. So much you never really "notice", even though you see it almost every day...

[rabbit73]

Thank you; glad I enlightened you a little.

Then I didn't waste my time with that investigation.

I also wanted to practice using the new (to me) profile software.