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Map transmission line software

post #1 of 16
Thread Starter 
I've been getting really unreliable reception on my Washington, DC locals even though they are just a few miles to my west and on an ostensibly unobstructed signal path. I have tried three antennas and replaced the entire rest of the reception link, and have used maybe half a dozen different tuners. I suspect that a six story building that was built to my west is the culprit, but I was using cable TV for my Washington, DC locals until two years ago and my off air antenna just for Baltimore, so I can't associate its construction with my signal disruption. When I swing the antenna maybe 20 degrees to each side of the approximated transmission path, the signal strength does not taper as one would expect with an unobstructed signal path.

Is there any free cartography program that can enable me to draw precise lines from my home to the three "co-located" transmitter towers so I can more definitively confirm my suspicion?
Edited by AntAltMike - 9/26/13 at 5:05pm
post #2 of 16
Using the tvfool interactive map option enabled me to solve a reception problem. The problem was caused by a large cargo crane in the signal path. There were two transmitting antennas on one tower at different heights. One signal was OK, the other was not; sort of like a limbo dance bar in the way.

http://www.avsforum.com/t/1340737/distribution-amp-problem/30#post_21023467

You should be able to see if the building is actually in the signal path using the map option as I did with the cargo crane.

The broad beamwidth that you are experiencing would seem to be caused by the combination of multipath signals. The signal strength is fairly constant, but the signal quality sucks. You might need the ultimate anti-ghosting antenna by Bill Naivar of Georgia Tech to select the best reflection or direct signal and reject the unwanted reflections so that the tuner would be exposed to fewer errors to process by the FEC.

http://www.prism.gatech.edu/~wn17/
http://www.prism.gatech.edu/~wn17/Web%20bill%20page%202.htm

note that there are 2 pages for his solution

Because of your extensive experience, I assume that overload is not part of the problem.
Edited by rabbit73 - 9/26/13 at 5:47pm
post #3 of 16
Thread Starter 
I used the TVfool interactive map and see that I am missing that building cleanly, so the problem must be the vegetation. I'll take comprehensive signal readings now and compare them to the next few months as the leaves fall and the sap thins out, but the prospects for reliable reception from that direction seems bleak. I might raise the antenna height by ten feet, but I live in a nanny-town and I'll probably get a "Courtesy Notice" door hanger forewarning me of an imminent $100 fine when I do. They fine us for not having lids on the trashcans here.

A few miles from here, I once had to fight with the reflections off Byrd Stadium when I was servicing the master antenna for a 400 site campground. Of course, in those days, with analog signals, you could see the ghost image so you could observe continuous improvements when migrating the antenna in any direction. At that site, I got my best reception by moving the antenna to a nearby location on the property that was lower and didn't have line of sight, but had a less severe multipath bounce off the stadium.

There was a trick we could use to locate the object we were getting a signal reflection off. The horizontal measure of the ghost displacement was proportionate to the extra distance that the ghost signal traveled, and I used to have a chart that said, for each standard picture tube size, how many feet of extra signal path each inch of screen displacement indicated. Armed with that information, it was easy to generate an elipse and then intersect that with the second azimuth on which the antenna could be peaked. At the time I was remedying that campground's problem, I couldn't actually see Byrd Stadium because of the foliage and didn't know the school campus well enough to even think of it, but the secondary signal path line and the ellipse intersected right on it.
Edited by AntAltMike - 10/2/13 at 10:14am
post #4 of 16
Oh WOW! You have some serious restrictions to deal with at your location.

Besides thinking of trying different heights for your antenna, you might try moving the antenna left or right. That's what I did with a temporary 2-bay antenna that was facing a tree line that made the wavefront very uneven. I positioned the antenna not only for max signal strength, but also for best presentation of the pilot signal (which the tuner needs to lock on) at the low end of the channel on my Sadelco 800 meter.

http://www.avsforum.com/t/381623/the-official-avs-antenna-and-related-hardware-topic/14940#post_22105317




Edited by rabbit73 - 9/26/13 at 6:26pm
post #5 of 16
There was an article in this months QEX (Amateur Radio technical journal) about using Google Earth for estimating paths. QEX is not online, but there are a few pics from the article available here.

http://www.arrl.org/files/file/QEX%20Binaries/2013/September_13/9x13_McCullers_Images.zip

The article also references this site.

http://www.softwright.com/

Ron
post #6 of 16
Quote:
Originally Posted by AntAltMike View Post


A few miles from here, I once had to fight with the reflections off Byrd Stadium when I was servicing the master antenna for a 400 site campground. Of course, in those days, with analog signals, you could see the ghost image so you could observe continuous improvements when migrating the antenna in any direction. At that site, I got my best reception by moving the antenna to a nearby location on the property that was lower and didn't have line of sight, but had a less severe multipath bounce off the stadium.

There was a trick we could use to locate the object we were getting a signal reflection off. The horizontal measure of the ghost displacement was proportionate to the extra distance that the ghost signal traveled, and I used to have a chart that said, for each standard picture tube size, how many feet of extra signal path each inch of screen displacement indicated. Armed with that information, it was easy to generate an elipse and then intersect that with the second azimuth on which the antenna could be peaked. At the time I was remedying that campground's problem, I couldn't actually see Byrd Stadium because of the foliage and didn't know the school campus well enough to even think of it, but the secondary signal path line and the ellipse intersected right on it.

I don't know how up-to-date TVFool is, but it does show 3 analog stations RF25, RF47, RF49 that you might be able to apply your trick.
post #7 of 16
Thread Starter 
Quote:
Originally Posted by retiredengineer View Post

I don't know how up-to-date TVFool is, but it does show 3 analog stations RF25, RF47, RF49 that you might be able to apply your trick.

The only one my TV detects is 47, and it is a prototypical example of "sandpaper" interference, with a powerful digital 48 spilling over it. I am actually about nine miles east by northeast of the transmitting towers, in an enclave called Berwyn Heights, a suburb of sorts of College Park. I think 25 is digital only,

An analog signal wouldn't be of diagnostic help in my situation if I'm not getting a single interfereing bounce. I am likely getting a signal blurr.
Edited by AntAltMike - 9/27/13 at 11:06am
post #8 of 16
Quote:
Originally Posted by AntAltMike View Post

I think 25 is digital only,
That is correct.

Which channels are unreliable?
post #9 of 16
Thread Starter 
Quote:
Originally Posted by Digital Rules View Post

That is correct.

Which channels are unreliable?

Every UHF channel coming from the west: from all three metropolitan towers and from Falls Church
post #10 of 16
Quote:
Originally Posted by AntAltMike View Post

Every UHF channel coming from the west: from all three metropolitan towers and from Falls Church

Based on your location, Berwyn Heights, I suspect you are receiving dynamic multipath reflections from the vehicles on the Capital Beltway which is practically in your backyard. I believe this because my reception always break-up when a helicopter flies behind my antenna.

I don't know how to ameliorate this but I have a theory you could try. Attenuate the antenna signal as much as possible. This is assuming the reflections have less signal strength so by attenuating them below the noise level, they won't affect the direct signal. This is just a theory. Let me know what happens if you try this. Thanks.
post #11 of 16
Thread Starter 
I'm over a mile south of the beltway. In fact, I'm over half a mile south of state Route 123 Greenbelt Road, which runs parellel to the beltway, and over a quarter of a mile from Kenilworth Road, Route 295 which runs perpendicular to the beltway but "behind" me. One thing we don't have to worry about here is reflections from helicopters, since even traffic copters have been banned from this airspace since 9-11.

I just ran my TVfool location and see that the field strength of Baltimore channel 46 is 30 dB weaker than that of Washington 48, yet, coming off identical directional antennas, the signal differential is just 12dB, and while TVfool says Baltimore 38 is 31 dB weaker than Washington 36, the actual measured difference between the signal levels from those same two targeted antennas is also 12 dB, so I am losing nearly 20dB more Washington signal through path interference than I am on the closest frequency Baltimore signals, and since there is 6 degrees of spread in the azimuths to Washington DC channels 36 and 48 and no tree obstructions for over a block, they are not getting degraded or obstructed by the same building or tree.
Edited by AntAltMike - 9/27/13 at 3:36pm
post #12 of 16
Quote:
Originally Posted by AntAltMike View Post

Every UHF channel coming from the west: from all three metropolitan towers and from Falls Church
So you get 7 and 9 ok, but problems with 4 and 5? I thought VHF digital was more subject to noise and interference than UHF. So must be multipath or I wonder if some type of wireless 4G/LTE interference?
post #13 of 16
Thread Starter 
"4.1" and "5.1" are really UHF 48 and 36, respectively. The problem is, my transmission paths are blocked by foliage so dense that the ambient signal strength here of the Washington, DC UHF transmitters is 20dB weaker than it would be if the signals traveled through clear paths. There isn't going to be a remedy. If I had been able to determine that it was a single building blocking me, then I could take a shot at moving the antenna 40 feet to the other end of the house or raising the antenna another ten or fifteen feet, but with dense foliage loss on three paths (251, 254 and 257 degrees, azimuth), any incremental improvement I can attain with antenna positioning will only make the pictures freeze less often. There will be no total victory here.

The saving grace is, of course, that most of the same programming can be gotten reliably from Baltimore, but Washington, DC is my sole source for CoziTV and Russia Today.
Edited by AntAltMike - 9/27/13 at 6:49pm
post #14 of 16
Quote:
Originally Posted by AntAltMike View Post

I've been getting really unreliable reception on my Washington, DC locals even though they are just a few miles to my west and on an ostensibly unobstructed signal path. I have tried three antennas and replaced the entire rest of the reception link, and have used maybe half a dozen different tuners. I suspect that a six story building that was built to my west is the culprit, but I was using cable TV for my Washington, DC locals until two years ago and my off air antenna just for Baltimore, so I can't associate its construction with my signal disruption. When I swing the antenna maybe 20 degrees to each side of the approximated transmission path, the signal strength does not taper as one would expect with an unobstructed signal path.

Is there any free cartography program that can enable me to draw precise lines from my home to the three "co-located" transmitter towers so I can more definitively confirm my suspicion?

There used to be a program called "TopoUSA", that was pretty handy. I used it a lot for SHVA studies. I don't know if there is a current version available.
You can often get a topo map via Google Maps, and can simply "Print Screen", copy to the clipboard, and use "MS Paint" to draw the lines.
post #15 of 16
Start by entering your location into www.tvfool.com, using the START MAPS option and then Check Mark "Show lines pointing to each transmitter" and "Hybrid" or "Satellite" option at the top. Should be just what you're looking for....

Although it may require messing around a bit, I've also used GoogleEarth to get both a Top-Down and a 3D View, using Ruler/Path to draw a line between my house and a transmitter. However, at the large scale needed to draw the line, there is very limited accuracy in locating the ends of the line....so not as accurate as method above. BTW: You can download a "Transmitter Icons" file from www.tvfool.com [and www.fmfool.com' for installation into GoogleEarth (after D/L, double click on file to install).
Edited by holl_ands - 9/29/13 at 2:36pm
post #16 of 16
Thread Starter 
Quote:
Start by entering your location into www.tvfool.com, using the START MAPS option and then Check Mark "Show lines pointing to each transmitter" and "Hybrid" or "Satellite" option at the top. Should be just what you're looking for....

That's what rabbit73 recommended I do in post #2 and that I reported having done in post #3, so unless someone wants further elaboration on how to set up two antennas for phase cancellation of a single, offending multipath signal, which is already being discussed in another, current thread, this thread should probably be closed.
Edited by AntAltMike - 9/30/13 at 5:31am
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