Questions about OTA TV reception and multipath problems

Thread Starter

Saluki

Joined Feb 23, 2019
69
Background:

A couple years ago 4 metal grain silos with the typical conical roofs were built to the West-northwest of me - the most NNE of those is right in the direction most of my desired (to view) OTA TV stations are at. One of these stations is 7 miles from me with a 1692 ft. tall tower. Full ERP power is said to be 679 kilowatts. On the ground in an open space a few hundred feet to the north of me I can see the top 1/3 of the tower. The other stations are further away, but even higher (being on hills instead of the floodplain that I and that 1st station are on helps), and more powerful. Before the silos, reception was never a problem on close stations, and even those "out on those hills" usually came in ok, although after the switch to DTV, a couple of the more distant stations required quite careful aiming of my mast-mounted outside antenna to make occasional brief pixelization of the picture "rare".
After the building of those silos, reception deteriorated considerably. Replacing the antenna wire with new wire, trying a new antenna, and experimenting with height did not help much. (I couldn't really go higher on this mast, but a bit lower helped slightly on one station while making others worse.) My guess is that there is considerable multipath bouncing off those silos. (The closest is roughly 110 ft. ft. away from my mast / antenna, and they form a sort of closely spaced "wall" blocking the view to the West-northwest, the most NNW silo right in front of and perpendicular to my line of sight to the stations' towers.) There is also a large tall metal roof open "truckport" (think - really big carport) maybe 80 ft. SSW of the silos.

This Spring another silo was added on the south end of "the wall", leaving a gap of maybe 35-40 ft. between the row of silos and the truckport. Reception deteriorated even further, to the point I almost never get reception from the NW off the outside antenna, and I can pick up the closest station maybe 50% of the time, with occasional pixelization / dropouts. Stations to the ENE and east (PBS and independents) I can still pick up by rotating the outside antenna. There have never been any receivable stations to the SE, S, or SW. But ABC, NBC, CBS, and Fox are all to the NW. (ABC is more to the NNW, not directly blocked, and a bit distant - on a few "good" days it still comes in, but in the past "good days" were MUCH more numerous.)

Now it's dicey as to whether or not (bad pun) I can even get & monitor severe weather warnings from the most nearby TV stations. (As I'm plumb located between the track of the Great Tri-State (F5) tornado and the Dec. 2021 Mayfield long track F4 tornado, this is serious stuff!!)

Discussion:

I "could" try to go higher than ~25 ft., but I'm not sure if I can go high enough without inordinate expense. What would be "high enough"? The vertical sides of those silos are around 35 ft. tall, and the peaks higher of course. Goodness knows what comes off the conical roofs. Given the proximity of that closest station, I believe that what the signal strength meters on the TV's (which I understand to actually be "signal quality" meters) are telling me is that I'm getting a ton of multipath. MAYBE if I put up a very directional antenna and hunt for best results which may well not be aiming directly at the station, I have a chance of getting some reception? Or am I just hosed any way I go about it?

Is there any way I can determine if multipath IS the problem? Is there a way to measure it? In analog days, the "ghosts" in the picture told me multipath was present, if it was. (On FM, I had (still have) a top-of-the-line Denon FM receiver that has a multipath meter and an output to feed an oscilloscope. I think there's a small FM station around 7 miles from me that those silos would "block and reflect" too...)

I really just want local TV stations for news and weather, and occasional sports events.

What do you all think?

Thanks!

P.S. Mods, I know this is a "circuits" forum, but from reading in the past here I know there are some posters who know quite a bit more about signal reception than I do. :)
 

Ya’akov

Joined Jan 27, 2019
8,973
Welcome to AAC.

The first thing I would do is use a line of sight calculator to determine if the silos are actually between you and the transmitters’ and antennas. If so, you could raise the antenna to a clear height if that‘s practical.

If the silos block the line of sight and you can‘t raise your antenna enough, there is little you can do. If the owners are cooperative, you could rig a passive repeater on top of one of the silos. This would involve two high gain TV antennas connected with a low loss and short run of coax.

One pointed at the transmitter and the other at your antenna. This is a very old school solution people who live in valleys have used. Here’s the basic idea.

Before I would approach the owners, though, I’d make a call to the FCC for advice. There may be rules that require the owners to mitigate the effects of their buildings. If so, it gives you some leverage if they are reluctant.
 

LowQCab

Joined Nov 6, 2012
3,937
A custom made, highly directional, Helical-Antenna,
may provide enough directionality to eliminate your Multipath problems.

The biggest problem your various Antennas probably have is
lack of Signal-Rejection to the rear, or "back", of the Antenna.

Using an old Satellite-Dish as a Reflector may also solve the problem.

Many commercially available Antennas are actually very poor designs.

Do You have any interest in building your own DIY-Antenna ?
.
.
.
 

nsaspook

Joined Aug 27, 2009
12,782
Background:

A couple years ago 4 metal grain silos with the typical conical roofs were built to the West-northwest of me - the most NNE of those is right in the direction most of my desired (to view) OTA TV stations are at. One of these stations is 7 miles from me with a 1692 ft. tall tower. Full ERP power is said to be 679 kilowatts. On the ground in an open space a few hundred feet to the north of me I can see the top 1/3 of the tower. The other stations are further away, but even higher (being on hills instead of the floodplain that I and that 1st station are on helps), and more powerful. Before the silos, reception was never a problem on close stations, and even those "out on those hills" usually came in ok, although after the switch to DTV, a couple of the more distant stations required quite careful aiming of my mast-mounted outside antenna to make occasional brief pixelization of the picture "rare".
After the building of those silos, reception deteriorated considerably. Replacing the antenna wire with new wire, trying a new antenna, and experimenting with height did not help much. (I couldn't really go higher on this mast, but a bit lower helped slightly on one station while making others worse.) My guess is that there is considerable multipath bouncing off those silos. (The closest is roughly 110 ft. ft. away from my mast / antenna, and they form a sort of closely spaced "wall" blocking the view to the West-northwest, the most NNW silo right in front of and perpendicular to my line of sight to the stations' towers.) There is also a large tall metal roof open "truckport" (think - really big carport) maybe 80 ft. SSW of the silos.

This Spring another silo was added on the south end of "the wall", leaving a gap of maybe 35-40 ft. between the row of silos and the truckport. Reception deteriorated even further, to the point I almost never get reception from the NW off the outside antenna, and I can pick up the closest station maybe 50% of the time, with occasional pixelization / dropouts. Stations to the ENE and east (PBS and independents) I can still pick up by rotating the outside antenna. There have never been any receivable stations to the SE, S, or SW. But ABC, NBC, CBS, and Fox are all to the NW. (ABC is more to the NNW, not directly blocked, and a bit distant - on a few "good" days it still comes in, but in the past "good days" were MUCH more numerous.)

Now it's dicey as to whether or not (bad pun) I can even get & monitor severe weather warnings from the most nearby TV stations. (As I'm plumb located between the track of the Great Tri-State (F5) tornado and the Dec. 2021 Mayfield long track F4 tornado, this is serious stuff!!)

Discussion:

I "could" try to go higher than ~25 ft., but I'm not sure if I can go high enough without inordinate expense. What would be "high enough"? The vertical sides of those silos are around 35 ft. tall, and the peaks higher of course. Goodness knows what comes off the conical roofs. Given the proximity of that closest station, I believe that what the signal strength meters on the TV's (which I understand to actually be "signal quality" meters) are telling me is that I'm getting a ton of multipath. MAYBE if I put up a very directional antenna and hunt for best results which may well not be aiming directly at the station, I have a chance of getting some reception? Or am I just hosed any way I go about it?

Is there any way I can determine if multipath IS the problem? Is there a way to measure it? In analog days, the "ghosts" in the picture told me multipath was present, if it was. (On FM, I had (still have) a top-of-the-line Denon FM receiver that has a multipath meter and an output to feed an oscilloscope. I think there's a small FM station around 7 miles from me that those silos would "block and reflect" too...)

I really just want local TV stations for news and weather, and occasional sports events.

What do you all think?

Thanks!

P.S. Mods, I know this is a "circuits" forum, but from reading in the past here I know there are some posters who know quite a bit more about signal reception than I do. :)
Counter-intuitively, RF signal attenuation can be a counter-measure for multi-path. Modern ATSC receiver chips are magnitudes better at multi-path rejection than early tuners so if it's a older digital set look for a TV with the latest gen chip.

As you say, the other is a highly directional antenna with a rotor can be set to receive only the reflected or ground signal. Adjusting the height can also help.

https://forum.allaboutcircuits.com/...ioshack-vu-190-tv-antenna.161631/post-1414588

I originally had really bad multi-path problems (major airport landing glide slope near the house) with early receivers (2nd gen) and less directional antennas.
https://forum.allaboutcircuits.com/threads/wind-and-television-reception.122530/post-983624

1701807558536.png
 
Last edited:

Thread Starter

Saluki

Joined Feb 23, 2019
69
A custom made, highly directional, Helical-Antenna,
may provide enough directionality to eliminate your Multipath problems.

The biggest problem your various Antennas probably have is
lack of Signal-Rejection to the rear, or "back", of the Antenna.

Using an old Satellite-Dish as a Reflector may also solve the problem.

Many commercially available Antennas are actually very poor designs.

Do You have any interest in building your own DIY-Antenna ?
.
.
.
YES!

(I was kinda thinking along those lines, but didn't want my OP to be too long or limit possibilities / ideas.)

My younger brother with help from an engineer neighbor built a ~ 6 ft. long UHF "single frequency" yagi back when we were teens. UHF Channel 30, IIRC? I'm guessing it was ~28-30 ft. up. That sucker was pulling in the desired station, 90 miles away. However, I don't think I want to go the yagi route as I don't have a tower as our parents did, to mount all sorts of goodies on.

Note, yes, I'm sure the indoor "flat" antenna has poor rejection / directivity, yet it does "better" often - possibly due to location / blockage of particular reflections - who knows...

I actually do have an old Dish Network "dish"...
 

Thread Starter

Saluki

Joined Feb 23, 2019
69
Counter-intuitively, RF signal attenuation can be a counter-measure for multi-path. Modern ATSC receiver chips are magnitudes better at multi-path rejection than early tuners so if it's a older digital set look for a TV with the latest gen chip.

As you say, the other is a highly directional antenna with a rotor can be set to receive only the reflected or ground signal. Adjusting the height can also help.

https://forum.allaboutcircuits.com/...ioshack-vu-190-tv-antenna.161631/post-1414588

I originally had really bad multi-path problems (major airport landing glide slope near the house) with early receivers (2nd gen) and less directional antennas.
https://forum.allaboutcircuits.com/threads/wind-and-television-reception.122530/post-983624

View attachment 309220

Yes, indeed, attenuation may (may!) be the reason the TV with the indoor antenna actually does better on the nearby station. It is also a newer TV (purchased 4 years ago, IIRC), the one on the outside antenna is around 10 y/o. I'll try the indoor antenna on the "old" TV, and I'll check those links - thanks!
 

Thread Starter

Saluki

Joined Feb 23, 2019
69
Welcome to AAC.

The first thing I would do is use a line of sight calculator to determine if the silos are actually between you and the transmitters’ and antennas. If so, you could raise the antenna to a clear height if that‘s practical.

If the silos block the line of sight and you can‘t raise your antenna enough, there is little you can do. If the owners are cooperative, you could rig a passive repeater on top of one of the silos. This would involve two high gain TV antennas connected with a low loss and short run of coax.

One pointed at the transmitter and the other at your antenna. This is a very old school solution people who live in valleys have used. Here’s the basic idea.

Before I would approach the owners, though, I’d make a call to the FCC for advice. There may be rules that require the owners to mitigate the effects of their buildings. If so, it gives you some leverage if they are reluctant.
Thanks!

To use the LOS calculator I'd need to enter my antenna's height minus the height of the silos, right? (Will be a negative number.)

I've thought of the passive repeater idea, esp. since the distance to the silos is so short. But, it seems like it'd be a bit pricey.

I've also thought about talking to the local station or the FCC, but I don't want to start a "war" with the farmer. (They actually built a big new home just a few miles south of me, a couple years ago, so, business must be good.) He supposedly is going to give me some fill dirt sometime (left over from their construction of the silos.)

Another problem (non-electronic!) is all the red grain "chaff" produced that "snows" on us in the fall. Egad... If I was going to try to force anything, it'd be a scrubber on the "processing" silo.

I suppose a good side of it is watching the helicopter crop duster / sprayer in the fields. Pretty dang impressive, esp. when he swoops up, just over the silos, when making a pass toward our place, coming from the other side of the silos...!
 

nsaspook

Joined Aug 27, 2009
12,782
That's a nice antenna if all you need is UHF (I know it says VHF but that's with marginal directivity with that antenna IMO). You may have VHF high or low stations that need to be received.
https://www.channelmaster.com/pages/tv-antenna-map-fairview-or-97024

Check the RF channel for the actual RF transmit frequency channel, not the digital channel number.

What is an RF channel?
The RF channel is the actual channel the tv station transmitter is using to broadcast over the airwaves. Don't get this confused with the channel numbers that appear on your screen, in many instances you can have a TV station broadcasting on RF channel 25 but the channel displayed on your television is actually 3.1, 10.1 13.1, etc. The RF channel number is typically only useful when selecting a tv antenna and determining which TV stations are being broadcast on UHF or VHF frequencies.

Map Key: Low VHF High VHF
 

LowQCab

Joined Nov 6, 2012
3,937
The important point is to increase the Corner-Reflector surface area to
reduce reflections coming from the rear.
This can be simply done by wrapping Brass-Window-Screening around the existing Reflector-Elements.

The problem with doing this is that it will increase the "Wind-Loading-Factor"
which could be a problem if your area experiences regular high-winds.

With a very High-Gain Antenna, You may want to experiment with a Signal-Attenuator.
A Signal-Attenuator may not work well with an Antenna that has a built-in RF-Amplifier.
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Thread Starter

Saluki

Joined Feb 23, 2019
69
That's a nice antenna if all you need is UHF (I know it says VHF but that's with marginal directivity with that antenna IMO). You may have VHF high or low stations that need to be received.
https://www.channelmaster.com/pages/tv-antenna-map-fairview-or-97024

Check the RF channel for the actual RF transmit frequency channel, not the digital channel number.

What is an RF channel?
The RF channel is the actual channel the tv station transmitter is using to broadcast over the airwaves. Don't get this confused with the channel numbers that appear on your screen, in many instances you can have a TV station broadcasting on RF channel 25 but the channel displayed on your television is actually 3.1, 10.1 13.1, etc. The RF channel number is typically only useful when selecting a tv antenna and determining which TV stations are being broadcast on UHF or VHF frequencies.

Map Key: Low VHF High VHF
One station is VHF (198.31 MHz) but is approved to move to Digital Channel 32 / 578.31 MHz.
 

Thread Starter

Saluki

Joined Feb 23, 2019
69
The important point is to increase the Corner-Reflector surface area to
reduce reflections coming from the rear.
This can be simply done by wrapping Brass-Window-Screening around the existing Reflector-Elements.

The problem with doing this is that it will increase the "Wind-Loading-Factor"
which could be a problem if your area experiences regular high-winds.

With a very High-Gain Antenna, You may want to experiment with a Signal-Attenuator.
A Signal-Attenuator may not work well with an Antenna that has a built-in RF-Amplifier.
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.
Brass would be incompatible with Aluminum reflector elements, no? Why not Aluminum screening?
 

LowQCab

Joined Nov 6, 2012
3,937
If You can find Aluminum-Screening that's fine too.

The Brass will last at least ~5-years or more in contact with the Aluminum-Screen,
and the Antenna is most-likely Anodized-Aluminum,
which will slow-down this process even further.
The surface-corrosion will not affect the performance because there is
very substantial Capacitive-Coupling to the Screen.

Solid Aluminum-Sheet is even more effective, but creates even more "Wind-Load" than the Screen.

Don't over-think it too much, nobody will be using Digital-OTA-TV in 5-years.
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LowQCab

Joined Nov 6, 2012
3,937
The "official" start of the "transformation" of the World and it's inhabitants was in 2012.
It does take a while to transform a Planet and ~9-Billion People,
but the Military are "fast-tracking-it" quicker than might be expected,
much, and in some places, all, Bureaucratic-Red-Tape has now been eliminated.

Nothing will remain the same-ole BS.
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Thread Starter

Saluki

Joined Feb 23, 2019
69
The "official" start of the "transformation" of the World and it's inhabitants was in 2012.
It does take a while to transform a Planet and ~9-Billion People,
but the Military are "fast-tracking-it" quicker than might be expected,
much, and in some places, all, Bureaucratic-Red-Tape has now been eliminated.

Nothing will remain the same-ole BS.
.
.
.
Well, all I can say is that most everywhere I have to deal with "stuff" there is MORE red tape... :(

But I don't want to get too OT here...
 

Thread Starter

Saluki

Joined Feb 23, 2019
69
If You can find Aluminum-Screening that's fine too.

The Brass will last at least ~5-years or more in contact with the Aluminum-Screen,
and the Antenna is most-likely Anodized-Aluminum,
which will slow-down this process even further.
The surface-corrosion will not affect the performance because there is
very substantial Capacitive-Coupling to the Screen.

Solid Aluminum-Sheet is even more effective, but creates even more "Wind-Load" than the Screen.

Don't over-think it too much, nobody will be using Digital-OTA-TV in 5-years.
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Isn't most (metal) window screen anodized Aluminum?
 

LowQCab

Joined Nov 6, 2012
3,937
"" Isn't most (metal) window screen anodized Aluminum ? ""
As far as I've seen, most Aluminum-Screen is not "Anodized", or the Anodization is quite poor/thin.

Most larger Hardware-Stores sell both Aluminum and Brass-Screening in bulk.

For DIY construction, I find that Brass is easier to work with, and stronger,
as well as not developing the "gray-fuzz" from the Surface-Corrosion of bare Aluminum.

Brass can usually be Soldered, on the other hand,
Aluminum must be glued, or otherwise "mechanically" secured.

Aluminum-Roof-Flashing is also very useful for DIY-Projects.
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