OTA TV reception problems

There's signal strength, signal quality/modulation, interference and tuner quality.

Having two stations on the same tower reduces the number of variables.

I'm only about 10 miles from the tower, but there are hills all around. Signal strength is high, but there are a lot of reflections. I did many experiments varying the antenna direction and changing signal strength into the tuners. Best picture stability was not always consistent with best signal strength. When trying to use one tuner and one antenna for multiple stations, I found that I had to attenuate the signal to get a picture on some stations.

My neighbor has a metal pole building. I found moving the antenna to the other end of the house made a dramatic improvement. Doesn't take much a reflection that might be from far away to wreak havoc on your signal due to multipath. Did Trump put up a new tower in your vicinity?

Currently, I have a win7 computer with 4 tuners. A single antenna and distribution amplifier with an output for each tuner. Over the years, I've upgraded the tuners so I no longer have to vary the signal strength to fit a particular tuner. I find that some tuners don't like specific channels. Luckily, media center will let me blacklist tuners on various channels.

Interference can come from unexpected sources. Your neighbor's wifi might be mixing in a corroded gutter junction with some other radio signal. The result trashes the signal quality of your TV station.

I once had a towing company radio mix with my radio repeater output that landed exactly at the IF frequency of my other radio.

If you have access to a spectrum analyzer, you can hook it to your antenna and look at the relative signal strengths. Look at the modulation for each channel. I found that signals were good when the "bart's head" display was flat on top. Didn't take much noise or tilt to render the channel unwatchable, even on very strong signals.

ATSC is not very forgiving.

The signal varies in strength and quality, you could be dealing with knife edge diffraction off of towers, hills, and buildings along the line of sight. At 60 miles, you're almost certain to have a potential problem with Fresnel zone diffraction. I can generate a path profile to see if there are any obvious problems, but I need to know the lat-long of your location and elevation of your antenna. Here's a sample output:

The antennas appear to be almost identical. I just checked the FCC

You might try checking what might be expected at your location in the way of TV reception: Check the calculated signal strengths and see if it's even theoretically possible to receive either station at your unspecified location.

Yes, due to frequency selective fading. What happens is that you may have two paths between the TV station and your receiving antenna. If the reflected path is some odd numbered multiple of 1/2 wavelength, the signals will cancel. At about 500 MHz, 1/2 wavelength is about

Oh, lots of theories. For example, a broken TV tuner that has a problem on some channels. Some kind of OTA TV amplifier with an uneven frequency response. Badly terminated or connected TV coax cable causing a notch at one frequency. TV antenna with a broken element causing a notch at one frequency. Local source of interference on one TV channel, but not the other. It might be that one TV station is having transmitter or antenna problems. I could probably conjure a few others.

The easiest way to troubleshoot this is by substitution. Start with a different antenna connected directly to the TV with a different coaxial cable. It will probably not be as good as a rooftop antenna, but it should hear something. Compare the signal levels of the two stations. If they're the same, you're problem is somewhere in the antenna, amp, or coax feed system. If they're still different, it might be the TV. Try a different TV.

Good luck.

Lenny-

If you provide data to Jeff, he can give you a more accurate prediction of how well you should receive the station.

As a rough estimate, the range of an signal in miles is the square root of twice the sum of transmitting and receiving antenna heights in feet. For 60 miles, the sum of heights would be 1800 Feet.

As others mentioned, reflections can make a difference. Was a large building erected about the time you noticed the reduction in signal?

Fred

On Sunday, November 6, 2016 at 7:40:38 PM UTC-5, snipped-for-privacy@gmail.com wro te:

holing that this time someone might read it who may have a theory as to wh at could be going on.

about 60 miles from here. Lately I as well as several other people I know have been experiencing intermittent problems with channel four. While most other channels are presently operating fine, for the past 10 days or so cha nnel 4's signal has been in the toilet. This station, WBZ TV operates on UH F channel 30, runs 825KW, and has an antenna height of 390 meters. By contr ast Channel 5, WCVB, operates on UHF channel 20, runs 625 KW, and shares th e same tower and has it's antenna at the same height as channel 4's, and we never have any problems with that channel. Could propagation be that much different 60 MHZ apart? What is really weird is that the signal just drops to almost nothing.

planation for this. Does anyone have any theories about this? Thanks, Lenny

That sounds as if you may have a multipath situation. The signal from the transmitters is reaching your receive antenna via two different paths - e.g. once directly, and once after reflection off of a building or mountain or ???.

If the two different paths deliver signals that happen to be of nearly equal strength, and nearly 180 degrees out of phase with one another, they will largely cancel out when they are combined by your antenna, and the signal strength will take a huge dive.

Because the effective length of the signal paths (measured in wavelengths) is a function of the frequency, it's entirely possible for two different channels transmitted from the same tower to behave very differently. Even a small frequency difference can shift the difference-in-path-length by 180 degrees. 60 MHz difference is far more than enough for this effect to show up.

Other possibilities:

- Somebody may have put up some sort of structure which happens to resonate at the UHF Channel 30 frequency, thus creating a frequency-selective reflector.

- It's possible that another station is now operating on Channel 30, somewhere within antenna range of you, and its signal is now interfering with WBZ. This might indicate that a new station has gone on-line (or an existing one has changed frequencies) or might indicate that there's some tropospheric ducting or other form of "skip" bringing an out-of-area station's signal to you.

- There might be some form of local interference - a spurious transmission on or near the Channel 30 frequency.

Coverage maps of WBZ and WCVB. Please note that WBZ has or had a transmit power upgrade application pending with the FCC to increase their output to 941kW. I'm not sure if the coverage map is for 825kW or 941kW. Both coverage maps look fairly close. However, at 60 miles you're well outside the "normal" coverage area. I'm wondering why WCVB works at 60 miles. What do you have for an antenna and amp at your end?

I'm otto time for this today. More tomorrow.

Anybody hit or knock down a pole in the area? I assume your neighborhood is wired for cable. Damage to poles can knock connectors partially loose, allowing a LOT of signal to flow onto the outer sheath. Could be a signal right on the same frequency as Chan 4. I remember a LONG time ago, we had a lightning storm, and someone in the area reported TV interference (back in the analog days, you could easily tell it was interference) . Turned out the lightning had blown out the output filters on a two-way radio base station, so it was radiating at the drive frequency. Could be something similar, a radio transmitter emitting unwanted frequencies. I've even heard of rusty fences and the like developing rectifiying junctions that were mixing various broadcast frequencies and blotting out one particular channel.

Are the others with the same problem very close to you, or some distance away? If very close, then likely it is a very local interference source, might be VERY weak, and darned hard to find. If they are miles away, then it is a larger source, and maybe something the station might be willing to send a guy out with a field intensity meter to see if he can find where it is coming from.

Hmmm, anybody put up a big building nearby? Some of these glass towers can become excellent near-microwave reflectors, and might be bouncing signals from some other area toward your location.

Could also be a wireless security system, baby monitor, wireless cameras, or some other gear of that sort that is out of adjustment.

Jon

On Sunday, November 6, 2016 at 4:40:38 PM UTC-8, snipped-for-privacy@gmail.com wro te:

This station, WBZ TV operates on UHF channel 30, runs 825KW, and has an an tenna height of 390 meters. By contrast Channel 5, WCVB, operates on UHF ch annel 20, runs 625 KW, and shares the same tower and has it's antenna at th e same height as channel 4's, and we never have any problems with that chan nel. Could propagation be that much different 60 MHZ apart? What is really weird is that the signal just drops to almost nothing.

If there's a nearby signal to "channel 30", it could be saturating your inp ut amplifier. It's counterintuitive, but try a passive attenuator and see if it improves your reception. The attenuator has to be between the antenna and the FIRST amplifier for the RF signal, so if you have a mast-mounted preamp, that's a problem.

Saturation can happen in an RF input amplifier, reducing the signal gain, d ue to an off-frequency signal that is completely filtered out in later stages. I'm not sure if y our signal indication would read the spurious signal or not.

If this is a longterm problem, the best solution is an RF trap tuned for th e too-strong signal. That won't hurt your signal strength for the other channel, like an attenua tor does.

On Sunday, November 6, 2016 at 7:40:38 PM UTC-5, snipped-for-privacy@gmail.com wro te:

holing that this time someone might read it who may have a theory as to wh at could be going on.

about 60 miles from here. Lately I as well as several other people I know have been experiencing intermittent problems with channel four. While most other channels are presently operating fine, for the past 10 days or so cha nnel 4's signal has been in the toilet. This station, WBZ TV operates on UH F channel 30, runs 825KW, and has an antenna height of 390 meters. By contr ast Channel 5, WCVB, operates on UHF channel 20, runs 625 KW, and shares th e same tower and has it's antenna at the same height as channel 4's, and we never have any problems with that channel. Could propagation be that much different 60 MHZ apart? What is really weird is that the signal just drops to almost nothing.

planation for this. Does anyone have any theories about this? Thanks, Lenny

Here is some background information from my previous posting: (I was thinki ng "drive" miles when I said that we were 60 miles from Boston). As the cro w flies we are about 45. Sorry for that bit of misinformation. The followin g previous post was when the problem first surfaced.

Sep 21 For the past ten days or so we have been having problems with TV channel 4. This station broadcasts on UHF from Boston Mass. and we are about 45 miles (as the crow flies) from the transmitter. The antenna is an old, but in go od condition, very high gain Channel Master 5 foot parabolic which is moun ted on a tripod about 6 feet off the roof. There is a mast mounted Winegard GA 8780 preamplifier with a 28 DB UHF section along with a very low noise figure mounted about 2 feet from the antenna. The cable is RG6 Quad which g oes into a two way splitter. We have several different receivers, Converter boxes) but the one I use for assessment because it shows signal quality as well as signal strength is a Channel Master 7001. Our elevation is 410 fee t and we are surrounded by trees, some deciduous and some pine.

Most of the time, in spite of this not so ideal situation, (location) I can receive the three networks and a few independents. The signal display on t he converter shows, as two horizontal bars, "signal quality" and "signal le vel". On most channels most of the time signal quality is pegged at 100 per cent and signal level runs between 45 and 55 percent. Within this window I usually have no problems with reception. As long as signal quality doesn't fold back I usually will get no drop outs. If it should falter excessively though both picture and sound will break up and intermittently freeze. So I 'm pretty familiar with what conditions will produce a good signal.

Lately Channel 4 although displaying 54 percent signal level and 100 percen t signal quality has had very slight "tearing streaks" going through the pi cture. If these aberrations only affected the picture we would be able to w atch the program. However this problem seems to chop up the sound as well. This makes it impossible to watch a program.

The weather of late has been hot and humid, which is atypical for New Engla nd this time of year. I've noticed in the past that during this type of wea ther we do sometimes lose reception on several channels for a day or two bu t never this long. I'm just wondering if anyone might have a theory as to w hat could be happening here. This only seems to affect channel 4, (where al l our shows happen to be). Thanks, Lenny

I also corresponded with the chief engineer at WBZ and got this back.

Lenny,

My apologies for the delay in replying.

I don?t have a good answer for why your reception has degraded rece ntly. We have not been having any trouble with our transmission systems.

Your installation sounds like a good one, though I think it may be a bit ov erdone, as a high-gain antenna in combination with 28 dB of amplification i s probably more than you need, even at that distance. For comparison, I li ve 43.1 air miles from the transmit antenna, and I use a Channel Master 422

Wish I had a more definitive answer?

cid: snipped-for-privacy@01CEC683.AF77500

Robert Yankowitz, CPBE

WBZ-TV WSBK BOSTON

Chief Engineer

file:///M:/pmasucc/Work/General%20Info/email-combo%20logos.jpg

o 617 562-5044

c 617 828-1041

f 617 787-7106

Then I replied back:

Lenny I wish I had answer for why your reception has degraded recently. We have not been having any trouble with our transmission systems.

Your installation sounds like a good one, though I think it may be a bit ov erdone, as a high-gain antenna in combination with 28 dB of amplification i s probably more than you need, even at that distance. For comparison, I li ve 43.1 air miles from the transmit antenna, and I use a Channel Master 422

Wish I had a more definitive answer?

cid: snipped-for-privacy@01CEC683.AF77500

Robert Yankowitz, CPBE

WBZ-TV WSBK BOSTON

Chief Engineer

file:///M:/pmasucc/Work/General%20Info/email-combo%20logos.jpg

o 617 562-5044

c 617 828-1041

f 617 787-7106

snipped-for-privacy@cbs.com

-------- Original message -------- From: Wufoo Date: 9/21/16 11:00 PM (GMT-05:00) To: CBS Local Site Contact Us , "Eich, Julie O" Subject: General Information - Boston - [#95913]

Name *

Leonard Stein

Email *

snipped-for-privacy@gmail.com

Phone Number *

(603) 887-4253

Direct Your Message To CBS Local Staff In... *

Boston

Link (if appropriate)

Please forwaed this to engineering dept.

Comment

For the past ten days or so we have been having problems with TV channel 4. We are located in Chester N.H. about 45 miles (as the crow flies) from the transmitter. The antenna is an old, but in good condition, very high gain Channel Master 5 foot parabolic which is mounted on a tripod about 6 feet o ff the roof. There is a mast mounted Winegard GA 8780 preamplifier with a 2

Most of the time, in spite of this not so ideal situation, (location) I can receive the three networks and a few independents. The signal display on t he converter shows, as two horizontal bars, "signal quality" and "signal le vel". On most channels most of the time signal quality is pegged at 100 per cent and signal level runs between 45 and 55 percent. Within this window I usually have no problems with reception. As long as signal quality doesn't fold back I usually will get no drop outs. If it should falter excessively though both picture and sound will break up and intermittently freeze. So I 'm pretty familiar with what conditions will produce a good signal.

Lately Channel 4 although displaying 54 percent signal level and 100 percen t signal quality has had very slight "tearing streaks" going through the pi cture. If these aberrations only affected the picture we would be able to w atch the program. However this problem seems to chop up the sound as well. This makes it impossible to watch a program. I am a TV repair technician an d I have never seen this type of choppy sound on either OTA or cable before .

The weather of late has been hot and humid, which is atypical for New Engla nd this time of year. I've noticed in the past that during this type of wea ther we do sometimes lose reception on several channels for a day or two bu t never this long. I'm just wondering if anyone there might have a theory a s to what could be happening here. This only seems to affect channel 4, (wh ere all our shows happen to be). Thanks, Lenny

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Add star Klem Kedidelhopper Sun, Oct 2, 2016 at 3:55 PM To: "Yankowitz, Robert B" Reply | Reply to all | Forward | Print | Delete | Show original Hi Robert

Thank you for getting back to me. One thing that I failed to mention is that this is not a new installation. We put this antenna up about three years ago and it has always seemed to perform well.

I hear what you are saying about overload, and in theory Chester NH is not such a haul from Boston. TV Fool never mentions the use of an amplifier for my location relating to Boston, and I have used that resource a lot to determine whether an antenna job at a certain location would be feasible or not. The preamp though has always seemed to make a substantial difference here as well as throughout town. I had a customer years ago who lived out of town near the top of the mountain that is partially blocking our South West view. He was watching everything from Boston including 10 and 12 from Providence, with rabbit ears. So I've always figured that it must be the foliage and the terrain that's attenuating my signal.

Before digital, for my own house I used separate VHF and UHF antennas. We never needed any help with VHF, but UHF was always a challenge for us. The UHF antenna at the time was an 8 bay. During this period Winegard had just come out with a commercial preamp that had slightly lower gain but boasted an unheard of 1DB noise figure. I had to try this so I ordered one and installed it after the 8 bay. I pointed it towards Boston but channel 50's transmitter in Hudson NH splattered across the entire band. Although having a very hot front end the commercial preamp was not nearly as forgiving of overloads as the 8780. I eventually put a 20 DB trap set for channel 50 in line and that solved the overload problem. However in spite of all this, UHF reception with the 8 bay from Boston was never really very good at our house.

Since as we all know it's not possible to watch a polar bear in a snow storm with digital three years ago I realized that I had to do something. This parabolic which I'm presently using is a 300 ohm antenna which I had liberated from a job about 20 some odd years ago. I had always planned to use it "some day" and it had been sitting in the woods behind my house since. It had a few broken reflectors which I repaired.I looked up the specs recently on this antenna and it seems to beat everything out there. Gain is between 13 to 16 DB, but it's narrow beam width is really where it excels. Early on I had considered that my problem could possibly be multipath, however just turning this antenna a few degrees and signal starts to drop like a rock.

We didn't have cable TV here in Chester until the early 1990's, and back then I used to install quite a few antennas and retrofit existing ones with preamps. I had a nice Sadelco signal meter that tuned up to channel 83. I no longer do antenna work so I don't presently have equipment to measure OTA signals. So now admittedly a lot of this is an educated guess. Back then most consumer equipment particularly antennas were 300 ohms, and since the GA8780's input impedance also was 300 ohms I kind of standardized on this amp for my retrofits as well as new installations. The noise figure was about 3 DB which was the best of the time, beating Channel Master's figure of 5. However the real attraction of this amp was the very forgiving limiter circuit. I never had one overload on me, including those used in installations much higher than mine.

So as you might imagine I've been very frustrated with this problem. However as of five days ago the problem has disappeared. Signal levels and quality as measured on my converter boxes show no difference, and if this was weather related we have had varying degrees of weather through this period as well. We do sometimes experience days at a time where reception is poor for whatever reason but it's always reflected on the signal strength and quality indication on the converter box meter. This was definitely not the case this time though. To the best of my recollection in this past three years this particular type of problem has never happened before.

I do have a theory though that I wanted to suggest. The orientation of my antenna when it is optimized for Boston puts it a few degrees South East of New York City. Do you think that skip conditions were such through this period of time that this could possibly have been CO channel interference from WNBC in New York? As I had previously mentioned no other channels were affected nor have I noticed anything unusual on any of the Amateur frequencies or my low band two way business radio system.

We do occasionally see what I believe must be tropospheric inversion, and we do seem to experience them at different times of the year. During these periods, which typically last up to five days, Boston UHF TV stations that I never can pull in such as 56 and 68 come bombing in, and many times with 90 percent signal strength. Then as mysteriously as they appeared, after a period of time they're gone. This episode however didn't seem to be an inversion, as there were no newcomers in my channel line up through this time.

In 1975 I decided that I wanted to work in broadcasting. I got my First and I was hired as a studio technician for a UHF TV station in Central New York. Much of that work involved translator maintenance. I still recall (although not fondly) those awful cold trips up the mountains when the snowmobile wasn't running to service those miserable things. After that stint I switched careers to military, and then industrial electronics. I took a hard look at my life after that and since I had been repairing TV's from the time I was a teenager I decided to go in for myself. So since 1983 I've operated my own consumer electronics service business. Now I'm semi retired, (whatever that means) and I haven't seen the inside of a TV studio no less a network studio in 45 years. I'm sure much has changed.

I'm sure that you are more than familiar with it than I but I found a rather interesting article on tropospheric propagation on Wikipedia, and there was also if you are interested some propaganda on my antenna.

Thank you very much for trying to help me evaluate this problem. I appreciate the time and trouble you've taken. Very truly yours, Lenny Stein, KC1CPX

BTW, here are my coordinates: and although the topo maps said different acc ording to Google my altitude is 115 meters 465 Derry Rd, Chester, NH 03036, USA Latitude: 42.930838 | Longitude: -71.281921

More than likely because you're posting from google groups.

• Killfiling google & XXXXbanter.com: jonz.net/ng.htm

Digital CATV uses QAM modulation, not ATSC.

What is your point? His point was that a leaky cable system with signals on channel 4 could interfere with the OP's over the air channel 4 signal. That is certainly possible even if different modulation schemes are used. (And by channel 4, we mean virtual 4 - RF 30).

Besides using different modulation schemes, cable channels are also interleaved with OTA channels to prevent mutual interference (via leakage and ingress). For example, broadcast channel 30 goes from

Most of the leakage I've seen from CATV systems comes from poor Type-F coax connector installations by home owners and unterminated coax cables. It takes quite a bit of cable leakage to produce interference with an OTA signal, but it might be possible in weak areas and if the OTA TV system uses a pre-amplifier.

(...)

I can see why you received no response. 357 lines of disorganized ranting is difficult to parse. Please get organized and save readers the effort of wading through your mess. Same as always:

1. What problem are you trying to solve? Keep it very simple.
2. What equipment do are you using? Numbers and details are good.
3. What have you done so far and what happened?

I'm busy for a few days and will hopefully do a path profile this weekend. I don't know if I can squeeze much out of the path analysis except that you might have some obstructions or Fresnel zone diffraction problems. From the plots I previously posted, the coverage of both stations look identical.

Did you do any of the substitution tests that I recommended? The best test would be just the TV, a length of RG-6/u, and a simple 1/2 wave (at 500MHz) dipole hund outside the window. No amps or splitters.

Did you run your address through TVfool.com to see what signal levels they predict?

Slight misunderstanding. I need the type of antenna you are using at your house, and its elevation above ground level. You can save me some trouble excavating the information from your archive by listing everything (inclusive) between the antenna and the TV receiver.

Thanks for using a decent (decimal degrees) format. I hate DMS.

but in NAD27. Converting the FCC DMS to decimal and datum into WGS84: (42.310278 N, -71.237222W) NAD27 -> (42.31025 N, 71.23669 W) WGS84. Antenna height above ground 387 meters (1270 ft). Nice little monster tower:

Well, I have a few minutes I'll throw together a Google Earth path profile. It won't be very accurate and won't show Freznel zones, but will show any obstructions. Looks like drawing a 1270ft tower is gonna be difficult, so I guessed: If you have Google Earth, here's the PRELIMINARY KMZ file: Looks like you have a rather large hill directly in the path and very close to you. A 150ft or so tower at your end would be needed to clear the hill.

Incidentally, I vaguely recall a similar OTA problem where one channel was uncharacteristically low in receive signal. It turned out to be an unterminated length of coax on a coaxial splitter. Even though the splitter was suppose to have perhaps 20dB(?) of isolation between ports, the device was so badly built that I'm sure it was much less. The unterminated length acted as a notch filter which just happened to land on the TV channel frequency. Replacing the spllitter and removing the coax or terminating it with 75 ohms solved the problem.

The OP is definitly in a weak area (45 miles from stations) and IS using an aplifier just under the antenna. Anybody within a fe miles in the general direction of the broadcast antenna could be trashing his signal. Without the proper equipment (portable spectrum analyzer), it could be quite hard to find the problem.

Jon

Yep, and there's another problem: That a really rough and crude guestimate of the path, which shows a

Yep. I didn't check for other UHF TV stations in his area. Overload (blocking) is possible, but usually affects ALL the channels. Since I determined that the theoretical signal strength from both WBZ and KVCB are almost identical, I don't see a nearby signal trashing one signal, but not the other. The lack of complaints about other channels also points to a specific problem on UHF channel 30.

Test equipment is always nice to have. However, I think this one can be nailed by simply substituting parts of the puzzle and comparing the effects on both WBZ and KBCZ. When something is replaced that makes the signals equal, then the problem has been found.

However, if you really want to use a portable spectrum analyzer, any of the RTL2832U SDR receiver dongles make a nifty spectrum analyzer. I run several RTL-SDR programs on my Google Nexus 7 tablet that acts something like a spectrum analyzer. The basic sensitivity of the typical USB SDR dongle sucks without an RF preamp, but should be good enough to see what's arriving from the antenna mounted amplifier.

The connectors on the trunklines and feeders are 5/8-27 thread, and are quite strong. The housings have a pressed in stainless steel insert so the threads don't strip out easily. Also, the 60VAC @30A, modified square wave that powers the trunk and bridging amplifiers is carried on the rigid coax. If it is loose enough t radiate, it will have a high enough resistance to prevent the amplifier from working. The RayChem heatshrink ceramic connectors we used in the mid '80s were so strong that the outer aluminum tubing would break, instead of the connector to shield connection.

Different modulation systems would not mesh, and cause a weak signal from phase reversal. Download the Blonder Tongue Design Guide, and read it. CATV systems rarely carried A TV station on the same channel that it was transmitted on. For instance, United Video in Cincinnati, had custom labels for their converters. Instead of Ch 2 to 37, they were labeled 1 to 36. So, Channel 12 was actually on Ch 13 to prevent problems with direct pickup. The actual Ch. 12 carried one of our in house generated channels.

Thanks, but the 2014 version is more current: Other documents and catalogs might be of interest:

-- Jeff Liebermann snipped-for-privacy@cruzio.com

I have several other dates archived, as well. Sometimes you need the older information for existing systems.

Several other companies had useful publications, but the slow conversion to Fiber Aided CATV killed them off.