Problem receiving KVUE in metro Austin area

[egatx]

Hi,

I am unable to receive KVUE-DT reliably, whereas other local stations (broadcasting from the same tower location) work fine.

Though my tuner (a SiliconDust HDHomeRun Dual) reports a relatively strong signal (80% signal strength, 85-100% signal quality, 100% symbol quality), this particular station glitches every 1-2 minutes (pixelation, audio drop-outs, etc.). I have no reception issues with the other stations I care about (KXAN, KLRU, KEYE, KNVA, KTBC).

Here is my TVFool signal analysis result.

And here is the antenna I'm using (an RCA ANT751 Yagi).

Here are some pictures of the antenna mounted on my roof:
basic antenna setup
view from antenna's perspective, pointing at Austin towers

The antenna does "look through" a relatively large oak tree in my yard, as you can see from the second picture.

To verify reception issues with just this one channel, I viewed each channel for 5 minutes or so, noting no reception problems on any station except for KVUE. Also, I ran a low-level network packet loss test, which also tests for reception issues (documented here), and this test indicated no reception errors on any channels except for KVUE. There was no network packet loss, only loss due to signal reception.

The only root cause I can come up with is interference (from the tree?), but I'd appreciate others' opinions, and I'd especially appreciate suggestions for removing the issue.

I should also note that I had previously used a different antenna (this one) in the same location, on the same mast, and I never had reception issues on any channel. Why did I change it, you ask? Through a series of unfortunate events, beginning with this SiliconDust issue (which I did not know about until weeks later), my HDHomeRun Dual stopped working, and I incorrectly concluded that it had died. So, I replaced it with the newer HDHomeRun Connect, which I could never get to receive a signal reliably (all channels were intermittent), having changed nothing else (i.e., same antenna, cabling, etc.).

This led to a series of hacks, including installing an antenna-mounted preamplifier, which worked great with the HDHomeRun Connect for about a day, but then stopped working (I later removed it). When I finally discovered the SiliconDust HDHomeRun Dual issue linked above, and installed the newer firmware, I was disappointed to observe that I could not reliably receive any channel (keeping in mind that this is the exact setup that previously was rock-solid, save for the new firmware and the fact that I "fussed" with the antenna to try to get the replacement HDHomeRun to work).

For better I worse, I concluded that I had damaged my existing antenna setup while playing around with the preamplifier, so I replaced it with the RCA Yagi noted above, which seemed like a better choice and was available in-store at my local Lowes.

Now, as stated originally, I can reliably receive all stations except for KVUE. Any ideas?

[Tower Guy]

I see too many variables to diagnose the problem.

Is it the antenna? Try the 2 bay again.

Is it the coax or a bad connection?

Is it the tuner? Try the tuner in the TV set

Is it the signal from KVUE? That's rare, but not impossible.

Is the time period between disturbances repetitive? If so, what's the period?

[egatx]

Thank you for the reply.

My original setup (CM 4220 antenna + HDHomeRun Dual tuner) was working fine for 5 years. Ignoring all the intermediate hijinks due to me trying to get a new tuner to work, I eventually returned to this original setup (with corrected tuner firmware), and it had stopped working (no reliable reception on any channel). I concluded I damaged my antenna and replaced it with the RCA Yagi.

I assume that if I replace my original antenna, it will still fail to work. I suppose I could replace it with a new identical unit (i.e., buy another CM 4220), but in evaluating this decision, it seemed like the RCA Yagi was a better choice given the channels I want to receive (especially the lone VHF channel).

Regarding the possibility of bad cabling / connections, wouldn't this affect all channels and not just one? Or is it possible that a bad connection can affect a single channel while not affecting others?

I haven't tried the tuner in the TV set, so I'll do that.

Viewing this problem a different way: if I were starting from scratch, given my location and desired channels, what antenna would this community recommend? I can't use indoor antennas, because my house uses radiant barrier materials.

Thanks!

[WIRELESS ENGINEER]

The 4220 (2 bay bowtie) antenna has much greater directivity so it would tend to reduce multipath

The RCA antenna is mostly a VHF antenna with fairly low gain and directivity on UHF

Looking at all the buildings around you, it looks like you are seeing a lot of multipath due to those buildings

A more directional UHF antenna may reduce the out of phase multipath signal enough to eliminate the issue

A 4 bay bowtie may do the job so something like the DB4e or equivilent would be my choice

[egatx]

Great suggestion, thanks. I'll look at the DB4e.

Is it possible the oak tree in my yard is interfering enough to degrade reception? The tree is ~40 feet from the antenna, and the antenna must point through it to aim at the Austin towers. I'm trying to determine whether or not I should try to move my antenna higher on my roof to aim around the trees. I suppose I could just try it and see...

[ADTech]

I'd especially appreciate suggestions for removing the issue

I'd recommend simply 1) moving the antenna so it's not right on the metal gutter and 2) move it so it isn't staring point blank into a tree. Both are commonly encountered but less obvious installation errors.

Proximity to large metal surface causes interference with anticipated antenna patterns and can, if the proximity is just wrong, act as a trap for a specific frequency.

Trees can cause unpredictable results and can cause dead spots for specific frequencies for a very specific location in the spatial environment behind the tree. With UHF wavelengths, moving the antenna by as little as 6" can move a receiving antenna either into or out of these highly localized dead zones. FWIW, I'm going to blame it on the tree until any other factor surfaces.

You do not need a different antenna, you just need to use the one you have more effectively.

[egatx]

ADTech, thanks for the response. My intuition is the tree also. I'll try moving my existing antenna and see what happens.

[rabbit73]

Your intuition is excellent. Trees block TV signals.
http://www.hdtvprimer.com/antennas/siting.html
scroll down to Trees and UHF

[egatx]

A quick update on this, with new information, and a new question:

I did more characterization on the channel that fails (KVUE), and using SiliconDust's diagnostic tool, I noted that the reception interference occurs very predictably and periodically, approximately every 30 seconds.

In this picture, a "t" in the command window on the left indicates a reception error. Though you cannot obviously discern the time period from the picture, the "t" occurs predictably and periodically, approximately every 30 seconds. Using SiliconDust's graphical tool (the window on the right), when the "t" occurs, the symbol rate drops. The rest of the time, the symbol rate is steady at 100%.

Assuming the diagnostic tool can be trusted, I would expect that the cause of the interference is not due to the physical environment (trees, etc.), unless the TV signal itself has a periodic component that only occurs approximately once every 30 seconds. I tend to think that there is some electronic device emitting an interfering signal on a periodic basis, though I don't know what this could be.

Any ideas?

[ADTech]

I noted that the reception interference occurs very predictably and periodically, approximately every 30 seconds.

That would eliminate both of my previous suggestions but, ironically, my recommendation might be the solution anyway.

Assuming that you're receiving periodic bursts of noise into your problem channel's bandwidth, relocation of the receiving antenna might be the solution. In addition to possibly getting the antenna into a spot where the interference is lessened, it would also likely improve the signal of the desired station thus improving the SNR.


Ideally, what you need is spectrum analyzer to assist in finding the source of the presumed interference. They're not inexpensive, though, and there's always the possibility that the interference is only within that channel's bandwidth and won't be seen anyway.

[Tower Guy]

Originally Posted by egatx

I did more characterization on the channel that fails (KVUE), and using SiliconDust's diagnostic tool, I noted that the reception interference occurs very predictably and periodically, approximately every 30 seconds.

Any ideas?

Yes, it's most likely a KVUE transmitter problem. It is caused by a momentary overload of the linearity correction sample amplifier. The Harris Apex exciter takes a new sample every 30-31 seconds. The solution is to add a 6 db attenuator to the sample input.

http://www.minicircuits.com/pdfs/VAT-6+.pdf

Very few receivers are bothered by this momentary disturbance. The one I dealt with was a Panasonic Plasma.

[rabbit73]

Fascinating!

The feedback correction system made the transmitted signal worse instead of better.

[egatx]

Thanks again for the quick responses. Someone on SiliconDust's forum referred me to this: http://www.silicondust.com/hdhomerun...s_solution.pdf

... which sounds like my issue. Indeed it does look like an issue on the broadcast side, with a potential firmware workaround.

[egatx]

Originally Posted by egatx

Someone on SiliconDust's forum referred me to this: http://www.silicondust.com/hdhomerun...s_solution.pdf

... which sounds like my issue. Indeed it does look like an issue on the broadcast side, with a potential firmware workaround.

I applied the firmware workaround in the linked doc, and the reception issue went away. I can now tune to KVUE reliably. I emailed KVUE, pointing to this thread, as an FYI, since it sounds like this is an issue on the broadcast side, though I'm satisfied with the workaround.

Thanks everyone on this thread for the informative responses.

[rabbit73]

Thanks for the update.

Well done!

Enjoy your system.

[ADTech]

Thanks for supplying the background info that only a broadcast station engineer would likely to know.