One channel issue, high VHF

[MikeBear]

Here is my TVfool: http://www.tvfool.com/?option=com_wr...8e03701cb62a56

Fmfool:



I'm up in North-Western Midland county Michigan, surrounded by 85-90' trees, and I've got all the OTA local channels in the Flint-Saginaw-Bay City DMA locked and working pretty well, with the exception of WJRT-12 VHF, which is only about 39 miles away from me.

I want to dump Dish Network and go OTA (Roamio Tivo), plus some streaming. I'm using a separate Y10-7-13 VHF antenna JUST for WJRT-12 and that's up about 35'~, into a (Holland) uvsj with a HDB91x UHF antenna (91xg clone) into the other side of the uvsj. That runs down to an MCM Electronics FM filter, and then into a Kitztech kt-200-coax amplifier. Installing the fm filter brought UP the signal on WBSF 46 by 15 points! Not sure why it would do that for so high of a UHF station, but it did.

Without that Kitztech amp, I lose half the stations. My Tvfool is posted above, though my signals are probably far less than what that shows, due to the heavy tree cover this time of year. For instance, WJRT-12 averages only 18-19db, which isn't much above the minimum. Channel 5 and 19 are by FAR my strongest signals, I wish all were as good as those two.

Ok, I'm in the woods, and surrounded by 85-90' trees, including pines. I have no hope of getting above or around the trees anywhere on my property. I have very strong FM stations fairly close, in fact WPRJ is only about 6 miles away, and is pretty much at the exact opposite magnetic heading that my VHF antenna is pointed at. So that station is trouble for sure without that FM filter, as my antenna is probably picking that up from the back and it's a harmonic for VHF 12. Though once again, this reception issue is completely random, and doesn't happen 100% of the time.

Anyway, something still is going on with my reception of VHF 12 (even with the FM filter), and I'm just not sure what it is. It's NOT 100% of the time, it doesn't seem to happen only when the trees move in the breeze, and I just am not sure what's left to try. The video and audio breaks up and pixelates at random. My TIVO Roamio basics diagnostics, shows RS Uncorrected errors, and that climbs higher at these times. My LG tv set (which runs off the same antennas, split through a high quality 2-way splitter) shows the "quality" jumping up and down from 100% to maybe 45%, then maybe 14%, then back up to 100% at the same time that the Tivo is showing errors and pixelating. However, the "strength" never varies more than 3 points up or down at this same time. This could go on for hours, or suddenly quit for a while.

The other day (Friday 8/7) was pretty bad, but then the rain started later in the evening, and the problem settled down and got better as the night went along and the signal level came up 5-8 points. It just beats me as to what's going on here. I'd think if it was some sort of multipath, that it wouldn't be quite so intermittent. But, maybe I'm wrong and it is simply multipath.

Anybody have any ideas? I did try TWO FM filters in series, (I did also even try an LTE filter) but it didn't seem to make a difference. I thought about some sort of electrical issue, but if it's that, I don't know what could be doing it, and why it would be intermittent. I don't have access to a spectrum analyzer that could check this, though I wish I did.

I can probably get my antenna UP at least another 5-10' or more, but that's pretty much the limit. Even then, it's still going to be behind trees.

[ADTech]

Move the antenna, try again. Repeat as needed.

[rabbit73]

My guess is electrical interference from power line noise, which is worse on VHF than UHF.

I have a VHF-Hi channel that is marginal. I can receive it sometimes when the SNR is 15-16 dB. When the noise level is higher, I can't receive it because the SNR is less than 15 dB. I am able to measure the signal and the noise in an adjacent unused channel, and my Sony TV gives me the SNR in the Diagnostics Screen. My old SLM (signal level meter) has an AM detector for the audio so I can hear the signal and the noise. It's the meter on the left; the newer meter on the right can also measure noise and signal.



I can sometimes track down power line noise using a portable AM radio. Try both ends of the AM broadcast band where there is no station. If you rotate the radio, you see a directional effect.

If you have a radio with an AM detector for VHF (like an aircraft band) that can also hunt noise. Using an FM radio doesn't work, because FM rejects noise.

MFJ makes a power line noise detector.
http://www.mfjenterprises.com/Produc...ductid=MFJ-852
http://www.arrl.org/files/file/Technology/HANDSON.pdf

The power line noise could be coming from inside your house from LED or CFL lamps, or switchmode power adapters; try cutting off circuit breakers.

Is the coax grounded with a grounding block? That helps reject interference.

Installing the fm filter brought UP the signal on WBSF 46 by 15 points! Not sure why it would do that for so high of a UHF station, but it did.

Good; that's from fundamental overload.

[No static at all]

Powerline interference is usually worst during dry weather (low humidity) from my experience. As humidity rises the interference tends to lessen, especially when raining.

[MikeBear]

Ok, I did find heavy interference (buzzing) on AM band at 530. It starts as I drive into my 220' long driveway, and stays as I get into my garage. This parallels the power line wires going to my house.

Anyway, I read on Denny's antenna site (he's only about 35 miles from me) about another person that unplugged a "power tender" charger, and got rid of the interference. I also have a $20 Harbor Freight power tender charging a battery in my garage. I unplugged it, and the AM interference stopped IMMEDIATELY! http://www.harborfreight.com/15-amp-...ner-99857.html

My wife is watching tv right now, so I can't check VHF 12 to see if this did anything for that issue. However, since my car radio could pick this up from over 200ft away, I'm betting (I hope!) it might now be cured.

Does/can interference like this actually BROADCAST itself along the incoming utility power cables?

[ADTech]

It usually radiates from the insulators due to dirt causing them to arc. I can routinely see the noise for up to several hundred yards on the spectrum analyzer.

Looks like rabbit73 gave you a good tip. Let's see how things turn out over time.

[MikeBear]

We have thunderstorms and heavy rain going on the last couple of hours, but in the lulls of heavy rain, I can already see that the signal level for VHF 12 has come UP to 60+%, and is over 25db on my Roamio (that was only around 18-19db earlier, before the charger was unplugged) My tv set's tuner is showing 65-66% signal strength, with locked 100% quality.

I think that's a good sign that the charger was causing the worst of it, but we will see as the next few days go by. I might still have to get the VHF antenna up a little higher just in general. Gotta have good fade margin with woods like these surrounding me.
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Edit: Well, it's 3 am here now, and I have now also discovered that my Dell Latitude E6410 90watt 19volt laptop power brick ALSO causes the VHF "signal quality" level to vary up and down from 100% - 0% and all points in-between at random. It only does this when plugged into the laptop, AND when the laptop is turned on. If I unplug the brick when that quality level is varying, it immediately jumps back to 100% and stays there with no fluctuation! At the same time, my Tivo Roamio stops throwing off RS errors. The laptop and power supply are in my living room, and the power outlets are on the same circuit.

So, guess I'll be getting a new power supply, and hope they all don't cause this same issue. If so, then I can take further steps to cure it, or I won't leave it plugged into my laptop all the time

[rabbit73]

Thanks for the report with positive results. I'm glad that I was able to point you in the right direction to make the tests.

You made my day, Mike.

[MikeBear]

Originally Posted by rabbit73

Thanks for the report with positive results. I'm glad that I was able to point you in the right direction to make the tests.

You made my day, Mike.

Thank YOU!, I appreciate you bringing up, and getting me to re-evaluate the whole thing,

I had thought about power-line interference, but couldn't think of what I had here that might cause it. I looked around a little, but never thought about that charger, OR the laptop power supply that's been running in my living room for years! (I wasn't using OTA tv much during that time)

I just didn't realize how INSIDIOUS power-line interference could be with digital tv.

Now, if I can only calm down the multipath on windy days. I'm going to try some things now to get my signal levels higher. That should help.

Does the "planar reflector" he built and added on the back of the Y10713 antenna here: http://www.antennahacks.com/hacks/myy10-7-13v.htm help with multipath?

[Tower Guy]

Try moving the VHF antenna up or down a few feet.

[MikeBear]

Originally Posted by Tower Guy

Try moving the VHF antenna up or down a few feet.

Moving DOWN, even by a foot (which is the easiest) lowers the signal and makes it permanently worse. It'll be sometime in the next week before I can mount it higher. I have a few logistics that need to be worked on for that, and changing out the mast pipe for a longer one.

Has anybody tried this Stellar Labs 30-2475 VHF antenna yet? It seems to have specs that should make it a little better than the AntennaCraft Y10-7-13 antenna. Also, it has a built-in 75 ohm balun, instead of the old-school balun you have to add for the AC antenna.

http://www.mcmelectronics.com/produc...ductid=30-2475

[ADTech]

Has anybody tried this Stellar Labs 30-2475 VHF antenna yet?

It would appear that MCM is importing this item from China and selling it under that part number: http://www.qiaohua.com/products/v-9h.htm That's the same Chinese company that supplies the rest of their house brand antennas.

I'd find it pretty unlikely that it would outperform the AC Y10-13. A general rule of thumb is that antennas with similar configurations will perform in similar manners. Given that the MCM offering is short a few directors and it's a lot shorter overall, it's likely to be several dB below the AC in forward gain. The two extra reflector rods would improve the F/B ratio, but wouldn't do much for forward gain. Most likely, the Chinese company is quoting gain in dBi as opposed to the dBd that AC used. Neither MCM or the Chinese company provide that information.

[rabbit73]

I agree with ADTech's evaluation of the MCM antenna.

[MikeBear]

This is just crazy! So, the main issues above have been cured by unplugging the Harbor Freight charger, and changing the Dell laptop power brick for an upgraded unit that works fine.

So, with slightly bad weather and fluttering trees, the Tivo Roamio has still at times been throwing off some RS Uncorrected errors now and again on Wjrt-12. Even with a higher signal level, which I figured could be normal due to weather conditions. At those times, the signal level might vary from 47-52, or 18-21db.

So, I haven't done anything else to my antennas as of yet, and we have 24mph GUSTY winds right now with 84 temps and sunny, and the trees in front of the antennas are fluttering, and waving around to beat the band. NO ERRORS are showing on the Tivo, even with the signal level still varying from 18-21db, or 47-52 signal level. I have to assume the changing levels are due to the wind moving the trees.

I'm happy there's no RS errors and the picture is staying locked, but, how come no errors right now? You'd think if I was going to get them, those conditions would cause it.

Just when I thought I had this figured out, lol...

[rabbit73]

Not too crazy, it's the nature of the beast.

Many things can cause errors in the digital stream. The BER (Bit Error Rate/Ratio) can be increased by a weak signal, multipath reflections (Static or Dynamic), and by electrical interference, as you found out. Any or all can be present at any time.

The FEC (Forward Error Correction) can correct a limited number of errors in the digital stream. Once that limit is exceeded, you reach the Digital Cliff, where you experience pixelation, picture freeze and finally dropout.

Forum member mulliganman was having an unacceptable number of uncorrected errors with his TiVo Roamio. This is his Diagnostics Screen readings before improvements:

Originally Posted by mulliganman

I went into the DVR diagnostics menu on the Roamio to get some info for all channels. Here is what it shown (as setup in the diagram I posted):

Channel 3-1 signal strength 55%, 22 dB SNR, RS Corrected 0, RS Uncorrected 66

Channel 3-2 signal strength 55%, 22dB SNR, RS Corrected 0, RS Uncorrected 60

Channel 3-3 signal strength 57%, 23 dB SNR, RS Corrected 0, RS Uncorrected 81

Channel 10-1 signal strength 67%, 27dB SNR, RS Corrected 0, RS Uncorrected 30

Channel 21-1 signal strength 52%, 21 dB SNR, RS Corrected 0, RS Uncorrected 132

Channel 21-2 signal strength 52%, 21 dB SNR, RS Corrected 0, RS Uncorrected 30

Channel 21-3 signal strength 52%, 21 dB SNR, RS Corrected 0, RS Uncorrected 60

Channel 27-1 signal strength 60%, 24 dB SNR, RS Corrected 0, RS Uncorrected 6

Channel 33-1 signal strength 60%, 24 dB SNR, RS Corrected 0, RS Uncorrected 0

Channel 33-2 signal strength 60%, 24 dB SNR, RS Corrected 0, RS Uncorrected 120

Channel 33-3 signal strength 60%, 24 dB SNR, RS Corrected 0, RS Uncorrected 45

Channel 49-1 signal strength 45%, 18 dB SNR, RS Corrected 0, RS Uncorrected 6

Channel 49-2 signal strength 45%, 18 dB SNR, RS Corrected 0, RS Uncorrected 0

and this is after improvements:

Originally Posted by mulliganman

I believe the coax from the 91XG to the attic amp to be less than 25 feet, so I made the following change as you suggested: 91XG > downlead > LNA 100 > AC7 ch 49 input. The C2V went into the other input of the AC7. I did a rescan, then as soon as I had a chance a little while later I went back into the DVR diagnostics menu on the Roamio. Here are the results:

Channel 3-1 67% signal strength, 27 dB SNR, RS Corrected 0, RS Uncorrected 0

Channel 3-2 65% signal strength, 27 dB SNR, RS Corrected 0, RS Uncorrected 0

Channel 3-3 67% signal strength, 27 dB SNR, RS Corrected 0, RS Uncorrected 0

Channel 10-1 72% signal strength, 29 dB SNR, RS Corrected 0, RS Uncorrected 0

Channel 21-1 72% signal strength, 29 dB SNR, RS Corrected 0, RS Uncorrected 0

Channel 21-2 72% signal strength, 29 dB SNR, RS Corrected 0, RS Uncorrected 0

Channel 21-3 72% signal strength, 29 dB SNR, RS Corrected 0, RS Uncorrected 0

Channel 27-1 72% signal strength, 29 dB SNR, RS Corrected 0, RS Uncorrected 0

Channel 33-1 67% signal strength, 27 dB SNR, RS Corrected 0, RS Uncorrected 0

Channel 33-2 67% signal strength, 27 dB SNR, RS Corrected 0, RS Uncorrected 0

Channel 33-3 67% signal strength, 27 dB SNR, RS Corrected 0, RS Uncorrected 0

Channel 49-1 62% signal strength, 25 dB SNR, RS Corrected 0, RS Uncorrected 0

Channel 49-2 62% signal strength, 25 dB SNR, RS Corrected 0, RS Uncorrected

I was surprised to see improvements in signal strength and the RS Uncorrected numbers across the board. I'm not sure if the "0" for the RS Uncorrected is just temporary because I had rescanned or not. I had never seen that on any channels other than 49-1 or 49-2 when looking at in the DVR Diagnostics menu on the Tivo Roamio (I had a similar setup just the LNA 100 after the AC7 combiner but didn't see the same results). Maybe someone else can jump in with an explanation of what they think is going on or if I should leave the LNA 100 as the only amplification on my setup.

[MikeBear]

Thanks Rabbit, I will read/study through that thread again to see If there's any ideas I can implement for myself. I know my antenna configuration is not 100% set in stone as of yet, there's many things I can try to tweak it a bit better.

For what it's worth, the Tivo Roamio is incapable at present of showing Corrected RS errors at any time, so that field will ALWAYS be 0.

That's what I have gathered after a search on Google from various sites. Perhaps Tivo company will put out a revised firmware sometime that will fix this issue, but I'm not holding my breath.

My problem (when it happens) also is seen on my tv set tuner hooked right next to my Tivo, so it's an inherent antenna reception issue, NOT just a Tivo issue. Not withstanding the fact of course that the Tivo has a built-in 4 way splitter and 4 tuners, which of course would explain signal % level differences between Tivo and tv set.

[MikeBear]

As a test, I removed the Kitztech KT200 pre-amp, and reinstalled my CM7777 preamp with an external FM trap, and the internal FM trap turned ON. So there is two FM traps installed on the input of the CM7777.

I see very little difference in the signal levels on my Tivo between the two pre-amps. The VHF levels on Wjrt-12 are exactly the same. Some of the UHF channels went a little bit higher.

Kitztech kt200 is supposed to be 24db for both, with .4db noise. Does anybody know (for SURE) what the CM7777 pre-amp is for db and noise level? I think around 2db noise, but not sure on the signal level.

As for getting my antennas up higher, I'm still working on the preliminaries. I have to manufacture a swivel bracket for the bottom of the new 21' mast pipe, so I can swing it up by myself without the possibility of dying or dropping the antennas with the old way I have the shorter one mounted.

Once I came upon the idea of using a swivel mount (I was reading about hinged towers at the time) everything CLICKED into place in my mind! So, I'm working on this, and hoping our weather soon clears up as it's been horrible the last few days.

Does anybody know of an available UHF/VHF preamp that has a higher level JUST for VHF?

[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?

[MikeBear]

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 would agree that I need more signal at the antenna. Yes, the antennas are maybe mounted too close right now, but I'll fix that with the new longer mast. My house is in a slight hollow, (and surrounded by woods) below the level of the houses to the South and South-East which are on a ridge probably 5-10ft higher. Even with my antenna mast at 35', I don't think the VHF antenna quite clears the roof of the house I have to aim over for vhf channel 12. Without an amp, I lose some of the channels, or they pixelate badly.

Even with my mast up another 10 feet, I will still be in the hollow and surrounded by trees. You should figure that my TvFool above shows signals more than probably almost DOUBLE of what I can actually receive.

[rabbit73]

I removed the Kitztech KT200 pre-amp, and reinstalled my CM7777 preamp

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

I see very little difference in the signal levels on my Tivo between the two pre-amps.

Are you talking about signal strength or SNR on the TiVo? Often signal quality as defined by SNR and errors is more important than signal strength with digital signals.

Does anybody know (for SURE) what the CM7777 pre-amp is for db and noise level? I think around 2db noise, but not sure on the signal level.

The old 7777 had a listed vhf gain of 23 dB and a noise figure of 2.8 dB; 28 dB gain and 2 dB noise figure for UHF. The new 7777 is 30 dB gain and "ultra low noise" noise figure, whatever that is. When the new version came out, they said NF ≤ 5 dB; now they don't say anything about NF.

Many of us techs were really upset with PCT when they bought out CM, closed the NC plant, and fired first grade RF engineers. But what really got us was when they redesigned the 7777, but kept the SAME model number to seemingly trade on the good reputation of the original 7777. This bothered many of us, so that we stopped experimenting with the CM preamps, stopped recommending them, and started recommending other brands. Then Winegard started shrinking and cheapening their preamp line. Then Antennacraft folded. We are left with CM, Antennas Direct, and RCA. Antennas Direct dropped their excellent CPA 19 and replaced it with the Juice, which is in short supply. There is also, as you are aware, a selection of very low noise preamps, but they have a history of sensitivity to static damage.

To answer your original question, the old 7777 figures are accurate according to my crude measurements. The new 7777 is an unknown.

Calaveras, of AVS, uses a Tin Lee 30 dB UHF MA-25U-77 preamp for his two 91XGs that he likes very much.

http://www.tinlee.com/MATV_headend.p...#AntennaPreamp
http://www.tinlee.com/MATV_headend.p...#AntennaPreamp
http://www.tinlee.com/PDF/MA-series-info.pdf

Does anybody know of an available UHF/VHF preamp that has a higher level JUST for VHF?

More gain for VHF?
I agree with No static at all.
You don't need more gain for VHF, you need to put the antenna where the signal is.

I don't think the VHF antenna quite clears the roof of the house I have to aim over for vhf channel 12.

First it was the trees, and now a house?

After looking at your tvfool report, I think a simple folded dipole antenna above the trees and house would be good enough for 12.