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-   -   One channel from same location pixelating (http://forum.tvfool.com/showthread.php?t=16275)

Bigbear 4-May-2017 2:16 PM

One channel from same location pixelating
 
http://www.tvfool.com/?option=com_wr...e6a403c11d2bb9

I got a new TIVO Roamio DVR and I'm having issue with WCAX-tv. It pixelates
while the other channels from the same direction do not.
I have an old antenna that came with the house. I have a pre amp on the antenna. I use 75 ohm cabling and a 4 channel in house amp as well. The cable to the TIVO also goes through a Monster power bar.
So far I have swapped the cable from the power bar to the TIVO, and switched the cable to the power bar.
So far nothing has helped. BTW with all the same cabling when using my old HD TIVO I did not have this issue.

Any ideas?

Thanks
Bear

ADTech 4-May-2017 2:49 PM

Eliminate one of the (unidentified) amps, for starters

One amp is usually more that adequate if properly selected. Two amps are only needed under very, very unique situations and, too often, cause new problems.

The Monster power bar is largely irrelevant for any reception concerns unless it happens to be defective. No evidence of that.

Multi-tuner Tivo's usually have their own internal amp prior to the splitter that feeds the individual tuner sections. That would make three of them (if incorporated) in your case....

Different receivers, including Tivos, have different capabilities. My suspicion is that your new Tivo is slightly more susceptible to strong signal overloading than was the old one. You'd have to contact Tivo and see if they would answer that question (doubtful).

Bigbear 4-May-2017 3:02 PM

Thanks AD tech, never considered that.

The 2 channels I mostly watch (WCAX and WPTZ) both display a signal strength of about 60%. With this signal can I still be over loading the signal? Then any reason why only one of my 2 favorite channels pixelate?

ADTech 4-May-2017 3:11 PM

Quote:

both display a signal strength of about 60%. With this signal can I still be over loading the signal?
Displayed percentage is largely irrelevant since it doesn't correlate to signal strength but rather signal quality. Excessive amplification degrades the quality of the signal.

Quote:

Then any reason why only one of my 2 favorite channels pixelate?
Because, according to your attached plot, those two stations are already your two strongest signals, both with calculated VERY, VERY strong signals.

Of course, assumptions are being made due to the lack of specifics (antenna, aiming direction, potential line of sight impairments, specific amplifiers in use, cabling, etc). The above is a generalization based only on the provided data.

Bigbear 5-May-2017 11:36 AM

I have an old antenna mounted about 20' on a pole with a rotor. The antenna is pointed to the NNW ( towards Montreal) as that is where the weakest signals come from. The local channels actually are received from the rear of the antenna. I have an Antenna craft (made by permacolor # 106212) mounted just under the antenna.
75 ohm cable goes down the pole to a grounding block, then into the house to the power tap for the pre amp. From there on to a Channel master 3044 distribution amp, then to 4 devices with about 20' or so of cabling.

The pre amp's gain setting is as low as it can go, and the FM tap is enabled.
Yesterday I unplugged the pre amp to see if the pixelation would stoop, but without power no signal is passed through.
I read somewhere that a distribution amp is preferable to splitters.


Do I need to go up and bypass my pre amp?

ADTech 5-May-2017 12:50 PM

Unplugging the power to a preamp typically turns it into a ~30 attenuator. Not a valid test unless you WANT to test reception with a 30 dB reduction of signal.

I can't find anything regarding the amplifier you identified but, based on my experience with all of the Radio Shack amps I'd accumulated back before I started working here, I don't have any confidence in them. All of them got chucked into the recycle bin when I tested them on my lab's gear a few years back, their performance was truly that abysmal.

The choice of preamp vs distribution amplifier isn't that simple, it requires some analysis and calculations. If a preamp is used, the a passive splitter is almost always the correct distribution device but, again, that decision should be based on the circumstances for each individual installation, got any general rules.

Amplification should be thought of as subject to the "Goldilocks" rule: Not too much, not too little, it works best when it's "just right".

Tower Guy 5-May-2017 3:59 PM

There are multiple issues happening simultaneously.

The antenna is misaimed when you are trying to pick up the US stations. This causes multi-path (ghosting). The Roamio is a bit fussy over multipath.

The preamp is not necessary for the US stations but critical for Canada.

The use of both a preamp plus a powered distribution amplifier simultaneously will cause problems due to the higher strength of the US stations.

That said, how do you fix it?

I'd keep the existing system aimed at Canada. I assume that it gets the two VHF stations, CFTM and CFCF. The CBC station from Montreal is not on the TVfool report, but CBMT is running lower power than the other UHF stations from Montreal that the radar report lists as too weak to receive.

Next I'd get a simple UHF antenna for WPTZ, WCAX, WFFF, and WETK. DB-2 or C2 are two possibilities. The UHF antenna will not want any amplification. Couple the two antennas using a UVSJ, but be careful to add the antenna after the preamp used for Canada. You may be able to get WVNY on VHF channel 13 off the back side of the existing antenna.

If that works OK, stop there. If not, replace the distribution amp with a four way passive splitter.

Bigbear 5-May-2017 8:07 PM

Thanks Tower guy.
I'm running an experiment now where I put a spliter before the distribution amp and sending the signal to the Roamio without the distribution amp.
Hope it works!

Tower Guy 5-May-2017 9:26 PM

That is easiest to try, but the least likely to fix the problem. The overload of the second preamp is most likely to occur when the antenna is aimed at Mt Mansfield. The Roamio is most likely to work when the antenna is aimed at Mt Mansfield. Note the catch 22.

Bigbear 6-May-2017 1:00 PM

Thanks
experiment inconclusive as it was very windy here the last day or so.

The thing that is still buggin me is the fact that WCAX and WPTZ come from Mt Mansfield. One has issues, the other not.

If I were to get a separate antenna to point at Mt Mansfield, when the 2 signals are combined wouldn't the over power issue remain?

Tower Guy 6-May-2017 2:20 PM

The trick is to pre-amplify the VHF signals from Montreal but not the UHF signals from Mt Mansfield. You do that using a seperate coax for each antenna and add them after the power injector for the RS preamp. The UVSJ will remove the UHF signals from the all channel antenna aimed at Canada.

Bigbear 6-May-2017 2:37 PM

So would something like this work? https://www.antennasdirect.com/store...Combiners.html
Or would I need to run another 75 Ohm lead into the basement and combine them there? Oh I guess you already answered that!

ADTech 6-May-2017 3:45 PM

Quote:

The thing that is still buggin me is the fact that WCAX and WPTZ come from Mt Mansfield. One has issues, the other not.
It is a common misunderstanding of how different frequency (channel) radio waves propagate over distance, terrain, and through trees to assume that they will all arrive at some arbitrary point in space (where your antenna happens to be planted) with adequate strength and quality. Also, we don't have any idea of what antenna you have or what its reception characteristics might be, especially from off-axis directions. The solution for such instances is to simply move the antenna and try again, repeating as needed.

Don't forget that there is also a VHF-13 on Mt Mansfield. If you can get it with the big antenna aimed at Montreal, then TG's idea will work. One other alternative is, if you can score a UVSJ made by Holland or Pico (SCARCE!), is to take advantage of those models' DC pass on their VHF side for VHF-only amplification. This would allow masthead amplification and avoid running a second coax. Note that the Antennas Direct UVSJ has DC pass on the UHF port and cannot be used for this alternative idea but it will work just fine with TG's suggested configuration.

Tower Guy 6-May-2017 4:36 PM

Quote:

Originally Posted by Bigbear (Post 57905)
The thing that is still buggin me is the fact that WCAX and WPTZ come from Mt Mansfield. One has issues, the other not.

You could ask it the other way around. Why are you lucky enough to receive WPTZ using a mis-aimed antenna?

rabbit73 6-May-2017 6:42 PM

2 Attachment(s)
Quote:

I have an Antenna craft (made by permacolor # 106212) mounted just under the antenna.
That is probably the 10G212 which has a gain of 30 dB.

http://www.solidsignal.com/pview.asp?p=10g212

Quote:

From there on to a Channel master 3044 distribution amp,
That has a gain of 22 dB.

https://www.amazon.com/Channel-Maste.../dp/B000GGFXW8

Waaaay too much amplification.

Quote:

The 2 channels I mostly watch (WCAX and WPTZ) both display a signal strength of about 60%. With this signal can I still be over loading the signal?
Overload can cause gain compression that will reduce the signal strength reading on the Roamio Diagnostics screen. Pay attention to the uncorrected errors on that screen; it should be no uncorrected errors.

The Roamio signal strength will not go to 100; it will max out before that.

Forum member mulliganman was using a TiVo Roamio and also had strong local signals. See his report in attachment 2. His signal strength never went above 72%.

https://forum.tvfool.com/showpost.ph...6&postcount=21

Try following the advice by Tower Guy in post #7.

The difference between your strong local signals and your weak desired signals is too much for your present system to handle.

Also, CFCF on real channel 12 has adjacent channel interference from WVNY on real channel 13.

Bigbear 6-May-2017 8:34 PM

Thanks
I'm thinking of going with tower guy's suggestion, but a little fuzzy on where to combine the signals. If it's up on the roof, will water be a problem?

Could you give me a suggestion of a UHF antenna to use?

BTW this is what I am using now http://forum.tvfool.com/attachment.p...6&d=1402837984

rabbit73 6-May-2017 11:56 PM

Thanks for the photo of your antenna. That looks like a medium gain all-band antenna for channels on VHF-Low, VHF-High, and UHF.
Quote:

Could you give me a suggestion of a UHF antenna to use?
The antennas suggested by Tower Guy are suitable.
DB2E
https://www.antennasdirect.com/store...r-Antenna.html
https://www.amazon.com/Element-Bowti.../dp/B0074H3JCS

C2
https://www.antennasdirect.com/store...-Complete.html
Quote:

Originally Posted by Bigbear (Post 57908)
So would something like this work? https://www.antennasdirect.com/store...Combiners.html
Or would I need to run another 75 Ohm lead into the basement and combine them there? Oh I guess you already answered that!

That is a suitable UHF/VHF combiner AKA UVSJ.

Quote:

I'm thinking of going with tower guy's suggestion, but a little fuzzy on where to combine the signals. If it's up on the roof, will water be a problem?
The problem is with the preamp. You need the preamp for the weaker VHF signals from 342 degrees using your present antenna, but you must not use a preamp for your local strong signals from the UHF antenna. If you put the combiner outside between the antennas and the power inserter inside, then the combiner must be able to pass power to the VHF antenna preamp. But, that type of combiner is no longer available; only the ones that would pass power to a UHF antenna preamp, which you don't need.

That is why you need two coax lines coming down.

Code:

                DB2E > coax > grounding > coax >
                                block          \
                                              UVSJ > splitter > TV           
                                                /
VHF > preamp > coax > grounding > coax > power >
ANT                    block            inserter

The first thing you must do is to use just the DB2E to get the locals OK. Then, add the VHF antenna with the combiner.

Bigbear 7-May-2017 1:59 PM

Thanks rabbit for the diagram. Now the only problem is finding a UVSJ. All the links I find lead to discontinued products.

Bigbear 7-May-2017 2:06 PM

Is this a UVSJ?
https://www.radioshack.com/products/...itter-combiner

JoeAZ 7-May-2017 2:13 PM

Bigbear, Another option might be to use a new, compact antenna for UHF/VHF
for your locals such as:https://www.walmart.com/ip/RCA-Attic...enna/146879296 or https://www.amazon.com/GE-29884-Outd.../dp/B01MYMVPVX Those antennas should provide satisfactory reception of RF 13 as well as your UHF stations. For your Canadian stations on VHF, continue to use your existing antenna, aimed at Montreal. Unless your RG6 cable runs are over 50 feet, you should not need
any amplification except perhaps a distribution amp. Run the two cables of
RG6 and use an A/B switch to change between antennas. I do
not favor combiners as they cause more problems than they solve.
Not the most convenient way but after installing antennas for 30 years,
it works best...........


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