One channel issue, high VHF

[MikeBear]

So, I need a house in that subdivision! lol

I'd LOVE to have a lakefront house right there at landfall. Unfortunately, even though some of the houses there are very old, people with money tend to buy them for around $300k, (for the property) scrape them off, and put up a new mini-mansion. Anywhere else in the area, and quite a few of those houses wouldn't be worth $100k.

I don't have that sort of money...

Once again, THANKS Rabbit! I very much appreciate your work in all this, and digital tv has forced me to have to analyze everything, when I'd much rather just watch tv! Now, if they'd only crank up the power on Wjrt just another 10k watts...

It's ridiculous that the FCC doesn't allow stations to broadcast at higher levels. At least with analog tv, you could watch a show even if it was snowy and faded-out.

[rabbit73]

So, I need a house in that subdivision! lol

Nah, you wouldn't be happy there. The taxes would eat you up and the neighbors wouldn't tolerate antenna experiments. Your location has a higher elevation:

Now, if they'd only crank up the power on Wjrt just another 10k watts...

The FCC set the power levels for DTV based on the assumption that everyone would have an outdoor antenna at 30 feet. They soon found out that their assumption wasn't realistic and have had to grant power increases to many transmitters.

DTV Coverage and Service Prediction, Measurement and Performance Indices

Oded Bendov, John F.X. Browne, Charles W. Rhodes, Yiyan Wu, and Pierre Bouchard

Quote:

Abstract-- It is now clear that methods used to predict the replication of NTSC service in the US were idealized and, for the most part, not validated. The need to review the methods and procedures now in
use is highlighted by the various field tests conducted in the US and elsewhere.

This paper outlines potential improvements in the modeling, methods and procedures now in use for prediction and measurement of DTV service.

INTRODUCTION

Early on, even before the 8-VSB standard was adopted, it was suggested that low-power HDTV transmission, as low as –12 dB average power relative to NTSC peak visual power, would provide for service replication to at least the Grade-B contour of NTSC stations.

It was generally thought that with incident field strength of 40.8dBu at 615 MHz, DTV receivers would be able to decode the signal and that higher field strength would not improve the reliability of reception. Those predictions were based on an idealized receiver, a multipath-free propagation channel and coverage prediction software that uses only terrain elevation data, but not terrain clutter data. Clutter data specify the land cover, such as forest, water etc. on top of the terrain elevation data. For these and other reasons, such as time availability statistics, it is now believed that the current predictions of DTV coverage and service will not be realized.

End quote

Dr. Bendov was certainly correct, as you have found out.

At least with analog tv, you could watch a show even if it was snowy and faded-out.

Right, there is no "Digital Cliff" with analog. With digital it's all or nothing.

[ADTech]

The assigned channel power of WJRT is actually on the high side of the typical US high VHF broadcasters. The greatest majority of them run between 15 and 30 kW ERP. A 30 kW VHF12 signal from a 1,000' tower and an omni antenna should easily cover a 60-65 mile radius before localized signal path and other environmental impairments.

With the looming spectrum repack, there's not going to be any changes to transmit power or operating channels in the near future except in very special cases.

[MikeBear]

Well, I just finished installing the higher mast an hour ago. Unfortunately, I'm TOTALLY exhausted as I spent 5 hours doing so, (lots of prep work) and have to quit for the night. My blood sugar is so low, I'm all charley-horsed. I need to get it all tuned in. I eyeballed the antennas directions before putting it up, and they are off on aim a bit.

I also thought I'd take the chance to swap out the coax going to the UHF antenna, and the UVSJ, and there's apparently something wrong with one or both of them. I'm getting almost no signal on any uhf station EXCEPT channel 5, which is the strongest one. I do get signal from the vhf antenna, but it's still at the same strength level as before. I'm sure the antenna aim is off a bit though.

That'll teach me to make too many changes at the same time... Anyway, once I get my strength back, I hope to figure out what's going on now with the killed signals on the uhf antenna, and get it all tweaked in and finished this week sometime.

[MikeBear]

Originally Posted by MikeBear

Well, I just finished installing the higher mast an hour ago. Unfortunately, I'm TOTALLY exhausted as I spent 5 hours doing so, (lots of prep work) and have to quit for the night. My blood sugar is so low, I'm all charley-horsed. I need to get it all tuned in. I eyeballed the antennas directions before putting it up, and they are off on aim a bit.

I also thought I'd take the chance to swap out the coax going to the UHF antenna, and the UVSJ, and there's apparently something wrong with one or both of them. I'm getting almost no signal on any uhf station EXCEPT channel 5, which is the strongest one. I do get signal from the vhf antenna, but it's still at the same strength level as before. I'm sure the antenna aim is off a bit though.

That'll teach me to make too many changes at the same time... Anyway, once I get my strength back, I hope to figure out what's going on now with the killed signals on the uhf antenna, and get it all tweaked in and finished this week sometime.

I don't get it. I've reconfigured twice since the above, and I STILL can't get hardly any UHF signal through the system! VHF is fine, and has better signal. UHF is almost dead as a doornail. Unless the (new model) CM7777 amp I've been using decided to go dead only on the UHF side (is that possible?) for no reason, there's really nothing left to try.

Y10-7-13 antenna at the top of the mast. That goes into a UVSJ. UHF antenna (91xg clone) below that, and that goes into the UVSJ. The output of that, goes into an MCMelectronics FM filter, and then into the CM7777 amp. The amp's FM filter is also turned on. The output of all that, goes through 100ft of coax and down to my tv and Tivo. The power inserter is working, and has power.

This is exactly the same system and configuration it's always been, just on a taller mast! It worked before all this, I just wanted more signal for channel 12...

Guess I'll have to swap out that amp next, unless somebody here has any other ideas why VHF would be fine, but UHF isn't.

[rabbit73]

Sorry to hear you are having trouble with UHF, but how is CH 12 now?

You are certainly justified in suspecting the preamp, but don't ignore the possibility that something before it, or even after it, in the UHF chain isn't working like it should.

In a worst case troubleshooting scenario you will need to substitute each part of the UHF chain with a known good part, all the way to a TV, until the system is functioning like it should.

You can also think of it in a signal tracing manner. Is there a good UHF signal coming out of the antenna, is it coming out of the coax from the antenna, is it coming out of the UVSJ, is it coming out of the FM filter, is it coming out of another known good preamp, is it coming out of the power inserter, and so on.

You might end up with a completely independent reception system, but you will know what went bad. It might be a lot of work, but it is better than the frustration of the shotgun approach.

[MikeBear]

Well, I just got back off the roof after dropping the antenna yet again. I swapped out the CM7777 preamp, and put back in the Kitztech kt-200 preamp.

Everything works PERFECT again! I have my UHF channels all back, and a few new ones! UHF signal levels are UP at least 10-15 points across the board with the higher antenna. My WJRT-12 VHF signal, is UP 22 points!!!

I still think there's maybe even a few more signal points I could get, once I make sure both antennas are peaked completely. I'm going to rest again for a day or so, and see how things shake out. I also think I have to make a few changes to strengthen up my guy wires. A 21 foot mast pole (chain-link fence top rail) isn't exactly strong enough to survive much wind without those guys.

Thanks, Rabbit! Your help and advice really made a difference to me, and I appreciate ALL the time you put into giving me that help!

I also appreciate ALL the other people here who added their input! Thanks everybody!!!

[rabbit73]

Thanks for the report with the good news, Mike.

Good job!

Glad that I was able to help you reach you goal.

[MikeBear]

Turns out my new model CM7777 pre-amp is actually fine. Raising the antennas higher caused the signal level to go high enough that it got swamped out. I'll keep it for a spare, and use attenuators in front of it if need be.

Everything has been nearly perfect the last two days, even with the monsoon 3" rain we got on Thursday!

I'm going to slightly turn the UHF antenna East maybe an inch or so, to balance out the signal levels between WBSF-46 at 129 degrees, and WSMH-66 at 162 degrees. That will change the present aim to slightly East of WEYI-25 (about 4 degrees).

Then maybe I'll try going after WUWB-20 again at an NM of 5.3 with a separate HDB91x antenna. That might be pushing it due to trees that way, but I can get WCMZ-28 solid at 62% on the main antenna at NM 5.8, and it has just as many trees that way. If I can get that channel 20 to lock, I'll have to get an AC7-CH.20U from Tin Lee and then try joining to the main system. I emailed them for a price quote, but no reply so far.

[rabbit73]

Turns out my new model CM7777 pre-amp is actually fine. Raising the antennas higher caused the signal level to go high enough that it got swamped out. I'll keep it for a spare, and use attenuators in front of it if need be.

Interesting; I did not consider that, but it makes sense. WNEM is listed as -43.0 dBm signal PWR for an antenna in the clear. If you add the antenna gain of at least 10 dBd, that brings you up to -33 dBm. If you then add the 30 dB preamp gain you are at -3 dBm which makes preamp and tuner overload probable.

ATSC Recommended Practice:
Receiver Performance Guidelines

Document A/74:2010, 7 April 2010

RECEIVER PERFORMANCE GUIDELINES

5.1 Sensitivity

A DTV receiver should achieve a bit error rate in the transport stream of no worse than 3x10E-6 (i.e., the FCC Advisory Committee on Advanced Television Service, ACATS, Threshold of Visibility, TOV) for input RF signal levels directly to the tuner from –83 dBm to –5 dBm for both the VHF and UHF bands.

5.2 Multi-Signal Overload

The DTV receiver should accommodate more than one undesired, high-level, NSTC or DTV signal at its input, received from transmission facilities that are in close proximity to one another. For purposes of this guideline, it should be assumed that multiple signals, each approaching –8 dBm, will exist at the input of the receiver.

Looking at it from the standpoint of Noise Margin, WNEM is 47.9 dB. If you add the antenna gain and the preamp gain, you are at 87.9 dB which is definitely Overload territory.



Interpreting Noise Margin in the TV Fool Report

http://www.aa6g.org/DTV/Reception/tvfool_nm.html

Then maybe I'll try going after WUWB-20 again at an NM of 5.3 with a separate HDB91x antenna. That might be pushing it due to trees that way, but I can get WCMZ-28 solid at 62% on the main antenna at NM 5.8, and it has just as many trees that way. If I can get that channel 20 to lock, I'll have to get an AC7-CH.20U from Tin Lee and then try joining to the main system. I emailed them for a price quote, but no reply so far.

Uh-Oh. You are turning into a dedicated antenna experimenter who wants "just one more channel."

[MikeBear]

Originally Posted by rabbit73

Uh-Oh. You are turning into a dedicated antenna experimenter who wants "just one more channel."

I know, but it's the last one I have a chance to get, and that I'd really want if I can get it.

I do enjoy working on the antennas setup and getting them to work properly for my needs. I just spent a little too long getting the main system working so well, and got a little burned out on it.

[rabbit73]

WUWB terrain profile:



WUWB coverage:

[rickbb]

Looks like if you just add another 200 feet to your mast you'll have it nailed. lol

[MikeBear]

Ok, just got back the quote for an AC7-CH.20U from Tin Lee. This is for adding a separate HDB91x antenna dedicated JUST for WUWB-20. Anybody want to weigh in on these specs, and maybe break them down a little better for me? The price is high enough that I just might forget it, or run a separate coax wire and put in and A-B switch. My TVfool is posted in the first post of this thread.

It seems like it should work well, though I'm a bit concerned about the 2.5db insertion loss, that might be too much. WNEM-5 broadcasts on channel 22, and it's a blow-torch compared to WUWB-20:
------------------------------------------------------------------------------

Single Channel Injector

CH.20 input

Bandpass CH.20: 2.5dB Insertion Loss

Bandpass 15dB Rejection: +/- 12MHz bandedge

50dB Rejection: +/- 50MHz bandedge

It has only 10dB rejection of CH.22. This may not be a problem if CH.20 antenna faces "opposite" CH.22

Thru input with CH.20 trap

Thru Bandstop: 16dB on CH.20, 3dB Bandwidth +/-15MHz from stopband edge

Common All Channel output

Thru Loss on UHF: 0.5dB except CH.20

This device does NOT pass UHF CH.19 and CH.21

[MikeBear]

So, I have/had ONE other problem child channel: WBSF-46 (actually broadcast on RF46) that's only 30KW, and 36 miles away. That channel shares a tower with a BLOW-TORCH channel that broadcasts on RF22 (WNEM), and that runs 1,000KW! All my other UHF channels run fairly high wattage also.

Anyway, WBSF 46 has been driving me insane, as even though it was coming in at around 62 on my Tivo Roamio (72 is the highest OTA signal measurable on a Roamio), the signal and quality would suddenly (frequently) go up and down constantly, and pixelate. This only started once I installed the much higher mast. I adjusted the aim of the HDB91x, even to the point of aiming RIGHT AT the tower! It made no difference. I was about ready to scrap getting this channel, but I wanted it for GRIT.

So, last night I started thinking: "I've re-aimed that antenna about 50 times, and it made no difference, it has to be some sort of multipath, and there MUST be a way to fix this"

I finally (at 3am I was on my roof, lucky for the full moon, don't tell my wife! lol) MOVED the UHF antenna to aim at around 155~ degrees, which points right at a couple of my UHF channels that are very high wattage, instead of 1/2 way in-between. The signal for WBSF-46 locked in, and settled right down!

So, anybody else with this sort of issue, don't give up too quickly. I spent almost a month messing with this off and on (I don't give up easily), before I eventually found a proper antenna pointing NULL point that balanced ALL the UHF stations in my DMA to where they would work right. It is at a position I never tried, as the antenna is now pointing very close to another station that is also almost 1,000KW (and on RF48). But it all works perfectly now, so go figure!

I really wish I had a spectrum analyzer, that would have made short work of this. I am really curious to know just what, exactly was fighting this station, and causing the multipath for this station.

[Nascarken]

On the channel master 7777amp they say it's a 30DBV in VHF/uhf 30,now they say when you T off one to vhf at 15,&uhf,15,so 15+15=30,N is,3: I ASKED a channel master TECH and that is what THEY sead about the,cM, 7777AMPLIFIER,and the Johansson,NOISE,is,3,5,VHF,30,DB gain /uhf,AT 40, I have used #30-2475,&76,,17channels I receive I don't see enny diffinrent between the two antennas and that was with the channel master,and then the Johansson, just a better picture with the Johansson amplifier,antennas Higth is 40/ft 01550,zip,And the A G L,30,tv fool report, in Massachusetts hills and mountains signal strength 80,rain or snow no dropouts,we'll good luck to you,