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Old 1-May-2011, 4:03 PM   #1
Billiam
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Need Reliable Picture On Ch. 7

Hello again:

http://www.tvfool.com/?option=com_wr...8d17611d6780d5

Here's the problem. I want to get a reliable signal for KQTV Ch. 7 out of St. Joseph. Some background. Initially I tried a single YA 1713 without a pre amp at 32 feet off the ground (15 feet off the top of the roof) and got nothing. When I added a Titan 7777 pre amp I was able to get a SNR reading of around 14 to 15db on my TV's Signal Strength Meter. Not enough to get a solid lock without a picture breaking up. BTW. I am only driving one TV and don't use a splitter.

Last November I mounted and coupled two YA 1713's with a CC7870 and the same pre amp. I noted a marked jump in Signal Strength to about an average of 20db on the Signal Strength Meter on the TV. Mast height did not change with the top antenna still at 32 feet off the ground. Total cable run is around 60 feet from the antenna to TV. RG6 quad shield is being used. At this point the picture was fine for several months. Antennas are properly spaced and cables cut to spec per a Winegard Tech.

Fast forward to mid April. Suddenly my 20db signal strength on Ch. 7 dropped several points to around 15 to 16 DB on the SNR reading on the TV's Signal Strength Meter. One suspect is the leaves on the trees. Another thought that crossed my mind is that water got into the coax even though I used a good quality tape recommended by broadcast engineer friend to seal the connectors. Now I rarely get a picture that does not pixelate all the time on Ch. 7. I can usually get a watchable picture if I lock in at 16 to 17db on Ch. 7.

In light of this I've decided to make some changes up there. Eliminate more connections because more problems can arise than with a single antenna. I built a wooden support system around the chimney to hold the current coupled antennas and I should be able to add two to five more feet on top of that along with a rotor and a single antenna. This seems to be the only spot on the property that will get Ch. 7.

Since all of my KC UHF channels will come in with any Yagi I use and KMOS TV from Sedalia comes in with any antenna pointed in that direction I've decided it would be best to replace the current YA 1713's with a single antenna to receive Ch. 7 to 51. My research has noted the VHF Hi sections on antennas like the HBU 55, 7697p and 7698p offer more gain on Ch. 7 than a YA 1713. And since I can mount a single antenna such as this a bit higher I do gain more signal according to the TV Fool report. Even mounting a antenna only 3 feet higher than the current 32 foot level will yield another .4db of gain on Ch. 7. I could probably get it up to 37 feet if I used a small antenna like an HBU 33 or 7694p.

Since UHF reception is not an issue I am only concerned with obtaining a reliable signal on Ch. 7. Eliminating the two channel setup will result in a bit lower loss in the shorter cable run with less connections plus the loss associated with the coupling unit. I figure if I can gain about 2db more signal either through shortening the cable run with a single antenna in combination with a antenna that has at least 1 to 2 db more gain on Ch. 7 than the YA 1713 then I will be in business.

I looked at Ken Nists' HDTV Primer modeling of various antennas and noted the YA 1713 in the real gain test only had about 7.1db of gain on Ch. 7 vs. what Winegard reports in their spec's on the website. Even the Antennacraft HBU 44 is a good full DB higher on Ch. 7 in his test! And this gain figure is accurate with the same figure being quoted for this antenna on Ch. 7 on the Antennacraft website. Antennacraft apparently does not inflate its spec's. The HBU 55 is rated at 9.6db gain on Ch. 7. The 7697p is rated at 10.9 by Winegard and the 7698p is at 10.4. Not sure how accurate the Winegard figures are.

What do you think? Would I be better off using a smaller antenna like a 7694p or HBU 33 at 20 feet off the roof at 37 feet off the ground or would a larger antenna like the HBU 55 or 7697p at perhaps 16 to 17 feet off the roof or about 35 feet off the ground be more apt to give me a little more gain and a reliable signal from Ch. 7?

Regards,

Billiam
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Old 1-May-2011, 4:40 PM   #2
GroundUrMast
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Thinking out loud...

Are the YA1713's stacked one on top of the other? (Or side by side?)

KOAM and KHQA are both strong enough co-channel interference sources to present a problem. Side by side stacking can produce a more narrow horizontal beam-width which would be desirable, as a means of rejecting the interfering signals.

Use of a reversed splitter (CC7870) as a combiner comes at the cost of about 3 dB. You still get the modified beam-width though. A pair of Antennacraft Y10713 with their 300 ohm outputs would lend themselves to combining via 1/4 (or 3/4) wave long sections of 450 ohm ladder line, thus less combining loss.

I think your consideration of the combo antennas is a viable option also. But you'll need to find an antenna with at least 3 or more dB additional gain to expect much difference.

I think the solution is going to be a combination of gain and interference rejection.
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Old 1-May-2011, 4:49 PM   #3
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Have you ever tried walking the antenna on the roof? The TV FOOL shows adequate signal, so I'm wondering if a new location may yield better results? A single YA-1713 should do reasonably well if the report is correct.

Not sure of the other antennas, but the 1713 is much better on VHF than the 7694. I've used the 7082, which has similar specs to the 7696. Performance seems about the same as the 1713 on VHF. Not sure how much difference the 7697 would make with only .09 db more gain?
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Old 1-May-2011, 4:50 PM   #4
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Originally Posted by GroundUrMast View Post
Thinking out loud...

Are the YA1713's stacked one on top of the other? (Or side by side?)

KOAM and KHQA are both strong enough co-channel interference sources to present a problem. Side by side stacking can produce a more narrow horizontal beam-width which would be desirable, as a means of rejecting the interfering signals.

Use of a reversed splitter (CC7870) as a combiner comes at the cost of about 3 dB. You still get the modified beam-width though. A pair of Antennacraft Y10713 with their 300 ohm outputs would lend themselves to combining via 1/4 wave long sections of 450 ohm ladder line, thus less combining loss.

I think your consideration of the combo antennas is a viable option also.

I think the solution is going to be a combination of gain and interference rejection.

Thank you for the thoughtful reply. Yes, they are stacked vertically, not horizontally. Not sure a horizontal coupling is going to hold well up there. I did not realize I was losing around 3db of gain with the coupler. The Winegard Tech told me I would actually lose no signal when coupling in this manner. That may be the problem then.
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Old 1-May-2011, 4:53 PM   #5
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Originally Posted by No static at all View Post
Have you ever tried walking the antenna on the roof? The TV FOOL shows adequate signal, so I'm wondering if a new location may yield better results? A single YA-1713 should do reasonably well if the report is correct.

Not sure of the other antennas, but the 1713 is much better on VHF than the 7694. I've used the 7082, which has similar specs to the 7696. Performance seems about the same as the 1713 on VHF. Not sure how much difference the 7697 would make with only .09 db more gain?
I've tried two other locations up there but to no avail. I can walk the roof but if I find a better location that requires an invasive mount to the shingles, I am hesitant to install there.

There are a lot of trees about 75 feet away in the direction of the station. No doubt that plays a role in the signal breakup.
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Old 1-May-2011, 5:17 PM   #6
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To clarify... the typical performance of a 2-way splitter is 3.5 dB loss. The theoretical gain from stacking two identical antennas will be 3 dB The net gain will be -0.5 dB. If the forward beam width is improved enough to reject interference, the net gain in signal strength may be of less concern.

The improvement in beam width is most often produced with horizontal (side-by-side) stacking.

http://forum.tvfool.com/showthread.php?t=1024
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Old 1-May-2011, 5:27 PM   #7
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Originally Posted by GroundUrMast View Post
To clarify... the typical performance of a 2-way splitter is 3.5 dB loss. The theoretical gain from stacking two identical antennas will be 3 dB The net gain will be -0.5 dB. If the forward beam width is improved enough to reject interference, the net gain in signal strength may be of less concern.

The improvement in beam width is most often produced with horizontal (side-by-side) stacking.

http://forum.tvfool.com/showthread.php?t=1024

Yes, this does make sense. I have read about this being a fact in some online resource. I just don't know if I can build such a mounting device and have it work correctly. How do you create a horizontal boom and then mount it to a mast?
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Old 1-May-2011, 6:25 PM   #8
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Quote:
Originally Posted by Billiam View Post
Thank you for the thoughtful reply. Yes, they are stacked vertically, not horizontally. Not sure a horizontal coupling is going to hold well up there. I did not realize I was losing around 3db of gain with the coupler. The Winegard Tech told me I would actually lose no signal when coupling in this manner. That may be the problem then.
I'd suggest that the problem is a combination of a weak signal and interference from KOAM.

Your pair of Y1713s can be stacked horizontally about 34" apart to null KOAM and still add 2-3 db to KQTV. http://www.hdtvprimer.com/ANTENNAS/ganging.html

When combined with a CC7870 they will add by about 2 db. If this arrangement works your problem is interference. If not, you'll need more antenna gain.
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Old 1-May-2011, 6:37 PM   #9
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I'd suggest that the problem is a combination of a weak signal and interference from KOAM.

Your pair of Y1713s can be stacked horizontally about 34" apart to null KOAM and still add 2-3 db to KQTV. http://www.hdtvprimer.com/ANTENNAS/ganging.html

When combined with a CC7870 they will add by about 2 db. If this arrangement works your problem is interference. If not, you'll need more antenna gain.
Where do I measure the 34" distance from on each antenna? The balun? Or elsewhere?

Also, what do I use for a horizontal boom?
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Old 1-May-2011, 7:41 PM   #10
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Are you inclined to fabricate a mount yourself? Product such as Unistrut and their competitors may be a practical option. http://en.wikipedia.org/wiki/Strut_channel Big box hardware / home improvement centers stock some selection in their electrical departments. I'm not a mechanical engineer but I would expect the main mast would need to be stronger than typical consumer grade TV mast material.

If not, you may want to look into the pricing of commercial product such as http://www.wade-antenna.com/Wade/highbandHP.pdf and http://www.wade-antenna.com/Wade/highbandDQ.pdf


Quote:
Where do I measure the 34" distance from on each antenna?
That's the distance between parallel booms.
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Old 1-May-2011, 8:08 PM   #11
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Where do I measure the 34" distance from on each antenna? The balun? Or elsewhere?

Also, what do I use for a horizontal boom?
If it were me I'd use a standard TV mast cut down. I've used standard TV mast for a pair of low band antennas.

I'd redrill the booms 90 degrees from the existing holes and slightly offset one way or the other. It's best if the horizontal boom is halfway between two elements. Next I'd drill two holes on the the horizontal TV mast to mount it on the vertical mast.
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Old 2-May-2011, 12:46 AM   #12
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Thanks. It is now more apparent that yes indeed the problem is a combination of signal strength and interference from a co channel. I would have recognized the latter problem if this were the days of analog but this my first experience with it or even adjacent channel interference in HDTV.
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Old 2-May-2011, 4:30 PM   #13
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Thanks. It is now more apparent that yes indeed the problem is a combination of signal strength and interference from a co channel.
I made a mistake on the 34" distance. I read the left side UHF distance for the third null. I should have read the right side VHF for the first null.

After a closer look there are two channel 7 co-channel stations. KHQA is almost as strong as KOAM.

The difference from KQTV to KOAM is 111. The difference from KQTV to KHQA is 124. To use the graph on the ganging page of the HDTV primer it's necessary to use the angle off the back of the antenna, so the angles become 56 and 69. To split the difference the correct distance is for the first null is 3.2' or 38.4". 34" should have helped, but 38.4" will be better.

Also note that the two baluns must be connected with the same polarity. I've never seen a balun with the polarity marked, but you must have resolved that problem when you stacked the antennas one above the other.
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Old 2-May-2011, 4:40 PM   #14
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TG. Thanks. The am trying to design a structure that will attach to the chimney that will permit a horizontal gang. Ch. 7 lays at a kitty corner angle from the chimney which means I don't have a simple installation. 38.4 inches then is the best spacing of the two booms. I will remember that.

I may try the single antenna option first because I can mount that a few feet higher than the ganged antennas and it will reduce the amount of cabling and connectors needed in the system. That alone may solve the problem.

I never see the co channel interference when I have a 20 db signal strength or better. When it is at 19db to 20db I only see an occasional sign of the other Ch. 7 but it is hardly a daily occurrence. In fact, this morning I was getting a normal 20 db plus reading and no interference until the last hour when the signal strength dropped to around 16db to 17db and the interference started to kick in again.

Is there any way to tell which antennas offer better rejection of signals off the side? It is pretty easy to tell for the back side if a Front to Back ratio is mentioned but I don't know how I can use that information to determine side signal rejection.
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Old 2-May-2011, 4:59 PM   #15
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Winegard and Wade/Taco offer polar plots with the other technical information and specifications for their antenna products. Something I wish the other manufactures would do as well. Sadly Winegard does not present the scale calibration with their plot. Ex. http://www.winegard.com/kbase/upload/ya-1713.pdf Wade is targeting a skilled professional customer base so it is in their interest to offer information that would confuse many non-technical consumers. Ex. http://www.wade-antenna.com/Wade/highbandHP.pdf

The polar plot is a practical method to convey information about the directivity of an antenna.
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Old 2-May-2011, 5:34 PM   #16
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GUM. Thanks. I looked at the plots and the Winegard has less rejection off the side on Ch. 7 compared to the rest of the channels they list.

Do you know how much the Wade antenna costs? That looks like a better antenna. Don't know where to find a Dealer though.

Another thought crossed my mind. The Antennacraft Y10-7-13 apparently has a little more gain than the Winegard YA 1713. Someone on the Canadian board modeled both antennas and found the Antennacraft model has about 2 more DB of gain. Makes sense since it is 20" longer. Since that antenna is so light I might consider still using two separates up there if I only need one VHF to obtain Ch. 7. I'd still be able to eliminate the coupler and would only need the pre amp. Still a better choice than ganging or stacking two VHF only antennas.

What do you think?
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Old 2-May-2011, 6:48 PM   #17
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http://www.wade-antenna.com/Contact2.htm You will need to contact Wade re. pricing and availability.

IMO Winegard has a slight edge in build quality vs. the Antennacraft, they are both good products. Winegard also publishs more information regarding the performance of their products.

However, the Antennacraft Y-10713 has a balanced 300 ohm feed point rather than an integral balun. This can be quite helpful when stacking because 450 ohm twin-lead (which can be field built of open wire or factory made) can be used as the impedance matching transformer/harness. The losses can be a few dB better than that of the reversed splitter method.

There may be some difference between the two antennas, but they are very close competitors. A difference of 2 dB would surprise me a bit.
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Old 2-May-2011, 7:03 PM   #18
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Is there any way to tell which antennas offer better rejection of signals off the side?
Look at the polar plot on the bottom left of this spec sheet.
http://www.winegard.com/kbase/upload/ya-1713.pdf

By convention the scale on the graph is a voltage ratio. The F/B has a voltage of .3 which is 10.5 db. That agrees with the channel 7 F/B listed in the table. The front to side ratio is about .2 in the areas of the interfering channel 7s. or about -14 db. The horizontal stack of 38.4" should increase that to at least -30 db.

Your real problem is that the signal strength of the two interfering stations fade up and down rapidly. TVfool is not designed to tell you the possible range of signal strengths. When the signal strength of both interfering stations waxes simultaneously, your desired channel 7 is wiped out.

In addition, expect more interference when the atmospheric conditions favor the distant stations. Generally, in the Midwest you'll see more interference in the summer and fall than winter and spring.

I'd expect the best reception of KQTV when the map over MO is black. http://www.dxinfocentre.com/tropo.html
That would mean less signal received from the two co-channel 7s.
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Old 2-May-2011, 7:12 PM   #19
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Still a better choice than ganging or stacking two VHF only antennas.

What do you think?
If you want to avoid a pair of stacked VHF antennas you could find a single antenna with excellent side lobe performance on channel 7.

The HD7698P has a ratio of .08 at the azimuths of the interfering channel 7s. That's -22 db; better than the YA1713, but not as good as horizontally stacked antennas.
http://www.winegard.com/kbase/upload/HD7698P.pdf

With an HD7698P I'd predict that you'd find many days where KQTV would still be wiped out by interference.
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Old 3-May-2011, 2:31 AM   #20
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If you want to avoid a pair of stacked VHF antennas you could find a single antenna with excellent side lobe performance on channel 7.

The HD7698P has a ratio of .08 at the azimuths of the interfering channel 7s. That's -22 db; better than the YA1713, but not as good as horizontally stacked antennas.
http://www.winegard.com/kbase/upload/HD7698P.pdf

With an HD7698P I'd predict that you'd find many days where KQTV would still be wiped out by interference.
I did some research on this antenna and noted the gain figure provided by Winegard is 10.4 db for Ch. 7. But the gain for Ch. 7 on the HD 1084p and 7697p is rated at 10.9.

I think I have a solution to this problem. I did some research on head to head comparisons between the YA 1713 and Y10-7-13. A couple of people have actually modeled these two antennas and others have done some other tests with different signal strength gauges. All of these studies, and they are independent of one another. found the Antennacraft antenna averages a good 2 db more gain on virtually every channel than the Winegard model. One guy using four of the Y10-7-13's in Canada raved about how good this antenna is at rejecting channels off the side and back. He also said the gain was excellent for this antenna.

Unless I hear back from Denny's with a recommendation for something better, I plan to use the Y10-7-13 at 20 feet and a 91XG below it into a Titan 7777. This combination along with less cables and no coupler should yield the desired result. If that does not work then a horizontal gang will be the next step.
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