[Billiam]

http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id=8d17cd664a0ccf

I'm not having any issues receiving every UHF signal from the top on down to KMOS TV. KMIZ is hit and miss with atmospheric conditions. I suppose if I set up my Channel Bastard 4251 parabolic I'd be able to get KMIZ most or all the time but I don't know whether or not I will be staying at my present location for more than another year to year and a half.

The problem child here is KQTV Ch. 7. A single YA 1713 didn't cut the mustard and so I stacked it with a second unit and coupled it into a CC7870. Pre amp is the CM 7777 Tighten. Height to the top antenna is about 32 feet. Phased cable and spaced antennas properly according to Winegard tech for Ch. 7. When installed last Fall I found this solved the problem for the weak signal. Gain on the TV's SSM was around 20db SNR with the stack vs. around 15 db to 16 db and near constant pixelating for a single antenna.

Fast forward to March 2011. Suddenly the signal strength has dropped down to an average of about 17 db SNR on the TV SSM and interference, presumably from a co channel or possibly a nearby FM station has occurred. The interference vanishes when the signal strength of Ch. 7 bounces back up to around 20 db or higher. But normally now the average signal strength is closer to 17 or lower and the interference kicks in and cripples the picture.

Unless I can get my hands on a now discontinued VHF deep fringe antenna or can find a way to make a YA 1713 or Y10-7-13 work, I am going to have to resort to either buying a very large combo antenna like a Antennacraft HBU 55, Winegard 7697p, Channel Bastard 3671 or Anntennacraft HD 1850 which would likely solve the problem due to the higher gain figures for Ch. 7 when compared to the YA 1713.

I found the following link and this concept interests me. http://www.antennahacks.com/Hacks/MyY10-7-13V.htm

I don't really have many tools to fabricate a metal antenna on its own but perhaps I can use a drill and a hacksaw that I have and come up with a modification of the Y10-7-13 that will give me the added gain and directionality needed to overcome the co channel or FM interference. Someone is sending me a FM filter and I plan to install that once it gets here but I do believe I will need more gain as well since I have seen a significant drop in just the last two to three weeks.

Since reading the head to head modeling and comparison of the Y10-7-13 and YA 1713 by "re nelson" and another test I found elsewhere on the web it is evident that the Antennacraft antenna has better gain on Ch. 7 than the Winegard antenna.

I would like some recommendations on what I can do to obtain a reliable signal on Ch. 7 and if that includes trying to hack a Y10-7-13 with a new segment with more directors then so be it. Suggestions are requested...

 

[300ohm]

Gain on the TV's SSM was around 20db SNR with the stack vs. around 15 db to 16 db and near constant pixelating for a single antenna.

Fast forward to March 2011. Suddenly the signal strength has dropped down to an average of about 17 db SNR on the TV SSM and interference, presumably from a co channel or possibly a nearby FM station has occurred.

A couple of other things could have occured over that time period.
In the early spring, trees fill up with water to get the leafing process going. In the fall they lose water. The extra water in the trees degrades signal strength.
The connections could have slightly corroded/degraded over that time.

 

[Billiam]

Yes, the leaf problem crossed my mind and I am certain that is contributing to the gain problem.

I used a high quality Botch 33 electrical tape wrapped tightly around the connectors to reduce the chance of water getting into the cable connectors and potential corrosions problems.

 

[300ohm]

I used a high quality Botch 33 electrical tape wrapped tightly around the connectors to reduce the chance of water getting into the cable connectors and potential corrosions problems.

Ahh, but do you have a way of letting any water get out ? Condensation can still occur with temperature changes that can build up.

 

[Billiam]

I have a friend that is a broadcast engineer (radio) that never mentioned this when he suggested this kind of tape for this application. I guess the answer is "no" I don't.

What do you suggest? That could be a part of the problem though clearly I doubt this is the sole problem in this situation. Since the signal is up one day and down the next and changes frequently even during the course of a few hours it does seem apparent the interference factor is definitely a problem.

 

[300ohm]

What do you suggest?

I dont know, I constantly debate with myself whether to seal or not seal, heh.

If I seal with coax sealant or silicone or even tape, messy residue remains after I unseal, a big downside if changing connections often.

A single YA 1713 didn't cut the mustard and so I stacked it with a second unit and coupled it into a CC7870.

I think you proved that the CC7870 doesnt have 3.5 db insertion loss as claimed. That would make your stack worse than a single, heh. Bizzaro world advertising.
http://www.solidsignal.com/pview.as...iner-Coupler-(CC7870)&c=Signal Combiners&sku=
Does your YA 1713s have built in baluns or are they the older style 300 ohm antennas ?
If the older style and youre using baluns the SD 3700 outdoor 300 ohm coupler may have less loss for you.
http://www.solidsignal.com/pview.as...V-Antenna-Coupler-(SD3700)&c=Signal Combiners

 

[majortom]

Something else that could have happened in ur neighborhood to degrade VHF CH 7 is manmade or electrical noise from nearby powerlines, or out band interference from a nearby VHF transmitter that may not have been there last fall. Powerlines can sway in the breeze, and cause disturbances, etc. And with the increased sensitivity ur preamp provides it'll pick that up easily. But agree, been a long winter, lots of things could have changed.

When u see it degraded from 20 dB SNR to 17 dB SNR, if it was consistently at 17 for long periods, I would suspect just normal fading, and what not.
But sounds like it's suddenly jumping up & down on you the way you've described it. Which lends to suspecting a local electrical disturbance or nearby intermittent transmission pumping up the noise floor. I live in an older suburban area and can see electrical disturbances quite a bit. I've posted pictures around here someplace, of what it looks like both in the video, and on a spectrum analyser when it's occurring. Since I have a bunch of Canadian Analog stations around here, I can easily spot the signs of it in the video.
With Digital, short of watching the noise floor on a spectrum analyzer, all ya can do really is watch the SNR trend like ur doing. Might be worth keeping an eye on the lowest UHF stations ur able to receive, and see if they also have a sudden degradation in SNR (even if it's not enough to degrade to pixelation) in the same time periods VHF 7 is having grief. As electrical Noise like that will tend to affect the VHF stations the most, but will also affect the lower UHF band as well.

And of course the weather's getting warmer so propagation may be getting more dynamic (tropo, etc), so might help to know where the nearest reuse of other VHF channel 7's are located. If you don't care about anything below VHF CH 7, you could install a VHF-Hi High Pass Filter, to rule out the
rogue VHF transmitter, Strong Local FM stations. That might be enough to clean up ur VHF-Hi Noise floor, and not affect ur UHF.
But if it's electrical disturbance in nature (powerlines, etc.) I wouldn't expect any amount of filtering to cure it.

All that's obviously after ruling out all the other obvious things like bad connections, as ur talkin about....

edit: another test u could do is insert like an additional 3dB attenuation in ur path. If ur monitoring VHF CH 7 while at 17 dB SNR, and u insert the
additional attenuation, the SNR should degrade further, likely below or near lock threshold if your system is Noise Limited (Good). If you see the same 17 dB SNR as baseline with the additional attenuation inserted, then the signal was already degraded by interference and or multipath (Not good).
Maybe repeat the same test when things are looking good on VHF 7 also.

 

[Billiam]

Tom. Someone is sending a FM filter which I plan to install to see if that resolves the issue.

I just installed a Splitter to see it affects CH. 7 and CH. 15. CH. 7 is going as high as 22 db on the SNR meter to below the threshold which makes it viewable (about 15 to 16 db). Right now it is at zero! It's more or less in a constant state of flux. When the Splitter is in I don't see very much change in the signal strength. In other words it still bounces all over the place.

CH. 15 bounces around a lot too but that is on a fixed antenna at 120 degrees which is about right to pick up CH. 17 when it comes in via skip. I did a test on my other TV which has a HD 7084p with it and when I rotated the antenna a few degrees towards the CH. 15 tower the signal stopped bouncing (had it set for CH. 17 previously) and stabilized at 24 to 25 db SNR on the TV SS Meter.

My guess is that interference of some kind is definitely the problem. There is a Ch. 7 in Hannibal which is 148 miles ENE of here and that is the most likely culprit. There is another Ch. 7 in southern MO also at 148 miles on the backside which is also a possible offender. I am going to install a Y10-7-13 at 20 feet above the roof this weekend to see if that helps. According to a couple of models done with this antenna i.e. shootouts with the YA 1713 it beats the Winegard for rejecting interference off the side and back and also apparently has a good 2db more gain on most of the VHF Hi band. If this does not work along with the filter then I will try installing a Antennacraft CS 1100 at 20 feet above the roof with the hope that will solve the problem. If that does not work then the horizontal stack concept might be the only way out. I will only try that though if I can find a cheap way to do it.

 

[majortom]

This looks like fun too.
http://home.iprimus.com.au/toddemslie/phase-cancellation.html

The electrical disturbances I was referring to around here affect everything right on up thru UHF CH 25 or so
when it occurs. There's only two digital / distant Edge channels here that might drop out a little because of it. It's
never strong enough to disturb the local digital channels. But doesn't mean their noise floor isn't pumped up a little
also.

snapshot of disturbance on TVO 19, Toronto
http://www.digitalhome.ca/forum/showpost.php?p=1198125&postcount=1169

Spec An movie clip of CHCH VHF 11, Hamilton
http://www.digitalhome.ca/forum/showpost.php?p=1198223&postcount=1171

homemade vhf-hi hpf, to eliminate nearby FM Transmitter.
Which helped the system considerably overall, but not for the electrical disturbance.
http://www.digitalhome.ca/forum/showpost.php?p=1231316&postcount=1222

 

[ProjectSHO89]

I think you proved that the CC7870 doesnt have 3.5 db insertion loss as claimed. That would make your stack worse than a single, heh.

A reminder: When the two antennas are stacked so their phasing is additive, that 3.5 dB insertion loss (which is real and is actually higher) changes to a gain of up to 2.5 to 3 dB. See Ken Nist's explanation at hdtvprimer:

The doubling of the output power is equivalent to a 3 dB increase in the signal. If the combiner is 90% efficient then a 2.5 dB gain is seen. Note the dichotomy:

· If the antennas point in different directions, there is a 3.5 dB loss at the combiner.

· If the antennas point in the same direction, there is a 2.5 dB gain at the combiner.

This is a 6 dB swing. 3 dB of this is just the adding of the second antenna, but the other 3 dB is from the combiner becoming a much more effective device.

 

[Billiam]

300ohm. I think the YA Tittles have built in 75 ohm connectors. They are about a year old now.

 

[Billiam]

Major Tom. I do know that there are both Circular and Horizontally polarized broadcast antennas for FM and I presume also TV. But I don't really understand how you can change the polarization of a TV reception antenna unless this has something to do with stacking and ganging horizontally or vertically.

Antenna height at less than 30 feet up to this point has produced a useless signal with the YA Tittles. Right now the top antenna is at about 32 feet off the ground and about 15 feet from the top of the roof. More elevation is going to produce more gain which is apparently needed to help reduce some of the co channel interference, if that is the problem. If it is occurring from some other source as you suggest and is not from a TV or FM transmitter then I have probably only one potential way to solve the problem. Switch out cable and hope something else has better shielding. I am already using Quad cable though and I'm not sure I can find something better. Would RG 11 be better at rejecting interference?

Someone on another board suggested the Phase Cancellation idea but at this point I don't know if I want to create such a monster on my roof.

 

[300ohm]

But I don't really understand how you can change the polarization of a TV reception antenna

Just turn/mount the antenna 90 degrees sideways.

 

[300ohm]

A reminder: When the two antennas are stacked so their phasing is additive, that 3.5 dB insertion loss (which is real and is actually higher) changes to a gain of up to 2.5 to 3 dB.

Yeah, but the thing is, theyre specifically advertising it with a 3.5 db loss. What a way to sell a product, heh.

I think with a 75 ohm coupler, the max additive gain will be less than 2.5 db.

 

[Billiam]

300ohm. Sideways? Well, it may be worth a try. Will have to drill new holes for the U bolt to mount it right though.

 

[300ohm]

Yeah, its as simple as that. But you may not like the pattern. A lot of times the vertical pattern on a horizontal designed antenna is narrower.

 

[majortom]

sorry for the confusion. Posting that link was more for the circuit/project,
cancellation of interfering signals using two antennas. A little further down the same page. u'll see Fig 3 consisting of a balun, two 5Kohm variable resistors, and two .01 uF Capacitors. This goes inline with the "interference antenna" as indicated in the block diagram discussed near the top of the page.
Looks like it could be a fun project.

 

[ADTech]

Based on my testing last year of several of the CC7870 splitter/combiners, calling it 3.5 dB insertion loss is an overly optimistic stretch.

I measured around 3.5-3.8 dB IL to about 400 MHz with up to about 5 dB IL on the non-DC pass port at 700 MHz. I opened one up and it's really just a conventional (transformer) power splitter in an outdoor enclosure that's fine for convenience but offers little in the way of RF ingress protection.

 

[300ohm]

Heh, now Im more confused about using 75 ohm splitters used as couplers than ever.
If the IL is that high, why do you suppose Billiam noticed a gain increase ?


Ive got an SD-3700 outdoor 300 ohm to 75 ohm coupler on order to experiment with.

 

[ProjectSHO89]

If the IL is that high, why do you suppose Billiam noticed a gain increase ?

See explanation posted in post #10.