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Old 14-Jul-2010, 2:15 AM   #1
Billiam
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Hey Tigerbangs

A couple of questions for you.

If you had a choice between stacking either two Delhi VIP 303SR's or two Winegard YA 1713's to obtain Ch. 7 or higher in your area, which would you choose?

Also, do you think stacking two 91 XG's would make for a more directional forward gain and reject signals off the sides and back better than a single 91XG?
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Old 14-Jul-2010, 5:34 AM   #2
John Candle
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Reception

http://forum.tvfool.com/showthread.php?t=491 , http://www.simplicitytool.com/Old%20...quad_array.htm

Last edited by John Candle; 14-Jul-2010 at 5:37 AM.
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Old 14-Jul-2010, 10:27 AM   #3
mtownsend
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Quote:
If you had a choice between stacking either two Delhi VIP 303SR's or two Winegard YA 1713's to obtain Ch. 7 or higher in your area, which would you choose?
Doubling-up your antennas gets you 3 dB of extra gain, at best. If the setup is not done right, you probably won't get the full 3 dB improvement.

For high-VHF, the VIP-303SR and YA-1713 are very similar in performance (around 9-10 dB), however, the VIP antenna is much bulkier because it also has elements for picking up low-VHF. The YA-1713 will be much lighter and have less of a wind/snow/ice load because of this.

A single VIP-307SR (out of production) gets about 13 dB in high-VHF, so it would actually out-perform a double VIP-303SR setup (9dB + 3dB = 12 dB).



Quote:
Also, do you think stacking two 91 XG's would make for a more directional forward gain and reject signals off the sides and back better than a single 91XG?
As a general rule of thumb, stacking antennas vertically (one on top of the other) will squash the antenna pattern in the vertical direction (i.e., flatten it more like a pancake). It usually won't alter the side-to-side beam width by much.

Stacking antennas horizontally (side by side) will squash the antenna pattern from the sides, creating a narrower side-to-side beam width, but leaves the vertical beam pattern about the same.

Either form of stacking can improve the forward gain by as much as 3 dB.

Vertical stacking will not do much to improve the rejection ratio from the sides. Horizontal stacking WILL improve the rejection ratio from the sides.

Neither stacking method will do much to change the front to back ratio.



If you have a specific signal to the side or back of your antenna that you wish to screen out, there may be other tricks to help eliminate it (e.g., antenna staggering, tuning of phasing lines, physical screens, etc.).



If you are really desperate to get every ounce of signal possible, you should also consider getting a very low noise figure pre-amp (with NF around 1 dB or less). This will get you another dB or two better than the more commonplace amps like the CM 7777 or Winegard AP-8700.
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Old 14-Jul-2010, 12:15 PM   #4
Billiam
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John. Thanks for the links. Very useful info. Not sure I want to go to this expense at this moment though. For VHF 7 I only need a couple more DB gain to lock onto the signal. Right now the picture breaks up a bit with a signal strength SNR around 14 to 15. The picture will lock at 15.50 and not break up on the TV. Since my current location is very likely temporary for only another 3 years or so, I don't want to spend that much to receive one signal that I won't watch very much.

UHF antennas look interesting and I might try one of those. I do know the 91XG and MXU59 are giving me excellent results but I may be able to find something with better gain and adjacent channel rejection among these models. Wish I could use a Parabolic Dish here but I doubt I can get it to stay up in this location without a tower. Rooftop install won't work for that location due to issues with trees.
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Old 14-Jul-2010, 12:20 PM   #5
Billiam
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Mtownsend. Good advice

I wanted to buy a VIP 307sr but they are nearly impossible to find now. Got my hands on two 303sr's that I can use if and when I relocate to an area that has a VHF low station. I will probably get another YA 1713 and stack that with the first one. Winegard makes a coupler that will make it easy to do. SD 3300 or SD 3700.

Sounds like I will have to try a horizontal stack for the UHF if I decide to go that route. I need to reject an adjacent channel while increasing the forward gain to have a shot at getting the signal on Ch. 17 that I desire. Comes in for part of the day but not the entire day.

I already have a Titan 7777 and Winegard 8275.

Can you recommend a lower noise pre amp? I understand there is one manufactured in the UK that is excellent but it is prone to catching fire. Don't want that to happen if at all possible.
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Old 14-Jul-2010, 5:19 PM   #6
mtownsend
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I found the post with your tvfool analysis.

How are you pointing the antenna now?

It looks like channel 18 is about 35 dB stronger than channel 17. If you have your antenna pointed directly at channel 17, the 129 separation between the two stations should knock down this difference somewhat. The power difference, as seen by your receiver might only be about 15 to 25 dB.

The adjacent channel rejection will vary from one receiver to the next. A strong adjacent channel may or may not be the cause of reception problems on channel 17.

Are you sure that adjacent channel interference is giving you problems? How are you able to tell?



If adjacent channel interference is the main cause of your problems, there are probably alternate things to try before resorting to antenna doubling. Most of your channels seem strong enough such that you shouldn't need the extra 3 dB gain of antenna doubling.

1) Try rotating the antenna. Even if the main lobe of the antenna pattern is not aimed exactly at channel 17, you might be able to get channel 18 into a deep null in your antenna pattern, making the adjacent channel power difference much smaller. If you can drop the power of channel 18 enough, then your receiver shouldn't have any problems with channel 17.

2) Try different antennas (if you have that luxury). Other antenna designs may have deep nulls in different spots in the antenna pattern. If your current antenna happens to have a strong side lobe at 129 off the main lobe, then you might see better results from another antenna that happens to have a null in that direction.



Before jumping into this and spending lots of time and money on it, it would be nice to know if adjacent channel interference is really a problem or not.



Quote:
Can you recommend a lower noise pre amp? I understand there is one manufactured in the UK that is excellent but it is prone to catching fire. Don't want that to happen if at all possible.
http://www.researchcomms.com/ is based in the UK and does make low noise amps. I haven't heard much about them catching fire, though.

http://www.kitztech.com/ also makes low noise TV amps and are based in the US.

Note that the amps from either of these companies do not come with weatherproof enclosures. If you plan on installing these outdoors close to the antenna, then you must provide your own weather protection.
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Old 14-Jul-2010, 5:46 PM   #7
John Candle
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Reception

Can also run RG-11 coax cable from preamp to Tv. RG-11 has less loss the RG-6. , Always mount the preamp close to the antenna.

Last edited by John Candle; 14-Jul-2010 at 5:49 PM.
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Old 14-Jul-2010, 6:21 PM   #8
Billiam
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^^^I have the 91XG pointed right at 129 degrees for KMIZ. Basically a couple of people told me the adjacent channel was going to be the primary problem for reliable reception of Ch. 17. However, since I am getting it reliably every night and into the morning for a few hours, I would have to believe that may not be the case. There are a lot of trees surrounding the property and I think that is the real impediment aside from the somewhat hilly terrain between my home and the tower.

I am going to try a C4 later this week to see if that makes any difference. According to Antennas Direct the gain the lowest UHF channels is slightly better than the 91XG. I may also switch out the 91XG for the MXU59 to see if that will make a difference. I plan to run a shorter cable run into the home and replace the RG6 with RG11. That should result in roughly another DB of signal gain.
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Old 14-Jul-2010, 6:59 PM   #9
mtownsend
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Quote:
Basically a couple of people told me the adjacent channel was going to be the primary problem for reliable reception of Ch. 17. However, since I am getting it reliably every night and into the morning for a few hours, I would have to believe that may not be the case.
If the signal improves every evening, then it is most likely benefiting from tropospheric enhancement. This phenomenon helps deliver more signal to you each night when the upper atmosphere cools off and the air near the surface gets warmed up by latent heat from the Earth.

Since you have a 91XG, you might want to take advantage of the "up-tilt" feature of its mounting bracket. You might be able to get a little bit more signal on average if you point the antenna up toward the sky a little bit (like 10). This puts the main frontal lobe of the antenna pattern up higher and might move some of the back/side lobes down into the ground a little bit. The difference might not be that much, but it doesn't cost anything to try since you're already set up.



Quote:
There are a lot of trees surrounding the property and I think that is the real impediment aside from the somewhat hilly terrain between my home and the tower.
This is another reason to try experimenting with turning the antenna a little to the left or right. Signal reflections off of trees, terrain, or buildings might be adding enough multipath interference to make KMIZ intermittent. By rotating the antenna a bit, you might be able to pick out a slightly cleaner version of the signal.

At the same time, this can potentially improve the adjacent channel interference situation with KCPT.



Quote:
I plan to run a shorter cable run into the home and replace the RG6 with RG11.
Since you have a pre-amp, the cable loss from the amp down to your TV will make almost no difference at all. This cable loss occurs after the signal has been boosted by the amp, so you are unlikely to notice any difference switching from RG6 to RG11.
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