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Discussion Starter #41
In addition to playing with the height and spacing, is it possible to run separate tests to see if one antenna is stronger- which might be causing problems possibly?
 

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Hi peano,

Try a comparison of one vs two with the amp bypassed before you get too worked up. ;)

It looks to me like you have some strong signals coming in there. I have weaker signals coming in at my location, a more tolerant amp (higher dbm input) and I have to attenuate. Before I figured this out, my twin stacked 4228hd's looked worse than a single 4228hd simply because the twin's stronger signal were causing even more overload distortion thus making some signals appear worse.

Good luck and keep us posted. :D
 

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The strong channels in the same direction as my weak ones are real 18, 26 and 35. I don't think those would affect 33? My 91XG is extremely directional, so I doubt off axis stations are overpowering the amp.

I am hoping it is a height issue and I need to find the sweet spot. What increments should I try lowering the mast?
 

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Peano, I'm an amateur at best.... but have you tried separating the antennas by more than 48".... from your pic it looks like you could mount the rotor on the short pipe (moving the rotor closer to the top of the tower which would also move a good chunk of mass closer to the support) and the longer pipe above the rotor so you can space the 2 antennas farther apart yet the top antenna would still be at the same elevation above grade. Did you try without the amp? If its not easy to take the amp out you could quickly just add a splitter before the RG6 goes into the tuner or a couple of splitters could Knock off a few db and if it improves things then you know the tuner is being over driven. By taking the amp out and things improved it could still mean the tuner was being over driven or the amp was over driven and sending junk/noise to the tuner.
 

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Hi peano. Its just a suggestion(and maybe you did it already) but did you put your coordinates into tv fool and run at 1 foot intervals. I did this with my location and I was quite surprised by the results.

For my two weakest channels I run it on and to my surprise @ 40' was not much better than @20'

I ran it from 5' height right up to 40' and recorded all the NM's and I noticed from 5-20' the greatest gain, and from 20-40', the least amount of gain. These are 2 edge signals so that probably has got something to do with it as it actually decreased at 22' before it started to slowly get higher numbers again.

Bob
 

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Thanks for the tips. I am 90% sure I am not overpowering the tuner. I did try to attenuate the signal and it just got weaker. A 48" separation will cause one antenna to be partially blocked by the neighbour's roof.

Tvfool shows better signal at 10 ft and 15 ft. I tried those heights on my test tripod and higher was always better.
 

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peano,

The strong channels in the same direction as my weak ones are real 18, 26 and 35. I don't think those would affect 33? My 91XG is extremely directional, so I doubt off axis stations are overpowering the amp.
Distortion will reduce signal to noise on all channels regardless of frequency and direction, it’s an amplitude thing: I can't throw a ball higher than 8 feet in my house because there is a ceiling there! Those channels with lower signal strengths will take the biggest hit due to the ratio. I will venture to say that most people are over driving there amps in a suburb environment and don't even realize it. I can see this and tropo confusing many people post after post here.

Thanks for the tips. I am 90% sure I am not overpowering the tuner. I did try to attenuate the signal and it just got weaker
Attenuation after an over driven pre-amp does nothing but further reduce the signal to noise.

Once you get sick of messing around try this:

Try a comparison of one vs two with the amp bypassed before you get too worked up.
You may have a unlikely situation where higher is not better, but consider more antenna and more height made things worse for you....you are increasing the distortion due to stronger signal...just my two cents!

What ever it is I hope it all works out,
Cheers
 

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peano,

Hey there...im changing stacking separations on my yagis and it makes a big difference as soon as you change the separation iether way (and remember up until now no matter what I did nothing seemed to change anything - inconsistent reception)...

So dont just go by that 25" rule, you will need to try from 2 to 3 ft separations...or have you done this?

Also, have tried the 0264?
 

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Discussion Starter #54
Attenuating Channels

I noticed 13 and 11 are pretty strong for your location- I wonder if you attenuated these channels, would 14 (WUTV) come in better?
 

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I wonder how well the top antenna would work if it was lowered to the location of the bottom antenna, and what the results would be, if you have not tried it yet? If so, was it also worse? I just wonder if the lower antenna might have a balun issue. I am also wondering even though it is a very slim possibility, if maybe the phase it reversed internally with one of the baluns? These are just thoughts. I am about ready to order another 91Xg to stack with my existing one, so I am curious too.
 

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I would open up the 91XG Balun boxes and do a physical comparison.....
Don't presume the assemblers ALWAYS connected the wires inside the same way
and NEVER made a mistake.....They might be out of phase....
 

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holl_ands,

Please correct me if im wrong, but I always read that if they were out of phase, you would basically receive very poor or zero reception on all channels (digital or analog)...
 

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Theoretically, when you are out of phase in a stack, there is only a perfect thin horizontal slice straight out where reception "should" be cancelled. While phasing my twin stack, I made the wrong 50/50 first guess and was surprised how strong things still were. It was weaker than one antenna but not by much.

As a reference: When the left to right phasing in a gang is wrong you would be amazed at how only 1 to 2 degrees of beam width actually gives you a total loss.

Also I once had a bad balun: It still partially worked and that why it caused me a lot of grief. It did not phase properly either way…. But I can't see this happening to often.
 
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