ChiwaukeeOTA's antenna modification thread - Page 3 - AVS Forum | Home Theater Discussions And Reviews
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post #61 of 73 Old 05-25-2020, 06:40 AM - Thread Starter
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I'll claim some success on my initial scans.

Thanks to all that offered to help.

Calaveras, Rabbit, and Tom B (Antenna Hacks).


I'm not done with this project. But I realize it's probably a little too much as it turns out it is highly specialized. So? I'll experiment with reflectors Etc...
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post #62 of 73 Old 05-29-2020, 03:42 AM - Thread Starter
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Well, I'm calling this my mod V because it's the fifth incarnation of this antenna.



I put the 4 Tube reflector on, just to see what it would do. Didn't seem to strengthen the signal much at all. FB ratio , I don't know, I don't have a way of testing that.



It also has a useful UHF Spectrum:

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post #63 of 73 Old 06-01-2020, 09:18 AM - Thread Starter
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91 XG Hack Successful

So I made lemonade out of lemons today. I ordered a couple of 91XGs through Amazon last week. I was excited when I got home from work, tore the Box open and found at the UPS handling system destroyed part of the antennas. The booms were bent. When I called Amazon to get the antennas replaced they said they would send two more and I could keep the bent ones.

I took that smashed up boom from the 91XG and I straightened it. It cracked in a couple places, not all the way through. I took a piece of half inch "C" channel and slid it in to the cracked booms. Better than new now.

I also made a new support boom out of my leftover 1 inch square stock with the .125" wall. It's overkill, just the way I like it! Between the "C" Channel inside the long booms and the under boom support, an amazingly strong antenna. I think it will hold up well in the wind.

I did several modifications as I went along. My first mod was to take an extra Center section, remove the front section and add that in between the original Center section and the front section. The signal was Stronger on some channels. Then I added an extra front boom. The results were dramatic. I was very happy with the results. I still have another short rear section that could be added for now I'm happy with what I've got.

I'll let the pictures tell the rest of the story.







Here's the modification to the support boom. The riveted end is for stability.



This end can slide in and out, I found it necessary as the spacing on the directors on the 91 XG is tight:








Boom sag before adding the enhanced boom support:



The last 3 pics just show the "C" channel that I inserted to reinforce the antenna booms:





Last edited by ChiwaukeeOTA; 06-01-2020 at 09:23 AM.
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post #64 of 73 Old 06-01-2020, 09:19 AM - Thread Starter
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Milwaukee Aim.

Well, here's the Spectrum analyzer shots. In summary that signal strength went way up. Later this week when my two replacement 91XGs come in I will test them against this modified 91XG antenna. Aimed at Milwaukee:







Noisy signals are from behind the antenna Chicago stations.

Last edited by ChiwaukeeOTA; 06-02-2020 at 08:21 AM.
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post #65 of 73 Old 06-01-2020, 10:00 AM
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Quote:
Originally Posted by ChiwaukeeOTA View Post
Well, here's the Spectrum analyzer shots. In summary that signal strength went way up.

[url=https://ibb.co/k3mVT8q][/url

Looks like there was some ducting going on in the nighttime image. If you double the length of the antenna you can get up to 3 dB increase in gain. In order to get 10 dB gain the antenna would have to be almost 16 times as long. Once you have a good antenna up in the air, getting a 10 dB increase is essentially impossible.
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post #66 of 73 Old 06-01-2020, 10:25 AM - Thread Starter
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Super 91 XG

Quote:
Originally Posted by Calaveras View Post
Looks like there was some ducting going on in the nighttime image. If you double the length of the antenna you can get up to 3 dB increase in gain. In order to get 10 dB gain the antenna would have to be almost 16 times as long. Once you have a good antenna up in the air, getting a 10 dB increase is essentially impossible.
Yes, that and the fact that the screenshot posted in your reply, there was quite a time difference as I was working on the setup of the antenna.

But, this week, I will get in two new 91XGs and I will put them on the same mast, one at a time. and do scans within minutes. I didn't have that luxury on that day.
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post #67 of 73 Old 06-01-2020, 12:06 PM
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Threads merged. Best to have the same reception project in the same thread.

Walking the fine line between jaw-dropping and a plain ol' yawn.
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post #68 of 73 Old 06-01-2020, 09:17 PM - Thread Starter
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Well, it looks like since the administrator moved my post some of the pictures aren't showing up anymore.

Anyhow, I retested tonight within minutes. I tested the Super XG versus a brand new 91XG.

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post #69 of 73 Old 06-02-2020, 07:44 AM
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Quote:
Originally Posted by ChiwaukeeOTA View Post
Anyhow, I retested tonight within minutes. I tested the Super XG versus a brand new 91XG.

I see a couple of dB on most channels. Makes sense. Hard to say what's going on with the two channels showing larger differences. It's very hard to get a perfect comparison with antennas in the real world.

What's going on with channels 20-26 and 33-36? Looks like a bunch of strong noise.
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post #70 of 73 Old 06-02-2020, 08:01 AM
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Quote:
Originally Posted by ChiwaukeeOTA View Post
Well, it looks like since the administrator moved my post some of the pictures aren't showing up anymore.

Anyhow, I retested tonight within minutes. I tested the Super XG versus a brand new 91XG.
If I understand your first post correctly, this thread was not a reception problem thread but an antenna modification thread. You merely used your Milwaukee channels as test signals for gain comparison because they are weaker than your Chicago channels.

Making gain comparisons using OTA signals can be tricky because they are constantly changing in strength. The most accurate comparison is when you instantly switch from antenna A to antenna B for just one channel. You did second best by making the scans as close together as possible, but I think you proved the modification was a success.

I was having trouble receiving RF11. I used an A/B switch like this to find out which antenna was better.:



These are the two antennas I compared:



The tuner was not able to pick up 11 with the GE34792 antenna:



But it did just fine with the GE 29884:



If there are trees in the signal path, the wind will mess with the signal:

https://www.dropbox.com/s/ig3va499k2...Path4.mp4?dl=0

The most accurate comparison would be to use a constant strength test signal as on an antenna test range instead of OTA signals.

Your report:
https://www.rabbitears.info/searchma...study_id=96970



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If you can not measure it, you can not improve it.
Lord Kelvin, 1883
www.megalithia.com/elect/aerialsite/dttpoorman.html

Last edited by rabbit73; 06-02-2020 at 11:05 AM.
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post #71 of 73 Old 06-02-2020, 08:15 AM - Thread Starter
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Noisy spectrogram.

Quote:
Originally Posted by Calaveras View Post
I see a couple of dB on most channels. Makes sense. Hard to say what's going on with the two channels showing larger differences. It's very hard to get a perfect comparison with antennas in the real world.

What's going on with channels 20-26 and 33-36? Looks like a bunch of strong noise.
In the previous screenshot the antenna was aimed at Milwaukee.The noise is 175 degrees opposite-Chicago making through the back of the antenna, I think. Chicago is 10 miles closer than Milwaukee. But there are trees behind the antenna.

Here's a spectrograph of Chicago aim :
Here's the layout:
C=Chicago
M= Milwaukee


I redid the scan this morning again. pretty much the same results, no time for a screen print on that one but the Super XG was stronger across the board. 2-5 dB some station stronger.

The test environment is tight right now. I have to keep them close due to space on the lower mast.



I am planning to go higher on the antenna mast later this week. I tested lower to check the XG structurally.



I added another boom clamp and a spacer, redundant. With the added boom clamp, I may not need my homemade spacer.


Last edited by ChiwaukeeOTA; 06-02-2020 at 08:19 AM.
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post #72 of 73 Old 06-08-2020, 10:22 AM - Thread Starter
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"163 XG" Final incarnation

Quote:
Originally Posted by Calaveras View Post
I see a couple of dB on most channels. Makes sense. Hard to say what's going on with the two channels showing larger differences. It's very hard to get a perfect comparison with antennas in the real world.

What's going on with channels 20-26 and 33-36? Looks like a bunch of strong noise.

Hi Calaveras,

I believe I've achieved my final modification on my Super XG. As you remember, I had taken 2 91XGs and added sections from each other to make a longer "135 XG". It worked well and I probably could have just stopped there.

I couldn't help myself. I saw the extra rear section closest to the dipole left over from the other donor antenna. I looked at spacing and sure enough if you removed every other reflector you could achieve the five and a half inch spacing of the front sections. I actually only had to drill a few holes for the mounting clamps and another because the director spacing wasn't optimal. 40 "x" elements now.

After flipping this rear section around and playing with the directors I was able to add the rear section to the front. We will call it the "163 XG":



Results were good. I think I have reached the point of diminishing returns. I also know I'm not testing under optimal laboratory type conditions. So I'll do back-to-back scans I tried to keep the test within 10 minutes of each other. Then I'll wait a while and do another back to back scan or even do it the next day. I'll test one and then the other and then the other guy back and forth scales with the same I can say to myself , yeah they are consistent. I always use the same components. Same preamp, same down cable, even the same UVSJ.



Next day:



I realize I was grandstanding on the 7 & 9dB improvement.. But still most stations are min 2 dB to as much as +6 dB improved looking at average eyeballing estimations.

There was quite a difference between yesterday and today. Although both days were clear, there may have still been some atmospheric conditions contributing to the strength of the scans I did this morning.



Last edited by ChiwaukeeOTA; 06-09-2020 at 09:27 AM.
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post #73 of 73 Old 06-22-2020, 09:21 PM - Thread Starter
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For review, After figuring out what the real problem was I seem to be making some gains with my quarter wave stubs...

Thanks to Calaveras and Rabbit. There was a lot of private messages, and it seems we got it worked out. To be honest, I don't know why more don't try the quarter wave matching Transformer stubs.






















Last edited by ChiwaukeeOTA; 06-24-2020 at 05:18 AM.
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