View Single Post
Old 25-May-2020, 7:00 PM   #2
Senior Member
bobsgarage's Avatar
Join Date: Mar 2016
Location: Beach Park IL
Posts: 292
Two 91 XGs different results. Baffled!

So, I climb the 22 foot ladder. I install my new piece I'm so excited! I carefully measure the spacing and aim my 91XG's. There are no leaves on the trees yet. I check all my connections, climb down the ladder and run a scan. What? How can this be. I run the scan again, I climb back up the ladder I take everything back apart I retighten. Nope.

I find out later that I made my matching section too short. 10 in is wrong for foam filled RG 8. That's for polyethylene filled RG 8. By doing the calculations, my trusted friend Rabbit figures out for me that it should be 12 in because the velocity Factor is different. Foam filled is slightly faster then the other. No problem that's all I need to do I'll make another section. This time I decided not to play around with combiner boxes I figured out a way to make an RG8 cable work, look and install just like a piece of RG 11.

I make my 12" RG 8 matching section. Back up the ladder, I need the exercise anyhow. I attach it run down in my basement and run my scans. Another disaster. I recheck all my connections, I'm back up the ladder several times trying to find out what the problem is. This just isn't working.

Okay, brain fart. Guess what I forgot? I forgot to tell the guys it was UHF that I would be combining when I got the measurements? I assumed the matching section would be the same.. Originally, the measurements I got were for a VHF matching section. However, combining my VHFs didn't go so smoothly either. Another story. Maybe that'll be another post for another day. Or I'll incorporated into this thread.

Since I didn't know the matching sections would be different between UHF and VHF, my mistake and because I had done the exact same thing with my VHF a few weeks earlier with no success and I had several different lengths of matching sections between 9 and 1/2 in + 13 and 1/2 in. None of it worked.

So, I find out that for UHF, its 3 and 1/2 inch RG 8 matching section if it's polyethylene insulated but it's 4.6" if it's foam filled. I'm thinking to myself, no wonder I had such poor results! My matching sections were three times longer than they needed to be!
I make a new matching section stub.

I climb the ladder, I'm pumped! I take the 12" matching section off of my Kitz KT200 amp. By the way, I don't know if you've ever taken a coax out of a Kitz Tech amp but it's not easy with your fingertips. Especially RG 11. It's an awesome designed Pre-amp but it takes some time to master reaching inside of it and starting the RG11 cable connectors especially when these are the Belden Aqua Tights. I've literally done this 50 times in the last 2 weeks with different testing I'm still not good at it. And you think I would have bent the 7/16" wrench by now.

Okay, where was I? Oh yeah, I put my freshly made 4.75" matching section in, checked all my connections twice, ran down in my basement and ran the scans again. Disaster strikes again.

After several private messages to different friends, it was suggested that maybe, just maybe I'm not getting the shielding into the connector correctly, yes I have been trimming shielding back because the connector goes deep under the skin of the RG 8 anyhow where I'm sure the connector makes contact with the shielding. No problem so here it is Memorial Day. Since it started out raining this morning I decided I would make one more attempt at making a 4.66" matching section.

I mentioned this before but even before I made my first matching section I was told to include the length of the connectors. However it was never fully understood that I was adapting an RG 11 connector to the RG8. You know, inside the RG11 connectors there's someone in pain that forms the actual contact whatever you're screwing the cable onto. So I figured I would outsmart myself and make this one longer. Because really, isn't it the function of RG8 length that matters?

So this time, I decided to make the cable itself 4 and 1/2 inches long and then solder on the contact tips from the RG11 connectors. Now, the overall length is 6.5" .

However, this didn't work either. I'm at a loss.. Could it be the "T" connectors?

It's not the cables and although antennas aren't really balanced, noted during previous testing a simple Holland GHS Pro splitter outperforms any type of matching wave section I have conjured up.

Attached Images
File Type: jpg 20200525_102708_copy_1024x485.jpg (138.9 KB, 330 views)
File Type: jpg 20200525_102609_copy_1024x485.jpg (121.1 KB, 339 views)
File Type: jpg 20200525_113605_copy_1024x485.jpg (283.6 KB, 330 views)
File Type: jpg 20200520_090434_copy_1024x485.jpg (104.0 KB, 325 views)
File Type: jpg 1590431575671_copy_768x934.jpg (129.0 KB, 329 views)
File Type: jpeg received_265394248179985_copy_1024x568.jpeg (97.8 KB, 327 views)

Last edited by bobsgarage; 26-May-2020 at 7:25 PM.
bobsgarage is offline   Reply With Quote