Jumper length.

[Michael M]

Hi Jim, you've go a good team on this forum! Interesting topic. After 40 years in radio, I'm still learning too!

To expand on one topic, use of chokes. I always use a 1:1 baluns (or choke) at the feed point to my antennas. In fact, I also use current baluns on my radio, to reduce noise. They are very handy.

The balun/choke will isolate the coax feedline from the antenna. With it, there is no need to have an exact length of coax to your antenna when you use an analyzer or SWR meter. As Crawdad said, the balun will remove any effects the cable might have on your antenna pattern (side lobes). They are easy to make also!

From Crawdad's link, **5 Turns of RG-213 4.25" diameter** would be the best for you application. (You'll need RG-213 for your high-power application)

After installing, if you are still having some strange SWR values, then you know the root cause is somewhere on antenna side. This is a cheap way to isolate portions of your system for better debug.



Just Curious, have you raised the antenna up in the air and checked the SWR?

Good luck

 

[Jim5570091]

Yes at least 100 times. There are multiple pictures in my media of various ways I tried connecting my coax to the stub rods. Nothing helped so I went to back to its original termination. If you want to look at them. will 5 mix 31 beads at the feed point work? if not I think I have some spare 213 coax laying around.

 

[Crawdad]

Reading this entire article changed my my mind about air-cored "Ugly Baluns":

https://web.archive.org/web/20180422195858/http://www.karinya.net/g3txq/chokes/

Effective, non-reactive chokes using Ferrite toroids are easy and in-expensive to make.
This is at the feedpoint of my 6m Yagi.

6ea. mix 43 Snap-it beads at the feedpoint of my HexBeam.

Having said all that, a choke will not cause or cure Impedance/SWR issues.

Not sure I completely understand what your issue is Jim.

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[Jim5570091]

With this antenna I can’t get a reasonable SWR reading. And different length of coax jumpers change the results. Everyone insist it’s the setup of the antenna itself. It has all original elements and matching stubs. If coax length isn’t the root cause then it has to be antenna issues. Moving the matching stubs terminations to achieve the lowest results are a min of 1.5 and climbs when you go either up or down from channel 20. Change the jumpers between amp and meter from a measured 1/2 wave length using app calculations for velocity factors to a 6’ jumper and it will go from 1.5 to a 2. That leads me to thinking common mode current on the coax shield. So trying to find a quick and easy way to rule that out.

 

[Crawdad]

With this antenna I can’t get a reasonable SWR reading. And different length of coax jumpers change the results. Everyone insist it’s the setup of the antenna itself. It has all original elements and matching stubs. If coax length isn’t the root cause then it has to be antenna issues. Moving the matching stubs terminations to achieve the lowest results are a min of 1.5 and climbs when you go either up or down from channel 20. Change the jumpers between amp and meter from a measured 1/2 wave length using app calculations for velocity factors to a 6’ jumper and it will go from 1.5 to a 2. That leads me to thinking common mode current on the coax shield. So trying to find a quick and easy way to rule that out.

Roger that. Are you checking this at the feedpoint or shack end of coax or through amp, etc.?

 

[Jim5570091]

Shack

 

[Crawdad]

Through amp?

 

[Jim5570091]

Antenna coax inside shack. I have 3 barrel so connectors mounted through a 2” piece of angle aluminum. I plug into those to choose all directional, vertical or horizontal. Budget alternative to a high power antenna switch. Use a jumper between meter and antenna chosen. Jumper between main amp and meter. Jumper between main amp and driver amp. Jumper between driver amp and keying controller. Jumper between radio and keying controller.

 

[Crawdad]

Seeing the same numbers if just your analyzer, jumper, coax connected?

Or just radio, meter, coax connected?

 

[Jim5570091]

Its a little better at 2 watt, with radio only.

 

[Jim5570091]

Thanks for trying to help me out here. I love the hobby!

 

[Crawdad]

Thanks for trying to help me out here. I love the hobby!

Makes two of us! Good luck with it, that's a monster.

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[Jim5570091]

All things out of the equation. If you seen SWR change with coax length in your shack. What would be your first thought to check? And try?Again thanks for your input.

 

[Crawdad]

If I suddenly see a SWR issue my first things to check are always coax and connections/PL259s. And I always check my antennas as close to the feedpoint as feasable with an analyzer, with a minimum number of devices between it and the antenna.

7 3

 

[Crawdad]

Just my opinion, but if you've got 1.5:1 or a bit higher on that antenna I wouldn't sweat it. The return losses are miniscule compared to what you're radiating.

Are the readings the same horizontal and vertical?