High SWR

[TheRealPorkchop]

I’ll agree. You can still have some issues. I too don’t chase the magic match and all that jazz.

 

[Slowmover]

I don’t run anything hard enough for 1.7, or even 2.0 to be an issue.

I did not always believe it to be the case, but I now think a setup, well bonded to a vehicles body, with good coax, and with a properly functioning amplifier and transceiver, can have common mode issues.

That said, my end game isn’t understanding holes and electrons, but operating my radio. Flip the same coin over; when there’s room for improvement to the end game I’m all in.

I think our pickups are a worthy test of defining what are (or, may be) Common Mode problems.

That said much of it will come to definitions.

The exactitude winds up being stuffing 6-lbs of sausage into a 5-lb sack.

Applegate and others note the difficulty of modern vehicles. First step, then, what is modern for this purpose? Your 2018 and my 2004 are a very long ways from circa 1959 where I start (Wow, alternators). But those dozen years has seen an increase in devices AND complexity.

I start here as “modern vehicles” aren’t just more difficult to wire, they have plenty of onboard noise sources. (My Peterbilt is overwhelmed with them).

That’s another thread. But the OP shouldn’t be surprised to find some noise is damnably hard to locate and address.

A pickup at least has the virtue of size where access may make distant collaboration more feasible. Comparing notes on visual aides.

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[Slowmover]

I tend to think an antenna mount could be well-connected to the body, and still have CMC issues which might cause the SWR to change with coax length.

But, I was just jesting anyway. Lol.

Yes. But, it doesn’t obviate the rule.

It’s best to find a first-edition Applegate from an estate sale.
Heavily notated over the decades by the late WWII-vet EE.

Getting comms to work despite adversity . . .

With mobile, we always have the excuse, well, it’s mobile (ha!).


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[Nick hatz]

Ok. Metered everything again. 102 whip 2:0. 5’5 Francis 1.7:1. Solid ground. I scrape the paint drilled and tapped the whole stainless steel bolt grounding strap instead of wire. Metered everything coax antenna mount everything meters perfectly fine.

 

[Nick hatz]

I have gone through and re-read all of the links that you guys have sent me conducted all of the tests and everything comes out good. The only thing that I could be thinking and you guys said it’s not is the coax length. The 5 foot five Francis antenna lowers the SWR. Might remove everything and start over from scratch

 

[Nick hatz]

Tested the coax barrel unplugged from the radio to ground and it reads good. I’m at a loss

 

[BJ radionut]

Did you measure the VSWR say on Channel 1...Channel 10...then 20...then 30...then 40?
Or is it 2:1 across the entire list?
Plus you checked to make sure you have a 102" whip? Some whips were 96" and made to use with 6" spring?

Just looking to help

 

[2NC995]

Tested the coax barrel unplugged from the radio to ground and it reads good. I’m at a loss

Have you checked the SWR on more than one frequency? I don’t want to reread everything, but it seems you noted the SWR on ch 20.

Maybe post what it reads on 1 and 40 (or beyond that if you can).

I know the conventional wisdom is that a 102” antenna is too short without additional length, that has never once been the case for me.

 

[Nick hatz]

Thought of another test went to 25.8550 and swr is 1:1.5. 27.205 - 2:1 , 29.9050 3:1

Does that make sense?

scratching my head

 

[2NC995]

I don’t typically rely on the radio’s meter, but just took this photo for illustrative purposes.

This is with a roof mounted 102” whip. No spring, riser, no nothing added on channel 20.

You can see what the radio detects for SWR...flat.

 

[2NC995]

Thought of another test went to 25.8550 and swr is 1:1.5. 27.205 - 2:1 , 29.9050 3:1

Does that make sense?

scratching my head

Makes perfect sense....your antenna is too long if you’re wanting lowest SWR on the regular 40.

Are you using any sort or longer than usual stud, riser, or spring? If so, can you take it out and check like that?

EDIT, Sorry. I did not see the photos included. That mount is very long. I believe, from what I have seen in a few installs, is that when you have a good ground to the vehicle and especially with a larger vehicle, the overall length of the antenna comes up shorter. Mount the same 102” whip on a Prius, and you may need 110”. You might just find that you need to trim the antenna from the top to get it lower.

Or better yet, get a hold of an analyzer or VNA and see it the antenna is actually resonant. You just might be in a position where lowering the SWR is not of any benefit.

 

[Nick hatz]

No just the mount that I posted pictures of.

 

[2NC995]

No just the mount that I posted pictures of.

Yes, I tried to clarify after seeing the photos. The mount is adding substantial length to your antenna....length that it appears you may not need in this application (at least if tuning by SWR is your goal).

 

[2NC995]

Take a look at this post by Marconi, where he was modeling 1/4 wave antennas on different vehicle types.

https://www.worldwidedx.com/threads/which-mobile-vehicle-model-here-performs-the-best.247381/page-2

Note how different the lengths are to come up with a low SWR on Ch 20.

The results are in post #17.

And another useful link on 1/4 wave antennas...

https://m0ukd.com/calculators/quarter-wave-ground-plane-antenna-calculator/

Note where he’s talking about shaping the radials to 42 degrees to give 50ohm impedance. Comparing the size and shape of your truck bed to the measured and angled radials, you can predict the impedance isn’t going to be the same...even with everything perfectly installed...and you’re not going to have a perfect SWR without some adjustment.

Obviously, you’re not going to be able to reshape and resize your truck bed to give a perfect 50 ohm match. About all you can do is trim the antenna, or better yet, get an analyzer on it and see if there is actually room for improvement.

 

[Tokin]

A vna/analyzer would be the route id go for more solid information about where that antenna really stands before banging my head any further.
Ive read of folks making an angle adjustable magnet mount that could be placed in different locations on the vehicle to find the vswr sweet spot before final mounting.
Im certainly no expert but all ive read over the years would lead me to checking that antenna on an analyzer next. Not a bad tool to have for $100.
https://www.ebay.com/itm/182182197520