Cannot bring down SWR

[jdaleo23]

I have a 2022 F150, using the below hardware, I cannot get the SWR below 4.5-6.5. I'm really just setting this up to use while camping with friends/family, so I don't need anything extreme. A few years back I used a Bearcat 880 with a Wilson 500 mag mount that I was able to dial in very well, but didn't have the space to mount the CB and the aluminum roof stops me from using the mag mount, can't seem to find it anyway. Not sure what I'm doing wrong here though.

Vehicle specific antenna mount - Amazon.com
Radio - https://www.amazon.com/dp/B06XJG6NYB
20' NMO to PL259 - https://www.amazon.com/dp/B0C1BPB6NB
NMO to 3/8" - https://www.amazon.com/dp/B010MAVD6M
Firestik II FS-2BK - https://www.amazon.com/dp/B004USX7EE

No matter where I put the tuning screw, it barely changes the SWR. I tried a different radio (Bearcat 880), multiple SWR meters to make sure the one I was using wasn't just bad, different cable (Amazon.com), adding a spring for some height (https://www.amazon.com/dp/B07MTCNL84), but same results. Wondering if it's possible that I just have a bad antenna, that's the only thing I didn't try replacing yet.

If anyone has any suggestion for a different cable and antenna that would work with the under hood mount I have, I'm all ears. Wasn't looking for anything huge or expensive, only going to throw it on the truck a few times a year, and for the rest of the time, take the antenna off and cap it. CB is connected through cigarette adapter (to make it easier to remove from truck when not in use.. wonder if that could be setting things off (but I used my old radio the same way and didn't have an issue), or if maybe the under hood bracket might not have a good enough ground (even though it bolted to the body) and I need to run a grounding strap somewhere or a direct line to the battery.

Thanks everyone!

 

[prcguy]

Could be the center pin of the NMO to 3/8 adapter is not touching the NMO center pad due to the mount being thicker than what the NMO is designed for. Take an ohmmeter reading from the coax connector center pin to the 3/8 threads, it should show a short. Then while your there check across the coax center pin to ground to make sure that's not shorted.

 

[jdaleo23]

Could be the center pin of the NMO to 3/8 adapter is not touching the NMO center pad due to the mount being thicker than what the NMO is designed for. Take an ohmmeter reading from the coax connector center pin to the 3/8 threads, it should show a short. Then while your there check across the coax center pin to ground to make sure that's not shorted.

Center pin of coax at the CB end shorts to screw tip at the end of the antenna. I tried checking between the center pin and the outside ring, antenna mount, and other parts of the body of the truck and there were no shorts. Everything seems sound when it comes to shorts.

 

[prcguy]

Center pin of coax at the CB end shorts to screw tip at the end of the antenna. I tried checking between the center pin and the outside ring, antenna mount, and other parts of the body of the truck and there were no shorts. Everything seems sound when it comes to shorts.

I would use an antenna analyzer which can show you the actual resonant or sweet spot which might be way outside of the CB band. In this case an SWR meter on ch 1 and 40 can read similar and high but maybe at 26MHz or 27.5Mhz the match is actually ok. I don't see a spring in your parts list and lack of that would raise the resonant frequency some.

 

[jdaleo23]

I would use an antenna analyzer which can show you the actual resonant or sweet spot which might be way outside of the CB band. In this case an SWR meter on ch 1 and 40 can read similar and high but maybe at 26MHz or 27.5Mhz the match is actually ok. I don't see a spring in your parts list and lack of that would raise the resonant frequency some.

Link to an analyzer that would work? I'll have to do some research on how they operate.
Here's the spring I tried today, same results. https://www.amazon.com/dp/B07MTCNL84

 

[K5MPH]

Maybe the tuning screw on top of the antenna is no good causing the antenna to short out.......

 

[jdaleo23]

Maybe the tuning screw on top of the antenna is no good causing the antenna to short out.......

Definitely possible! I tried removing it completely and it was still around the same level, possible that there's an internal issue. Replacement antenna will be here Friday. I can't believe tuning this is so difficult. I've tuned regular magnetic antennas before with no problem, I thought the Firestik was supposed to be pretty fool proof.
Any suggestions on a different antenna setup I can go with? I like it mounted to the hood bolt, it's clean and easy to remove when not in use, and with it being aluminum, mag mount isnt an option, but I'll try anything at this point.

 

[mmckenna]

Not sure about this specific antenna, but some of them are designed to have a spring at the base. That gives it the length it needs to tune correctly. If its designed for the spring, and you don't have it, it'll be too short (screw or not) and it'll resonate too high. No amount of screw adjustment will make it long enough to resonate at 27MHz.

or, that NMO-3/8x24 adapter is throwing things off.

Personally, if you have the NMO mount, just get something like a Larsen NMO-27 and be done.

 

[jdaleo23]

Not sure about this specific antenna, but some of them are designed to have a spring at the base. That gives it the length it needs to tune correctly. If its designed for the spring, and you don't have it, it'll be too short (screw or not) and it'll resonate too high. No amount of screw adjustment will make it long enough to resonate at 27MHz.

or, that NMO-3/8x24 adapter is throwing things off.

Personally, if you have the NMO mount, just get something like a Larsen NMO-27 and be done.

Yep, I think I'm going to try that antenna. Hopefully that'll be easier to tune!

 

[KC5AKB]

Some links,

The Antenna Farm, Your two way radio source

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theantennafarm.com

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