I hate tuning CB antennas

[smittie]

I have a Laird C27 antenna on an NMO mount with 17 feet of RG8A/U coax. Mounting it in a 2021 Jeep Gladiator connecting to a Cobra 25.

Before installing the coax in the vehicle I connected it to the NMO mount and tuned it to the radio. Got an SWR of 1.7 on 19.

Installed the coax in the vehicle, no cuts, no nicks one medium bend.

SWR is now mid 3s.

Let's start with I'm stupid and don't know what I'm doing.

Is this normal?
Do I just start with a new whip and retune?
Do I just buy two cans and a string?

 

[slowmover]

1). Are you using a separate SWR meter?
You need one if not.

2). Test coax:

https://palomar-engineers.com/wp-content/uploads/Palomar-Engineers-Common-Mode-Noise-on-Coax-User-Diagnosis-Test-1.pdf

How To Test for a Defective CB Coax

An defective CB coax cable will result in sky-high SWR. Fortunately, testing CB coax is very straightforward and we show you how.

www.rightchannelradios.com

3). Your C-25 is telling you it’s ready to retire.

See:

2023 Best Mobile CB

Via mobile experience as an OTR truck driver. Several thousand hours annual use. Earlier references to the Qixiang factory’s new circuit board elsewhere. Several brands. The above possibly the best known example at present. Paired with the equally new Driver Extreme DRX-9010 External Speaker...

forums.radioreference.com

.

 

[smittie]

Thanks, @slowmover.
I have tested the coax but I will test it again. Maybe something got damaged.
I am using a stand alone RadioShack SWR albeit one that I have had for quite some time, 10 years or so.
I am planning on getting a new radio so I am going to wait before trying to tune the system again.
The GMRS antenna was 1.3 right out of the box. I want more of that.

 

[K6GBW]

Firstly, yes it's normal. 27MHz is a big wavelength for vehicles. Install the antenna completely first and THEN tune it. Use the SWR meter to check channel 1 and channel 40. Is one higher than the other? If the SWR is lower on channel one and much higher on 40 then the antenna is too long. If it's high on 40 then it's too short. A common mistake with the baseloaded antennas is to cut off too much of the whip so take your time.

The location you place the antenna is also very important. A base loaded antenna on a jeep is tricky as it needs a ground plane. Where did you mount it? I found with Jeeps I get the best results with a ball and spring mount on the left side. The rear tire carrier works "okay" with antennas like a Firestik. Mounts that come out of the side of the hood usually don't work worth a damn because there's basically no ground plane at all under them.

The problems associated with large CB antennas is one reason GMRS is becoming so popular with the Jeep and Off-Road crowd. GMRS antennas are super easy in comparision.

 

[smittie]

@K6GBW, thank you.
I learned the lesson of big chunks the hard way. Now, I take off about 1/2 inch chunks until I get channel 1 down below the 3 mark and while 40 is still high. After that I take off 1/4 and 1/8 inch chunks.
The antenna is mounted on the driver's side using a Rugged Radio mount. I have tested ground continuity to the radio. However, per your statement that might be why I have such a hard time getting down to 1.5 SWR.
I plan on replacing the Cobra 25 with a President Harrison FCC. I am going to wait for the new radio to attempt tuning the antenna again, this time with the antenna and coax fully installed.
The GMRS radio is already in and working perfectly. The GMRS gets used a LOT more than the CB. The CB is there as much for nostalgic reasons as practical. There are still a number of guys in my off-road crowd that use CB. I would like to get it working as best as possible given the limitations of the install.
Respectfully,
Smittie

 

[Ensnared]

I buy CB antennas that are known for being close to the optimal setting. I get very low readings on these antennas: Wilson 1000; K40; and my trusty TRAM 3500. I have never every tuned any of these antennas. I know these are not fancy ones, but I get out.

I leave tuning to the experts, LOL.

 

[K6GBW]

@K6GBW, thank you.
I learned the lesson of big chunks the hard way. Now, I take off about 1/2 inch chunks until I get channel 1 down below the 3 mark and while 40 is still high. After that I take off 1/4 and 1/8 inch chunks.
The antenna is mounted on the driver's side using a Rugged Radio mount. I have tested ground continuity to the radio. However, per your statement that might be why I have such a hard time getting down to 1.5 SWR.
I plan on replacing the Cobra 25 with a President Harrison FCC. I am going to wait for the new radio to attempt tuning the antenna again, this time with the antenna and coax fully installed.
The GMRS radio is already in and working perfectly. The GMRS gets used a LOT more than the CB. The CB is there as much for nostalgic reasons as practical. There are still a number of guys in my off-road crowd that use CB. I would like to get it working as best as possible given the limitations of the install.
Respectfully,
Smittie

Understood. The Rugged Radio mount and being right next to the windshield pillar is going to be the biggest problem. I doubt you'll be able to get a really good match with that set up. That said, if you will only use it for listening and maybe the occassional short conversation, just try and get it below 2:1 and it should be fine. The radio won't blow up or anything. It certainly won't be a DX talking barn burner, but I get the impression you need it for just trail communications and it should work well enough for that and yes, GMRS is certainly the way to go these days!

 

[prcguy]

I have a Laird C27 antenna on an NMO mount with 17 feet of RG8A/U coax. Mounting it in a 2021 Jeep Gladiator connecting to a Cobra 25.

Before installing the coax in the vehicle I connected it to the NMO mount and tuned it to the radio. Got an SWR of 1.7 on 19.

Installed the coax in the vehicle, no cuts, no nicks one medium bend.

SWR is now mid 3s.

Let's start with I'm stupid and don't know what I'm doing.

Is this normal?
Do I just start with a new whip and retune?
Do I just buy two cans and a string?

Where is the NMO mount? About the only place that will work on a Gladiator is on the hood. Did you cut the length of coax between the first test and the final install? If the ground plane is inadequate, the coax shield does most of the work of being the ground plane and if you compare having all the coax outside the vehicle vs routed inside the metal box it will diminish the ground plane effect of the coax. This will not matter if the antenna ground plane is ok but will detune the antenna if not.

 

[smittie]

The NMO mount is from Rugged Radio and mounts at the cowl immediately behind the hood hinge and just in front of the A pillar.
I did not change the coax when installing in the vehicle. All of the coax was in deed outside the vehicle in the first tuning test and it is now inside the vehicle skin.
Ground plane is a concept I am still figuring out. The engine hood is aluminum so I assume that counts as some ground plane. The roof of the vehicle is fiberglass so, no help.

Thank you for contributing to my learning experience.

Respectfully,
Smittie

 

[slowmover]

Big truck aftermarket mirror mount puts antenna too close to A-pillar, so adjustable forward tilt is utilized to get it away.

High reflect means high SWR.

I had to go from a 22” to 44” SS shaft to dial back tilt to the minimum 12-degrees. Get the coil “high”.

Top load fiberglass (Skipshooter brands) avoid this somewhat by virtue of design. Unfortunately, driving the Great Plains subjects the antenna to sometimes constant 90-110/MPH winds. Whips it all over the place. The 6’ gives up performance the 7’ allows.

Sirio 5000 not as affected. It’s at just over 7’ at present. Performance saved, but now need to have custom XHD mount built.

There’s always something.

.

 

[prcguy]

The NMO mount is from Rugged Radio and mounts at the cowl immediately behind the hood hinge and just in front of the A pillar.
I did not change the coax when installing in the vehicle. All of the coax was in deed outside the vehicle in the first tuning test and it is now inside the vehicle skin.
Ground plane is a concept I am still figuring out. The engine hood is aluminum so I assume that counts as some ground plane. The roof of the vehicle is fiberglass so, no help.

Thank you for contributing to my learning experience.

Respectfully,
Smittie

Sounds like its similar to this which should tune up and work just fine. Just make sure the NMO lip mount screws dig into the underside of the hood and make a good connection. In this case the hood is the only ground plane which equates to any flat metal under the antenna and has little to do with grounding to the frame or back to the battery.

I took my ground plane a little further and removed the plastic pieces just behind the antenna and the curved ones down the side and lined with aluminum tape to extend the ground plane a little, but mostly for VHF/UHF antennas. I have 4 antenna mounts on my 2021 Gladiator Mojave.

 

[slowmover]

I buy CB antennas that are known for being close to the optimal setting. I get very low readings on these antennas: Wilson 1000; K40; and my trusty TRAM 3500. I have never every tuned any of these antennas. I know these are not fancy ones, but I get out.

I leave tuning to the experts, LOL.

The basics aren’t hard, just tedious. Top-load whips (Skipshooter, for example) make it painless.

It’s a little more stressful when cutting a steel whip to size. (Unless, like me, one’s learned to buy a second whip at initial purchase).

Bonding can/will change total length so review and apply that technique to best effect early on.

Of course, one could ruin the self-induced agonies and buy, borrow or steal a NanoVNA or RigExpert.

.

 

[smittie]

I took my ground plane a little further and removed the plastic pieces just behind the antenna and the curved ones down the side and lined with aluminum tape to extend the ground plane a little, but mostly for VHF/UHF antennas. I have 4 antenna mounts on my 2021 Gladiator Mojave.

Neat idea. I think I'm going to try this. Did you see an improvement on the SWR for either the VHF/UHF after applying the aluminum?
Respectfully,
Smittie

 

[prcguy]

Neat idea. I think I'm going to try this. Did you see an improvement on the SWR for either the VHF/UHF after applying the aluminum?
Respectfully,
Smittie

I don't recall any change in SWR but it should help the radiation pattern a little.

 

[smittie]

I don't recall any change in SWR but it should help the radiation pattern a little.

I can't imagine it hurts, it's simple and cheap, and there is reason to expect that it probably helps, if only a little. I'm going to try it.

Smittie

 

[prcguy]

I can't imagine it hurts, it's simple and cheap, and there is reason to expect that it probably helps, if only a little. I'm going to try it.

Smittie

Here is one of the plastic pieces I coated with aluminum tape.

 

[smittie]

Ordered a nanoVNA H after watching several YouTube videos. It looks WAY easier than SWR meter method.

Thanks to all. More questions to follow.


Respectfully,
Smittie

 

[slowmover]

SWR Meters are inexpensive. It’s inside the ballpark “good”.

(Read up on freeband before tuning finished).

.

 

[mmckenna]

Ordered a nanoVNA H after watching several YouTube videos. It looks WAY easier than SWR meter method.

Thanks to all. More questions to follow.


Respectfully,
Smittie

I have one of those, and they are an excellent tool to help tune antennas.

As for the videos, there's a lot of really awful ones. You may need to watch several to find one that is any good and explains it in a way that makes sense to you.

 

[smittie]

@mmckenna, so I discovered. It looks like a far better method for building an antenna system. It also looks like it is capable of a lot more than just tuning antennas. I'm kind of excited to see what it can do and what I can learn through it.

Thanks again.

Smittie.