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Tuned SWR to ch20 with poor results on ch1

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Austin83

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According to the user manual for my President McKinley radio, the SWR should be tuned on channel 20 when using either the internal or an external SWR meter. Based on the internal SWR meter, I’m able to get about 1.1 on channel 20, and just for grins, I checked channel 40, and I was getting 1.4, but I’m getting a dismal 2.0-2.2 on channel 1. Should I just stick with the owner’s manual and be happy with 1.1 on channel 20, or do some adjusting and try to find a happy medium between the lower and upper channels? Setup is on a Toyota Tundra with a stake mounted 3’ Firestik II, and 18’ of FireRing coax. Any advice or opinions are greatly appreciated.
 

jassing

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tuning it mid-range is usually wise. You will only have your antenna "tuned" for 1 frequency. Ever. So if you know you're going to live on ch 32 ,tune it using ch 32 and then live with the rest. 3' antenna is pretty small, but usable - just don't expect vast distances.
The "goal" is for swr 1.5 or less; but swr of 2 is still usable. You'd only run the risk of burning your radio if you run an amplifier.

I would do a more traditional way of tuning CB; IF SWR reading on
  • CH 40 > CH 1 = antenna too long
  • CH 40 < CH 1 = antenna too short
Also don't forget to avoid coiling excess coax - if you have to coil it up and then pull it together in the center with a zip tie; otherwise you create an RF choke.
 

ForestRunner98

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That firering coax could be the culprit too. Haven’t heard too many good things about those. I have a 4runner with an antenna near the driver side taillight. I know not the best spot. I have all the doors, hood, tailgate and exhaust bonded. Did wonders for SWR across the board. It barely bumps the meter at 1 and 40. Amp “on” its at 1.4

I also started with a 3’Firestik but results were meh. I have moved on to a 6’ skipshooter in the same spot. What a difference!!!

just like jassing said...tune it to where you are usually at if you want the low SWR. 2.0 wont kill your rig but with that small antenna you won’t get out too far. I am new to this too. As of January of this year...but did a lot of reading and trial and error.
 

RFI-EMI-GUY

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what is grounding your stake mount? If it is just touching paint, you have no ground to the vehicle and the coax is acting as counterpoise. A fire-stick is a terrible antenna. If you want great, look at a Larsen NMO-27 and be prepared to drill a hole in your roof.
 

mmckenna

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what is grounding your stake mount? If it is just touching paint, you have no ground to the vehicle and the coax is acting as counterpoise. A fire-stick is a terrible antenna. If you want great, look at a Larsen NMO-27 and be prepared to drill a hole in your roof.

Here's the plot for my Larsen NMO-27 mounted on the roof of a full size pickup:

Nice and even across the band. Center of the cab, permanent NMO mount.
Marker 1 is CB Channel 1. Marker 2 is CB Channel 19. Marker 3 is CB channel 40. The entire span of the trace is 26MHz to 28MHz.
Here's a close up:

This shows -just- the CB band. Marker 1 on the far left of the screen is Channel 1. Marker 2 is Channel 19, center of the band. Marker 3 is Channel 40, on the far right side.

I suspect if you put your antenna on an analyzer, you'd see your lowest dip would be somewhere above channel 20. I think your antenna might be a tad bit short.

But with your antenna mounted off to one side of the vehicle, it's going to suffer from a messed up ground plane. I understand that mounting them dead center of the vehicle roof isn't always an option, but it certainly has some benefits.
Depending on how much you are willing to tolerate to get your CB to work well, you may want to consider taking the next step, and putting a proper antenna on a good ground plane. It really does make a difference.

Unfortunately the people selling the gear want you to think it's all easy, bolt on stuff and it'll work fine. That's resulted in hobbyists missing out on a lot. Compromise antennas might be easier to install, but they don't always work well. If folks would understand how important antenna system are, they'd have a lot more luck with their radios.
 
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RFI-EMI-GUY

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Folks spend a lot of time and money chasing the magic no hole, no tuning, no ground plane, invisible, magnetic mounted, tiny antenna.

Doing it right requires only a proper antenna and hole saw.
 

prcguy

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Even if well grounded, a stake bed mount only has the skinny top bed rail as a ground plane and performance will be compromised. The Firestick fire ring setup is suppose to tune up with little or no ground and I think if the antenna can be lengthened a bit the match at band edges would probably fall into place to make the radio happier. A roof mount Larsen would work noticeably better but you should be able to get up and down the road for many miles with the Firestick.
 

Austin83

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Thanks for the help guys. I decided to give a longer antenna a shot, and I swapped my 3’ Firestik out with a 4’ Firestik. I found it much easier to tune, and I was able to get 1.2 on Ch1, 1.1 on Ch20, and 1.2 on Ch40.
 

KA9QPN

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I have a similar setup on my Ram Pickup, only with RG8X cable. The only good thing about the 3' FireStik is that it fits in the garage. It's good enough for up and down the interstate. If I want to actually use the radio, I have a 4' Francis whip.
 

AC9BX

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Also don't forget to avoid coiling excess coax - ... otherwise you create an RF choke.

An RF choke is almost always a good thing. When working with coax ideally there should be no RF current flowing on the outside of shield. An RF choke helps prevent this.
Coax has loss. Small/cheap coax has a lot of loss, Thus, the shorter the better. But coiling the excess is probably the best practice.

A perfect match SWR of 1 : 1 though coax with a lot of loss will perform poorly. Let's say the coax sucks, drops 3dB, your 4Watts of carrier power is now only 2Watts even though SWR is perfect. At SWR of 2 : 1 you have an additional mismatch loss of 0.35 dB. Through the same coax you'd now lose 3.35dB resulting in 1.85Watts ... not much of a concern.

An SWR of 2 isn't so bad. The CB band is narrow so a good setup ought to be better than 2 : 1 over the whole thing. At 2 : 1 you have about 11% power being reflected back to the radio due to the mismatch. That's bad but not horrible. However, it may not be as bad as it sounds. If there's a mismatch appearing at the radio some (or all) of that power is reflected back toward the antenna. There's a lot going on. With low loss coax regardless of SWR most of the power will be delivered by the antenna.

Coax loss will make SWR appear better than it truly is.

The Firestick isn't that hot.

A vehicle is a fairly rotten place for an antenna.
 
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