High SWR Readings

[terryb]

I've previously used a CB on my Jeep and am switching over to GMRS, which I know nothing about and there doesn't seem to be a lot of tuning info on the Internet. 

 

I'm getting high SWR readings and not sure how to fix since it's unlike readings I've ever seen on CB's.  Here's my setup.

 

Midland MXT275 15W

Midland MXT26 6dB gain antenna

Midland MXT24 6m antenna cable

 

My antenna is mounted on the drivers side window cowl (not a lot of options on a soft top Jeep).  The bottom of the antenna is about 2" from the driver's window support beam (whatever it's called), 8" in the middle and 15" at the top.  The bracket I bought goes into a nut which was mounted in a piece of plastic so I added a ground strap (verified ground with DMM).  The cable is ran away from electronics as much as possible and the extra is tied in a figure eight pattern.  No kinks and tested for continuity.

 

I'm testing with a Youmei RS-50 SWR meter.  I can't find any decent directions but it seems pretty simple, although I could be misreading it.  Here's the readings I get and any confirmation that I'm reading this properly would be great.

 

Channel PWR REF SWR

1 4.37 1.26 2.43

7 4.34 1.22 2.43

15 8.01 2.45 2.48

 

Looks to me like I'm getting horrible SWR.  I have not cut the antenna but since all the readings are close together would that do any good?  I'm used to a CB where you adjust the antenna based on whether the bottom or top channel is lower or higher than the other.  The only thing I can think of is the position of the antenna being so close to the metal window surround.  Any input is appreciated.

 

P.S. - Why am I only getting 8W on channel 15?

[tweiss3]

You are still getting better than 80% transmission to the antenna (less than 20% reflected) which is a little bit worse than ideal, but still acceptable.

 

https://antennatestlab.com/antenna-education-tutorials/return-loss-vswr-explained

[quarterwave]

Post a picture of where the antenna is. I think I know what you mean, and it's a hard spot if it's close to the metal structure. 

[marcspaz]

Ditch the Midland antenna and cable.  They are not good... and when they are good, its not for long. 

 

The part of the window/roof frame you are talking about is called an A Pillar.  The small UHF antennas need to be at least 8"-10" away from the A Pillar.  The cowl cover is fine for an HF Firestick for the CB, but its too close for the GMRS antenna.

 

You are very close to radio damage territory with those SWR readings.  I wouldn't use it until its fixed.  No more than 2.0:1.  1.5:1 or better would be ideal.

 

Your power reading on 8 is low because the SWR is bad.  The lower the SWR, the more the forward power increases.  If you have a 1.1 or 1.2 to 1 SWR, it would be close to 13.5 watts (assuming the PA's a putting out the advertised 15w).

[terryb]

Thanks for the fast responses.

 

Here's a photo of the mounting.  I was afraid of that.  I could move the bracket to the mounting screw that is farther forward in the photo.  That would provide about 9" separation at the bottom of the antenna.  Would that be sufficient?

 

Marcspaz, what antenna and cable would you recommend?

 

https://surfinjeepsafari.com/wp-content/uploads/2020/05/IMG_1318.jpg

[marcspaz]

Here's a photo of the mounting.  I was afraid of that.  I could move the bracket to the mounting screw that is farther forward in the photo.  That would provide about 9" separation at the bottom of the antenna.  Would that be sufficient?

 

 

You can try using the front bolt.  On my JK, I had to use a lip mount on the hood, centered between the O and the N on the Rubicon graphic.  On my JT, I mounted my antennas to the top of the bed rail.

 

 

 

 

Marcspaz, what antenna and cable would you recommend?

 

 

For the Jeep, I had great luck using a Diamond K400s and K400c mounts on the lip of the hood (which come with cables) and a variety of antennas.  The best performing antenna I have used so far is a Comet CSB-790a Super Beam, but its 62" tall.  Many people are looking for low profile. 

 

If you are looking for mid-sized, I like the Comet CA-2x4SR or the Diamond NR770HB.  The SWR and performance are not as good as the CSB-790a, but its better all around than the traditional 1/4 wave antennas without the massive height.

 

Then, if you want a traditional 1/4 wave, I have had good luck with both the Browning and the Tram.  I have heard lots of good things about Larsen and Laird, too.  However, you would need to get the Diamond Diamond K400sNMO or Diamond K400cNMO if you go that route, as most 1/4 wave antennas are NMO style.  So, be sure to pick your antenna first, and then get the proper mount.

[marcspaz]

I can't find any pics with the Diamond mount.  I'll look around some more.

 

Here is a Comet NMO mount and the Comet CA-2x4SR on my JK.

 

http://fiveguysracing.com/marc/HAM-GMRS/Comet_Mount_And_Antenna_1.jpg

 

 

Same mount with the Tram antenna

 

http://fiveguysracing.com/marc/HAM-GMRS/Comet_Mount_And_Tram_Antenna_.jpg

 

 

 

This is my JT with the Ham antenna (screwdriver) on the passenger's side and the GMRS antenna on the driver's side.

 

http://fiveguysracing.com/marc/JT_Rubicon/JT_Drive.jpg

[terryb]

Nice JT.  I'll get a new mid-sized antenna and try moving my mount forward.  If that doesn't do it, I'll go with one of the mounts you recommended.  How low did you get your swr with that setup?

 

Thanks a lot Marcspaz!

[PRadio]

I can't find any pics with the Diamond mount.  I'll look around some more.

 

Here is a Comet NMO mount and the Comet CA-2x4SR on my JK.

 

http://fiveguysracing.com/marc/HAM-GMRS/Comet_Mount_And_Antenna_1.jpg

 

 

Same mount with the Tram antenna

 

http://fiveguysracing.com/marc/HAM-GMRS/Comet_Mount_And_Tram_Antenna_.jpg

 

 

 

This is my JT with the Ham antenna (screwdriver) on the passenger's side and the GMRS antenna on the driver's side.

 

http://fiveguysracing.com/marc/JT_Rubicon/JT_Drive.jpg

 

Hey Marc,

 

How did the 1/4 wave perform in that position? I have considered it since it is fairly easy for me to route a wire into the vehicle from there. 

 

Thanks,

 

Phil

[marcspaz]

Nice JT. I'll get a new mid-sized antenna and try moving my mount forward. If that doesn't do it, I'll go with one of the mounts you recommended. How low did you get your swr with that setup?

 

Thanks a lot Marcspaz!

I would have to check my notes about the JK. I won't run a radio if I have anything higher than a 1.5:1. On the Gladiator, it floats between 1.1 and 1.2 depending on weather.

 

 

Hey Marc,

 

How did the 1/4 wave perform in that position? I have considered it since it is fairly easy for me to route a wire into the vehicle from there.

 

Thanks,

 

Phil

 

It was somewhat directional. On the blind side, off the back, the simplex range was just less than if I am driving toward the other station. The SWR was fine and I could work repeaters 20+ miles away with no issues.

 

It's my go-to antenna when I'm going 4-wheeling.

[gortex2]

I use the same mount on my JK but with a 1/4 wave UHF whip and see barely enough reflected to worry about. the one thing I did do when installing was grind the paint from the bottom of the bracket as the NMO was not even getting a ground prior. Check with a DVM to see if you have a good ground. I did try a gain style antenna but like the short whip.

[terryb]

I use the same mount on my JK but with a 1/4 wave UHF whip and see barely enough reflected to worry about. the one thing I did do when installing was grind the paint from the bottom of the bracket as the NMO was not even getting a ground prior. Check with a DVM to see if you have a good ground. I did try a gain style antenna but like the short whip.

Excellent point, but I did run a ground strap and verified with meter.  I noticed during installation that on the JL the mounting bolt is going into a nut which is installed in a piece of plastic so there is no ground unless you run your own.  Honestly, it's a pretty ill-conceived product.  Kind of surprised out of Rugged Radios.

 

Interesting you see little ref.  Could the fact you're using a quarter wave make that big a difference?  Not asking you specifically, just wondering out loud.

[PRadio]

 

It was somewhat directional. On the blind side, off the back, the simplex range was just less than if I am driving toward the other station. The SWR was fine and I could work repeaters 20+ miles away with no issues.

 

It's my go-to antenna when I'm going 4-wheeling.

 

Thanks Marc.

[gortex2]

I think the only reason the 1/4 wave is better is it is more wide band than most gain antenna's. I actually run 1/4 on my work vehicle for this reason. I can go from Ham to T Band without much difference. I wouldn't say its the best solution but worth a try to see.

[quarterwave]

Bandwidth is one thing, but it will not necessarily affect reflected power in within a band range. The main difference is the gain... so think of the output of a 1/4 wave looking like a ball, and the gain (antenna) looking like a ball you are squeezing between your fingers, it becomes an ellipse. The higher the gain the flatter the ellipse.  

[terryb]

Wanted to follow up on my results after installing new equipment. 

 

Laird BB4505CS - 32 inch 450-470 MHz

Laird cable

Fender mount from Right Channels that installs between below the start of the O on Rubicon

 

Channel  1 PWR  3.59 Ref  0 SWR 1.03

 

Channel 22 PWR  15 Ref  0.3 SWR 1.31

 

Interestingly enough replacing the cable gave me the largest improvement in SWR.  From 1.72 to 1.03 and this was after the new mount and the antenna was cut for the GMRS frequencies.

 

I'm curious why the Channel 1 power dropped from 4.37 when the SWR was 2.43 to 3.59 when I've got a great SWR.  On the other hand the high power channels went from 8.01 to 15.

[terryb]

Just for grins I went back to the Midland antenna and got the same results as with the Laird.  So the only difference is the mount, which I can't see making any difference, and the antenna cable which dramatically improved the SWR.

 

I did check ground on the new mount and it was fine.  Also checked ground at the cable and verified no shorts between the cable copper wire and copper mesh.

 

Should I order a new cable?  Or any other thoughts.

[marcspaz]

I thought you already changed the cable?

 

Yes, quality cables will make a dramatic improvement.

 

As far as the power reading being low on ch 1... it could be a meter accuracy issue. Most power meters are the most accurate in the upper 1/3rd of the scale.

[terryb]

Yes I did already change the cable, just out of ideas.

 

I agree on the meter issue other than it did read 4.37 before.  Also, and I have no clue how accurate the bars on the radio are, but I got full bars on channel 1 before and now only get partial bars.  This would tend to confirm the meter reading.

 

Edit 6/7/2020: I ordered a dummy load and will be able to test the accuracy of the meter once I get it.

[terryb]

Just got my dummy load and now I’m totally confused. With the dummy load I get 3.0 watts on channel 1 and 9.5 watts on channel 22. With the antenna with good swr readings as listed above I get 3.66 watts and 15.06 watts respectively. I verified the results with my buddies swr meter. 
 

Shouldn’t I get max output with the dummy load?

[kidphc]

Just got my dummy load and now I’m totally confused. With the dummy load I get 3.0 watts on channel 1 and 9.5 watts on channel 22. With the antenna with good swr readings as listed above I get 3.66 watts and 15.06 watts respectively. I verified the results with my buddies swr meter. 

 

Shouldn’t I get max output with the dummy load?

 

The antenna says it has 5.0dbi gain. So theoretically, I would expect a best of 3w input and 15w at the antenna. What does the SWR look like across the band?

[terryb]

Channel 1 is 1.03 and channel 22 is 1.31.  Can you explain your calculation regarding gain and power.  Went completely over my head.

[berkinet]

The antenna says it has 5.0dbi gain. So theoretically, I would expect a best of 3w input and 15w at the antenna. ...

Well not exactly. Just to keep it accurate you would have a received signal strength at certain locations, depending upon the design of the antenna, that would be equivalent to 15 W into a 0 gain antenna.