Advice on high SWR with new setup?

[theboyk]

Hey there,

I just installed a 2' Firestik off the back of my Subaru Crosstrek (using a door jamb mount off the back hatch jamb). I'm getting an SWR on channels 1 & 40 of 2.5 and no amount of antenna tuning will bring it down (but, tuning got me to an even 2.5 across 1 & 40).

I've spent the last day+ troubleshooting and I think I've ruled out the coax cable and any RF grounding issues. Some of the things I've checked/done...

- removed paint/primer down to metal around screws/plate for the mount
- checked continuity (or lack of) on the coax itself (pin A to pin B, pin A to jacket A, pin B to jacket B, pin A to jacket B, etc.) and all results are good/as expected;
- checked continuity (or lack of) of all hot/ground on various mounting components (fire-ring, stud assembly, the mount itself) and all results are good/as expected;
- checked continuity from the tip of the antenna (weather cover removed) to the pin at the terminating end of the coax, all good;
- checked ground continuity from the mount to a known good ground at the back of the car, all good;
- checked ground continuity from the mount to a known good ground at the inside-the-cabin fuse panel area, all good;
- checked ground continuity from the mount to a known good ground in the engine bay, all good;

I feel like I've checked what I could check and nothing stood out as "bad". The only thing I can think of, at this point, is my mounting location. The mount itself is just above my tail light, which means 2/3 of the antenna is below the roof. As well, the antenna runs vertical (for that 2/3 below roof), about 6–8" from the surface of the back of the car (mostly metal frame, but also some of the back window) and wondering if that might cause too much inference/high SWR? My next move it to raise the mount so more of it extends beyond the roof (going to aim for 1/3 below, 2/3 above), but I can't do that until next weekend (can't get to a good, open area to test SWR in the city).

So, just wanted to see if there was anything else anyone could suggest looking into in the meantime?

Thanks,
Kristin.

 

[DaveJacobsen]

You don't mention what your using for an SWR meter. If you're using the "built in" meter, they are notoriously faulty.
2/3 below the roof is not going to do much for you, except reward.
2' CB antennas (and I ama firestik fan) are, well, crap.

 

[mmckenna]

DC ground and RF grounds are different things.

Putting an already compromised antenna on the rear edge of the vehicle with most of it below steel is probably going to cause issues and will impact performance.

Moving it higher up the gate would probably help.

Trying to get a good ground plane through hatch hinges is going to be difficult. You could try some braided straps to make sure you have a good RF ground to the rest of the vehicle body.

And x2 on the SWR meter.

While I personally detest magnetic mounts, I have an even greater dislike for clamp on mounts like that. The set screws that hold it in place will eventually work loose. Question will be if you catch it in time, or will the mount come loose and cause damage.

Getting the antenna centered on the roof will help performance and getting a low SWR. You can try making changes to the existing install, but there's going to always be some drawbacks/issues. Big choice to make is if you want to spend a lot of time trying to make it work as is, or cut your losses and get a different antenna.

 

[FPR1981]

DC ground and RF grounds are different things.

Putting an already compromised antenna on the rear edge of the vehicle with most of it below steel is probably going to cause issues and will impact performance.

Moving it higher up the gate would probably help.

Trying to get a good ground plane through hatch hinges is going to be difficult. You could try some braided straps to make sure you have a good RF ground to the rest of the vehicle body.

And x2 on the SWR meter.

While I personally detest magnetic mounts, I have an even greater dislike for clamp on mounts like that. The set screws that hold it in place will eventually work loose. Question will be if you catch it in time, or will the mount come loose and cause damage.

Getting the antenna centered on the roof will help performance and getting a low SWR. You can try making changes to the existing install, but there's going to always be some drawbacks/issues. Big choice to make is if you want to spend a lot of time trying to make it work as is, or cut your losses and get a different antenna.

All of this, except a general disdain for all magnet mounts.

Unfortunatley, with that antenna location, you are fighting an uphill battle. Unless you're installing a 102-inch steel whip, no antenna is going to do worth a crap that low on the body.

 

[theboyk]

OK, so definitely going to move the mount up to the top of the body this weekend and give it a check. That'll give me a minimum 2/3 above the roofline. If that doesn't cut it, I'll have to change the setup to either a roof-mount that I can fold down (as I don't have the clearance on this vehicle/garage for an always-up), or mount it from the front hood jamb.

Also—I probably wasn't clear on the mount; I'm not mounting to the hatch itself (so hatch hinges aren't a problem for the RF ground). I'm on the hatch jamb's body-side, so attached to the main body/chassis of the vehicle.

The mount is a Firestik MK-204R—mmckenna, are you saying that style mount isn't any good?

As for the SWR meter, it's nothing fancy, but it's external. A PDC2 dual power/swr meter.

Thanks again,
Kristin.

 

[FPR1981]

OK, so definitely going to move the mount up to the top of the body this weekend and give it a check. That'll give me a minimum 2/3 above the roofline. If that doesn't cut it, I'll have to change the setup to either a roof-mount that I can fold down (as I don't have the clearance on this vehicle/garage for an always-up), or mount it from the front hood jamb.

Also—I probably wasn't clear on the mount; I'm not mounting to the hatch itself (so hatch hinges aren't a problem for the RF ground). I'm on the hatch jamb's body-side, so attached to the main body/chassis of the vehicle.

The mount is a Firestik MK-204R—mmckenna, are you saying that style mount isn't any good?

As for the SWR meter, it's nothing fancy, but it's external. A PDC2 dual power/swr meter.

Thanks again,
Kristin.

A PDC2 is fine. We just wanted to make sure you were using an external meter and not one in the radio

 

[mmckenna]

The mount is a Firestik MK-204R—mmckenna, are you saying that style mount isn't any good?

That should be OK if you have it all assembled correctly.
There will be challenges getting it all to work well with it mounted down low on the vehicle. Ideally you want antennas up high and in the clear. Where you have it installed is going to be a serious compromise and you'll suffer from reduced performance. I'd absolutely try moving it up a bit higher.

Some things to consider:
Trying to cram a CB antenna into 2 feet of whip is going to result in some poor performance. An antenna is going to enjoy being 1/4 wavelength long, at CB frequencies, that's 108". Trying to cram 108" of antenna into a 24 inch package is going to result in some disappointment. I understand the limitations due to the garage, but you may want to consider a bigger antenna that you can remove when you pull into the garage. As it stands, the setup you have now is not going to be a stellar performer in any way.

If you can move the antenna base up, that may help performance and may help SWR a bit. But I'd not expect miracles from a 2' tall CB antenna.

I'm not personally a fan of magnetic mount antennas, there's a number of drawbacks to them, but in an application like this, it may be a better solution. Antennas want a ground plane under them to work correctly. Center of the vehicle roof works best. Putting it off to one edge of the vehicle will impact performance.

As for the SWR meter, it's nothing fancy, but it's external. A PDC2 dual power/swr meter.

That should work fine if you are using it per the directions.

 

[FPR1981]

Magnet mount antennas have come a long way. I realize 102 inches of steel is the ultimate, but it isn't practical. The Wilson, Tram and Stryker antennas do a fine job, with the Stryker being the best of the bunch.

Don't get me wrong, i would love a 102 inch steel antenna, but it would look like hell on my Honda Accord 😅😅😅

 

[K4EET]

<snip> Don't get me wrong, i would love a 102 inch steel antenna, but it would look like he!! on my Honda Accord 😅😅😅

Go for it!!! Just bend that rear mounted 102 inch monster down to the front somewhere using an "Antenna Whip Tie Down" and you will look sooooooo cool!!!

 

[FPR1981]

Part of me wants an old crapper pickup truck so that I can put a 102 incher on it with a giant linear 😅😅😅😅

 

[mmckenna]

Magnet mount antennas have come a long way.

The physics governing RF haven't changed.

But let us not get off topic here.

The antenna cannot be ignored in any sort of setup where you want reliable communications. 2 feet is not going to radiate very well.
And low SWR isn't the only measure of a good antenna.

 

[jonwienke]

A short antenna mounted below the roofline is going to perform poorly, regardless of what you do. You're getting high SWR because RF is being reflected off the vehicle body, reabsorbed by the antenna, and fed back down the coax to the radio. You want all of the antenna above the metal body of the vehicle, preferably near the center of the roof, for best performance.

 

[theboyk]

Thanks all for the advice. Going to raise it up this weekend and see where that gets me. From there, I'll look into different mounting options, along with a longer antenna for sure. Thanks again!

 

[FiveFilter]

I've had great satisfaction with magnet-mount antennas on the roof, ranging from a 35-inch K40 or Lil Wil, to a 55-inch Wilson 500 on my Mazda, to a 62-inch Wilson 1000 on an F250 RV-towing pickup.

It takes just a few seconds to put them on and take them off, but it would get old to do that everyday. Since I only need a CB for highway travel or when in a group, I don't use one every day, so the mag-mounts are perfect for me.

No matter what type antenna you get with the possible exception of a specialized motorized unit, if you have one that is too long for where you park every day, you will have to get out and put it on and take it off every time you roll into or out of the garage. But it sure is nice to get everything you can out of your equipment with an antenna on the roof where there is the biggest, broadest and highest ground plane possible on most vehicles.

 

[FPR1981]

I've had great satisfaction with magnet-mount antennas on the roof, ranging from a 35-inch K40 or Lil Wil, to a 55-inch Wilson 500 on my Mazda, to a 62-inch Wilson 1000 on an F250 RV-towing pickup.

It takes just a few seconds to put them on and take them off, but it would get old to do that everyday. Since I only need a CB for highway travel or when in a group, I don't use one every day, so the mag-mounts are perfect for me.

No matter what type antenna you get with the possible exception of a specialized motorized unit, if you have one that is too long for where you park every day, you will have to get out and put it on and take it off every time you roll into or out of the garage. But it sure is nice to get everything you can out of your equipment with an antenna on the roof where there is the biggest, broadest and highest ground plane possible on most vehicles.

I've had fantastic luck with many of the magnet mount antennas as well. My Tram 3500 talks across multiple county lines with ease, and maintains a 1.2 SWR across the band. My Tram 300 (Little Wil knock-off) only performs about 20 percent less than the 3500.

 

[Tumbleweed1954]

I think the best result you can get is drill a hole in your roof and mount it permanently. A lot of people don't want to do this but it will sure help bring the SWR's down.

Part of me wants an old crapper pickup truck so that I can put a 102 incher on it with a giant linear 😅😅😅😅

I used to have twin 102" whips on a Chevy Chevette! It looked like a cockroach.

 

[KC3SNR]

Not a fiberglass fan. Maybe a BigStick or BigStick II but mobile nah. Stryker SR-A-10 or Wilson magnetic mount. Can't go wrong. Having a good "known working" SWR meter also makes less of a mess of guess work.

 

[FiveFilter]

I think the best result you can get is drill a hole in your roof and mount it permanently. A lot of people don't want to do this but it will sure help bring the SWR's down. QUOTE]

I think the best way to get the SWR adjusted is to adjust the length of the stinger, not to drill a hole. I've had no problems with SWR on a hole-less magnet mount.

 

[mmckenna]

I think the best way to get the SWR adjusted is to adjust the length of the stinger, not to drill a hole. I've had no problems with SWR on a hole-less magnet mount.

That's not the same as a ground plane. That's hiding high SWR in the cable length by creating 1/4 wavelength sections.
Simply hiding the SWR from the radio isn't the same as having a properly tuned/resonate antenna.

 

[jonwienke]

Tweaking the coax length to an odd 1/4-wave multiple does absolutely nothing for antenna performance. It just disguises the fact that you have a problem. Fix the antenna problem.