Ground Plane controlling SWR

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Ground Plane controlling SWR

Post by toober » Monday, 16 September 2013, 8:27 AM

I seem to be having issues tuning a new installation.

the setup:
Everhardt SOTT 1.5 Wave Tiger CB Antenna in center of bed rail right behind the cab window.
fold-down adapter
**NON-SPONSOR** truck rail mount with a 3 inch (non braided) ground strap to bed with a screw through the rhino lining and metal.
same grounding straps from the bed bottom to the frame and from frame to the cab
18 foot cable from antenna through frame to female-to-female adapter and a 3 foot cable to meter/radio (midland 1001z).

Nothing is shorted or open.
I tried a different straight 18 foot cable (97%) from antenna to box with same results.
Lil Wilson magnet mount on top of cab (near the door, not centered, not tuned) yielded 1.5 swr. (but I'd prefer to not have a magnet mount)

Before the grounding straps, swr was in the red (about 5). Now with straps and calibrated on channel 20, my readings are 2.6 on channel 1 and 3.2 on channel 40. I'm going to check again without the fold-down adapter but I don't have much hope for the swr improving that much. Any other ideas?




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Re: Ground Plane controlling SWR

Post by MDYoungblood » Monday, 16 September 2013, 9:26 AM

Hi toober,
Try testing the SWR without the fold-over adapter, I believe that the antenna is too long using it . If the SWR goes to an acceptable number than you will have to pop the top off the antenna and remove some wire to use the fold-over. CB antennas are made inheritablely long because of differences in applications

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Re: Ground Plane controlling SWR

Post by 231 » Monday, 16 September 2013, 10:13 AM

Could be allot of things going on. I have some questions though;

- Exactly which SOTT did you install? (i.e. 3', 4', 5', etc.)
- Is the loading coil above the top of the cab?
- You say you are using a **NON-SPONSOR** mount, but they make several. Did you use a metal sheet or is this some sort of clamp mount?
- Which coax connection type did you use at the feed point (i.e. SO-239 / PL-259, lug-crimp, etc.)
- Have you pulled the stinger out of the antenna to see what it reads? If so, what was that?
- Is the bed fiberglass (i.e. Newer Toyota, etc.)

Frankly, no antenna likes being next to metal or within inches of the cab like that. The Everhardt antennas are no different. However, they tend to be a little more forgiving sometimes provided you get the majority of the antenna above the image plane or at a very minimum, the loading coil. The SOTT is much less forgiving though the shorter you go...so if you are using a 3' or 4' antenna, that makes all the difference in the world.

If I were you I'd consider a front fender mount or move it further back on the bed rail. Use at least 1 self taping screw into the bed's metal at the mount and common grounding point. Remember your counterpoise (aka 'ground') is the other half of the antenna. There is no room for error on that. Your ground straps help for sure...but if the counterpoise is still lacking it'll continue to be a problem no matter what antenna you choose.

Part of the reason folks mount them in the middle of the vehicle is to reduce it's directional properties. However, it's not that big of of performance difference between the front fender and middle. I've been running mine there for probably the last 20 years or more without issues. It is much better to allow the antenna (any antenna) to work as designed in a less than optimal location than to try and force it to work someplace it cannot.

Here is an SOTT-5' mounted on the front fender of my '04 Dodge pick up. As you can see, I use an HD-Spring and quick disconnect. Works great there.

Image

Good luck

231



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Re: Ground Plane controlling SWR

Post by toober » Monday, 16 September 2013, 12:36 PM

See answers in quote...
231 wrote:Could be allot of things going on. I have some questions though;

- Exactly which SOTT did you install? (i.e. 3', 4', 5', etc.) 4'
- Is the loading coil above the top of the cab? it is coiled more at the top
- You say you are using a **NON-SPONSOR** mount, but they make several. Did you use a metal sheet or is this some sort of clamp mount? (non sponsor link removed by bozo)
- Which coax connection type did you use at the feed point (i.e. SO-239 / PL-259, lug-crimp, etc.) PL-259 at all coax ends
- Have you pulled the stinger out of the antenna to see what it reads? If so, what was that? yes, don't think it changed reading much, I'd have to do it again to verify
- Is the bed fiberglass (i.e. Newer Toyota, etc.) 2013 Ram, thought they were still metal

Frankly, no antenna likes being next to metal or within inches of the cab like that. The Everhardt antennas are no different. However, they tend to be a little more forgiving sometimes provided you get the majority of the antenna above the image plane or at a very minimum, the loading coil. The SOTT is much less forgiving though the shorter you go...so if you are using a 3' or 4' antenna, that makes all the difference in the world.

If I were you I'd consider a front fender mount or move it further back on the bed rail. Use at least 1 self taping screw into the bed's metal at the mount and common grounding point. Remember your counterpoise (aka 'ground') is the other half of the antenna. There is no room for error on that. Your ground straps help for sure...but if the counterpoise is still lacking it'll continue to be a problem no matter what antenna you choose.

Part of the reason folks mount them in the middle of the vehicle is to reduce it's directional properties. However, it's not that big of of performance difference between the front fender and middle. I've been running mine there for probably the last 20 years or more without issues. It is much better to allow the antenna (any antenna) to work as designed in a less than optimal location than to try and force it to work someplace it cannot.

Here is an SOTT-5' mounted on the front fender of my '04 Dodge pick up. As you can see, I use an HD-Spring and quick disconnect. Works great there. I initially had to remove the spring I had, the antenna swayed WAY too much

(can't quote photobucket yet)

Good luck

231

Monday, 16 September 2013, 16:14 PM

Since a link to the exact retail product in question is prohibited (sorry mods), you'll have to search for it yourself to see the item. Currently I have the shorter version but may move to the longer one depending on the tonneau I install. Search for: breedlovemounts "front bed rail bracket"

Monday, 16 September 2013, 19:03 PM

Okay, here we go. Got some pics and new readings.... Pictures are before removing the fold-down adapter.

Height of antenna. The antenna is coiled loosely on the bottom half and very tight at the top. Physically, 1/3 of the antenna is below cab roof line but since it is top loaded, more than 2/3 of the wire is above the roof.
Image

Closeup of mount. The antenna has good ground to mount. The mount is grounded with the bonding strap to the screw into the bedrail. This mount clamps onto the rail. Screw connections are shiny where it matters, not painted. Except for the rail, the screw is only touching where it goes through the metal. It is a self taping screw but since it wouldn't tighten completely, I added a butterfly anchor underneath of it (which is probably touching factory paint).
Image

Grounding Bonding straps underneath. The big round body mounts in the picture were not conductive so I didn't use those. The top is the bed strap going to the frame (next to the body mounts), then another strap from there to the body. The screw in the body is one I installed for the side steps. All straps and screws read ground conductivity.
Image

The adjustable part of the antenna is 4.25 inches long. I calibrate on channel 20 only.

Tip removed, fold-down adapter removed:
ch 1=3.6 ch 20=4 ch 40=4.2

Tip inserted all the way down, fold-down adapter removed, and rain (I kept going):
ch 1=1.85 ch 20=1.9 ch 40=2.5

I know adjusting the tip any would only help level the end channel readings. So it's good it is now below 3 on both ends, but I feel it should be below 2. Correct?



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Re: Ground Plane controlling SWR

Post by 231 » Monday, 16 September 2013, 23:06 PM

Okay...you have a 4' SOTT...cool. Your stinger will probably need to be trimmed some but don't worry about that yet. Without question the straps you've added aren't nearly enough. You've used existing bolts which help, but the surfaces are painted. "Shiney metal" is your friend when trying to achieve a counterpoise.

Is the strap you've attached to the mount just bolted or is it a self tapping creating a good solid shiney metal contact to the bed?

Here is the counterpoise connection I did on my Jeep TJ Wrangler with the ball mount. I'm not a fan of the SO-239 connectors because they can pull free and create a dead short. But that's here nor there at the moment.

Image
Image

Now I show you this because just that simple self tapping stainless screw is enough to make the counterpoise connection...but there was only a very small pilot hole drilled first. With the exception of the bolt I see on your first strap to the bed, they all appear to be bolts. Meaning they simply aren't making good enough contact with shiney metal. I wouldn't adjust the antenna at all until you are sure you have the counterpoise connection sufficient. And believe me, you'll know.

Typically the SOTT-4' will dip around 27.065 MHz or so...and be very broad banded compared to other 4' fiberglass antennas. Your height is fine...it's still a counterpoise issue I'd lay odds on.

231




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Re: Ground Plane controlling SWR

Post by 'Doc » Tuesday, 17 September 2013, 5:22 AM

Something to keep in mind is that most antennas are at least 'close' to the required length when sold. If you add to that length by using a disconnect, spring, whatever, you have to shorten that antenna to make up for the added length.
Grounding can be a real PITA. That 'shiny metal' thingy is true to a great extent! It boils down to there having to be electrical contact. How you get that 'contact' can be almost anything. 'Star' washers, or such, do just fine in a lot of cases if they penetrate to the metal. Adding straps is certainly one way of doing it, but making that electrical contact -at- the mount's mounting would be better, nothing 'extra', you know?
Antennas would rather be above metal than beside metal and don't like being under metal at all. That's a 'given'. There are ways of compensating for that 'beside metal' thingy, but it usually means a compromise in some way, usually performance. But if it works well enough for you then who cares, right? "Then why do they even make such a mount?", because someone wanted one.
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Re: Ground Plane controlling SWR

Post by toober » Tuesday, 17 September 2013, 7:24 AM

The screw into the bed rail is a self tapping but I was able to keep ratcheting so I added the butterfly anchor underneath. The straps all have star washers (on the truck side) that you can't really see in the pics. For grins I re-tested the swr when I got in the truck this morning and the readings were .3 higher. The only difference may have been that I was in the passenger seat for yesterdays readings and the rain quit. Do you think it would help if I removed the bedrail screw and used solder instead? Would scraping off rhino lining and paint be better where that screw is or under the mount that only clamps on?



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Re: Ground Plane controlling SWR

Post by 'Doc » Tuesday, 17 September 2013, 8:12 AM

I think that change in SWR can be attributed to rain more than where you were sitting. What would be better soldering ot a screw/bolt? I don't really think there would be any super great difference if either is done correctly.
Changes in SWR are normal, it won't stay the same all the time. Depends a lot on where you are, what's around etc. The time to worry is if it changes and doesn't 'recover'/change again if/when you move. Small'ish changes in a mobile are 'normal', big ones can mean a problem. The trick is recognizing the difference...
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Re: Ground Plane controlling SWR

Post by 231 » Tuesday, 17 September 2013, 11:29 AM

toober wrote:The screw into the bed rail is a self tapping but I was able to keep ratcheting so I added the butterfly anchor underneath. The straps all have star washers (on the truck side) that you can't really see in the pics. For grins I re-tested the swr when I got in the truck this morning and the readings were .3 higher. The only difference may have been that I was in the passenger seat for yesterdays readings and the rain quit. Do you think it would help if I removed the bedrail screw and used solder instead? Would scraping off rhino lining and paint be better where that screw is or under the mount that only clamps on?
I think simply adding a stainless self tapping screw through the mount/bed would probably help allot. It may take more than one...but they don't have to be huge or anything. I would also drill a small pilot hole (smaller than the screw) just to make sure the screw doesn't drag any Rhinoliner down in the contact point with it during installation. I have had times when I'll use the strong body/frame bolts for the main support of the mount and added self tappers for counterpoise. Whatever it takes to make the connection. Once it's all done and you are good to go, simply drop some silicone or some other sealer over the counterpoise connections for longevity. I did that with my wife's Jeep XJ in 1994 and had to replace the connections only once since then.

And I agree...the rain will change things some no matter what. But once things are functioning properly you'll see it's not usually allot of difference. Ice is a different story though. LOL

Best of luck

231



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Re: Ground Plane controlling SWR

Post by toober » Tuesday, 17 September 2013, 11:42 AM

231, are you indicating that my current mount ground is not good enough? Is the bolt I'm using on the mount not good to use for the strap? I would have to completely disassemble the entire mount to drill a hole there. Would bonding the hood be helpful?



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Re: Ground Plane controlling SWR

Post by dirtyjob » Tuesday, 17 September 2013, 13:48 PM

everyone i know that mounted their antenna behind the cab like that have had swr issues, get it totally above the cab roof and see if it helps.


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Re: Ground Plane controlling SWR

Post by toober » Tuesday, 17 September 2013, 13:59 PM

I see what you're saying dirtyjob. Can't argue with stats. I'm going to put on the tonneau and then see where the swr stands. Maybe I'll bonding strap the tonneau, might help. I've seen many trucks with antennas in the stake mount next to the cab. How much of a better location is that really, edge of cab as opposed to center of cab?



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Re: Ground Plane controlling SWR

Post by 'Doc » Tuesday, 17 September 2013, 14:39 PM

A stake-pocket mount tends to get the antenna further away from the cab, which is good, less interaction. It will also 'slew' the radiation pattern a bit, but in most cases you'll never know it. If it were mounted in the center of the cab's roof there would still be some slight 'slewing of that radiation pattern, just in a different direction, sort of. That 'slewing' isn't a biggy at all, all antennas radiation patterns are never absolutely symmetrical.
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Re: Ground Plane controlling SWR

Post by 231 » Wednesday, 18 September 2013, 10:08 AM

toober wrote:231, are you indicating that my current mount ground is not good enough? Is the bolt I'm using on the mount not good to use for the strap? I would have to completely disassemble the entire mount to drill a hole there. Would bonding the hood be helpful?
Yes
Yes
Why?
Maybe, but not likely

The problem is you don't understand that an RF connection is more difficult to achieve than a simple electrical connection. Bolts only work if you scrape every bit of insulating material off to shiney metal. And while you may have that on your strap, the part that matters (the bed of the truck) isn't done. The same can be achieved with a small self tapping screw (or two) in about 2 minutes without re-doing your entire set up.

I'd agree your mount is pretty close to the cab and moving it back might make things easier. However, generally speaking with the SOTT-4 and the majority of the antenna (especially the loading coil) above the image plane, I'd expect to see a standing wave more close to 2:1 IF the counterpoise (aka 'ground') connection is sufficient. You aren't even close to that as far as I can see...considering all of the Everhardt SOTT series I've ever worked with would tune better than 1.5:1. The vast majority of 4' would tune flat (1.1:1) on the analyzer. So the narrow bandedness you are displaying along with hardly under 3:1 tells me something else is going on...and more often than not it's the counterpoise connection (aka 'ground'). I think I'd also dump the fold over until you get things resolved. The lengthening of the antenna can cause problems too (as someone has mentioned) and right now, you need to find out what's going on...so the simpler the better. You can add it back once things are going okay. In fact, you may need to in order to drop the standing wave...we'll see.

Something I just noticed in your image below. It appears you've got an insulator on the bottom of the stud assembly. Seems to me stud assemblies that use an SO-239 (like yours) make the connection for the shield at the mount. So having an insulator on the bottom would keep that from happening. This is the critical point at which the rest simply won't matter if this connection is not done right. It is also why I don't like those type of stud assemblies. They rely heavily on the connection you make at the bracket for the counterpoise, and with enough force (heavy antenna) short out internally. Or am I just looking at the image wrong? Did you paint the surface prior to installing the stud?

Image

When in doubt, start over examining the stud assembly and it's installation.

Just a few more thoughts.
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Re: Ground Plane controlling SWR

Post by toober » Wednesday, 18 September 2013, 12:58 PM

231, you may be seeing it wrong, which is easy to do since I've painted some of it. I would have waited had I know I was going to have all these issues with it. This is the first time I've ever used a non-whip (and first time with this vehicle). The fold-over adapter is off and not going back on and only remains in the initial pictures I took. The unpainted screw in the bed is a self taping screw like you keep saying to use... When I test for ground thread continuity at the radio end of the coax, it is there, which means the coax is grounded to the mount-strap-screw in the bed which is touching metal. The antenna center does not have continuity to the ground shield.

The antenna mount is a normal so-239 on the bottom with shield metal touching the mount (shiny parts there), and the antenna on top insulated from the mount with the included white nylon washer insert. In fact, I actually insulated the antenna center a little more with a thread protector with the end cut off, and it is snug against the positive antenna thread at the bottom where it goes through the mount/nylon washer, so the antenna center bolt threads are double insulated.The part the coax and antenna screw onto was bought at Flying J, then painted the outside of it, the threads are still shiny. I also sandpapered the paint off the mount, washer, and underside of the bolt where I added on the bonding strap in the pic.

On a side note, looking at the antenna again, since it now sits lower without the fold over adapter or spring I initially tried, I would say half of the physical antenna length is below the top of cab and half is above, with most coils still being above.



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Re: Ground Plane controlling SWR

Post by 231 » Wednesday, 18 September 2013, 23:21 PM

toober wrote:231, you may be seeing it wrong, which is easy to do since I've painted some of it. I would have waited had I know I was going to have all these issues with it. This is the first time I've ever used a non-whip (and first time with this vehicle). The fold-over adapter is off and not going back on and only remains in the initial pictures I took. The unpainted screw in the bed is a self taping screw like you keep saying to use... When I test for ground thread continuity at the radio end of the coax, it is there, which means the coax is grounded to the mount-strap-screw in the bed which is touching metal. The antenna center does not have continuity to the ground shield.

The antenna mount is a normal so-239 on the bottom with shield metal touching the mount (shiny parts there), and the antenna on top insulated from the mount with the included white nylon washer insert. In fact, I actually insulated the antenna center a little more with a thread protector with the end cut off, and it is snug against the positive antenna thread at the bottom where it goes through the mount/nylon washer, so the antenna center bolt threads are double insulated.The part the coax and antenna screw onto was bought at Flying J, then painted the outside of it, the threads are still shiny. I also sandpapered the paint off the mount, washer, and underside of the bolt where I added on the bonding strap in the pic.

On a side note, looking at the antenna again, since it now sits lower without the fold over adapter or spring I initially tried, I would say half of the physical antenna length is below the top of cab and half is above, with most coils still being above.
Okay...good, thanks for clarifying that. And good deal on the self tapper, but the fact you are able to keep ratcheting tells me it's possibly not snug enough. I'm not kidding, you need a very tight connection there to the shiney metal. I've also had the occasion where running a jumper wire from where the SO-239 touches the mount over to another ground point was the solution. Had to do a field jump like that on a friend's Jeep CJ on the trail. Worked fine afterward.

Well, continuity doesn't insure an RF connection because of the skin affect of RF. It's an added component that is critical. I've installed allot of SOTT antennas over the years, and never had a problem with them. Of course I never put them that close to the cab either, but I still think you should be seeing a better standing wave...under 2:1 anyway (which at one point you were). It's times like this an analyzer would sure be handy. But the fact it's so narrow banded tells me perhaps it's just not liking the cab being there. I've just not seen an SOTT-4 that narrow banded. Heck, I have some of the 5', 4', SOTT's, 5' SOT's, a slew of TSM-4', and some TSM-3' here I bought up. Hands down they are the best performers for the money. Too bad I'm not closer...I'd throw my analyzer on there and/or compare one of them I have for you.

You may need to move it further on the bed just like the gang has said. Hate to say it because you've done so much work already.

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Re: Ground Plane controlling SWR

Post by toober » Thursday, 19 September 2013, 21:12 PM

Let's bring this to a conclusion for those following along. Thank you all who have contributed to this thread!! I did this test just for grins and based on suggestions from others....

Image

Note the mount is just sitting there on the rail and the thin grounding wire loosely stuck on for this test. Again, calibrated on 20 only.
ch 1=1.5 ch 20=1.25 ch 40=1.35

What the? aww sheesh, yup. Apparently the cab was kicking back an extra 1.5, give or take, on the swr meter. Moving the antenna so the cab was only blocking 1/4 the antenna instead of 1/2 really made a huge difference. And obviously I have learned quite a bit about rf grounding plane during this venture. Well, I went ahead and put on the tonneau and the antenna mount had to go slightly to the right about 3-4 inches to allow for the tonneau rails. I grounded the mount with more grounding strap to the small screw I already had in the bed (and removed the white wire used for the test pic). Without tuning my readings are slightly higher, about 1.5 on the ends, probably due to more cab in the way, but usable nonetheless. I would suggest anybody wanting to mount an antenna in the middle of the bed rail by the cab to use a whip or a 5 foot top loaded antenna at minimum. Otherwise, you're much better off, with a lot less hassle and risk to your radio, if you mount the antenna near one side of the vehicle or the other, or on top of the cab. And if you get this same mount, get the longer one, it'll put your antenna up a couple inches higher which is always good, and it will have more room for the pl-259 coax to accommodate most tonneaus.

I meant to run a short ground strap from the mount to the metal tonneau cover but I forgot. It was easy to forget after I started this evening, 30 minutes into it at dusk, a drizzle started. That quit after 5 minutes. The another hour of dusk and darkness before I remembered my truck has a cab light, hah! So I got to use that for about 15 minutes until it turned off on its own, dangit. I was near done and had a flashlight by that point that I used to finish up. I'll tune the antenna tip to even out the swr ends next time I get a chance, hopefully this weekend.



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Re: Ground Plane controlling SWR

Post by Slyguy » Friday, 20 September 2013, 15:05 PM

toober wrote: Note the mount is just sitting there on the rail and the thin grounding wire loosely stuck on for this test. Again, calibrated on 20 only.
ch 1=1.5 ch 20=1.25 ch 40=1.35
Am I missing something here? Why would you only calibrate on ch20??


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Re: Ground Plane controlling SWR

Post by 'Doc » Friday, 20 September 2013, 16:37 PM

The only thing I'll add to this is that if the mount is done correctly, both a good mechanical and electical connection to the metal of the bed, a ground strap/wire isn't necessary. You should also make sure the metal bed is connected electrically to the frame and so to the rest of the vehicle. Various ways of doing all that, pick the one that's 'best' for you.
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Re: Ground Plane controlling SWR

Post by toober » Friday, 20 September 2013, 23:17 PM

I only calibrate on 20 because that is what the antenna is generally tuned to and to keep readings consistent. I can take more time to calibrate on 1 and 40 but it shouldn't alter the antenna tuning. The mount I used was designed to clamp onto the bed rail. Most bed rails are painted. Mine is also rhino'd. That is why I added a grounding strap to it. I do not intend to remove any of the grounding straps I put underneath the truck. So long as my readings are usable, the straps can't be hurting much. More than likely, they are probably helping.



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Re: Ground Plane controlling SWR

Post by 'Doc » Saturday, 21 September 2013, 5:45 AM

The last few pickups I've had have had a sprayed on bed liner. If you make sure the connection is metal to metal there should be no problem. Of course, getting and keeping that metal to metal contact isn't always simple, but it's not impossible by any means. Connecting all the various body parts electrically is a good idea. Do it however you have to or can. I'm definitely not say to un-ground what you have already. The 'catch' to that grounding thing is that if it's done incorrectly it can cause a thingy called a 'ground loop'. That deals with things being the 'right' length to cause current circulation in the wiring where it shouldn't be. The easiest 'cure' for that is to just not add any unnecessary grounds.
It doesn't matter much what a bed-liner is made from or applied, they don't have a humongus affect on things. They are also very nice thingys for pickups! If they amount to an electrical insulator, just sort of 'by-pass' them an make connections to metal. Is that always simple? Nope, but it's also not impossible.
- 'Doc



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Sporty Mike
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Re: Ground Plane controlling SWR

Post by Sporty Mike » Saturday, 21 September 2013, 8:01 AM

I believe he's got it now , glad you got it figured out Toober. I just wanted to say that as I was reading along I agree with 231 , been there and done all that myself and learned the hard way about the shiney metal. My antenna mount is half of an aluminum mirror mount like truckers use , the half that the antenna goes through is mounted directly to the flat inner side of my bedrail , I used a die grinder with a sanding wheel to remove all paint and primer down to bare shiny metal before attaching it with bolts and nuts and then tightening them down to a Herculean level. With a S.S. 102 and 4" spring the SWR's dont even move the needle on Ch. 20. Does the metal ever rust under the mount? Sure it does , about once a year I remove the mount and resand to shiny , simple as can be.
Now if you wanna have great SWR's , get out and hear equally well , use no tools , cut and drill nothing , spend 80 bucks and slap a wilson mag mount in the center of the roof and be done with it. :biggrin:
Only mobile antennas I'd ever run are a Wilson Mag Mount or a S.S. 102.



Mike


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