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Therealporkchop
Advanced Member
Username: Therealporkchop
Post Number: 712
Registered: 11-2002
| | Posted on Friday, May 19, 2006 - 8:31 pm: | 
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Ok, I've been thinking of trying something I saw on the net about how to properly ground mirror mounts on fiberglass doors. I'm thinking of changing from the mag-mount setup to mirror mount.
Now I know that I've always heard if you decide to run co-phased antennas(which I am not) that you should put a dummy load to one side and set the other. Then swap sides with the load and set the other antenna.
Ok, would the dummy load show a good SWR even if there wasn't a sufficient ground plane? I mean mine shows a good SWR in the shack, and there isn't any ground plane in there. Or am I using the wrong type of dummy load?
I want to use this method if possible to test and see if the grounding instructions work before I go through the trouble of taking my mag-mount setup apart. |
Tech808
Moderator
Username: Tech808
Post Number: 10044
Registered: 8-2002
| | Posted on Friday, May 19, 2006 - 8:46 pm: |
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I have never used a dummy load before for adjusting SWR on dual antennas.
Below is the method I have used for many years now with great result's which is the same information on the Firestick website.
DUAL ANTENNAS
Measurements and determination of short or long conditions are the same as the single antenna procedure. However, when tuning co-phased antennas, if you adjust one antenna, it is advisable to adjust the other in equal amounts to keep them in perfect balance.
Setting the SWR of Your Antenna
Hope this help's,
Lon
Tech808
CEF808
N9CEF
CVC#2 |
Therealporkchop
Advanced Member
Username: Therealporkchop
Post Number: 713
Registered: 11-2002
| | Posted on Friday, May 19, 2006 - 11:16 pm: |
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Maybe I fudged up and didn't make myself clear. I'm actually not trying to set SWR, not yet anyway.
This truck has factory installed co-phased antennas. Somehow they get a good SWR. The coax is rather cheap and it doesn't handle a lot of power very well. Also even with Wilson 5000 truckers, you can't seem to hear as well or get out.
So what I want to do is install my own coax and mount system. The problem is the truck has fiberglass doors, and my experience with these trucks is you won't get a good SWR. You won't unless there is a fix for it, and I'm trying to find it.
I was wondering if I mounted my own mirror mount bracket and ran new coax, could I use the dummy load to see if there was a ground present? Since the dummy load is suppose to be a perfect match, then if I have a good ground, I should have a good SWR. If I don't get a good SWR, then I know I still have grounding problems. Kind of like cheating, I could make small changes and check it everytime to see what happens. And I wouldn't have to re-adjust an antenna. Cause after all if I can't get a good ground, and can't get a good SWR, then how do I know when the antenna is tuned right.
So I want to use the dummy load kind of like a tuned, perfectly matched antenna. The only question I really have is that if I use this load in my shack, I see a good SWR. But there is no ground plane. So would it give a true reading on the mobile or would it show good regardless of a ground or not?
And what would be the correct way to go about grounding the doors since they are fiberglass? |
Tech808
Moderator
Username: Tech808
Post Number: 10045
Registered: 8-2002
| | Posted on Friday, May 19, 2006 - 11:26 pm: |
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Therealporkchop,
On our Pete and KW I ran 10 gauge wire from the mirror mounts down to the door hinge and drilled thru right below the door hinge bolts and ran the wire directly to the frame on each side.
Then I replaced all of the coax to both antennas with Mini 8
I also went directly to the batteries for Power to the radio's and amps and ran the Ground from the radio's and amps directly to the frame.
I had No problem's and the SWR stayed at a flat 1:1
Hope this help's,
Lon
Tech808
CEF808
N9CEF
CVC#2 |
Hollowpoint445
Senior Member
Username: Hollowpoint445
Post Number: 1229
Registered: 6-2004
| | Posted on Saturday, May 20, 2006 - 9:27 am: |
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To answer your question - Yes, a dummy load is purely resistive. No RF is radiated (well, a negligiable amount anyway), so no counterpoise is necessary for a good VSWR.
One of the CB shops here installs a whip pointed straight downward to act as the counterpoise for the vertical whip. Sort of the same theory as the "rooster booster" ground plane kits, but better and less goodbuddyish. |
Therealporkchop
Advanced Member
Username: Therealporkchop
Post Number: 718
Registered: 11-2002
| | Posted on Saturday, May 20, 2006 - 11:39 am: |
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HA-HA...goodbuddyish....man I'm rolling. HAHA..goodbuddy is kinda like strawberry cowboy or rootfairy...haha.
Oh man...I better stop.
Lon, do those two trucks have fiberglass doors? The only KW I am familiar with is the T600 & T800. They have metal doors, but I think the T2000 has fiberglass doors. Not sure about the Pete, cause I've not paid a lot of attention to them.
Did you test the SWR before you ran the grounds? Or did you just start off running the ground wire anyway? I tried the ground wire from the mirror mount bracket straight to the frame before on another Sterling truck I was working on. Maybe the ground wire was too small or too long or some other variable I am not aware of. But it didn't work for me. Most likely it was one of the above mentioned things, seems like I saw something about grounding fiberglass doors before, but I can't remember where.
So basically 445, you are saying I could connect the dummy load to my coax and throw it out the window and check the SWR and it would read good? So it WON'T be an accurate way to check to see if I've got that mount grounded and with a good ground plane.
SO in conclusion it's only a good way to set up co-phased antennas on already properly grounded, good ground plane doors.
OK...so this post is changing to:
HOW TO GROUND YOUR MIRROR MOUNTS ON FIBERGLASS DOORS TO ACHIEVE A GOOD GROUND PLANE
Input please...Lon can you give more detail or help? Could you send me pics or anything else helpful? |
Hollowpoint445
Senior Member
Username: Hollowpoint445
Post Number: 1230
Registered: 6-2004
| | Posted on Saturday, May 20, 2006 - 12:38 pm: |
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Yep, that's right.
Is the entire cab fiberglass? If not, you could run some copper strap inside the door to the nearest metal point. The hinges maybe? Don't forget to tin the copper before you bolt it to steel or the electrical connection won't last long. |
Therealporkchop
Advanced Member
Username: Therealporkchop
Post Number: 722
Registered: 11-2002
| | Posted on Saturday, May 20, 2006 - 3:58 pm: |
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No, the cab is metal. Just the hood & doors are fiberglass.
Seems like I read somewhere that you could take some type of screening and fiberglass it inside your doors and under the hood and ground it to the chassis to create a ground plane. But I don't know if that works or not and I don't want to put all that junk on my truck it not work.
I had also read about running the ground wire from the mount to the chassis, but like I said I still couldn't get a good ground plane. Or I think I didn't cause I couldn't get a good SWR. And I'm sure I didn't do it completely or something cause it seems like that would work. Maybe the wire wasn't large enough? I'll try doing it again with strapping and see what happens. I'll let you know.
Anything else I should try? |
Hollowpoint445
Senior Member
Username: Hollowpoint445
Post Number: 1231
Registered: 6-2004
| | Posted on Saturday, May 20, 2006 - 8:54 pm: |
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Try to use strap or ribbon that's as smooth and as wide as you can so there will be as little inductance as possible. The greater the surface area, the better it'll work, and the same goes for the contact surface with the cab's metal.
If you connect it to the hinges on the door side, you may want to use some graphite powder as a lubricant in the hinges so they're electrically conductive, otherwise you may have to span the hinge with strap to get a good connection to the cab's metal.
I guess the extreme method would be to disassemble the door and line it with a sheet of copper or aluminum foil - as heavy as possible and as completely covering as possible so it would be as close to a metal door as possible. That's probably a lot of work so I'd try the strap first to see how well that works. There are copper tapes with conductive adhesives, but I don't know if you'd want to go that route. It seems to be as tedious or more than just putting a sheet of foil in the door.
That's all I can think of at the moment - other than buying metal doors that is. Is that an option?  |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1641
Registered: 9-2004
| | Posted on Saturday, May 20, 2006 - 10:20 pm: |
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i too like the idea of adding a groundplane to the doors.
industrial strength alum foil and some spray 90 should do it.
maybe you can get some copper foil.
sounds cool!
matt |
Therealporkchop
Advanced Member
Username: Therealporkchop
Post Number: 725
Registered: 11-2002
| | Posted on Saturday, May 20, 2006 - 10:24 pm: |
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Hmmm... I don't know if I can replace the doors with metal ones or not. I'd think if I could, I'd only need to replace the drivers side cause that is the one I'd put the antenna on. I'll have to check into that. I had actually thought of trading the truck on something else that comes with metal doors. I know Sterling offers a light weight cab, but it's aluminum.
I read somewhere today that you need to run a ground wire from the mirror bracket inside the door to the top hinge bolt. Then run another wire to the bottom bolt from the top bolt. Then take off from there and run a wire to the chassis. I don't know why so many hops, but that's what I read. I don't even remember where I saw it.
I was gonna try it this afternoon, but rain delayed that and my wife coming home and wanting to go out. So I'll try to get to it Sunday or Monday and I'll let you know what that does.
Now for a better question. Let's say it does work and I can get a good SWR that way. How do the Predator fans think the 10K will work on a mirror mount? |
Dale
Intermediate Member
Username: Dale
Post Number: 404
Registered: 12-2002
| | Posted on Sunday, May 21, 2006 - 9:43 am: |
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run the grounds like tech808 said if ya simply run a ground from mirrior 2 frame then that acts as part of the antenna and messes everything up.run a groung strap or bare copper wire from mirrior 2 top of door hinges.then another one from bottom of door hing 2 frame .the 10k will work on a mirrior just make sure 2 mount it as far out/away from cab as possible and get the coil above the cab if ya dont do either one of these and antenna will see refect and cause a high swr also grounding will be needed if mirriors are fiberglass |
Therealporkchop
Advanced Member
Username: Therealporkchop
Post Number: 729
Registered: 11-2002
| | Posted on Sunday, May 21, 2006 - 10:51 am: |
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Yeah like I said, I tried the ground wire to the frame before without any luck. I read somewhere last night about the very thing you are saying about going with a straight shot of wire. That is exactly what I did, and hence the reason then that it didn't work.
So yeah, I'm gonna try it the way Lon said and see what happens. I'd rather keep it on the roof but having to go under silos to get loaded it's rather tall. Right now I'm laying it down everytime I go under. Putting in on the mirror would drop it down a bit more. The tip to where the whip exits is only like 4 inches from the bottom of the silo frame. So I have to lay it down or it'll roll it off into the bed and it'll be buried in asphalt and become a total loss. |
Dale
Intermediate Member
Username: Dale
Post Number: 408
Registered: 12-2002
| | Posted on Sunday, May 21, 2006 - 8:32 pm: |
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yea from mirrior 2 frame ground wont work .has 2 be like tech808 said.sorry if my postr was confusing but from mirrior2 top of door hinge
then another from bottom of doof hinge 2 frame.im not sure of the gage wire 2 run but keep runs short as possible.if ya do the mirrior
mount there are other varibles 2 cause refectlion or high some other things id do is
1mount antenna as far out on mirrior as possible ,2 close 2 cab will cause high swr
#2mount verticle not tilted,tilting may cause refectlion swr problems
#3assuming it will have some type of coil keep coil above cab,if not swr problems will most likely happen if i had more info on antenna this may help. |
Wildrat
Advanced Member
Username: Wildrat
Post Number: 888
Registered: 12-2003
| | Posted on Tuesday, May 23, 2006 - 8:43 pm: |
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If you go to a marine store like West Marine they sell copper foil designed for making ground plane on sail boats. It's 3 inches wide, 50 feet long and about 1/64 of an inch thick. It cost around 40 bucks. |
