Ok, Ive got a new Galaxy DX929, Wilson 2000 antenna, Wilson mount, and 18ft Wilson coax. I have an 04 670 Volvo with a bird perch on the passenger side. SWR is 2 to 2.25 and I cant seem to adjust it any lower. I did have a 4' Francis which wasnt any better and is broken and gone now anyway.
I did notice that if I open the door and key up the mic, the SWR will get increasingly lower as I open the door farther. It will actually get down close to 1 with the door open all the way. Obviously I cant drive down the road with door hanging wide open. So I'm guessin my problem is in the distance of the antenna from the truck cab? Might I be better off to just put a couple of fiberglass antennas on the factory mirror mounts? Or get another wilson 2000? I have sunk alot of $ into this antenna setup.....ugh. Don't mind spending the $ IF it works......
Btw, I measured the distance from the wilson antenna to the cab, with the door all the way open, and its 15 inches. Also measured the distance from the factory mirror mount to the cab....15 inches......hmmmmm. Any good suggestions?
Okay, let's do something simple and no cost first. I am guessing that the 18 feet of coax has a lot of excess cable laying around. I would like you to coil that excess coax in the shape of a "Figure 8" that is about 12 inches long. Then secure the Figure 8 with tape or string to maintain its shape.
Next, recheck your SWR reading but DO NOT ATTEMPT TO TUNE THE ANTENNA at this time.
If the SWR is still to high, I suspect an insufficient ground plane. Check the resistance between:
. 1. the antenna mount and the door. It should be zero. If not run a ground strap,preferrably a flat one like the vehicle grounds the negative battery terminal to the frame, from the antenna mount to the top of the door hinge on the door side.
. 2. Also check the resistance between the antenna mount and the door frame. This should also be zero. If not run a short strap from the top of the hinge on the door side to the top of the door hinge on the door frame side. You also may need a short strap from the bottom of the top of the hinge on the door frame side to the top of the bottom hinge on the door frame side.
. The purpose of the ground straps is not to electrically ground but is to actually "Bond" all the major metal body components as one large RF (radio frequency) ground plane. This is necessary for the antenna tol work correctly.
I do not believe your SWR problem is the antenna. Sorry for the long post.IUFAN87 Thanks this.
Thanks for the replies.
Xcis, I forgot to mention that I did run a 10ga "ground" wire from the bird perch, to behind the lower bolt on the inside grab handle. Didnt seem to affect the SWR any. But I suppose if its a ground plane issue it wouldnt have helped anyway. Left my DVOM at home so I guess I will run back over to Autozone and get one so I can check continuity. Need one for the truck anyway. Tried the figure 8 with the coax with no affect. Curious what the idea behind that is. I had read that coiling up all the excess wire in one loop was a bad idea so it was just kinda had it layin loose on the floor. I will check those resistances and go from there.
Rambler, its an 04 670 and it has the ground straps. One of the factory antennas is broken off and gone. The other is still there but has a break in the coil of wire going round the outside. What is a top loaded antenna btw?
Have you trimmed the antenna whip any? What kind of coax are you running and how do you have it routed? Have you checked your coax for any cuts, splits, exposed wire? Where do you have your bird perch attached? It almost sounds as if your coax is being "pinched off" somewhere and then when you open the door it's "un-pinching". Check you coax very good from end to end for any damage and get back to us.
Hillbilly and Gummy have a point -- coax only works right if it gets to maintain the spacing between its inner and outer conductors correctly, and pinching or folding the line too sharply can compromise that. In severe cases, a pinched point can actually make a dead short between the inner and outer conductors and, like OSHB says, opening the door might be enough to undo the short.
Since you've got all that extra coax anyway, *unless it's a "no-ground-plane" antenna, you can feel free to cut off extra coax. If you're comfortable putting on a new connector at the antenna end (it's not rocket science, but it *is* more critical than a DC ring terminal), pull enough of your slack out so that you've got a whole "new" chunk of the line that's going through the door panels and out to the antenna, etc. That will let you eliminate the part of the coax that gets more abuse as the culprit.
Also, as Xcis mentioned, a "DC ground", one that you can measure with a regular ohmmeter, is completely different from an "RF ground", which is the second half of the antenna (the first half being the whip you already see). If a coax short or pinch isn't what's causing the problem, then you've identified it by moving the door panel closer to the antenna, which adds capacitance to the antenna system.
If you've got a second working whip, a quick swap into the existing mount will let you make sure it isn't a whip failure. If you get pretty much the same results, here's an inexpensive fix that's worked for lots of vehicles that don't have an adequate RF ground, i.e., ground plane, to work with.
You can test this theory without investing in a new whip, or drilling any holes in whatever you've got clamped onto your perch mount. Take about 9 feet of, say, 14 gauge wire from a chunk of Romex®, baring a couple of inches at one end, and clamp the bare end under one of the bolts on the antenna mount that's on the perch. (This is just one conductor; black, white, bare ground, doesn't matter for this test.) I suggest the Romex strand because it's stiff enough to stay where you put it for the test and won't try to coil back up like a piece of stranded wire. If it reaches the ground, just bend the end a little, or put a bit of a bow into the wire; it's not critical.
Now get in the cab, close the doors and check SWR. It should be way better already and, more importantly than just mere SWR, the antenna should be actually putting way more signal into the air. If you've got interminable energy and patience, you can start trimming an inch or two from the *bottom* end of the wire and see how that affects the SWR. If you've got a lot of ballast like I do, have a helper do that part.....
Make sure to do this in the clear, rather than right next to another parked truck or a garage wall. And have your cutting-pliers-chum step far away enough so as not to affect the readings (10 feet or so).
So -- if this test wire, also called a "counterpoise", has the effect we're looking for, it establishes that what your antenna needs is a better RF ground/ground plane/counterpoise/other-dipole-half. At this point, cuz it's not gonna be practical dragging around a 9-ft chunk of wire like a streamer from your driver door hardware. And I kinda think my idea from the link above is a bit more elegant.
Not that I'm an elegant kinda guy, but I don't wanna get blamed when people start tripping over that chunk of wire.....
Hope that helps,
-- Handlebar --
P.S. If you know a tech with a good active antenna system analyzer, like the MFJ f'r instance, it can be much faster than what it took to type this all out, but doing it for oneself is a good learning experience, too.
Update: Got a meter and did some troubleshooting. Figured out that there was no continuity through the center of the mount. Bottom line the Wilson gumdrop mount was junk. Replaced that and brought my SWR's down to from just below 2, to just above 1.5. Something I've noticed is the SWR is lower when its raining. wth???? I did try hanging an extra wire off the mount and did note a slight decrease in the SWR (only bout a 2 foot piece of wire though). So I think I will do a little more experimenting with that when I get home.