i installed a Monkey Made Mm9 on my Dodge Ram pickup. I mounted it in the center of the bed behind the rear window with the coil above the roofline. On my MFJ 259 it came in resonant at 25.200. Check the grounding and had good continuity. Thought maybe it was having interaction with the cab, so I moved it to the rear of the bed ...same thing. But when I touch my hand to the base of the antenna(stud mount) and the mount the SWR drops in perfect. Any ideas?
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Mobile antenna problem
- Thread starter tunedandloaded
- Start date
poor ground...
You may want to try something like what I did on my Tacoma...This is a Monkey Made "Big John". Riser is made out of 1" square tubing from the local Home Depot, and with some L brackets it's bolted to the beds floor...Also you want to run some ground straps under the bed, from the bed to the frame for better grounding of the bed (1 in each corner of the bed to the frame)
You may want to try something like what I did on my Tacoma...This is a Monkey Made "Big John". Riser is made out of 1" square tubing from the local Home Depot, and with some L brackets it's bolted to the beds floor...Also you want to run some ground straps under the bed, from the bed to the frame for better grounding of the bed (1 in each corner of the bed to the frame)
Thanks! I was thinking it was a ground problem but I had continuity between the bed and the mount. I also ran a ground strap from the mount to the frame. But maybe the bed is not grounded good. Will try it!poor ground...
You may want to try something like what I did on my Tacoma...This is a Monkey Made "Big John". Riser is made out of 1" square tubing from the local Home Depot, and with some L brackets it's bolted to the beds floor...Also you want to run some ground straps under the bed, from the bed to the frame for better grounding of the bed (1 in each corner of the bed to the frame)
if it sets at 25.500 it is showing to be long have you tried to adjust the whip on it?? should be an adjustment set screw to loosen then just push whip down into antenna and set then check again,,,
"Continuity" between the bed and the mount means nothing. Continuity is typically measured using DC, while the antenna system is operating at ~27 MHz. You need to bond the bed to the chassis/frame, and bonding around hinges (tailgate, doors and hood) definitely won't hurt. At RF, sliding contact, as in a hinge, all too often means "no contact".
I found the problem. I have a plastic bed liner that was acting as a giant capacitor effecting the loading coil. I trimmed a different stinger about 9 inches as now have a flat match.
Gee! I never knew plastic can act as a capacitor...
Your problem all along was you needed to trim your whip . At 25.200 MHz where your analyzer shown a resonant point, you were just above the 12 meter band and your antenna was too long for the CB band.
When you touch the bass of the antenna, you, yourself are adding capacitance not your plastic bed liner. Antenna matching devices or tuners usually use capacitance or inductance or both to match radio's to mismatched antenna loads. That's why your antenna seem to match up when you touched it.
When you have a bad ground on a mobile CB antenna, you usually see a high SWR of 3.1. across the CB whole band and even higher on other bands and will not likely show a good match anywhere.
poor ground...
You may want to try something like what I did on my Tacoma...This is a Monkey Made "Big John". Riser is made out of 1" square tubing from the local Home Depot, and with some L brackets it's bolted to the beds floor...Also you want to run some ground straps under the bed, from the bed to the frame for better grounding of the bed (1 in each corner of the bed to the frame)
Nice installation on your truck!
Thanks...Gets the job done anyway...With these small trucks, room inside and out is not much, so I did a in-dash install which IMO turned out pretty good...(kicker's in the toolbox out of the way, but I have a remote switch for it also on the dash)
