Antenna help..

[rattlesnake]

Ok i bought a piece of metal for a wilson 1000 mag mount so i could use the 1000 as a base antenna for a while until i get a real base antenna..When i go to put the antenna on the metal i get a lot of noise in the signal is there anyway to stop the all that noise in the signal i cut back on the swr but i still get backround noise..Becuz when i put it on the car its fine but when i put it on the piece of sheet metal it isnt relly fine..I got a reading of like below 2 on channel 1 but on channel 40 its like a 2 or higher..Do u think its not grounded good enough..And is there a way to add a ground to it..

[556]

There is no good way to use a mag mount mobile antenna as a base antenna. In my opinion you did very good to get your SWR under a three like that. I'm thinking you've got it as good as your gonna get. I wouldn't talk very long on it, or run any power through it because of the HIGH possibility you will burn up the final in your radio.

[231]

Looks like the antenna is a bit long. Did you trim the stinger (whip) at all? If not, you may need to...probably 1/4"- 1/2" at a time and try it again. You trim the bottom of the whip by the way and bottom it out again when testing the standing wave. Wouldn't surprise me to hear you got a 1.2:1. And by the way, lots of people run mobile antennas on the base.

The noise you are hearing is probably generated by electronic devices or nearby power lines. There may be allot of things that could be causing it. You may find antenna placement makes a big difference in that. You'll have to just play around with it and see.

Good luck.

[Circuit Breaker]

Where is the antenna located? Are you using only the amount of coax that came with the antenna? If so, and you're using this at home, then the antenna is simply picking up radiated noise from all the devices you have in your house due to its proximity to them. If you were able to get this antenna up on the peak of your roof, I'm willing to bet that the noise level would go down.

[Ronin]

Part of the problem is that the metal (that you are using in this case) is technically only an attachment for the magnet. The antenna is not "seeing" that metal as it does the vehicle body. When the mag mount is on the vehicle, it "sees" the body as a ground plane even though it is sometimes referred to as a "long path" to the ground of the vehicle. With an antenna that is bolted to, or drilled into the vehicle body, the ground for the antenna is a direct connection. With a mag mount it is different. The vehicle frame and body are grounded and connected to the negative terminal on the battery. The Radio itself is connected to negative terminal of the battery (either directly to the battery, or indirectly through the cigarette lighter or fuse panel) as well as the chassis of the radio. The SO-239 chassis mount antenna connector on the radio is also connected to the ground through the chassis of the radio. So in using a mag mount, the radiator actually does "see" a ground plane to work against, even though it may not necessarily be quite as efficient as some kind of direct connection of the antenna mount to the vehicle body.

I have helped people set up lower profile stations by using a mag mount on a window air conditioner or the central AC unit outside the house which works pretty decent because again, the antenna is seeing a long path to ground through the A/C (from the ground on the Air Cond) into the power supply then into the radio. You will probably have better luck with that type of installation if you used an antenna and mount that could be bolted to or physically attached to the metal.

[Circuit Breaker]

Mmmm, sorry, but that's not true. A magnet mount does "see" the metal of a vehicle body through capacitive coupling, or what is referred to as a capacitive ground. If a magnet mount antenna got its "ground" connection via the coax connected to the radio which is then connected to the frame of the vehicle through its power connection, then it wouldn't matter if you had the antenna on a metal body or where you mounted it. The reason it does matter is because the "ground" connection through the coax and the chassis of the radio is more of a DC ground and passes very little, if any, RF. The same holds true when using a magnet mount on an A/C unit, the ONLY ground its getting through the unit is a DC ground. Nothing more. That ground connection on the AC unit is essentially dead to RF due to high impedance. If you had a good match with a magnet mount on an AC unit, removing or disconnecting the power and ground will likely change the SWR very little if at all. What makes a difference is the surface area of the metal under the magnet mount and the size of the magnet. The larger the magnet, the more efficient the capacitive ground connection.

[Sporty Mike]

I've never used a mag mount as a base ant. but I have used a 102 SS whip bolted to a mast using a mirror mount. Had it up at about 24 feet to the base, did pretty well.
Just flatten one end of the mast pipe with a sledge, then drill holes to mount the mirror mount, using just one half of an aluminum mirror mount.


Mike

[BobCB]

My first foray into the cb world was a small center-loaded Cobra magnet mount running to a Midland 1001z that got its power from a car battery jump starter(the kind with jumper cables). I've come a long way since then.

On mine I had the mag-mount on the bottom-center side of a 3 foot diameter steel bucket which was precariously perched on the roof of my cb shack. The bucket was grounded with copper wire. It was a temporary setup, and more or less just to see if this was a hobby I wanted to pursue. If I were you I'd try to make sure it is far enough away from other electrical devices; you'd be surprised at what can cause static on a radio. If you still get static I wouldn't let it bother you too much, as long as your SWR is low, since you said it's only a temporary setup.

I will say that using a mag-mount as a base antenna while a quick fix was a lot of trouble in the end. My SWR was all over the place and since my bucket had a small edge on the bottom side, water would gather and send my SWR up. Because of the short length of the antenna, my receive wasn't the best in the world. However, I still look at that old mag-mount fondly, as it was a learning experience and because of it I was able to learn more about antennas overall.

[Ronin]

Circuit Breaker, in some aspect you are saying what I was trying to explain in simplistic terms. And you are correct in referring to the passing of RF from the chassis... in essence the shielding of the coax. But I wasn't referring to the passing of RF... just the fact that the mag mount antenna sees the vehicle body as a ground plane... in the same way that the shield of the coax is coupled to the radials of a ground plane antenna and gives the radiator something to work against. But if you experiment with the mag mounts as much as I have, you'll soon see that some of the antenna and RF theory, is pretty much only rule of thumb. A fair amount of my experimenting came from a friend who is blind and lives in a high rise apartment and I tried numerous mountings to get him on CB, 10 meters 2 meters, 220, 440 as well as 6 meters. It was a project building different mounts and contraptions and in the end, the window mounted AC's yeilded the best matches as well as the best on the air testing. An oddity that didn't match up to some of the antenna theory was that when the power supply was plugged into the same outlet as the AC was when I achieved the lowest VSWR and impedence match. Use a differnt outlet for the PS, and the VSWR climbed a bit..... Use an HT on battery and it climbed more.... not horribly bad, but enough. I've learned in the past 35 years of radio that regardless of what is written in ARRL books, antenna books, electronic manuals..... just experiment and try it anyway. It's surprizing what they say can't, won't or shouldn't work.... sometimes does. And yep,.. the blind friend is operating on all bands with mag mounts. CB is pretty decent with about an S-8 to my place about 5+ miles away with about a 18"x24" footprint on the top of the AC, Lil Wil, a 1.2:1 on ch 20 and 1.4: at the band edges... and on 2 meters, he regularly works a repeater about 55 miles away (he is on the 8th floor, but in the lowest part of the city... 200 ft ASL at ground level... so not too bad). It's sort of like the leg of a dipole that the shield is connected to.... you just have to get the radiator of the mag mount to work against something...like a counterpoise.

[Kobo]

[quote="Ronin"]Part of the problem is that the metal (that you are using in this case) is technically only an attachment for the magnet. The antenna is not "seeing" that metal as it does the vehicle body. When the mag mount is on the vehicle, it "sees" the body as a ground plane even though it is sometimes referred to as a "long path" to the ground of the vehicle. With an antenna that is bolted to, or drilled into the vehicle body, the ground for the antenna is a direct connection. With a mag mount it is different. The vehicle frame and body are grounded and connected to the negative terminal on the battery. The Radio itself is connected to negative terminal of the battery (either directly to the battery, or indirectly through the cigarette lighter or fuse panel) as well as the chassis of the radio. The SO-239 chassis mount antenna connector on the radio is also connected to the ground through the chassis of the radio. So in using a mag mount, the radiator actually does "see" a ground plane to work against, even though it may not necessarily be quite as efficient as some kind of direct connection of the antenna mount to the vehicle body.

I have helped people set up lower profile stations by using a mag mount on a window air conditioner or the central AC unit outside the house which works pretty decent because again, the antenna is seeing a long path to ground through the A/C (from the ground on the Air Cond) into the power supply then into the radio. You will probably have better luck with that type of installation if you used an antenna and mount that could be bolted to or physically attached to the metal.[/quote]



On that note, Couldnt he benifit then by running a ground wire to the sheet metal?

K

Have a Magical day

[Kobo]

My first foray into the cb world was a small center-loaded Cobra magnet mount running to a Midland 1001z that got its power from a car battery jump starter(the kind with jumper cables). I've come a long way since then.

I am kind of in the same place you were back then!

Fighting high swr, playing around, I came up with the idea of using a piece of sheet metal, grounded. and a mobile antenna I borrowed, after I added the sheetmetal my swr plummeted to 1.1:





I changed the antenna to a wilson 2000, with the same results & now I am playing with a 102" whip. The swr is higher but I am reaching further.

K

Have a Magical Day

[BobCB]

My first foray into the cb world was a small center-loaded Cobra magnet mount running to a Midland 1001z that got its power from a car battery jump starter(the kind with jumper cables). I've come a long way since then.

I am kind of in the same place you were back then!

Fighting high swr, playing around, I came up with the idea of using a piece of sheet metal, grounded. and a mobile antenna I borrowed, after I added the sheetmetal my swr plummeted to 1.1:





I changed the antenna to a wilson 2000, with the same results & now I am playing with a 102" whip. The swr is higher but I am reaching further.

K

Have a Magical Day

Rattlesnake needs to check out your pics. I did the same thing with my antenna. I just got a length of copper wire and ran it between my bucket and the ground. In an instant my SWR went down, watt output went up, and my receive was excellent with little static.

[Kobo]

I did the same thing with my antenna. I just got a length of copper wire and ran it between my bucket and the ground. In an instant my SWR went down, watt output went up, and my receive was excellent with little static.

Exactly.

In my case I drilled a hole slightly over 1/2 to allow the antenna mounts insulator to fit through; the sheet metal rests between the insulator and the mounting bracket. I soldered a eyelet onto a length of copper wire (the ground wire from a length of regular household wiring) and attached it to the bracket via one of the mounting screws. My garage is wired for electricity so I just clamped the other end of the ground wire to the pipe housing the wiring that is coming up from the floor to the breaker box

It has been a bit rainy here this week and in examining the sheet metal I see specks of rust forming between it and the bracket. So, to avoid losing a good ground connection between the two, I will attach a piece of copper wire directly from the sheet to the bracket as well.

At some point in time I hope to have a regular base antenna, but with the trees I have to deal around my garage I will probably want to mount that sucker really high:




K

Have a Magical Day