help! swr changes when moving mic around

[patrick96814]

I have a Cobra CB in my car and am trying to match it to a Radio Shack magnetic mount center loaded antenna.
I have a external SWR meter hooked up between the radio and antenna.
The problem is when I transmit to get a reading and move my microphone around at the same time, the SWR reading changes, going from nearly zero when I pull the mic far from the radio to over 2.5 when I move it back.
So does anyone know what is causing this? I checked all the antenna connectors and they are not loose. My only guess left is my mic cable?

 

[Beetle]

I'm guessing here: the radio chassis is not well grounded. The antenna is looking for some sort of counterpoise, which it sees when you stretch the mike cable out.

 

[BOOTY MONSTER]

does the swr change when you move your coax around ?

 

[patrick96814]

I'm guessing here: the radio chassis is not well grounded. The antenna is looking for some sort of counterpoise, which it sees when you stretch the mike cable out.

That is an interesting idea. Though the antenna is on the roof of my van so I thought that would have served as the ground plane.
How would I ground the radio in the car? It is a Cobra 148gtl, coincidently the same as the pic in this forum topic header pic. I am powering it through the cigarette lighter plug.

does the swr change when you move your coax around ?

You know, I didn't try that. I plan on trying it later today.
What would it mean if it did change?

 

[Splash1]

put a coiled rf choke right next to the antenna and the problem will be gone ..

 

[GunSlinger338]

get a wilson 1000 mag mount
I bet the problenm is at the coax connection at the radio
The wilson will smoke any radio shack antenna any way ........ might as well upgrade
JMO

 

[190]

what gunslinger said. the wilson 5000 mag mount has got even better coax.

 

[W5LZ]

SWR changes because the 'antenna' changes in some way. If moving the mic around makes it change, then it's a pretty safe bet that there's a connection not made correctly somewhere. First guess would be a ground that contributes to isolating the feed line/antenna from the rest of the stuff that ain't 'right'. Where? Beats me, lots of possibilities. First guess would be radio grounding. Sort of isolating what's inside that box or connected to that box (mic) from the feed line/antenna system. [Ain't THAT gonna be fun?]
Good luck!
- 'Doc