Hey folks,

I recently installed a 4' Firestik Firefly antenna with an 18' Firestik coax with the Firestik side-mount on my license plate holder. I ran the cable up through the wheel well and down and over to the passenger side along the sill to under the glove box where I have my Cobra 75 WX ST control box mounted.

When I attempt to tune the antenna, I get decent SWR readings using a Radio Shack SWR meter of 1.2 (CH1), 1.5 (CH19) and about 2.0 (CH40), which I believe is considered to be a "long" antenna condition. But these values are achieved with the adjustable tip threaded all the way down. As soon as I put the rubber boot cover over the tip, the readings all go to 3.0 or higher on the meter!!

I have the antenna mount connector grounded to my rear left side brake line bracket frame bolt, with soldered 12AWG wire to ring terminals on both ends, (getting good continuity, reading 0.2 ohms with my Fluke from ground stud on mount to frame rail).

Any thoughts/comments?? Kinda strange huh!

 

I believe it's in the firestick tuning instructions to put the rubber tip back on before you test the swr. so it might be a matter of turning the adjusting screw out some, putting the tip back on and testing again.

 

You are correct. You have to tune with the cap on the antenna or you will get false readings. I know it is a pain in the butt to do this, but it has to be done. Also, make sure you have all the doors closed and in an open area before testing. Not sure why, but I read this somewhere that it can mess with your readings.

 

Not strange, at all. There are more reasons for too high VSWR than just the tuning of the antenna. If you have successfully brought the VSWR down to the lowest possible reading then the antenna is tuned to resonance. That does not change when you put the cap on. Yes the VSWR does change when the cap is installed but it is due to dielectric loading. The tip of the antenna is a very "hot" place, electrically. The voltage and the impedance are the highest at this point and any object that can absorb or change the electrical field (near field) will change the antenna loading and thus the impedance. This change in impedance (very slight) is what causes the VSWR change. Ignore it.

 

This information is correct. The vehicle doors and any other objects within the near field will affect the VSWR readings. It does not affect the antenna tuning, however.

 

Important things to know:

1. Ohm meter readings are not useful for judging quality of RF connections.
2. Standard hook up wire is not adequate to establish a RF connection to the body. To be effective, the connection to the body must be established directly at the mounting location by the mounting hardware.

 

From firesticks site, look for the section on tuning.

http://www.firestik.com/Tech_Docs.htm

This link may help you some too. It goes into a good bit of the how to's and why for's.
http://www.roadtripamerica.com/Equip...io-Antenna.htm

 

Thanks to all for responses!

I was able to get tuned pretty well, after reading the Firestik tech pages.

I drove to a nice big open tobacco field here in NC to adjust the SWR with my meter, while sitting inside the jeep with doors closed.

I ended up eliminating the adjustable tip, locknut, and O-ring completely and trimming the vinyl tip cover to about 3/8". This resulted in SWR readings of 1.1 (CH1), and 1.4 (CH40).

With the vinyl cover removed completely, the readings were somewhat flip-flopped, i.e. "short." So I leave as is for now and check tuning periodically.