The other week I installed a Cobra 75 in my Jeep with a 4' Firestik antenna, mounted as shown. When I bench tested the radio it worked relatively well. I was inside a garage and getting some static on the untuned antenna, but I could hear people coming across at least. Once I ran the coax through the car however that all changed.

All I get is static from the mic and interference at varying levels. Could this be the way I ran the coax? I ran it along the driver side of the car, paralleling the other wire bundle going up that side of the vehicle.

How did you guys run your wires?

(Sorry, only picture I could find with the antenna. Its a Firestik mount as well)

 

You have not mentioned setting the SWR levels. Have you done that? Running the coax next to the wiring harness should have no affect if the coax has no damaged areas.

 

I didn't tune it yet since I didn't see a point in it if it worked prior to install in it but not now.

Would that make that large of a difference?

 

When tuning the antenna, the JK should be in an open space, not near buildings or trees with at least 30' clearance in all directions including up. When taking the actual SWR readings the doors on your JK should also be closed and the plastic tip should be on the antenna. There are several detailed instructional threads on this forum. Check out the SEARCH function and select the one you like. OR - read the instructions that came with the antenna. they are printed on the back of the cardboard. Lastly, after you tune your antenna, use the Squelch dial to tune our the static then press the Sound Tracker (ST) button to fine tune both local and distant noise.

 

SWR is a must for transmitting with the radio... as for receiving signals it's not..
and it's a lot easier to receive a signal then to transmit.
you could have a SWR of 3+ and still hear people..

I can't always hear people when I turn on my radio. you really have to have someone trying to contact you for a good radio check.
A SWR also might help tell you if the system has a new problem.. broken contact.... etc.

 

If you're that unsure drive to a bridge over the highway. You'll hear plenty of traffic on the net. The traffic you heard when you bench tested the equipment may have moved out of range. The above advice about tuning is also very good.

 

Most often a problem with excessive noise is caused by a grounding issue. You have to be absolutely sure to install the antenna so that it has a good connection to the body of the jeep. Your antenna position is good, but did you scrape the paint from the body panel so that the connection is good? Also, ensure that your power and ground connections are directly to the battery and that there is a fuse on both the power and ground.

If you want to see if there is a problem with the wire routing and crosstalk, just listen to the difference on the reception between a running vehicle and one that is turned off. Ignition noise and power switching noises will not interfere if the engine is off.

Finally I agree with others in that to understand how well you can receive a signal requires that you tune your antenna and then have someone else who you can work with to give you a radio check. If their radio is also tuned well, then they can drive around and talk to you to give you an idea about reception capability.

Tuning your antenna is a must for both reception and transmission. A low SWR reading is indicative of how well the antenna resonance is matched to the desired frequency. Yes, you only get an SWR reading when transmitting, but that is just because an SWR meter is easy and cheap to use to take the measurement.

 

So, I did a bit of research on the Firestick Antenna. What is the model number of the antenna you have. KW4. or FS4.

 

It's a FS4, with the tuneable tip. I've tried playing with it a little but to no avail.

I'm going to try running an additional ground wire to see if that helps with the problem. I definitely do have more interference in the radio when the car is running vs when the ignition is off.

 

1 Is your 12V power source the + terminal of the battery?

2 When you hear all of the static on a channel, what happens when you rotate the Squelch dial from stop to stop?

3 Same as in #2, what happens when you depress the "ST" button?