800mhz Mobile Antenna

[gkovar]

I have been using my handheld scanner in my car for a while. I finally got frustrated sticking it in the cup holder and built a mount for it with the intent that I would setup an antenna.

Well, I ran my RG-58 50 ohm with BNC on both ends. I hooked up a coupler for my RS 800mhz antenna and the cable and mounted the antenna on the INSIDE of my car. It's much higher up in the car and as darn near vertical as it's going to get (off by maybe 5 degrees).

Here's the weird thing. My reception is good when the car is sitting still (engine off or on, doesn't matter), but when I'm moving the reception stinks. In fact I had better reception when the radio was in my cup holder.

What is going on? What other information is needed to sort out this mess?

 

[kf4lne]

A Few questions

Well, some more information could be helpful in this situation.

What kind of car is it?
Where in the car did you mount the antenna?
How much coax did you use?
Did you use a good grade of coax or the cheap crap from Rat Shack?
Is the antenna close to factory tinted windows or a defroster?

If you installed the antenna in the back dash the signals may be getting attentuated enough from the defroster in the window to cause picket fencing. Also, some factory tinted windows use a metallic powder in the glass to get the tint and this has been known to play hell with antennas. I am sure someone else will add some questions to this list to try to get the overall picture of whats going on.

 

[gkovar]

Wow, had no idea so many things needed to be taken into consideration.

Ford Focus hatchback. I ran 12 feet of coax (needed around 8, so some is tucked in) that I picked up at RS. The antenna is not installed near a defroster and the windows aren't tinted.

 

[trooperdude]

Wow, had no idea so many things needed to be taken into consideration.

Ford Focus hatchback. I ran 12 feet of coax (needed around 8, so some is tucked in) that I picked up at RS. The antenna is not installed near a defroster and the windows aren't tinted.

What type of antenna and mount ?

12 ft. of Radio Shack coax at 800mhz is like getting signal through a semi-wet noodle.

 

[kf4lne]

Did you coil up any of the coax? If so that can cause problems. And trooperdude is right, 12 feet of RS coax at 800MHz is like passing signal thru a semi-wet noodle. My guess is that the loss in the cable degrades the signal enough to cancel any benefit of a better antenna location.

 

[gkovar]

The cable is not coiled, it is loosley hung in a side panel. However it does turn back on itself at one point.
I'm using the same antenna I used on the device when it was handheld, RS 800 mhz.
The mount is one I made by taking a suction cup and attaching it to a BNC coupler. I put the cable on one end and the antenna on the other.
I follow your logic for the most part. (By the way, what are some ways to identify good quality antenna cable?)
But my reception only stinks when I'm moving, when I'm sitting still things are as clear as I've ever heard them. What would cause that?

 

[jimyleg]

BRAKES? metal rubbing metal is an EM nightmare! I'm sure its the increase in electricity running around the car.. the fact that your moving and the signal is comming and going through trees buildings etc.. somthings in the motor speu em. get better cable. Cable must be as good or better than your antenna. You will not recieve your signal if you use noodle cable.