Radio question

You got me on that one ....Just maybe your out in the open and can hear weak signals better

 

Probably like going to a hilltop to DX. You're raising your antenna at least 25 feet? The noise floor is higher up there.

Ted

 

EXTERNAL noise floor yep I know from almost 50 years on the radio that nothing makes your radios day more than being out in the open no matter what band. Yep I know from the Skyway bridge here in St. Pete at almost 200 foot over Tampabay you can hear signals 30 - 50 miles away on even 440 mhz ....

There is also a INTERNAL noise floor which is the point a signal goes into the receiver noise no matter how quite the external noise is. This is the XX db s/n rating you see on the radio .5 UV is common .....

You got to love how radio waves travel .....

 

Also consider that the antenna's ground plane is more efficient on most bridges than over regular highway. We use the term "ground plane" usually to mean the roof, or as much horizontal metal as we can get attached to the ground side of the coax, but the actual ground plane is the ground we're driving over. The vehicle is really just a huge capacitor that we're using to couple to that ground plane.
Typical dirt & rock, asphalt, etc. that we typically drive over can have varying amounts of "ground losses", meaning kinda what it sounds like: poor signal due to poorly conducting "stuff" under the truck.
Get up on an overpass, and what are you driving on? Well, from the ones I've seen being built (and the ones that have collapsed), lots & lots of steel running the length of the span, and crossing from side to side, and in the supports, and.... see the pattern?
When you're on a bridge, your ground losses decrease, radiation resistance increases (a good thing), and the antenna transfers more signal to and from the radio because the antenna is "more ideal" than it was over just plain ol' cruddy dirt.
So you hear better. If you didn't have to contend with idiot four-wheelers (like me) jockeying for position on the overpass, and had a little more time, you'd maybe be able to talk out farther, too, because of both the height increase and the better actual ground plane.

Either that or something else. <------ Handlebar's Universal Disclaimer, &#174;Handlebar Enterprises, Inc., 1981