riddle me this antenna man?

[weatherman49]

so here it is set up small radio midland 886c
cobra magnet mount mobile antenna
radio is on power supply in house antenna mounted to car outside coax thru window (redneck I know but wanted to see if would work) here's the riddle with the antenna on the car 5 TO 8 ft from my trailer I get swr of 1.8 to 2.0 I had to walk over the coax so I just stuck it on an old motorcyle frame that leans against the house it dropped to 1.2 go figure I would think that on the car it would be better because of the larger ground plane and also the fact that on the bike its within 8 in of the metal siding on the trailer any answers as to why the bike works better and recieve and transmission is fine at least 10 miles

 

[Marconi]

It is probably a ground plane problem and it sounds like you have one with both setups. It is very difficult to really tell what the antenna sees as a GP on a mobile installation or any other that is like the bike deal. Maybe the bike is lower and you are seeing high ground losses and it makes the antenna appear to have a better match.

 

[Captain Kilowatt]

You are changing the ground beneath the antenna and that will affect SWR.Also since it is only 8" from the metal siding there is a certain amount of capacitance reactance that can cause detuning of the antenna.Perhaps the antenna is a bit inductive (too long) and the added capacitance canceled it out.

 

[DTB Radio]

A local tried something similar here. He ended up just sitting the mmagnetic antenna on his trailer roof. Its sheet aluminum, so no magnetic effect, but still had the capacitive ground coupling, and it worked out alright.