One antenna works and the other doesn't

[Flameout]

I was (and still am) using a mobile Nagoya UT-72g and although it works, it's very touchy as to it's position. I am using it inside my garage, on a vehicle and it needs to be in a very specific spot to hit the one repeater I'm using. If I move it even a foot, I can't hear the repeater, but in that one specific spot, it picks up great

I bought a GMRS specific Slim Jim, mounted on my roof, with a clear shot to that repeater, which is about 14 miles away and it will not pick up that same repeater at all. How can that mobile, inside my garage pick it up but the roof mounted one can't? Could it be that cable or maybe the connectors? I made a PVC "C" to hold the Slim Jim (I attached a photo - the other antenna in photo is my 2m/440 Comet GP-6) I think I may eventually just get a Comet CA-712EFC. The other photo is the view from my roof and that repeater is over in that direction

 

 

[Radioguy7268]

I'm following what Gman is putting down as far as receiver desense, but I'm also wondering if there's a multipath issue due to the metal roof - and that metal reflector is creating a null where the antenna is mounted outside. The fact that there's a "magic spot" indoors where everything seems to work is making me think there's a possibility that some kind of multipath effect going on.  

If you are walking around indoors with the antenna do you find some other magic spots? 

What Gman is questioning is also possible, but the fact that you seem to have tried it with different radios makes me think it's more than just a poor receiver being overloaded. I believe we've confirmed that the Wouxun KG-805G is a superheterodyne design receiver, and has some decent receiver specs.