wierd mobile installation problem (antenna)

[batdude]

i have a diplexer installed on a lowband antenna mounted on my truck - this splits the antenna into low band (1.3-60 Mhz and 125-950Mhz)

the low band side feeds my syntor x9000 low band radio and the other port is (going to) feed a BC796 scanner.

when the coax plug for this antenna (pl-259) is screwed into either the diplexer or the scanner directly (via a PL259 to BNC adapter - verified GOOD) ... no signals are received ... i use NOAA Wx as my test freq.

now the funny part .... if you unscrew the PL259 just enough to break the "ground" .. the outer shell of the connector, leaving only the center pin electrically connected... you get full signal strength.

it seems as though that the ground on the PL259 is shorting to the center pin... and once you break the ground...everything is cool and works fine.


anyone ever seen this?

i suspect this is a crappy PL259 (crimp)

thanks,

doug

[KG6EAQ]

Have you ohmed it out?

[apco25]

What brand of diplexer? I've seen this problem before with for lack of a better term "ham" CRAP.

Damn problem drove us nuts on a kenwood - it was utterly deaf on the VHF port and was shorted.

[jim]

If you break ground and the signal increases, there is usually a short in the load. Check the connectors first.

[MSS-Dave]

Going the other way....have you hooked the X9000 to the antenna through a wattmeter bypassing the diplexer? If this measures a low reflected power, the antenna is good and the diplexer probably is too since you said you can't hear anything on the scanner direct to the antenna. Can you hear any low band stuff on the scanner direct to the antenna? If you do, the matching network on the antenna probably looks like a RF short at VHF Hi and UHF, pulling the connector part way out opens one side of the coax and your antenna becomes a random wire.

Dave