Dead short with antenna / OK without!

[glsmith1544]

Larsen NMO HF antenna used most recently on a magmount (Larsen) & for several years previously on my original fender/hood mount (Larsen). Got a new Larsen fender mount & installed yesterday. Never SWR checked in all these years, simply set per Larsen instuctions for CB freqs, with good results. Connected my Uniden 68XL today and as soon as I keyed up I could see per the radio's meter that something was off. Purchased a RS SWR/Pwr meter, SWR over 3 on both 1 & 40. Was concerned I messed up soldering the PL259, checked w/ ohm meter, sure enough, dead short from shield to center conductor. HOWEVER, removed antenna & no short. Shouldn't be that way, should it? Did my old antenna just happen to go bad just now???

 

[wavrider]

There is a diference between DC ohm measurment and RF short.

The antenna will look as a DC short on an ohm meter if there is any type of impedance matching network.

 

[mackmobile43]

Unless the antenna is shunt fed it should show no continuity from center to shield.

 

[glsmith1544]

Thanks for replies, between these & responses on other forums I'm real hopeful of curing everything tomorrow!

 

[Shockwave]

The matching transformer in the Larsen is indeed shunt fed. Seeing a DC short here is normal. Adjust the whip for minimum SWR or check to insure the base is seeing a good ground.