Defective? Brand new Larsen NMO 2/70B

[KM6MXD]

Hi all, newbie here and I have a basic question please. I am in the process of hooking up my mobile radio in my 4Runner and I tested continuity between the center pin connection of the base of the Larsen NMO 2/70 (base seems to have model NMO-2/70BCO) and the actual whip ferule mount and it is open circuit. To my surprise I find continuity between the threaded NMO internal threads of the base and the antenna whip ferule.

All of this is just holding the antenna base and doing simple continuity testing. Am I crazy, or is this backwards? To say this another way, once installed the antenna whip itself will be directly connected to the coax shield (ground) and the center conductor of the coax will show open circuit to the whip.

Of course, what I dont know is what electronics are in this base and how it works. If it makes a difference, the Larsen web site says this is a center loaded, 1/2 wave for the 2M and I guess collinear for the 70cm. I dont know what all this is and how that connects to a simple whip and if that explains my continuity question.

I bought this brand new from HRO and they are closed today so I cannot ask them this technical question.

Thanks in advance and please shed some light on this for a newbie.

 

[ko6jw_2]

You are measuring DC continuity. The antenna is base and center loaded. What looks like a dead short at DC is some value of inductance at 2 meters and 440 and is not a short at radio frequencies. This is very likely nothing wrong with the antenna. Other than inductors there are no electronics in the antenna.

 

[nd5y]

Other than inductors there are no electronics in the antenna.

Unless they changed the design recently it also has a capacitor.

 

[KM6MXD]

Thanks for the reply. So the center pin will have some inductance at frequency and "connect" to the whip.

The antenna whip is actually directly connected to the ground (as measured with DC). Is this what you would have expected?

Thanks!

 

[KM6MXD]

I guess my last response did not post?? Anyhow, I appreciate your input but I am still hesitant. Can you confirm that it is normal for the whip to have DC continuity to ground?

You can see the square contact in the middle. The threaded portion has DC to the whip and this, of course, also goes straight to ground.

 

[mrweather]

Yes, that's how the antenna is designed.

What appears to be a short at DC is not necessarily a short at AC (RF).