[TowerTalk] Tdr reading with dc grounded antenna?

[Jim Brown]

On 9/17/2021 6:23 AM, WW3S wrote:
> Using a AA-230 tdr, trying to diagnose a Diamond dual band antenna prior to climbing. SWR is 4.*:1, ….should the tdr see a short when it hits the antenna?

I don't know how that unit does TDR, but many do it with a broadband 
sweep, then do an inverse FFT to transform frequency to time, looking 
for reflections, indicating issues with the feedline. Since it's a 
broadband sweep, the far end will be mismatched at most frequencies, so 
seeing a strong reflection is normal.

TDR is not the right method to check the antenna itself. A better method 
is to sweep at the frequencies of interest (2M and 440 MHz), export the 
data to a program like SimSmith, and use the feedline length learned 
from the TDR to subtract it out (by adding coax of the type you are 
using with that negative length). That will show the impedance of the 
antenna at those frequencies. For 2M, I would sweep 144-148 MHz, and 
430-450 for that band.

73, Jim K9YC