Antenna length question

[dennisjamesnc]

I am trying to trim a mobile antenna to be tuned to the specific 800 MHz channels I listen to the most. My antenna holder allows about ½ inch of the antenna to slide into the holder. See attached picture of the holder.

My question is; In order to trim this antenna as accurately as possible, do I make any allowance for the portion of the antenna that is inside the holder or do I measure from the top of the holder ?

e.g. I will use rounded numbers for simplicity sake. Let’s assume for a second that the antenna needs to be 13.5 inches to be tuned exactly. The antenna holder receives ½ inch of the antenna whip. Do I cut the antenna to 14 inches, 13.5 inches or some value between 13.5 and 14 inches ?

Thanks,

Dennis

 

[gewecke]

Are you going to transmit on that antenna? There's no need to be that exacting,because the difference would not be critical if you're only using it to monitor.
N9ZAS

 

[dennisjamesnc]

Are you going to transmit on that antenna? There's no need to be that exacting,because the difference would not be critical if you're only using it to monitor.
N9ZAS

No, no transmitting. I am just using it to listen to my scanner. Also, I've actually attached the picture of the mobile base this time.

Dennis

 

[jim202]

Normally the measurement is made above the metal support part of the antenna base.

If your not transmitting on the antenna, it will not make much difference if the antenna is 14
inches or 13 inches. The so small difference in the tuned or not tuned antenna on receive
will not be able to be measured even on the best of test equipment.

Jim

 

[gewecke]

Right. Pretty much what I said. If you wanted you could order a gain antenna with a helical design which might make a little difference,but it might be overkill.
N9ZAS