[TowerTalk] Ground Mounted Vertical Question

donovanf at starpower.net donovanf at starpower.net
Thu Jul 10 16:56:10 EDT 2008

Hi Dick,

The antenna you've installed is not a base fed, ground mounted quarter wave vertical.  Your antenna length is measured from ground level (the bottom of your 5 foot pipe) to the top of the vertical.  Your antenna is actually five feet longer than a quarter wavelength.

Your feed system is known as an elevated feed, which has higher
impedance than a base fed quarter wave vertical.  Of course, the lack of a radial system also increases your feedpoint impedance.  Your 100 ohm feed impedance is not surprising on the higher bands.

What band did you design this antenna for?  The effect of 5 foot elevated feed on feedpoint impedance is small on 160 meters, but much more significant on the HF bands.


---- Original message ----
>Date: Thu, 10 Jul 2008 19:39:16 EDT
>From: RLVZ at aol.com  
>Subject: [TowerTalk] Ground Mounted Vertical Question  
>To: towertalk at contesting.com
>Hi Guys,
>I'm installing a full-size ground mounted 1/4 wave vertical.  I  mounted the 
>vertical on a 5' pipe.  The vertical is insulated from the mast  pipe using a 
>base from an old Hustler 4BTV vertical.  I will now get  to work on the ground 
>Question: With the full-size ground mounted vertical connected only to the  
>5' mounting pipe, no radials, I thought I'd see what the SWR and impedance  is. 
> I was expecting a low impedance of about 10 ohms.   (poor ground = low 
>impedance = low performance)
>However, using a MFJ-259B at the input of the antenna the  impedance, at 
>resonant freq. is 100 ohms.  (SWR over 2:1 as would  be expected at 100 ohms).
>I'll install the ground radials next... but the above doesn't seem  right.
>All thoughts appreciated!
>Dick- K9OM  
>**************Get the scoop on last night's hottest shows and the live music 
>scene in your area - Check out TourTracker.com!      
>TowerTalk mailing list
>TowerTalk at contesting.com

More information about the TowerTalk mailing list