Re: [IRCA] Short antenna radials

[Dennis Gibson <wb6tnb@xxxxxxxxx>]

KFI's original tower was there before the industrial complex was built. The new tower was built at the same place as the old and uses the same ground radials. 

KFBK and the KSTP day site both use Franklin antennas, the only two in the country. A Franklin antenna consists of two 180 degree electrical height (one half wavelength) antennas separated by an insulator, stacked vertically and fed at the center. The top half radiates and the bottom half is the ground. There are no ground radials. 

Date: Sat, 30 Nov 2013 13:50:34 -0800 (PST)
From: Stephen Airy <pianoplayer88key@xxxxxxxxx>
To: w7swl@xxxxxxxxx, irca@xxxxxxxxxxxxxxxx
Subject: Re: [IRCA] Short antenna radials

I've been recently wondering about this myself (short-radial efficiency, or lack thereof), but more from the standpoint of low-power part 15 transmitting setups.  One example I'm thinking of is such that the total length of the antenna AND all ground radials is 3 meters, and does it make much difference if you use a base-fed radiator with radials vs a center-fed segmented short dipole without radials. (The rule in 15.219 specifies the antenna, transmission line, and ground lead cannot exceed 3 meters.)  There's other scenarios I'm wondering about, but I'll leave them off as I think it's beyond the scope of this list.

As for KFI, I believe the original tower was there long before the industrial complex was built. So, I think there could be ground radials there already, and the new tower was hooked up to them?  Or maybe they have another way of grounding it. KFI *is* a few dB weaker at my house than KNX, in spite of being 12 miles closer (99 vs 111).  I think it's primarily the partial saltwater path for KNX in my case, though.  At a friend's house in Moreno Valley, as well as at my grandma's house in San Gabriel, KFI is considerably stronger, like 10-15 dB.

There is a very efficient station that I believe doesn't have ground radials - 1530 KFBK in Sacramento, CA.  Also I suspect 1500 KSTP St Paul, MN's daytime site may also not have ground radials, but I'm not totally positive on that one.

73, Stephen

Sent from my iPad
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