On 2019-09-06 3:47 PM, David Gilbert wrote:
>
If you make the combination of the length of the radial(s) plus the
length of the tower above the radial(s) equal to an electrical half
wavelength, everything on the tower below the radial(s) is choked
off. You can easily see this by looking at the current distribution
in EZNEC.
EZNEC misses the effects of connection to real (lossy) ground. NEC 4
show significant issues when feed/control line and lossy ground are
(correctly) included in the models. The current below the feedpoint
is no longer zero or very low.
73,
... Joe, W4TV
On 2019-09-06 3:47 PM, David Gilbert wrote:
If you make the combination of the length of the radial(s) plus the
length of the tower above the radial(s) equal to an electrical half
wavelength, everything on the tower below the radial(s) is choked off.
You can easily see this by looking at the current distribution in EZNEC.
So yes, N4KG's approach should work fine, although I don't see how it's
any simpler than using a shunt feed. Both require you to find a
suitable point on the tower, and I'm not sure trimming radials is any
easier than adjusting a capacitor.
It seems to me that the advantage of N4KG's approach would be that wire
is cheaper than a good quality capacitor, and possibly that elevated
radials require less wire than a radial field.
73,
Dave AB7E
On 9/6/2019 9:09 AM, Dave Thompson wrote:
Gang,
This is my annual request that there is a simpler way to feed a
tower. Tom N4KG wrote an excellent article on his reverse feed system
in the April 1994 QST. With Tom's system using elevated radials
(either loaded or full length) you feed the coax to a radial and the
shield to the tower. We used a MFJ 259 to find a place to attach the
radials for a match on the tower. Tom also had an excellent section
of calculating top load to get electrical length. If you don't have
the actual QST you can down load the article.
Cebik contributed an article on reverse feed of towers and showed that
there little ground loss that W8JI and others predicted.
We did two towers one 60 feet and one 90 feet and the results were
very good with great DX. Tom ran several towers and most low band
DXers know his results. Sadly Tom became a SK last year. Best DX was
Zone 17 on CW and Zone 25 UA0 from GA on SSB.
73 Dave K4JRB
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