[TowerTalk] Shunt Feeding a Vertical an easier wat

[Joe Subich, 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.

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