[TowerTalk] Shunt Feeding a Vertical an easier wat

[Joe Subich, W4TV]

On 2019-09-06 4:07 PM, David Gilbert wrote:
 >
> I actually found a post that N4KG himself made a couple of years
> after his QST article where he mentioned that the performance of his
> inverted system seemed to be worse than what he once had with a full
> set of buried radials under a shunt fed tower.
If one were talking strictly about 160 meters, keeping the elevated
radials 20' above ground *and* placing a detuning skirt below the
radials to decouple the tower from ground might work.  In addition
every cable would need to be bonded to the tower at the top and
bottom of the detuning skirt.

However, since the original question was for use at 475 KHz a
'reasonable height' elevated radial system would be 80' - 100' high
and the radials would require significant loading to accommodate a
vertical that is only ~1/8 wave above the radials.

73,

    ... Joe, W4TV


On 2019-09-06 4:07 PM, David Gilbert wrote:
> 
> I actually found a post that N4KG himself made a couple of years after 
> his QST article where he mentioned that the performance of his inverted 
> system seemed to be worse than what he once had with a full set of 
> buried radials under a shunt fed tower.  He pointedly stated that the 
> lower the elevated radials on his inverted system, the worse the 
> performance even when matched.
> 
> As you say, SWR doesn't tell the full story for actual performance.
> 
> 73,
> Dave   AB7E
> 
> 
> On 9/6/2019 12:55 PM, Joe Subich, W4TV wrote:
>>
>> The N4KG system looks good when evaluated for SWR and ease of
>> installation.  It, however, has serious performance issues.
>>
>> 1) W8JI and others are right - there can be significant ground
>>    losses depending on the division of current up/down the
>>    tower from the "feedpoint".  The only time that loss is
>>    truly negligible is if the tower is *NOT* grounded (mounted
>>    on insulators) and all feed/control lines have high impedance
>>    chokes at ground level.
>>
>> 2) The division of current up/down the tower can also result in
>>    significant skewing of the take off angle and cancellation
>>    (currents are out of phase due to the ground connection) at
>>    critical angles.
>>
>> Unfortunately, Cebik's models understated ground effects - particularly
>> real (lossy) ground.
>>
>> 73,
>>
>>    ... Joe, W4TV
>>
>>
>> On 2019-09-06 12:09 PM, 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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