[Antennas] Next dumb question

[C.Whitaker]

de WB2CPN
For those of  you who live in North New Jersey, in sight
of NYC, there was, or is, a group of four radio towers
which have hats on them.  I understand they were used
for commercial oversees radio circuits.  Maybe McKay (?)
or Federal.  (Armstrong's FM test site is a bit further
up the road, in Alpine, NJ.).  (Also, Federal's TACAN
aircraft navigation test facility was on Route 3 in Nutley, NJ.
New Jersey had a lot going for it back then.
73  Clete
+++++++++++++++++++++++++++++++++++++++++
On 11/26/2012 2:01 PM, Terry Conboy wrote:
> Indeed, a large enough capacity hat can reduce or totally eliminate 
> the need for a loading coil.  Use of capacity hats can increase the 
> bandwidth and radiation resistance significantly, which can improve 
> efficiently for a given ground loss resistance.  One thing to be 
> careful of is to not to mount any loading coil too close the the hat, 
> or the added parallel capacitance across the coil can increase 
> circulating currents in the coil and lower the effective coil Q 
> (increase losses). Probably a good rule of thumb is to space it away 
> from the hat by at least by the length of the coil.
>
> Also, if the hat conductors slope down from horizontal, the fields can 
> partially cancel the radiation from the vertical conductor which will 
> slightly lower the radiation resistance.  Sometimes adding more hat 
> wires of shorter length is a viable solution, if you are stuck with 
> supports that give a similar droop angle. Obviously, there are 
> tradeoffs for maximum efficiency between coil size and making drooping 
> hat wires longer.
>
> Generally, it's a good idea to keep the capacity hat conductors 
> symmetrical around the vertical.  Any asymmetry can result in high 
> angle horizontally polarized signals, which can be good or bad, 
> depending on desired path lengths.  (The inverted-L can be thought of 
> as a single wire hat, and it can produce significant NVIS signals.)
>
> 73, Terry N6RY
>
> On 2012-11-23 7:28 PM, fred forbush wrote:
>> Concerning the cap. hat the way I understand it is that the 
>> electrostatic
>> field surrounding the hat interacts with the electromagnetic field of 
>> the
>> loanding coil beneath it. I've found that using a cap. hat reduces the
>> amount of coil needed when tuning to a frequency.
>> 73, Fred
>> k6kub
>>
>>
>> On Fri, Nov 23, 2012 at 11:08 AM, Michael Josefsson <mj at isy.liu.se> 
>> wrote:
>>
>>> On 23 Nov 2012, at 18:39, Jim Miller wrote:
>>>
>>>> Is a capacity hat electrically connected (metal to metal) to the 
>>>> antenna
>>>> itself or is it just sitting there insulated but "capacitively 
>>>> coupled"?
>>>>
>>> It is electrically connected.
>>>
>>>> The coil I bought was supposed to be for 15 to 80 meters.  Well.. 
>>>> It only
>>>> tunes down (no coil) to about 4.1 and SWR is too high to use even at
>>> 3.963
>>>> MHz (and it won't go into the 15 meter band either, 20 is tops).  OK,
>>>> shorter whip for 15.
>>>>
>>>> But, for 80 meters, thinking about stationary operation and adding a
>>>> temporary top hat to bring me into the top end of the band.
>>>>
>>>> Better yet, also thinking about adding a few turns of extra coil at 
>>>> the
>>> base
>>>> to bring the whole thing down a bit. How much would it take me to move
>>> from
>>>> 4.1 down to 3.9 or so using existing coil for adjustment and my 102 in
>>> whip?
>>>> Say #12 THHN close wound on a 2 inch form (6,8,?)
>>>>
>>> Everything depends on everything else... Trial and horror is your 
>>> path :/
>>>
>>> Cheers anyway:)
>>>
>>> /Micke
>>>
>
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