[Antennas] Capacity Hat Information

[George, W5YR]

Brief explanation of the capacity hat.

1. the presence of added capacity to ground causes the antenna to appear to
be electrically longer than its physical length. The reasons for this are
complex and mathematical in the general case. The main thought is that
anything that increases the capacity to ground of the top portion of the
antenna will cause the antenna to operate as if it were electrically longer
than it really is. And the longer the electrical length of the antenna
itself, the less inductive loading is required for resonant operation. 

2. for a base-loaded vertical like the MP-1, the advantage to adding the
hat would be that a smaller inductance - fewer turns - could be used in the
coil to tune the antenna system. Fewer turns means less loss in the coil. A
large enough hat could possible allow the coil to be removed altogether on
the higher bands.

3. for any coil-loaded vertical, the coil is in a sense "resonated" by the
capacity to ground of the portion of the antenna above the coil. With a
proper (large enough) hat, the whip portion above the hat can be removed
altogether without any decrease in performance.

4. with any coil-loaded antenna, the hat must NOT be placed too close to
the top of the coil or coil losses will increase due to the added
capacitance that appears across the coil which raises the circuit Q and
increases circulating current in the coil. It should be not closer than the
coil length from the top end and preferably further than that.

The real question is whether or not adding a hat to the MP-1 will
appreciably improve performance. I don't know since I have not tried it,
but my gut feel is that it would but to a degree probably not justified by
the effort. Coil losses are probably reasonably low already and reducing
the coil inductance by 10% or so by adding the hat probably would not make
a noticeable difference in overall performance.

But, this is amateur radio! Try it and see!

Make a hat of some sort and fasten it to the whip near the top. Try to
measure the output signal in some manner - field strength meter? - before
and after adding the hat and retuning the coil, etc. The results will show
you what and how much you have gained.

Be sure and tell the rest of us!  <:}

73/72, George    
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe   
Amateur Radio W5YR -  the Yellow Rose of Texas
In the 57th year and it just keeps getting better!


"Juan A. Bertolin" wrote:
> 
> Hi to everybody again,
> 
> Following with my trying of improving the performance of MP-1 (I already
> added better radials, a counterpoise to the rig, built my own
> inducti-match,..) and observing an improvement I would like to try with the
> capacity Hat so many times mentioned in different articles of vertical
> antennas.
> 
> I've found some instructions about how to build one but ... I would like to
> know where to find the theory of this stuff in order to understand better
> how it is working, the basis and why it is improving the performance,
> etc... I was looking for in internet but most of the sites (I'm still
> checking out from the 5360 found) just mention the capacity hat as a
> feature of the antenna shown but not the theory.
> 
> I will appreciate any help on that
> 
> 73 Juan EA5XQ