View Single Post
  #8   Report Post  
Old April 28th 06, 02:09 PM posted to rec.radio.amateur.antenna
Cecil Moore
 
Posts: n/a
Default Missing Degrees in Mobile Antennas?

Tom Ring wrote:
Cecil Moore wrote:
No, in the case of a base-loaded antenna, the "missing"
degrees are filled in at the impedance discontinuity
*between* the coil and the stinger.


And that differs from your bugcatcher how?


The whole point is that it doesn't differ.
That's how my bugcatcher works.

Here are the three parts to the answer.

1. The base-loading coil furnishes a delay equal to
a certain number of degrees which is nowhere near zero
degrees. Half of a coil self-resonant at 4 MHz would
provide 45 degrees of shift.

2. Using EZNEC to add a stinger to resonate the antenna
on 4 MHz, I find that's 11.5 degrees of straight element.
45 degrees plus 11.5 degrees is 56.5 degrees.

3. 90 - 56.5 = 33.5 degrees which is the "missing"
degrees filled in by the impedance discontinuity.
We can even estimate the ratio of the Z0 of the coil
to the Z0 of the stinger to be 5.0.
--
73, Cecil http://www.qsl.net/w5dxp