[Elecraft] Portable antenna

[Charles Greene]

At 02:37 PM 9/28/2002 -0700, k6se@juno.com wrote:
>Chas, W1CG wrote:
>
>"I really can't explain why the vertical is so low noise (my house isn't
>that noisy), and I would have guessed it would have performed a little
>less well than the doublet and the vertical antenna with a fair number of
>radials. I can understand why it is better on the long haul stuff, as it
>has nothing between it and the frezonal zone a mile or two away. I would
>appreciate any comments."
>==========
>As far as receive noise goes, a vertical in a noise-free environment
>should not be significantly different than a high horizontal.  The only
>difference would be a slight increase in ambient (atmospheric) noise
>because the vertical's pattern is omnidirectional.
>
>In the presence of man-made noise, the vertical will be significantly
>noisier than the horizontal because man-made noise is predominently
>vertically polarized.


Earl,

Good point.  My horizontal antenna is about 90' from the electric company 
power lines and parallel to them.  I always attributed the excess noise in 
the horizontal antenna to this fact.  It could be that the multiband 
vertical antenna is picking up more noise from the power lines than the 
single band one, as it is also 90' from the power lines and the single band 
vertical is 140' from them.  It also could be that the multiband vertical 
is picking up more lower frequency noise being longer, and it is feeding 
through.  I'm not sure this last statement has too much technical merit.


>Even though the 20-meter vertical has fewer radials than the multi-band
>vertical, they are obviously over more highly-conductive soil at the
>ocean's edge than the vertical with 22 radials.  My studies have shown
>that few radials over extremely good soil conductivity (moist salt)
>results in less ground loss than a lot of radials over average soil
>conductivity.
>
>Another factor might be that the 20-meter single-band vertical is simply
>more efficient than the multi-band vertical due to losses in the traps or
>whatever other devices are present to make the multiband antenna work on
>other bands.


The bandwidth of the bands on the multiband vertical are much narrower than 
the single band vertical.  This usually means higher Q.  The lower Q of the 
single band vertical may be due to increased ground losses.  When I 
modelled the single band vertical using EZNEC, it said the impedance should 
be 28 ohms (for the configuration I am using).  The measured impedance was 
50 ohms.  I really don't know why the difference, but it is possible that 
ground losses may be causing the measured impedance to be higher than the 
modelled impedance.

As this subject is not on the approved list, I will respond to other 
correspondance privately.  Tnx for the comments.


>73, de Earl, K6SE


73, Chas, W1CG
K2 #462