Topband: Modeling the proverbial "vertical on a beach"

[Tom W8JI]

> Definitely, as I'd mentioned, less site-to-site variability would be shown 
> with a full-size efficient transmitting type antenna, whether a vertical 
> over a good ground system or a high (>150 ft. elevation) horizontal dipole 
> / yagi.
>
> Smaller receiving loops and active whips exhibit the greatest influence 
> due to surrounding ground conductivity and elevation profiles.  This is 
> particularly the case on groundwave or very low angle skip.  High angle 
> skip is largely unaffected by the nature of the surrounding landscape; 
> certainly by the time you get to Near Vertical Incidence, that can work 
> even if you are surrounded by tall buildings or mountains.
>

Why would it matter?

The receiving antenna does not matter, provided it responds to the wave 
angle at the receive site. It doesn't matter if it is loop, a 10 foot 
vertical, or a 200 foot vertical so long as the antenna does not null the 
primary wave angle for the incoming signal. It does not matter if it is a 
large receiving array or a whip, provided each are not nulling the primary 
signal arrival.

When broadcast station are measured, the engineer walks around with a hand 
held loop. The loop is calibrated in volts. If someone changes TX antenna 
pattern or power or efficiency, it shows as exactly the same change no 
matter what the soil under the test meter. As a matter of fact, as long as 
you don't need to know absolute levels (which Hams virtually never need to 
know) the meter does not need to be calibrated to any voltage reference. 
You can throw a 20 dB pad in the system, and as long as the internal 
sensitivity and noise does not limit the reading, the change would still be 
linear.

The only critical thing is the transmitting reference signal we are 
comparing with, and filtering out QSB and selective fading with a lot of 
averaging. Any of us who grew up in the AM days are likely to remember all 
about frequency selective fading.  :)

73 Tom