[TowerTalk] 80M Delta Loop

[Jim Brown]

On 7/25/2024 5:01 PM, Brian Beezley wrote:
> That's a good use of the FCC map, Jim. I had completely written it off 
> for ham use once I discovered that it applies only to the AM broadcast 
> band. Values will be quite different at HF. But ranking 1 MHz ground 
> conductivity by location should yield the same HF ranking.

I couldn't open the dropbox file -- it wanted me to sign in. But I do 
have some background on this -- one of my summer jobs while in EE was 
working for Pete Johnson in his consulting office using that map to plot 
contours of patterns we'd computed for directional arrays he designed. 
Those plots of curves of field strength vs distance on a log-log scale 
are called a "nomograph," and my freshman EE curriculum included a 
course in creating and using them.

This was in 1961-2. I strongly suspect that the map is at least a decade 
older than that. And I do think I know how the data were obtained -- by 
running radials (that is, measuring field strength along a radial line 
extending from an AM broadcast transmitter at a large number of points 
and matching graphs of attenuation vs. distance for measured data to 
corresponding curves that are part of FCC AM Technical Regs.

I mention Pete Johnson, because he and Carl Smith wrote those technical 
regs after WWII. Carl was better known as the proprietor of an 
electronics and radio technical school in Cleveland.

And yes, the data are quite coarse -- but I was able to say that 
conductivity on low HF is poor in that area, because everything around 
it is low. :)

73, Jim K9YC