[TowerTalk] 80M Delta Loop (bobtail curtain)

[Jim W7RY]

You guys need to investigate a bobtail curtain.
I used one on 40 meters and it worked phenomenal in southwest Missouri. 
An 80 meter one would work fine too.

73, Jim W7RY



On 7/25/2024 10:49 PM, Jim Brown wrote:
> 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
>
>
>
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-- 
Thanks and 73, Jim W7RY