[BC] Part 15 LPAM Questions?

[Richard Fry]

Willie wrote about using 55 gal drums or equivalent for Part 15 AM

> I'm just curious how the numbers would work for
> such a "fat" radiating element as that.

Changing the OD of the 9.84 foot vertical monopole in my earlier post to 
25" reduces its Xc to 351 ohms.  This reduces coil losses, and also reduces 
the change in Xc versus a change in frequency, which means that the VSWR 
bandwidth can be wider.

>Also, seeing as only about 1% of the power is being radiated
> by such a short antenna, (thus only 1mw) how does this explain
>the verified coverages of up to a mile using the Rangemaster
>transmitters? Can it all be caused by the ground structure radiating?
>(Mounted on an existing steel frame structure, such as a
>tower or large billboard, storage tank, etc.)

Yes it can.  If you follow the link 
http://rfry.org/Software%20&%20Misc%20Papers.htm  to Paper 3, it shows the 
additional gain resulting from the scenario there, where the Part 15 tx + 
3-m whip was elevated only 6 meters above the ground.  The radiation from 
the conductor to the buried r-f ground gave an improvement of over 12 dB in 
field strength at a given distance, for the same tx power.

IMO, that's why these elevated systems are so popular, and so zealously 
promoted/defended by those who either don't understand the physics here, or 
do understand it, but hope nobody else will :)

RF