Topband: Measuring field strength

[Herb Schoenbohm]

I mentioned the www.fcc.gov website where there is an excellent inverse 
distantce field strength caculator in the last post.  Even though its 
frequency data entry tops out at 1700Khz it is close enough to 1800Khz 
to make reasonable calculations without any heavy lifting. I have 
included an example on one such calculation for a model 90 foot tower at 
1700 Khz with 90/90 foot radials.  From this you can derive that an 
80-85 foot tower on 1.830, with a modest ground system, should work 
well, especially if top loading is obtained with a beam at the top. At 
least with the calculator you can quickly see what works best for you.

The Inverse Distance Fields calculated here are in units of mV/m at 1 
MILE .

Frequency: 	1700.00 kHz
Number of Radials: 	90 radials
Correction for number of radials: 	-6.0000 mV/m @ 1 MILE
Average Length of Ground Radials: 	27.432 meters
90.000 feet
0.156 wavelengths
56.000 degrees
Correction factor for length: 	-18.0000 mV/m @ 1 Mile
Wavelength: 	176.349 meters
578.571 feet
Tower Height: 	27.432 meters
90.000 feet
0.156 wavelengths
56.000 degrees



73

Herb Schoenbohm, KV4FZ