View Single Post
  #24   Report Post  
Old January 3rd 04, 09:51 PM
Richard Harrison
 
Posts: n/a
Default

Richard Clark wrote:
"The "earliest high frequency antennas" were in fact BCB."

Yes, but not in Ed Laport`s book. Ed`s book covers LF, MF, and HF. Ed as
Chief Engineer of RCA International was most interested in RCA`s
maritime service, radiograms, shortwave broadcast, and radio relay
services. These were conducted above 1700 KHz. Ed observes that HF
propagation is a statistical business, as the ionosphere is always in
flux. Ed gives guidance in using the NBS Central Radio Propagation Lab
publications, hardly the advice of someone stuck in low gear.

Ed gives some of the most complete information to be found on horizontal
rhombics and rhombic arrays, hardly the advice of someone treating the
use of low frequencies.

Richard Clark wrote: "And guess what, they (earliest high frequency
antennas) are still Vertical antennas.

I agree that 1.7 MHz is medium wave as the break is often chosen as
3MHz. I also agree that MW broadcasting antennas are universally
vertically polarized.

The primary service area of a MW broadcast station is defined by the FCC
as the area well served by the ground wave. Of course vertical polarized
antennas are used because horizontal polarization produces no ground
wave.

Art Unwin started this thread it seems because he faulted a vertical
antenna for not having a 100-mile range using low power.

The vertical has a null overhead almost guaranteeing no short-hop sky
wave.
Low power obviates ground wave DX.

To make an evening sky wave trip of 100 miles at 160 meters, Art needs
an antenna with a lot of high-angle radiation, 60 or 70-degrees more or
less to use the ionosphere for short skip, or he needs enough effective
power to punch a signal through along the ground.

A horizontal dipole could provide the high-angle radiation for the sky
wave.

A vertical antenna could provide the ground wave signal which only needs
enough power to work day or night.

A 1/4-wave vertical antenna can produce an unattenuated field strength
at the earth`s surface of about 195 mV/m at one mile. At 100 miles, the
field strength is 1%, or about 2 mV/m.. Depending on the soil
conductivity, the actual signal reaching a receiver at 100 miles is
likely much less than the unattenuated value. In a quiet location, not
much signal is needed.

Best regards, Richard Harrison, KB5WZI