What is the Best 75M High Angle Local Antenna?
Submitted by Tom K1JJ
From a Bulletin Board posting:
: What antenna at what height offers the maximum high angle radiation for
: What would be the best at any cost?
: What would be the best a more modest cost?
Here's some actual observations I've made on low and high antennas for 75M.
It depends on conditions, but generally angles centering around 60-70 degrees takeoff are optimum for local / medium distance 75M AM work. This would equate to a dipole between 50'-70' above TRUE ground.
I've tried MANY "cloud burner" antennas here. The most elaborate was a pair of homemade full sized 75M rotary dipoles - one at 60' and the other at 190', fed out-of-phase to produce a beam straight up. (according to the modeling)
I could not detect ANY difference between this array and a reference dipole at 60' for local work. I knew it was working 'cuz when the dipoles were switched in-phase the close-in guys would drop 20db and the DX came way up. Took it down and used the aluminum for something else.. :-)
So, at the present time for local work, I've settled on a dipole at 50' with a tuned reflector below it at 10'. I cut the reflector at 130' long and found it resonated about 200kc low, according to the MFJ-259B analyzer..
So, a reflector cut to about 127' and placed 10' above the ground, directly below the dipole is about right. It appears to add about 1.5 db to the high angle component according to modeling.
When tested against the high antennas, this low dipole with reflector is about 15-20 db louder for the locals... It does what I ask.
I notice the cross over point between the low and high antenna is usually about 400 miles away....good local coverage. After 1500 miles, the high 75M Yagi at 130' is usually about 10 db louder. Real close in, like 100 miles or less, the low dipole is 15-20db louder than the high Yagi.
In summary, for local work, the best antenna is a simple horizontal dipole put up as flat as possible between 45'-60' high. (a reflector below is optional) A second dipole at 130' high, if possible, will fill in the low angle area that this low dipole lacks, and is the perfect complement to it.
BTW, the ONLY cloud burner I've seen work is a pair of stacked 40M yagis fed out of phase. (140' and 60') It produces about 4 db gain at 60 degrees takeoff when out of phase. On 75M that would equate to a yagi at 280' and 120' high...fantasy. (You asked for the most expensive idea, right?)