Hi George,
> I'm convinced that my flag is performing as a directional antenna on MW
> frequencies. At SW frequencies however, my results are quite different
> and disappointing. My main interest was to use this antenna for the 90
> and 60 meter tropical bands. At these frequencies however, the antenna
> was quite deaf. Above 6 Mhz, gain returned somewhat, but directionality
> was lost. Gain was not equal to the dipoles or T2FD, but the flag could
> be used up to 20 Mhz or so.
The Flag, EWE and others like the K9AY act like a pair of phased
short verticals.
At low frequencies, the ground below the antennas helps stop the
horizontal wires from radiating very well because it pushes the
radiation resistance of the horizontal sections lower. The return
wires in the closed "loops" also have this effect.
The result is the vertical, or vertically sloped, wires receive much
better than the horizontal wires. The better the ground below the
antenna, the more the antenna works this way.
At higher frequencies several bad things happen.
The ground has more loss. It cancels less radiation from the
horizontal wires.
The horizontal wires are further apart, and cancel each others
radiation less.
The vertical section spacing can become so wide the antenna no
longer has a unidirectional pattern (that would happen when the
effective length of the antenna reaches just over 1/4 wavelength).
For higher frequencies, you'd have to build a shrunk-down Flag (or
EWE or whatever) and you might have to install it over a ground
screen.
At my last QTH ..none of these antennas worked really well
because the soil was so poor. The EWE was useless, and the
"Flag" only somewhat useful. I had to install a large screen below
the antenna, and then they worked.
You could run into the same thing, with certain soil conditions on
certain frequencies.
> Finally, this was my first attempt at winding an impedance matching
> transformer, so I'd like some reassurance that I did this right. I
> wound the 35 turns on one side of the toroid, and the 10 turns on the
> opposite side of the toroid.
If anyone needs ten turns for a 75 ohm winding of a broadband
receiving transformer for HF, they are using the wrong core
material. One or two turns should be enough.
A 2 to 7 turns ratio transformer wound on a 73 material core with
about one inch of core material parallel to the wire inside the
winding would be enough. One mistake often made is people look
at the initial ui of the core, rather than the permeablility or
impedance at the operating frequency. Then they wind up with a
VLF transformer that takes too many turns for 160 meters and up.
73, Tom W8JI
w8ji@contesting.com
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