I'm trying to design a Flag antenna for 9 to 12 Mhz.
I have the standard 14ft by 29ft Flag. It seems to lose
it's front to back ratio as the frequency gets above 4Mhz or less.
So I suspect it needs to be reduced in size for higher frequencies.

Would I scale the size the same as the frequency ratio?

I'm using the demo version of EZNEC, the dimensions of length
to height seem quite forgiving.

Could this be the limited segments (20) of the demo, or are
the design dimensions just not that critical?

Your input is appreciated, I haven't found much info on higher
frequency Flag antennas.
Thanks,
Mike

amdx wrote:
I'm trying to design a Flag antenna for 9 to 12 Mhz.
I have the standard 14ft by 29ft Flag. It seems to lose
it's front to back ratio as the frequency gets above 4Mhz or less.
So I suspect it needs to be reduced in size for higher frequencies.

Would I scale the size the same as the frequency ratio?

I'm using the demo version of EZNEC, the dimensions of length
to height seem quite forgiving.

Could this be the limited segments (20) of the demo, or are
the design dimensions just not that critical?

Your input is appreciated, I haven't found much info on higher
frequency Flag antennas.
Thanks,
Mike


Mike,
The flag will need to be scaled down, but I don't remember the
details. I just scaled down an old .EZ model I made for 160 years ago,
and reduced the segments to 20. The bottom wire is 5' above ground and
the top is 13' above ground. The length is 16'. This shows a f/b of
26.21 for 7, and 22.78 for 12. With many segments I get a f/b of 27 for
7, and 32.55 for 12. This model can be improved with some tweaking, and
will complain when using just 20 segments. E-mail me if you want me to
send you this .EZ file, or I can investigate further with my full
version of EZNEC.

73,
bob WA5JOT

bob wrote:
amdx wrote:
I'm trying to design a Flag antenna for 9 to 12 Mhz.
I have the standard 14ft by 29ft Flag. It seems to lose
it's front to back ratio as the frequency gets above 4Mhz or less.
So I suspect it needs to be reduced in size for higher frequencies.

Would I scale the size the same as the frequency ratio?

I'm using the demo version of EZNEC, the dimensions of length
to height seem quite forgiving.

Could this be the limited segments (20) of the demo, or are
the design dimensions just not that critical?

Your input is appreciated, I haven't found much info on higher
frequency Flag antennas.
Thanks,
Mike


Mike,
The flag will need to be scaled down, but I don't remember the details.
I just scaled down an old .EZ model I made for 160 years ago, and
reduced the segments to 20. The bottom wire is 5' above ground and the
top is 13' above ground. The length is 16'. This shows a f/b of 26.21
for 7, and 22.78 for 12. With many segments I get a f/b of 27 for 7, and
32.55 for 12. This model can be improved with some tweaking, and will
complain when using just 20 segments. E-mail me if you want me to send
you this .EZ file, or I can investigate further with my full version of
EZNEC.

73,
bob WA5JOT

Mike,
After more experimenting, about the best I can do with the f/b @ 25
degrees takeoff, and freq = 7-12 is 8' X 17' with the bottom wire about
13' above ground. If you are thinking of getting the full EZNEC from
Roy, Version 5 is out, and worth every penny.

73,
bob