Tuning angle of groundplane antenna.
 

I've recently dug out an old groundplane antenna I built years ago to
play around with. I've lost all my old papers and haven't been able to
find the tuning equation for setting the proper angle of the base
emitters down from the verticle emitter to a certain freq. Setting the
lengths is no problem, it's the angle I haven't found. I believe I
originally pulled them from an old Satellite Times Mag about 15 years
ago which has long since gone the way of the wind. Would anyone lend a
hand?

Tuning angle of groundplane antenna.
 

On 13 Dec 2006 15:24:43 -0800, "bj" wrote:

Setting the
lengths is no problem, it's the angle I haven't found.

Hi OM,

Actually, the lengths and the angles BOTH impact the resonance and the
match (varying from 30 odd Ohms to 70 odd Ohms). One solution is to
cut the radials and start depressing them until you get the match you
want. If they don't match, cut them shorter and repeat.

73's
Richard Clark, KB7QHC

Tuning angle of groundplane antenna.
 

I've always drooped my (VHF and UHF) radials at 45 degrees and they have
always worked OK.

Scott



bj wrote:
I've recently dug out an old groundplane antenna I built years ago to
play around with. I've lost all my old papers and haven't been able to
find the tuning equation for setting the proper angle of the base
emitters down from the verticle emitter to a certain freq. Setting the
lengths is no problem, it's the angle I haven't found. I believe I
originally pulled them from an old Satellite Times Mag about 15 years
ago which has long since gone the way of the wind. Would anyone lend a
hand?

Tuning angle of groundplane antenna.
 

Richard Clark wrote:
On 13 Dec 2006 15:24:43 -0800, "bj" wrote:


Setting the
lengths is no problem, it's the angle I haven't found.


Hi OM,

Actually, the lengths and the angles BOTH impact the resonance and the
match (varying from 30 odd Ohms to 70 odd Ohms). One solution is to
cut the radials and start depressing them until you get the match you
want. If they don't match, cut them shorter and repeat.

73's
Richard Clark, KB7QHC
That's it. Richard, whether you like it or not, you're helping us
newbies...and I (finally) appreciate it. Thanks.

Let no one concern themselves, arcanum still rules on this NG.

Tuning angle of groundplane antenna.
 

Scott wrote:
I've always drooped my (VHF and UHF) radials at 45 degrees and they have
always worked OK.

A droop of 45 degrees brings the impedance at resonance very close to 50
ohms. EZNEC example file VHFGP.EZ has 45 degree drooping radials. At
resonance (around 142.2 MHz), the input resistance is about 51.4 ohms.

Roy Lewallen, W7EL

Tuning angle of groundplane antenna.
 

"Roy Lewallen" wrote in message
...
Scott wrote:
I've always drooped my (VHF and UHF) radials at 45 degrees and they have
always worked OK.

A droop of 45 degrees brings the impedance at resonance very close to 50
ohms. EZNEC example file VHFGP.EZ has 45 degree drooping radials. At
resonance (around 142.2 MHz), the input resistance is about 51.4 ohms.

Roy Lewallen, W7EL

I heard once it is the sin of the angle times the impedance of a dipole.
Not sure if it is correct but it works for 50 ohms OK. Also heard that if
divide the sine of the angle inot the impedance of a 1/4wl antenna with
ground plane at right angles to the antenna it also works. Again maybe just
for 50 ohms. Might be fun to check out with EZNEC.

Jimmie