Richard

Do you know the approximate input impedance of a 0.1 lambda diameter
single turn loop?

Jerry


"Richard Fry" wrote in message
...
JM Do you have an actual application for this circularly
polarized directional UHF antenna with the "loop" included?

A*s*i*m*o*v Just curious about the UHF loop antenna as it is
said to have a gain of +1dB in the vertical position and -3dB
in the horizontal position.
________________

A planar, circular loop of diameter ~0.1 lambda is linearly polarized,
with peak gain* in the plane of the loop. This loop will have vertical
polarization when in the vertical position, and horizontal polarization
when in the horizontal position.

Lacking ~equal h-pol & v-pol gain at the same time, such a loop is not
circularly polarized -- even though the physical configuration of the loop
is a circle.

*theoretically about 1.74dBi (far field, free space)

RF

"Jerry Martes"
Do you know the approximate input impedance of
a 0.1 lambda diameter single turn loop?
__________

About 2.5 ohms.

RF

"Richard Fry" wrote in message
...
"Jerry Martes"
Do you know the approximate input impedance of
a 0.1 lambda diameter single turn loop?
__________

About 2.5 ohms.

RF

Richard

Can you guide me to a web site where that loop input impedance is given in
R+jX? I will set up and measure some loop input impedance at 137 MHz
within the next few days. But, I'd like to have a better "feel" for what
I'm doing before I take time to build the loop and set up the test
equipment.

Thanks
Jerry

"Jerry Martes"
Can you guide me to a web site where that loop
input impedance is given in R+jX?
_____________

I don't know of one off-hand. Maybe Google, or you could download free
EZNEC to experiment with.

If it will do, a quick NEC-2 model of a ~0.1 lambda diameter loop I just did
shows 2.20831E+0, -1.31989E+03. This R is a little lower than the first
number I posted -- which I had looked up in Kraus, 3rd edition.

RF

Richard Fry wrote:
"This R is a little lower than the first number I posted--which I looked
up in Kraus, 3rd edition."

An excellent source for everything about antennas, I think. I chose
Arnold B. Bailey who has a special affinity for loops, I think. In "TV
and Other Receiving Antennas" on page 403 Bailey says:
"The small loop has a very low resistance (not much over 0.5 ohm for a
circumference of 0.25 wavelength) and a very high positive Q indicating
inductive reactance. The Q will depend on the thickness of the cross
section of the conductor (P factor, as previously used for rod
antennas). For 200-Mc balanced circular loops, where L=0.25 wavelength
(coil diameter=0.25 wavelength/pi), the following Q`s are
representative:
1. For 1-inch diameter rods, QA = 175
2. For 1/4-inch diameter rods, QA = 280
3. For No. 10 wire, QA = 400."

Bandwidth is about equal to 2/QA.

Q is about X/R, or X is about RQ.

The loop radiation resistance of 0.5 ohm is so small that loss
resistance likely may affect the actual loop resistance total.

I`ll leave the reactance (RQ) for the user to calculate for whatever
frequency and Q may interest him.

Best regards, Richard Harrison, KB5WZI

On Mon, 07 Mar 2005 19:13:14 GMT, "Jerry Martes"
wrote:


"Richard Fry" wrote in message
...
"Jerry Martes"
Do you know the approximate input impedance of
a 0.1 lambda diameter single turn loop?
__________

About 2.5 ohms.

RF

Richard

Can you guide me to a web site where that loop input impedance is given in
R+jX? I will set up and measure some loop input impedance at 137 MHz
within the next few days. But, I'd like to have a better "feel" for what
I'm doing before I take time to build the loop and set up the test
equipment.

Thanks
Jerry


Hi Jerry,

The free version of EZNEC should cope with this simple problem. To
answer your question it reveals:
Impedance = 4.887 + J 853 ohms

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Mon, 07 Mar 2005 19:13:14 GMT, "Jerry Martes"
wrote:


"Richard Fry" wrote in message
...
"Jerry Martes"
Do you know the approximate input impedance of
a 0.1 lambda diameter single turn loop?
__________

About 2.5 ohms.

RF

Richard

Can you guide me to a web site where that loop input impedance is given
in
R+jX? I will set up and measure some loop input impedance at 137 MHz
within the next few days. But, I'd like to have a better "feel" for what
I'm doing before I take time to build the loop and set up the test
equipment.

Thanks
Jerry


Hi Jerry,

The free version of EZNEC should cope with this simple problem. To
answer your question it reveals:
Impedance = 4.887 + J 853 ohms

73's
Richard Clark, KB7QHC

Thanks Richard I like it when you do all the work and I just sit here
and read off the good data. If I wasnt so lazy I'd go out and build a loop
so I can se how it works,
I'd like to get a loop to match to 100 ohms of +jzero.

Thanks again
Jerry

On Tue, 08 Mar 2005 04:54:53 GMT, "Jerry Martes"
wrote:

Thanks Richard I like it when you do all the work and I just sit here
and read off the good data. If I wasnt so lazy I'd go out and build a loop
so I can se how it works,
I'd like to get a loop to match to 100 ohms of +jzero.

Thanks again
Jerry

Hi Jerry,

You are welcome. You could use your slotted line to test the model
too. Then add some parasitics to see what happens....

73's
Richard Clark, KB7QHC