RadioBanter - UHF Load Design

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What's the best reference source I can use for designing loads in UHF
antenna elements? (To make physically shortened elements electrically
full-size.) For example, 200 ohms reactive at 500 MHz with Q 75-100?

Thanks.

George K6GW

George wrote:

What's the best reference source I can use for designing loads in UHF
antenna elements? (To make physically shortened elements electrically
full-size.) For example, 200 ohms reactive at 500 MHz with Q 75-100?

Thanks.

George K6GW

Just curious, George! Because antennas at that frequency are relatively
small to begin with, I've never considered loading anything like that. I'm curious
as to why you would want to -- there must be a good reason, isn't there?

Irv VE6BP
--
--------------------------------------
Diagnosed Type II Diabetes March 5 2001
Beating it with diet and exercise!
297/215/210 (to be revised lower)
58"/43"(!)/44" (already lower too!)
--------------------------------------
Visit my HomePage at http://members.shaw.ca/finkirv/
Visit my very special website at http://members.shaw.ca/finkirv4/
Visit my CFSRS/CFIOG ONLINE OLDTIMERS website at http://members.shaw.ca/finkirv5/
--------------------
Irv Finkleman,
Grampa/Ex-Navy/Old Fart/Ham Radio VE6BP
Calgary, Alberta, Canada

Yep, there is. I'm designing a very small hand-held antenna for direction
finding. The smaller the better. On paper so far I have shortened
"half-wave" dipole elements to 0.32 lambda and am giving up 1 dB of gain in
the process, assuming the coils I mentioned in each side of the dipoles.

Now the question becomes, is it practical and buildable?

BTW, congrats on your numbers! I, too, have seen a big improvement in my
own cholesterol numbers as a result of diet and exercise, not to mention
overall fitness ... :o)))

George K6GW

"Irv Finkleman" wrote in message
...
George wrote:

What's the best reference source I can use for designing loads in UHF
antenna elements? (To make physically shortened elements electrically
full-size.) For example, 200 ohms reactive at 500 MHz with Q 75-100?

Thanks.

George K6GW

Just curious, George! Because antennas at that frequency are relatively
small to begin with, I've never considered loading anything like that.
I'm curious
as to why you would want to -- there must be a good reason, isn't there?

Irv VE6BP
--
--------------------------------------
Diagnosed Type II Diabetes March 5 2001
Beating it with diet and exercise!
297/215/210 (to be revised lower)
58"/43"(!)/44" (already lower too!)
--------------------------------------
Visit my HomePage at http://members.shaw.ca/finkirv/
Visit my very special website at http://members.shaw.ca/finkirv4/
Visit my CFSRS/CFIOG ONLINE OLDTIMERS website at
http://members.shaw.ca/finkirv5/
--------------------
Irv Finkleman,
Grampa/Ex-Navy/Old Fart/Ham Radio VE6BP
Calgary, Alberta, Canada

"George" wrote in message
nk.net...
Yep, there is. I'm designing a very small hand-held antenna for direction
finding. The smaller the better. On paper so far I have shortened
"half-wave" dipole elements to 0.32 lambda and am giving up 1 dB of gain
in
the process, assuming the coils I mentioned in each side of the dipoles.

Now the question becomes, is it practical and buildable?

BTW, congrats on your numbers! I, too, have seen a big improvement in my
own cholesterol numbers as a result of diet and exercise, not to mention
overall fitness ... :o)))

George K6GW

"Irv Finkleman" wrote in message
...
George wrote:

What's the best reference source I can use for designing loads in UHF
antenna elements? (To make physically shortened elements electrically
full-size.) For example, 200 ohms reactive at 500 MHz with Q 75-100?

Thanks.

George K6GW

Just curious, George! Because antennas at that frequency are relatively
small to begin with, I've never considered loading anything like that.
I'm curious
as to why you would want to -- there must be a good reason, isn't there?

Irv VE6BP
--
--------------------------------------
Diagnosed Type II Diabetes March 5 2001
Beating it with diet and exercise!
297/215/210 (to be revised lower)
58"/43"(!)/44" (already lower too!)
--------------------------------------
Visit my HomePage at http://members.shaw.ca/finkirv/
Visit my very special website at http://members.shaw.ca/finkirv4/
Visit my CFSRS/CFIOG ONLINE OLDTIMERS website at
http://members.shaw.ca/finkirv5/
--------------------
Irv Finkleman,
Grampa/Ex-Navy/Old Fart/Ham Radio VE6BP
Calgary, Alberta, Canada

Irv

George

I'm not sure of the lengths of your "dipole" elements . I'm going to
assume you have a 1/2 wave dipole antenna shortened to about 1/3 wavelength
overall. That would have two identical elements about 1/6th wavelength
each. If this understanding is correct, I could suggest a method of
including 200 ohms in series with each 1/2 of the dipole.

A 1/6th wavelength long piece of 120 ohm coax would look like a 200 ohm
inductor if it was shorted at its other end.
Perhaps I could describe a method of building an antenna by using two
pieces of 100 ohm coax. It would look much the same as a conventional
centerfed dipole but its total length would be shorter than the usual 1/2
wavelength. If you dont already have a picture of what I'd try to describe,
maybe I can write more. But, I want to consider the outside of the coaxial
stub to be the radiating surface.

Jerry

For a loading coil of j200 ohms at 500 MHz you need an inductance of 0.057
uH.

Wind 4 complete turns of 16 awg wire on a former 5.6 mm diameter, 10 mm
long. Q will be around 600.

For the above little calculation and many others use program SOLNOID3.
Download in a few seconds from website below and run immediately.
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

Reg,

Nice program! Thanks much ... :o)

73,
George K6GW

"Reg Edwards" wrote in message
...
For a loading coil of j200 ohms at 500 MHz you need an inductance of 0.057
uH.

Wind 4 complete turns of 16 awg wire on a former 5.6 mm diameter, 10 mm
long. Q will be around 600.

For the above little calculation and many others use program SOLNOID3.
Download in a few seconds from website below and run immediately.
----
.................................................. .........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. .........

I think I see where you're going with that, Jerry...that's pretty
cool. In fact, I can imagine making the center out of tubing and the
outer ends out of rod, and having it so the rod can be unscrewed or
otherwise unfastened and pulled out, making a very compact (narrow)
package for storage. Would have to be careful to make the rod
attachment a reliably low resistance so the Q of the effective
inductance would stay high. If the coax stub part is filled with
dielectric (like Teflon) it would give more flexibility about the
lengths and impedances.

Cheers,
Tom

"Jerry Martes" wrote in message ...
....

I'm not sure of the lengths of your "dipole" elements . I'm going to
assume you have a 1/2 wave dipole antenna shortened to about 1/3 wavelength
overall. That would have two identical elements about 1/6th wavelength
each. If this understanding is correct, I could suggest a method of
including 200 ohms in series with each 1/2 of the dipole.

A 1/6th wavelength long piece of 120 ohm coax would look like a 200 ohm
inductor if it was shorted at its other end.
Perhaps I could describe a method of building an antenna by using two
pieces of 100 ohm coax. It would look much the same as a conventional
centerfed dipole but its total length would be shorter than the usual 1/2
wavelength. If you dont already have a picture of what I'd try to describe,
maybe I can write more. But, I want to consider the outside of the coaxial
stub to be the radiating surface.

Jerry

Tom

I was actualy thinking about George's antenna with the coax's center
conductor as being the little 'rod' and the outer jacket of the coax as the
'tube'. I was suggesting that the twin line feeding the pair of elements
could be connected to the two 'rods'.
There would be alot of lattitude for changing this concept. Loading the
coax with any dielectric could effect the mechanical rigidity and, of
course, the electrical length inside the coax shorted stubs. You have some
good ideas, already.

Jerry

"Tom Bruhns" wrote in message
m...
I think I see where you're going with that, Jerry...that's pretty
cool. In fact, I can imagine making the center out of tubing and the
outer ends out of rod, and having it so the rod can be unscrewed or
otherwise unfastened and pulled out, making a very compact (narrow)
package for storage. Would have to be careful to make the rod
attachment a reliably low resistance so the Q of the effective
inductance would stay high. If the coax stub part is filled with
dielectric (like Teflon) it would give more flexibility about the
lengths and impedances.

Cheers,
Tom

"Jerry Martes" wrote in message
...
...

I'm not sure of the lengths of your "dipole" elements . I'm going
to
assume you have a 1/2 wave dipole antenna shortened to about 1/3
wavelength
overall. That would have two identical elements about 1/6th wavelength
each. If this understanding is correct, I could suggest a method of
including 200 ohms in series with each 1/2 of the dipole.

A 1/6th wavelength long piece of 120 ohm coax would look like a 200
ohm
inductor if it was shorted at its other end.
Perhaps I could describe a method of building an antenna by using two
pieces of 100 ohm coax. It would look much the same as a conventional
centerfed dipole but its total length would be shorter than the usual
1/2
wavelength. If you dont already have a picture of what I'd try to
describe,
maybe I can write more. But, I want to consider the outside of the
coaxial
stub to be the radiating surface.

Jerry