Hi Yuri

What's the best way to measure the resonant frequency of the 450 MHz
dipole?

I've got a simple UHF return loss bridge and a counter.

What else would I need?

Thanks

MikeN ZL1BNB

On 15 Apr 2004 14:04:09 GMT, oUsama (Yuri Blanarovich)
wrote:


I have a design based on EZNEC. Total shortened "half-wave" dipole length
is 0.32 lambda. Half of that of course is in each of the two elements.
There is a loading coil in the middle of each element. EZNEC assumes zero
length, non-radiating coils. In reality, the coil length is significant
compared to the element length.



Welcome to real world. If you want to read more about the loading coil
controversy, go to my web page www.K3BU.us and snoop around ARTICLES, you will
get the picture. Eznec doesn't understand real coils, you can try to substitute
the coil with hairpin stub of the same inductance for modeling.

With 450 MHz dipole you will "research" this subject faster by taking piece of
wire or tubing, make about 3 turns in the middle, put the dipole up, measure
the resonant frequency and then snip the ends untill you get it where you want
it. Fine tuning can be done by squeezing or expanding the coil turns.

To make it more efficient, you can just bend the ends 90 deg. in L or T shape,
instead of using coils.

Yuri, K3BU.us

Mike, ZL1BNB wrote:
"I`ve got a simple UHF return loss bridge and a counter.

What else do I need?"

To measure the resonant frequency of the 450 MHz dipole, you need an
appropriate variable frequency signal source.

Return loss is the difference between incident and reflected powers at
the antenna. At resonance, antenna reactances cancel removing a large
impediment to power acceptance by your antenna.

Energy absorbed by the antenna is not reflected back toward the signal
source so you have the greatest difference between incident and
reflected powers near resonance (greatest return loss).

Best regards, Richard Harrison, KB5WZI

Resonance will be the frequency at which the feedpoint reactance is
zero. You may have difficulty with your simple equipment determining
that point, but it will be vanishingly close to the frequency at which
the SWR is minimum -- or the point of maximum return loss -- on a 50
ohm line feeding a dipole. Be sure the line is properly decoupled
from the antenna: use a balun. Generally you won't need a counter,
because the resonance will be quite broad and there's no practical
need to get the frequency closer than a percent or even a few percent.

Cheers,
Tom

MikeN wrote in message . ..
Hi Yuri

What's the best way to measure the resonant frequency of the 450 MHz
dipole?

I've got a simple UHF return loss bridge and a counter.

What else would I need?

Thanks

MikeN ZL1BNB

On 15 Apr 2004 14:04:09 GMT, oUsama (Yuri Blanarovich)
wrote:


I have a design based on EZNEC. Total shortened "half-wave" dipole length
is 0.32 lambda. Half of that of course is in each of the two elements.
There is a loading coil in the middle of each element. EZNEC assumes zero
length, non-radiating coils. In reality, the coil length is significant
compared to the element length.



Welcome to real world. If you want to read more about the loading coil
controversy, go to my web page www.K3BU.us and snoop around ARTICLES, you will
get the picture. Eznec doesn't understand real coils, you can try to substitute
the coil with hairpin stub of the same inductance for modeling.

With 450 MHz dipole you will "research" this subject faster by taking piece of
wire or tubing, make about 3 turns in the middle, put the dipole up, measure
the resonant frequency and then snip the ends untill you get it where you want
it. Fine tuning can be done by squeezing or expanding the coil turns.

To make it more efficient, you can just bend the ends 90 deg. in L or T shape,
instead of using coils.

Yuri, K3BU.us