Mike,

Take a look at LB Cebic's (W4RNL) Moxon square
articles, and particularly "Building a 2-Meter Moxon"

Shows directivity pattern you are looking for.

ray, w6fya
"MikeN" wrote in message
...
Hi

I need to develop a cardiod radiation pattern for a 70 cm local
coverage repeater - forward gain isn't too important, but radiation
pattern is.

The repeater is located on a coastline, any radiation out to sea is
unwanted and will interfere at times of enhanced propagation with
another repeater using the same frequencies, which has a wide area
coverage from an elevated (1400 ft) site, approx 70 miles away across
a sea path.

The local coverage area is mainly inland, opposite in direction to the
distant repeater, hence we need good forward radiation and good front
to back ratio. We also need good side radiation to cover the
developed coastal strip.

A cardiod fits our needs exactly. A yagi will have nulls in the
coverage area, and a corner reflector won't have sufficient radiation
sidewards.

Is it difficult to get the phasing and matching correct, for say a
pair of phased dipoles at UHF, so as too get the correct element
currents to develop the cardiod pattern?

What calculation and adjustment processes should I use.

I'd be grateful for some guidance on this scenario.

Thanks

MikeN ZL1BNB

Hi

I need to develop a cardiod radiation pattern for a 70 cm local
coverage repeater - forward gain isn't too important, but radiation
pattern is.

The repeater is located on a coastline, any radiation out to sea is
unwanted and will interfere at times of enhanced propagation with
another repeater using the same frequencies, which has a wide area
coverage from an elevated (1400 ft) site, approx 70 miles away across
a sea path.

The local coverage area is mainly inland, opposite in direction to the
distant repeater, hence we need good forward radiation and good front
to back ratio. We also need good side radiation to cover the
developed coastal strip.

A cardiod fits our needs exactly. A yagi will have nulls in the
coverage area, and a corner reflector won't have sufficient radiation
sidewards.

Is it difficult to get the phasing and matching correct, for say a
pair of phased dipoles at UHF, so as too get the correct element
currents to develop the cardiod pattern?

What calculation and adjustment processes should I use.

I'd be grateful for some guidance on this scenario.

Thanks

MikeN ZL1BNB

Hello,

The easiest way is to mount the dipoles less than a 1/4wave from a pole or
mast. This makes the pattern a cardioid. Even with two dipoles!
Very easy to do.

"MikeN" wrote in message
...
Hi

I need to develop a cardiod radiation pattern for a 70 cm local
coverage repeater - forward gain isn't too important, but radiation
pattern is.

The repeater is located on a coastline, any radiation out to sea is
unwanted and will interfere at times of enhanced propagation with
another repeater using the same frequencies, which has a wide area
coverage from an elevated (1400 ft) site, approx 70 miles away across
a sea path.

The local coverage area is mainly inland, opposite in direction to the
distant repeater, hence we need good forward radiation and good front
to back ratio. We also need good side radiation to cover the
developed coastal strip.

A cardiod fits our needs exactly. A yagi will have nulls in the
coverage area, and a corner reflector won't have sufficient radiation
sidewards.

Is it difficult to get the phasing and matching correct, for say a
pair of phased dipoles at UHF, so as too get the correct element
currents to develop the cardiod pattern?

What calculation and adjustment processes should I use.

I'd be grateful for some guidance on this scenario.

Thanks

MikeN ZL1BNB

Two vertical (dipoles or groundplanes) spaced 1/4 wave physical apart with
3/4 (electrical) of coax between them - then feed at one dipole. I forget
which end the null is. I know it is in the Fox hunting book
http://members.aol.com/homingin/index.html
but not where to find it on the web.

Also a vertical on one side of a tower can do it also. Commonly done in
communication.

--
Steve N, K,9;d, c. i My email has no u's.

"Ray Gaschk" wrote in message
...
Mike,

Take a look at LB Cebic's (W4RNL) Moxon square
articles, and particularly "Building a 2-Meter Moxon"

Shows directivity pattern you are looking for.

ray, w6fya
"MikeN" wrote in message
...
Hi

I need to develop a cardiod radiation pattern for a 70 cm local
coverage repeater - forward gain isn't too important, but radiation
pattern is.

The repeater is located on a coastline, any radiation out to sea is
unwanted and will interfere at times of enhanced propagation with
another repeater using the same frequencies, which has a wide area
coverage from an elevated (1400 ft) site, approx 70 miles away across
a sea path.

The local coverage area is mainly inland, opposite in direction to the
distant repeater, hence we need good forward radiation and good front
to back ratio. We also need good side radiation to cover the
developed coastal strip.

A cardiod fits our needs exactly. A yagi will have nulls in the
coverage area, and a corner reflector won't have sufficient radiation
sidewards.

Is it difficult to get the phasing and matching correct, for say a
pair of phased dipoles at UHF, so as too get the correct element
currents to develop the cardiod pattern?

What calculation and adjustment processes should I use.

I'd be grateful for some guidance on this scenario.

Thanks

MikeN ZL1BNB