The antenna gain of a half-wave dipole relative to an isotrope is
1.61.

What are the gains relative to an isotrope of -

A dipole with one reflector.
A dipole with one reflector and one director.
An N-element dipole array like a Yagi.

Only approximate answers are needed.

Thanking you in anticipation.
----
Reg.

"Reg Edwards" wrote in message
...
The antenna gain of a half-wave dipole relative to an isotrope is
1.61.

2.14 dbi ...Shirley ??.......

Lee......de G6ZSG....


What are the gains relative to an isotrope of -

A dipole with one reflector.
A dipole with one reflector and one director.
An N-element dipole array like a Yagi.

Only approximate answers are needed.

Thanking you in anticipation.
----
Reg.

On Fri, 21 Apr 2006 06:47:41 GMT, "Lee"
wrote:


"Reg Edwards" wrote in message
...
The antenna gain of a half-wave dipole relative to an isotrope is
1.61.

2.14 dbi ...Shirley ??.......

The number one commonly sees is 1.64 (which is about 2.14dB)... not
far off 1.61.

Owen
--

"Reg Edwards" wrote in message
...
The antenna gain of a half-wave dipole relative to an isotrope is
1.61.

2.14 dbi ...Shirley ??.......


Hook line & sinker into Reg's trap.

1.61 linear gain not dB.

73
Jeff

"Jeff" wrote in message ...
"Reg Edwards" wrote in message
...
The antenna gain of a half-wave dipole relative to an isotrope is
1.61.

2.14 dbi ...Shirley ??.......


Hook line & sinker into Reg's trap.

1.61 linear gain not dB.

Trap or not , i`m still correct ....... ;-)

Lee....de G6ZSG...


73
Jeff

The number one commonly sees is 1.64 (which is about 2.14dB)... not
far off 1.61.

Owen
====================================

Yes, the difference is nearly 1/75th of an S-unit. That's almost
enough to make some people lose a contest.
----
Reg.

"Reg Edwards" wrote in message
...
The number one commonly sees is 1.64 (which is about 2.14dB)... not
far off 1.61.

Owen
====================================

Yes, the difference is nearly 1/75th of an S-unit. That's almost
enough to make some people lose a contest.
----
Reg.



You could be right Reg....

Lee.........G6ZSG.

Reg Edwards wrote:

The antenna gain of a half-wave dipole relative to an isotrope is
1.61.

What are the gains relative to an isotrope of -

A dipole with one reflector.
A dipole with one reflector and one director.
An N-element dipole array like a Yagi.

Only approximate answers are needed.

Thanking you in anticipation.
----
Reg.



In a yagi gain is not related to the number of elements (as long as
there are enough) once the boom gets significantly long. The point at
which it is significantly long could be argued to be somewhere between
1/4 of a wavelength to a wavelength, where the effect is hard to see at
1/4, and absolutely there at 1.

Are you looking for some way to reasonably predict yagi gain? If so,
there are a couple 3 equations which do a very fair job. Basically you
need one for short yagis, and another for long. If you're interested,
I'll dig the short boom out for you, but I can't right now, as I'm
already waaaay behind schedule for getting to work.

Here's the one that works best for long booms -

G = 10 log (5.4075 B + 4.25) for B GT 1

Where G is gain in dBd and B is boomlength in wavelengths.

tom
K0TAR

"Tom Ring" wrote
Here's the one that works best for long booms -

G = 10 log (5.4075 B + 4.25) for B GT 1

Where G is gain in dBd and B is boomlength in wavelengths.

=======================================
Thanks Tom,

If we have 5 or 6 elements spaced approx 1/4-wave apart, that makes a
boom length of 1 wavelength and a gain of 10 dB relative to a dipole.

Can experienced users of Yagi design programs confirm that 10 dB is in
the right ballpark?

Yes please, I would like to see the equation for short booms and fewer
elements on your return from the salt mine.
----
Reg.

Reg Edwards wrote:

"Tom Ring" wrote
Here's the one that works best for long booms -

G = 10 log (5.4075 B + 4.25) for B GT 1

Where G is gain in dBd and B is boomlength in wavelengths.

=======================================
Thanks Tom,

If we have 5 or 6 elements spaced approx 1/4-wave apart, that makes a
boom length of 1 wavelength

Make that: "If we have 5 or 6 elements optimally spaced along a boom
length of 1 wavelength, we can hope for something in the region of"

a gain of 10 dB relative to a dipole.

Can experienced users of Yagi design programs confirm that 10 dB is in
the right ballpark?

That's about the best gain we can hope for, given a one-wavelength boom
to play with. On the other hand, poor choices of element lengths and
positioning will produce many dBs less forward gain... or even gain in
the opposite direction.


Yes please, I would like to see the equation for short booms and fewer
elements on your return from the salt mine.

There isn't really "an" equation for gain versus boom length, because
boom length is only an indicator of the potentially achievable gain. But
nothing "makes" a yagi deliver any particular gain figure.

Quite the opposite: very often, yagi designers will deliberately
sacrifice some forward gain to obtain better performance in other
important respects. These can include a cleaner pattern, a more
convenient feed impedance and better tolerance to element loading by
rain and ice; and all maintained over a wider bandwidth.

Yagis that have been single-mindedly optimized for maximum gain tend to
be poor performers in other respects - especially tolerance to element
loading.

The equation that Tom quoted is just the best-fit line through the gain
figures for one particular family of reasonably good long yagi designs.
Other good designs will have similar gain, but different performance in
other respects. And for every good yagi design, there are many more that
come nowhere near this level of performance.



--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek