Understanding Yagi antenna

I've posted a picture on >alt.binaires.schematics.electronic<
to an effort to help me get a better understanding of an antenna.
It is a 2.4Ghz antenna about 18" long
The driven element is a copper ribbon 0.2" wide by 0.032" thick.
The copper ribbon forms a loop about 2" wide by 0.625" tall.
The gap in the ribbon would be 0.020", but note; in the pictures
a moon shaped piece has been cut from both ends. I think this
moon cut effectively make the gap look larger.
The total coax length is 2.350", the shield a bit shorter at 2.08".
There are 4 toroids on the coax. These are under a piece of heat
shrink, so I have no idea what material they would be.
All element spacings are all equal and element lengths are within
..030" of each other. I think they were designed to be the same but
manufacturing tolerances made the differences. The reflector is longer.
So now what can the group tell me about;
Driven element impedance
the gap
coax length impedance transformation
the 4 toroids
Thanks for the help, if you need any other details let me know.
Mike

Hi Mike,

That is a very complex subject. I would go to the library and check out a
good book on antenna theory. "The ARRL Antenna Book", while aimed at amateur
radio operators would still provide you with more theory than you're likely
to even need to know. An excellent book!

--
HTH,
Curt

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"amdx" <amdx@knology.net> wrote in message
news:c5c3c$46eafa66$18d6b40c$17868@KNOLOGY.NET...
| I've posted a picture on >alt.binaires.schematics.electronic<
| to an effort to help me get a better understanding of an antenna.
| It is a 2.4Ghz antenna about 18" long
| The driven element is a copper ribbon 0.2" wide by 0.032" thick.
| The copper ribbon forms a loop about 2" wide by 0.625" tall.
| The gap in the ribbon would be 0.020", but note; in the pictures
| a moon shaped piece has been cut from both ends. I think this
| moon cut effectively make the gap look larger.
| The total coax length is 2.350", the shield a bit shorter at 2.08".
| There are 4 toroids on the coax. These are under a piece of heat
| shrink, so I have no idea what material they would be.
| All element spacings are all equal and element lengths are within
| .030" of each other. I think they were designed to be the same but
| manufacturing tolerances made the differences. The reflector is longer.
| So now what can the group tell me about;
| Driven element impedance
| the gap
| coax length impedance transformation
| the 4 toroids
| Thanks for the help, if you need any other details let me know.
| Mike
|
|

On Fri, 14 Sep 2007 16:17:42 -0500, "amdx" <amdx@knology.net> wrote:

>I've posted a picture on >alt.binaires.schematics.electronic<
>to an effort to help me get a better understanding of an antenna.
>It is a 2.4Ghz antenna about 18" long
>The driven element is a copper ribbon 0.2" wide by 0.032" thick.
>The copper ribbon forms a loop about 2" wide by 0.625" tall.
>The gap in the ribbon would be 0.020", but note; in the pictures
>a moon shaped piece has been cut from both ends. I think this

yes, it was made on a moonday.

>moon cut effectively make the gap look larger.
> The total coax length is 2.350", the shield a bit shorter at 2.08".
>There are 4 toroids on the coax. These are under a piece of heat
>shrink, so I have no idea what material they would be.
> All element spacings are all equal and element lengths are within
>.030" of each other. I think they were designed to be the same but
>manufacturing tolerances made the differences. The reflector is longer.
> So now what can the group tell me about;
>Driven element impedance
>the gap
>coax length impedance transformation


>the 4 toroids
noise reduction ferrite beads or toroids
Line filters get rid of RF travelling along the outer surface of the
coax's shield and avoid, consequently, any TVI/BCI. The best
performance can be seen when connected right into the feed line at the
antenna base!




>Thanks for the help, if you need any other details let me know.
> Mike
>
hard not to be cynic.
w.

"Helmut Wabnig" <.... .-- .- -... -. .. --. @ .- --- -. dot .- - > wrote in
message news:s3gqe3l0nq3fjch8miu5ekolge908m57o6@4ax.com...
> On Fri, 14 Sep 2007 16:17:42 -0500, "amdx" <amdx@knology.net> wrote:
>
>>I've posted a picture on >alt.binaires.schematics.electronic<
>>to an effort to help me get a better understanding of an antenna.
>>It is a 2.4Ghz antenna about 18" long
>>The driven element is a copper ribbon 0.2" wide by 0.032" thick.
>>The copper ribbon forms a loop about 2" wide by 0.625" tall.
>>The gap in the ribbon would be 0.020", but note; in the pictures
>>a moon shaped piece has been cut from both ends. I think this
>
> yes, it was made on a moonday.
>
>>moon cut effectively make the gap look larger.
>> The total coax length is 2.350", the shield a bit shorter at 2.08".
>>There are 4 toroids on the coax. These are under a piece of heat
>>shrink, so I have no idea what material they would be.
>> All element spacings are all equal and element lengths are within
>>.030" of each other. I think they were designed to be the same but
>>manufacturing tolerances made the differences. The reflector is longer.
>> So now what can the group tell me about;
>>Driven element impedance
>>the gap
>>coax length impedance transformation
>
>
>>the 4 toroids
> noise reduction ferrite beads or toroids
> Line filters get rid of RF travelling along the outer surface of the
> coax's shield and avoid, consequently, any TVI/BCI. The best
> performance can be seen when connected right into the feed line at the
> antenna base!
>
>
>
>
>>Thanks for the help, if you need any other details let me know.
>> Mike
>>
> hard not to be cynic.
> w.
Do you mean a cynic, as in ;
a faultfinding captious critic; especially : one who believes that human
conduct is motivated wholly by self-interest.
Well yes, I ask the questions because (I) want to know, but if someone
else learns from the answers, I don't care.
"Moonday" hurumpf ;-}
Mike

On Fri, 14 Sep 2007 16:17:42 -0500, "amdx" <amdx@knology.net> wrote:

>I think this
>moon cut effectively make the gap look larger.

Hi Mike,

It is simply a function of the mechanical connection of the line at
that point (the inner conductor needs the cut-out and the shield has a
closer point of attachment).

> So now what can the group tell me about;
>Driven element impedance

50 Ohms.

>the gap

the distance between the closest points of contact before the line was
installed - i.e. the thickness of the inner conductor's insulation
(true for absolutely every antenna built).

>coax length impedance transformation

Not sure that matters if in fact it has been designed to be a Z
transformer. If so, then you have one of several dimensions possible
n/4 wavelength or n/2 wavelength where n is odd.

>the 4 toroids

Decoupling.

73's
Richard Clark, KB7QHC

"Richard Clark" <kb7qhc@comcast.net> wrote in message
news:ohmqe3tjmtbedm1hcgfeg93ldhkm2ppfh4@4ax.com...
> On Fri, 14 Sep 2007 16:17:42 -0500, "amdx" <amdx@knology.net> wrote:
>
>>I think this
>>moon cut effectively make the gap look larger.
>
> Hi Mike,
>
> It is simply a function of the mechanical connection of the line at
> that point (the inner conductor needs the cut-out and the shield has a
> closer point of attachment).
>
>> So now what can the group tell me about;
>>Driven element impedance
>
> 50 Ohms.
>
>>the gap
>
> the distance between the closest points of contact before the line was
> installed - i.e. the thickness of the inner conductor's insulation
> (true for absolutely every antenna built).

I had to go back and look at the picture, but that's interesting, the
cutout
makes for a good fit for the mechanical connection to the coax.
And I'll use that,
> "i.e. the thickness of the inner conductor's insulation"
for the gap in the antenna I'm building.
Thanks

>
>>coax length impedance transformation
>
> Not sure that matters if in fact it has been designed to be a Z
> transformer. If so, then you have one of several dimensions possible
> n/4 wavelength or n/2 wavelength where n is odd.
>
>>the 4 toroids
>
> Decoupling.
>
> 73's
> Richard Clark, KB7QHC

Curt Christianson wrote:
> Hi Mike,
>
> That is a very complex subject. I would go to the library and check out a
> good book on antenna theory. "The ARRL Antenna Book", while aimed at amateur
> radio operators would still provide you with more theory than you're likely
> to even need to know. An excellent book!

To learn specifically about Yagi antennas, it's hard to beat Lawson's
_Yagi Antenna Design_.

Roy Lewallen, W7EL