"Richard Clark" wrote in message
...
On Wed, 15 Aug 2007 14:38:46 -0500, "amdx" wrote:

I've build a 2.4Ghz Patch antenna. It has gain. I move the feedpoint to
change the
input impedance. Now it has more signal strength, so I move in the same
direction again
and it shows even more signal strength, 2 more adjustments more signal, 1
more move
and signal strength looks like it's starting to go down in signal
strength.

Hi Mike,

Looks like you found away to get a low SWR (does it really matter how
much it is if you can't improve the output?).

Oh, there's always a but,
I cut the foil to the antenna in a wifi adapter and soldered a 2" piece of
coax to the
foil and ground, my Patch is at the other end. The wifi adapter is a dongle
mounted
at the antenna. See Picture at;
http://www.tp-link.com/products/product_des.asp?id=47
Now the question is: Is the wifi adapter output really 50 ohms? If it's
not 50 ohms
then I need not attempt impedance matching with 1/4 Lambda length coax.
I searched for several hours looking for specs on the RF chip in the wifi
adapter
without any success.

(These moves were about .060" each.)
Now I see a VSWR meter at http://pe2er.nl/wifiswr/
I wonder if this can help me get a handle on adjusting for proper
impedance?

It looks like a pretty good design. Remember to observe the power
limit.

The reason I want 50 ohms is because I want to build an array of 4
Patches.
The 50 ohms is important to impedance matching with 1/4 wavelength coax.
I'm using this site as info for the matching and connections.
http://www.darc.de/distrikte/g/T_ATV...d-Array-GB.pdf
Yes, I'm using Patches instead of Biquads.

The element lengths will vary (as will the pattern to some degree).

PS. What do you think about the antenna spacing?

You should stick to THOSE shown on the previous link.

So now the problem I don't know what the input impedance is.

You've got the plans for a good SWR meter, let it go at that. You
could probably build it faster than waiting for the final benediction
here.

73's
Richard Clark, KB7QHC

I don't mind waiting, I don't have any parts for the VSWR meter.
(I was looking for confirmation that it would be useful.)
Regarding the spacing; The literature I've seen shows spacing of
0.2, 0.3 or 0.4 Lambda before grating lobes form. But the Patch is 0.5
Lambda wide so you can't get them closer than 0.5 Lambda.
Here's one source;
http://www.orbanmicrowave.com/The_Ba...nna_Arrays.pdf
At this point I have a working Patch with good signal strength, so now I'm
just trying to see if I can improve on it, The project has got complicated
because
the only measurement tool I have is the software signal strength meter that
came
with the wifi adapter card.
Thanks for your input,
Mike

On Wed, 15 Aug 2007 16:12:29 -0500, "amdx" wrote:

Now the question is: Is the wifi adapter output really 50 ohms? If it's
not 50 ohms
then I need not attempt impedance matching with 1/4 Lambda length coax.

Hi Mike,

There are very, very, very few antenna designs that arrive out of the
box with 50 Ohms Z. You usually have to manipulate something (feed
point or linear loading, or coupling between elements or other
radiators) to get it.

The good thing about microwaves is that you can build and test so
quickly - and throw away what doesn't work. This isn't like you are
making jewelry after all.

The scale of construction is one you can get your arms around at the
kitchen table. If someone reliable built one and documented it enough
(both of these provisos are, admittedly, built on a LOT of trust);
then you don't need any instrumentation at all.

I searched for several hours looking for specs on the RF chip in the wifi
adapter without any success.

It sometimes takes some deep digging.

Regarding the spacing; The literature I've seen shows spacing of
0.2, 0.3 or 0.4 Lambda before grating lobes form. But the Patch is 0.5
Lambda wide so you can't get them closer than 0.5 Lambda.
Here's one source;
http://www.orbanmicrowave.com/The_Ba...nna_Arrays.pdf

Pretty tedious stuff, that. EZNEC can do it all in real time - even
the free version is sufficient for your purposes. For one, don't
confuse matching with the radiation lobes - those issues are separable
and you can ignore matching to examine lobes.

At this point I have a working Patch with good signal strength, so now I'm
just trying to see if I can improve on it,

Give yourself the benefit of the doubt and just move forward - the
rest is analysis paralysis.

73's
Richard Clark, KB7QHC

"amdx" wrote in message
...

Now the question is: Is the wifi adapter output really 50 ohms? If it's
not 50 ohms............................

Possibly, but it is immaterial. It is probably meant to drive rated power
into a 50 Ohm load.

Tam