"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