Hi John,
"At best"? Interesting... I've seen many diagrams about mounting two linear YAGIs at 90 degrees from each other on the same cross arm, with the appropriate phasing harness. My plan is to mount the two panels the same; one next to the other, rotated 45 degrees in opposite directions on the cross arm, with one pushed out 1.23 inches by a block of wood. How bad will this be? One will surely get some elliptical effects when the satellite is off-axis, but keeping them aimed at the satellite is what the rotor and computer are for...
I understand that I'm losing some NF by not using a proper splitter, but I don't have one handy, and this is (was) supposed to be a low effort adventure. Again, for AO-51 VS, I should have plenty of margin.
I've built several helixes, both 2.4 ghz for the feed to my BBQ grill, and my current L-band uplink, and could do the same here. But, back to the low effort part of things...
If this simply isn't going to work, then I'll just leave my current setup alone. It consists of a 3 3/4 turn helix feeding a 30 inch BBQ grill, lined with window screen. All combined, it's kind of heavy, and the wooden cross arm is showing the effects of the weight and its age. It was built for AO-40, and for the current satellites I don't really need this much gain, hence the replacement idea.
Bad idea?
Greg KO6TH
Subject: Re: [amsat-bb] CP antenna from 2 WiFi panels From: [email protected] Date: Mon, 7 Jun 2010 07:37:17 -0700 CC: [email protected] To: [email protected]
Hi Greg,
These panels are patch style antennas and as such you will not be able to place one behind the other to obtain circular polarization. Placing one next to the other will at best produce an elliptically polarized pattern, and you should use a 50 ohm splitter to keep your impedance 50 ohms. The shape of the patch and position of the feed point is typically how you obtain circular polarization with a patch antenna.
Or, you can obtain RHCP with the same or more gain and less trouble by making a Helix. A sheet of aluminum, #8 copper wire and and a piece of PVC of the right diameter is all you need. http://brneurosci.org/helix-antenna.html
Or, you can try just a single panel and see how it performs for a while.
Good luck!
73, John W9EN DM13le [email protected]
On Jun 6, 2010, at 1:15 PM, Greg D. wrote:
Hi folks,
Before I start nailing stuff together, I just want to verify what I'm doing...
I want to make a 2.4ghz Right-Hand Circular antenna from two flat panel Wi-Fi antennas. The idea is to mount them at 90 degrees from each other, with one 1/4 wavelength in front of the other. Combine the two feeds with a simple Tee (the feeds are of equal length), and into the pre-amp. Since I'm not transmitting, I'm not too worried about the resulting 25 ohm impedance (or should I be?).
If it matters, the panels are from HyperLink Technologies, their model HG2414P, with a claimed 14dBi gain.
So, the questions:
1/4 wavelength at 2401 mhz is ((3 x 10**8 / 2401 x 10**6) / 4) meters, or about 1.23 inches. Right?
Most of our 2.4 ghz satellite downlinks seem to be either linear or RHCP, so I'm guessing that RHCP is probably the preferred construction. (Yes?)
Looking at the Satellite Experimenter's Handbook (figure 7-10), I believe the panel rotated 90 degrees counter-clockwise as seen from behind the panels should be the one farther out in front, for RHCP. (Their picture shows clockwise for LHCP.) Is this correct?
Thanks,
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