[amsat-bb] Re: CP antenna from 2 WiFi panels
w9en at arrl.net
Mon Jun 7 20:47:29 PDT 2010
What I meant by "at best" is that it will certainly be a challenge (at 2.5 GHz) to get one panel just a perfect 1/4 wavelength forward from the other. It will be equally as challenging (at 2.5 GHz) to make 75 ohm phasing cables some odd multiple of 1/4 wavelength.
I say that because I found it quite challenging to make phasing cables for 1.3 GHz and even 440 MHz and I had a network analyzer to help me. Just when I thought I had it cut perfect I put the connector on and found myself 10 to 20 degrees off. That will affect the circularity of the polarization. I finally gave up and mounted the elements of one yagi 1/4 wavelength forward from the other and used equal length cables.
Physical spacing is easier to achieve within a few degrees at the lower frequencies (VHF/UHF). Another alternative would have been to use a 90 degree broadband hybrid (that can handle 25 watts) but that was much more $ than I wanted to spend.
If you have a helix already, I would use that. But don't let me talk you out of experimentation. It is possible and might be fun.
Sent from my Verizon Wireless BlackBerry
From: Greg D. <ko6th_greg at hotmail.com>
Date: Mon, 7 Jun 2010 20:22:22
To: <jbelstner at yahoo.com>
Cc: <amsat-bb at amsat.org>
Subject: RE: [amsat-bb] CP antenna from 2 WiFi panels
"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.
> Subject: Re: [amsat-bb] CP antenna from 2 WiFi panels
> From: jbelstner at yahoo.com
> Date: Mon, 7 Jun 2010 07:37:17 -0700
> CC: amsat-bb at amsat.org
> To: ko6th_greg at hotmail.com
> 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.
> Or, you can try just a single panel and see how it performs for a while.
> Good luck!
> 73, John W9EN
> W9EN at AMSAT.ORG
> 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. 1/4 wavelength at 2401 mhz is ((3 x 10**8 / 2401 x 10**6) / 4) meters, or about 1.23 inches. Right?
> > 2. 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?)
> > 3. 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,
> > Greg KO6TH
> > The New Busy think 9 to 5 is a cute idea. Combine multiple calendars with Hotmail.
> > http://www.windowslive.com/campaign/thenewbusy?tile=multicalendar&ocid=PID28326::T:WLMTAGL:ON:WL:en-US:WM_HMP:042010_5
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The New Busy is not the too busy. Combine all your e-mail accounts with Hotmail.
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