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Old Nov 01, 2010, 10:28 PM
Engineer for Christ
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Amherst, VA
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Quote:
Originally Posted by Bill Sanford View Post
Concerning your home brew antenna tracker, I was thinking along the same lines. I assume you're thinking pan only. Tilt seems rather irrelevant unless you're going for very high altitudes or live in the mountains like Trappy! For us flatlanders, pan should be just fine.

Concerning your schematic. I'm not quite sure what the purpose of the 2k and 390 ohm resistors is on the output of the LM393 op amp??

I haven't looked at an NE555 spec sheet for quite a few years. Is there an easy way to get it to change duty cycle based on a varying input voltage? I don't recall that being a feature of the chip. I'll have to get a data sheet from Digikey on the 555 and check it out. At any rate, this scheme should work with the addition of a circuit to convert the varying comparator voltage to a pulse train with varying duty cycle.

To make it work in application, you'll need two identical high gain antennas (Patch, BiQuad, or Yagi) pointed anywhere from 10 to 30 degrees apart horizontally depending on antenna beam width, etc.

All this being said, the more complex GPS based systems do have their advantages. I could see this system tracking a side lobe and getting confused. A GPS based system won't be fooled like this.

You should start another thread so we can begin discussing this. I like the idea of a simpler antenna tracker without all the complexity of GPS, return link, etc.

The big question is: Will it track well? It should be a fun experiment!

Bill
Bill,

The side lobe problem is why I plan to use BiQuads. no side lobes to worry about. Also, your plane would only be in a a sidelobe for a short period of time, so the tracker would stay on track.

The purpose of the 2K and 390 ohm resistor is a voltage divider. The LM393 is not an op amp, but is an impedance amplifier. You need to put a voltage (and resistance) on it's output to generate a usable signal. The 390 Ohm pulls down the high voltage signal down to 2V so the servo can recognize it. If you put 12V on the servo it will just jitter

The 555 pin 5 does regulate duty cycle, sort of. It changes the capacitor discharge time. Since I need a 10% duty cycle, I had to use the shorting diode in parallel with the 30K resistor.

Also, altitude really isn't a problem even in the mountains. Even with a 2:1 slope, if you have your antenna aimed upward 20 degrees (which I how I aim mine), you will have a 60 degree beam ceiling. That I can live with

-Alex
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Old Nov 04, 2010, 09:16 PM
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Ok, what do you think about this one? Man these spaces are close! It really goes against all I have learned to have the shield and center conductor connected! I know that in RF it is different that DC etc, but it still makes me twinge!

Anyway, see anything glaringly wrong with my build? Does the geometry look close enough?

I may have to remove the RX from the back like it is now so it will mount on my tracker correctly.
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Old Nov 04, 2010, 09:39 PM
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That looks excellent actually. Perhaps a little over braced, but that's not a problem.

Here are three that I built tonight. The two in the boxes are going to be part of my antenna tracker for 910 MHz. The other is my WiFi booster.

-Alex
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Old Nov 04, 2010, 10:01 PM
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Cool thanks. Yeah after I got it together I could tell that it was pretty sturdy after soldering to the center piece and probably could do without the spacers.

Nice on the 2 for your tracker. Can't wait to see them in action.

By the way, there shouldn't be any problem using about 6 inches of plain old RG6 to connect this antenna to the receiver should it?
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Old Nov 05, 2010, 03:09 PM
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I have an antenna tracker and am considering getting biquads...would it makes sense to put two biquads angled away from center 40 degrees on a pan/tilt antenna tracker?
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Old Nov 05, 2010, 04:43 PM
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I've been following this thread for a while now and I'm trying to figure out one thing. Are the 2 diamonds one piece of wire? Is one end connected to the center center of the Coax and the other connected to the shield? Sorry if this seems like a basic question, but the photos that are close enough are too blurry, and the clears ones too far away for me to confidently conclude that is indeed the it's set up.
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Old Nov 05, 2010, 05:44 PM
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Quote:
Originally Posted by russ_hillis View Post
I've been following this thread for a while now and I'm trying to figure out one thing. Are the 2 diamonds one piece of wire? Is one end connected to the center center of the Coax and the other connected to the shield? Sorry if this seems like a basic question, but the photos that are close enough are too blurry, and the clears ones too far away for me to confidently conclude that is indeed the it's set up.
Yes, one piece of wire. The 'middle' of the wire is connected to center/active conductor and the ends (which meet) are on soldered to the coax shield. It probably doesn't matter which end goes where though.
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Old Nov 05, 2010, 06:31 PM
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Alex,

Thanks for this info. I'm going to build one.

A quick question:

Instead of using nylon bolts to space the bowtie, will it hurt to instead use a sheet of foam, between the bowtie and reflector? I think this might help protect the bowtie's form better. Will the piece of foam have any effect on the antennas properties?

Thanks!

JBB
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Old Nov 05, 2010, 09:51 PM
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Quote:
Originally Posted by AdamChicago View Post
I have an antenna tracker and am considering getting biquads...would it makes sense to put two biquads angled away from center 40 degrees on a pan/tilt antenna tracker?
I would just use one with an antenna tracker, unless you are copying my DIY tracker. The beam is fairly wide for a tracker.

-Alex
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Old Nov 05, 2010, 09:53 PM
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Quote:
Originally Posted by scrtsqrl View Post
Alex,

Thanks for this info. I'm going to build one.

A quick question:

Instead of using nylon bolts to space the bowtie, will it hurt to instead use a sheet of foam, between the bowtie and reflector? I think this might help protect the bowtie's form better. Will the piece of foam have any effect on the antennas properties?

Thanks!

JBB
Technically, yes. In fact, any dielectric will cause a shift in SWR. That said, use the smallest piece of foam possible. Open cell is better than closed cell. If you look at my other BiQuads I made, I used a small wooden block.

-Alex
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Old Nov 05, 2010, 09:56 PM
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Quote:
Originally Posted by Vantasstic View Post
Yes, one piece of wire. The 'middle' of the wire is connected to center/active conductor and the ends (which meet) are on soldered to the coax shield. It probably doesn't matter which end goes where though.
You are correct. It doesn't matter whether the tips of the bowtie or the center is soldered to the active element. It is the same electrical path anyway.

If you look at the way I made it, I first bent the wire in half, then bend the ends to make a "W". From there I made the other 4 90 degree bends all in the same direction.

Coming soon will be the double biquad (13dbi) and the stacked BiQuad (14dbi)

-Alex
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Old Nov 06, 2010, 04:23 AM
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The original Martybugs article:
http://martybugs.net/wireless/biquad/

Buy one (if you must):
http://www.biquadantenna.com/biquad_sales.html

Nigel.
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Old Nov 06, 2010, 12:43 PM
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Two big problems with prebuilt units: They come with RP SMA ends and they are only for 2.4 GHz
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Old Nov 06, 2010, 02:12 PM
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Quote:
Coming soon will be the double biquad (13dbi) and the stacked BiQuad (14dbi)
Nice!

BTW, If I use two biquads, polarised 90 apart to feed a diversity unit, is there an optimum distance to put them from each other? like one wavelenght or whatever?
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Old Nov 06, 2010, 08:25 PM
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Alex,

Just finished my Biquad. I have some reservations about the standoffs I used. They are from a plastic cutting board. Do you think the size is a problem? I could not find any nylon bolts longer that 1.5" which is too short for MHz.

OK,....... well that didn't work. I was trying to post a couple of pictures of the biquad but when I select inset image it asked for a URL link. They are on my camera hooked to the computer but there seems to be no option to select them......What am I missing?

Thanks,

Tom
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