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23-cm BiQuad Antenna with Lips

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Old 04-01-2011, 09:39 PM
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Default 23-cm BiQuad Antenna with Lips


I had been inspired to try ATV (amateur TV) on 23-cm and built this antenna to feed an old 10-foot C-band satellite dish I had.

The design is based on plans for a WiFi biquad that I found on the Internet:

Biquad Antenna Construction

I scaled these dimensions for my frequency and made adjustments along the way.

I first bent a length of 12-guage solid copper wire (common house wire), a total of 19.5 inches, into a shape to make two squares with the ends at the center of the long dimension.

Then I made a reflection plane with an additional 1/2-inch on each side to help the directivity (the lips).

I fed the antenna with some semi-ridged scrap coax and adjusted the offset from the reflection plane for lowest SWR (about 1/4-wave away).



I’ve added an SMA connector to fit with my 23-cm ATV station.

Below is an SWR plot I made with an antenna analyzer. The SWR shown is a bit off as the station it is used with is a 75-ohm station and the analyzer is 50-ohm. It works well nonetheless.



I also made gain measurements comparing to a reference dipole antenna from a distance of 30 feet and measured a 9.9 dBd gain at operating frequency. This comparison worked well given the flat dipole's nominal impedance of 72-ohms.

I’ve been most pleased with this design and have even made a DTV antenna that works just as well as commercial antennas. I would suggest one for directed 70-cm operations over many of the popular yagi style antennas, as I believe they have a better F/B ratio.
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Last edited by C2; 04-01-2011 at 09:52 PM.


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Old 04-01-2011, 09:57 PM
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Niiiiiiice!
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Old 04-01-2011, 11:16 PM
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C2,

Would you mind going into some more detail on your ATV station and what type of activities you're doing with it? In all honesty, I understand the principles of ATV, but I've never really talked to anyone about the details of how to do ATV and why I would want to try it. Are there a lot of stations in your area doing it?

Also, how are you making that main element stand off from the reflector? I can't quite figure it out from the pic.

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Old 04-02-2011, 04:56 AM
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Nice work.

I built a double biquad and use it for 1900MHZ reception on wireless ISP.

I used solid metal for the reflector and put it on an old hughes net parabolic dish.

Hard to beat those biquad at such high frequency with a parabolic reflector.

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Old 04-02-2011, 08:17 AM
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Quote:
Originally Posted by Moleculo View Post
C2,

Would you mind going into some more detail on your ATV station and what type of activities you're doing with it? In all honesty, I understand the principles of ATV, but I've never really talked to anyone about the details of how to do ATV and why I would want to try it. Are there a lot of stations in your area doing it?

Also, how are you making that main element stand off from the reflector? I can't quite figure it out from the pic.
The main element is soldered to semi-rigid coax. The outer shield is usually tin or copper, and I just soldered the coax to the screen. It is not super strong, but strong enough for what I was doing. I will add some standoffs at the tips to secure the element better.

ATV was more experimenting than regular use. I have a 23-cm station from low power modules that I bought off ebay from a Norwegian fellow. Similar to the ones here:

ATV Special Offers, Pakage Deals and Offers Amateur Televsion

Just plug in your monitor, cam, and mic and you can run a full duplex station. My stuff is boxed up now, but I was just using my TV and point-n-shoot cam.

My area has K6BEN, a 23-cm repeater station that downlinks to one of the 70-cm ATV stations, and it can be received on a regular CATV with just rabbit ears. He runs a net every Wed. night and is crosslinked on several repeaters in 70-cm, 1.25- and 2-meters.

The Silicon Valley ATV Group

I tried to hit his repeater, but I think there is a building in the way...
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