23-cm BiQuad Antenna with Lips

[C2]

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.

 

[Robb]

Niiiiiiice!

 

[Moleculo]

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.

 

[wavrider]

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.

 

[C2]

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...