Hey guys,
What's happening? I thought everything came out great! but the BiQuad I just built doesn't seem to show any increase in signal strength while using Netstumbler! I can't see where I went wrong can you?
How can the center pin be connected to one side of the element and the other side of the element be connected to the board? Seems like a short to me. Thanks guys!
Pete
I've read on some URL that if you don't use wire down the center stub, it will skew the pattern. Also what is the spacing between PCB and Biquad, the picture makes it look to close.
At dc it would be a short, at 2.4Ghz there's a lot of inductance and capacitance.
Mike
Knight hath wroth:
Yep. Your construction in the photo is totally wrong. It won't work as shown. The ground ends of the quad elements must be soldered directly to the ground sleeve of the coax connector, or to short coax extension. In addition, that looks like a BNC or F connector, which is a different problem. The center conductor is far too long, the connector is lossy at 2.4GHz, and it might be a bit flimsy. You'll find that most construction articles demand an "N" connector or coax cable extension.
I scribbled a detailed rant on the subject at:
It should give a list of biquad construction articles that work, along with a list of one's similar to yours that will not work.
My favorite are the ones that do not use any connector, such as:
Mike, The spacing is about 15 mm like the article I followed to build it suggested. I think I have it working now. Don't think the card was connected! duh. But that wire down the center just doesn't seem like it would matter after all that center casing is part of the wire if in fact you do solder one in!
Pete
Jeff,
It is a "N" connector. A "N" bulkhead connector.
Guys, heres a screenshot of what's happening while the quad is connected. Does it look OK to you? Doesn't look bad to me!
Pete
Knight hath wroth:
Ok, I couldn't tell the size from the photo.
Looks like about 8dBi of gain over what you were using as a reference antenna. That's about what I would expect from a Biquad. I guess it's working.
A while ago, I got into a debate over the construction of biquads and how much creativity can be tolerated. So, I ran some models and got a suprise. See:
A proper biquad:
A creatively built biquad-junk:
Despite the miserable 7:1 VSWR mismatch, the junk antenna still manages to get about 11dBi of gain, the same as the proper biquad. So, if your radio can handle the crappy VSWR, feel free to throw it together any way that seem workable.
Jeff, Earlier you wrote "Your construction in the photo is totally wrong"
I guess it really doesn't matter then does it? Seems to be working ok! Can that be? Would it work better the other way? Pete
Knight hath wroth:
Yep. It's totally wrong. However, it appears that such creativity doesn't have as much effect as I original assumed. Look at it this way: Anything is better than the stock rubber ducky antenna.
Yep. My simulation of doing it the wrong way shows that it works well enough. You decide if it's good enough for your purposes and if it's worth your time doing it the right way.
Yes. The rather high VSWR (impedance mismatch) will certainly have an effect on gain. If I plug the estimated antenna impedance from:
as 58.7 -j106 ohms into a mismatch calculator at:
I get about 3dB of loss with this mismatch. In theory, you should be able to recover most of that by proper construction.
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