Discussion in 'VHF/UHF - 50Mhz and Beyond' started by KA0EIV, Nov 2, 2016.
Here's what they look like when overlayed.
Appears to be doing its job. I worked a station 269 air miles away with 30-45 watts on a ho-hum night. He said I was 5/6 in to en54. Really surprised me with signals up and down last night.
What's the feed point z of the optimized antenna?
The beauty of the quagi is its long term performance when it rains and snows and water can't get into the matching network cause it ain't got one to go bad !
To the op :
May I suggest its time to get some calibrated attenuators and start using the attenuator substitution method of measuring relative gain.
You were not clear if the forward signal went up more than the back (ratio) between the two antenna's.
And in general no yagi-uda antenna or derivative (quad/quagi) will benefit from 2 or more reflectors.
What are the dimensions for the optimized 8 El quagi? As was previously asked, what is the feed impedance?
This thread has inspired me to look through the ARRL archives on Quagis to learn the real dope.
The MAIN advantage of the Quagi is that the matching issue is SO much simpler than the gamma match of a yagi...especially at UHF and above. While with enough twiddling you CAN get excellent results with conventional yagis, the Quagi feed almost guarantees that the rest of the thing is going to perform per specs. The Quagi just plain gives a better results-to-fiddling ratio. For most average antenna builders, this is a strong deciding factor in favor of the Quagi.
Eric, all the important stuff is likely in the link I posted above.
There is of course no reason to build a yagi with a gamma match these days. If you add an extra element close spaced to the driven element in a yagi you can get a direct-50 ohm feed yagi. Or build one of the LFA yagis which are similar. Just add a simple ferrite choke at the feedpoint- no twiddling needed.
I've built yagis and quagis both for VHF/UHF and actually found the yagis easier to build than the quagis. With the quagis you have to build a 3D support structure. And things like wire insulation change the driven element lengths in unpredictable ways.
I also tried modelling the quagi designs in the ARRL antenna book (which I also built)- while their gain was ok, the pattern was not very good.
Could you please attach that Quagi EZNEC file here, or email it to me? I'd love to play with it in EZNEC+ 5 here.
I have never heard / read anything about a quagi being the "optimum" VHF / UHF antenna. Yes, it is possible to build a yagi, etc., that can outperform a quagi. However, the quagi is a "cookbook" design in that, if the instructions are followed, the antenna works fine without having to do any tuning, modifying, etc. As such, for the novice antenna builder, who has little, or no, experience building VHF / UHF antennas, they can get an antenna that performs well for a very low cost.