View Full Version : Quagi antenna: Best of both Worlds
09-18-2012, 02:29 PM
PJ49T was on 40M last night with a big sig from Aruba. After I was lucky enough to make a contact with Bob a G3 OP came on freq. and was very strong from GB. Listening to the QSO the PJ4 station inquired what antenna the G3 OP was running. His reply was a 6 element Quagi for 40M with a 100' boom for the antenna. I didn't get the G3 OPs call but he did say the AA4MM designed the antenna for him.
100' boom, 6 elements on 40M and up 150' on a tower equals big sigs for the G3 OP. So does the quagi take the best features from both antennas and combine them? I know the quads are very quiet antennas on the recieve side does the quagi carry over these same traits on the recieve side? I have heard 1 other OP in Ca. run a quagi on 20M and he too had a very big signal on that band. :)
09-18-2012, 03:12 PM
I know the "inventor" of the Quagi quite well (Wayne, N6NB -- published the design for VHF-UHF use back in a 1977 QST article).
The objective wasn't really to take the best features from a quad and a yagi; it was to make an easy-to-feed-without-special-matching-devices yagi and it evolved experimentally, before antenna modeling software was available.
I don't know why anyone would make one for 40 meters, when a 6L yagi on a 100' boom should work exactly as well.:o The slick thing about the Quagi is with proper design, loop size and element spacing, you can achieve a perfect match to 50 Ohm coax without using any sort of balun, beta match, gamma match or anything else that might introduce inconsistency or loss at VHF-UHF frequencies. But on 40 meters, conventional matching systems have about no loss anyway...so the advantage of the Quagi at 7 MHz escapes me.
09-18-2012, 05:21 PM
...so the advantage of the Quagi at 7 MHz escapes me.
Some advantages is the idea that it helps to increase wind loading and adds more mechanical complexity to the design so more frequent maintenance is required?
I recall Quagis have been popular for VHF for a long time.
I tried a cubical quad many years ago on the basis they worked well at low heights Vs a Yagi.
Mother nature defeated this antenna with two severe thunderstorms a week apart. Blew it down off my garage top mast twice and then I gave up,.:(
09-19-2012, 04:45 AM
I built the Quagi from the article in QST written by N6NB. Simple to make, easy to match and good gain are an unbeatable combination. The whole idea behind the Quagi was to make a driven element that didn't have the problems that were being found in antennas in the VHF/UHF range at that time. Can't say if it was quiteter than another type antenna because that was my only antenna I had. It sure did work!
The size at 2 meters is still small but one on 40 meters is almost impossible to handle and the antennas in the HF portions didn't have the problems that were showing up at VHF/UHF. There is absolutely no good reason to make a Quagi for the HF bands. It's a waste of time and resources. The mentality was to try something different and experimenting is fun. In this application it's kind of like the CB days where antennas were being introduced all the time. Each touting they were superior to anybody else's. The more bizzare the antenna configuration the more the darn things sold. When it came down to it, the conventional ground plane antennas of that time perfromed well and often much better then that new super-duper thingamajig all the CBers were flocking to.
It's your choice to experiement with antennas of any configuration you want. Just look into the efforts expended and determine if that is worth the energy and resources you have available.
There's a calculator available online that tells you what you would need to have in order to make a Quagi for any frequency you desire. Which, strangely I can no long locate. Think it might be the property of AntennaX now but that's just a guess.
The normal size for the element is a well known and detailed bit of information. Since antennas are, for the most part, scalable then all you have to do to get the new spacing and element lengths is to find the multiplier for the band you want. As an example, 145Mhz to 7Mhz gives a ration of 20.71. Just multiple everything by 20.71 and you'll have just about the exact figures to make a Quagi for 40 meters. The normal driven loop of a 2 meter Quagi is 80 inches. The length for a 40 meter driven loop is about 138 feet. The reflector on 2 meters is 82 inches. So for 40 meters the reflector is about 141.5 feet. These measurements to me seem off a bit but it's just an example. The boom length for a 2 meter 8 element Quagi is a little over 13.5 feet. For 40 meters the antenna would be over 279 feet in length. The antenna would need to be up at least 1 wave length to perform at the proper level. So you would be putting up a 279 foot antenna up in the air at 141 feet.
Yagi's are smaller and easier to construct when you go down in frequency.
09-19-2012, 12:39 PM
Thanks to the folks that posted all of the answers. :) I have never made it up past 28 mhz and have no idea what the VHF bands are all about. Maybe 1 day I will make it up to 6 M and above, but for now I really do enjoy HF work. I can see the interest in these higher freq. bands as the antennas are a lot smaller and more practical for a lot of folks out there. There is nothing like the Human resources of knowledge here on the ZED. TNX once again for all of the replies. :)
I can not think of any reason a quad would be any quieter than a Yagi- unless we are talking specifically about static dissipation.
And the idea that a quad works better at lower heights is myth and easily disproved by modelling.
09-19-2012, 10:02 PM
I rather think any uk station with an antenna as big as that on 40 metres would be heard all over the world whether it was a quagi or not !
09-22-2012, 04:45 AM
As WIK pointed out, the "Quagi" was originally designed for ease of construction and matching at VHF and UHF. Wayne Overbeck. N6NB was able to demonstrate that after the first two "quad" elements, (reflector and driven elements) there was no significant difference in gain or other performance parameters whether the directors were also cubical, or merely linear elements as used in a traditional Yagi-Uda antenna. The linear elements being simpler (and less expensive) to construct, the "Quagi" was born. With the same number of elements, and same boom length, the performance of a Quagi or traditional Yagi should be equivalent.