Hello,
My personal point of view would be: that it is a bit more complicated.
And I also state: there is no commercial benefit for me, since im into quads aswell as yagi’s.
Ill first start by mentioning the "page" was made already 15 years ago and although there is a large portion of truth, it also lacks the explination behind it. The reason we have changed the site is cause we are now in the progress of updating the site. For sure the quad versus yagi story will become different in the future. The site was made especially to get ride of a lot of “rubbish” . I know many people have used it as a guide line and still do. That was and is the intention to give a honest point of view without a commercial aspect.
Oke, Ill explain where some of the statements came from and will try to give you a other perception.
A dipole with a 1,5 mm thick radiator will have a SWR 2:1 bandwidth of 2 Mhz
A single Quad loop with a 1,5mm thick radiator will have a 1,8Mhz 2:1 SWR bandwidth
Both can be easily verified using NEC. Attached you can find the SWR plots for verification, and ill be happy to share the models with you if needed.
Yes, you are absolutely right to place remarks to my statement which I have made: a quad has a narrow bandwidth compared to a yagi ...although (as just prven) I wouldn’t call it false, but there is more to it... It is not as black as white as …a quad has a low Q there for a better SWR bandwidth.
Say we have the 3 elements quad described by cebik and scale it to 11 meters.
The antenna will have about 9,2dBI, and a 2:1 swr bandwidth of 1,7 Mhz. The boomlength is 4,1 meters.
Now we are going to "design" a similair antenna but then in a yagi design.
We take for example a 4 elements yagi on a 3,8 meters boomlength.
The gain will be less (also smaller boom and boomlength equals gain) roughly 8,5 dBI.
But the antenna has a SWR bandwidth of 2:1 Mhz of almost 2 Mhz.
Now, this is where it goes wrong...there are also some designs where a quad has a wider SWR bandwidth compared to a yagi and vica versa is true aswell.
It all depends on the design you have made or what you want.
There are a large number of different designs now a days..and some got names ...
Like OWA, F-yagi, etc.
It is quite possible to design a yagi with a lower Q compared to a Quad.
But again, vica versa is also possible.
And although antenna Q is of course close related to SWR, if one would calculate the Q of a antenna there is more to it.
I would recommend to read this:
http://www.qsl.net/yu1aw/Misc/yagi_q_factor.pdf
I also state on my site that a low placed Quad will have a lower take off angle.
This is also true, however , !!!!! and that is a big however;
The difference is so small you cant measure it in real live. So, all the sites giving that as a advantage are inaccurate.
On my site you can also see a expected “gain curve”. The difference which can be seen is too large. The gain difference between the two is less and never exceeds 0,5db.
I have some friends who work for "large" companies like VOA/ Deutsche Welle and of course the military.
They have spend actually more money than we will ever see, trying to find out what is best.
The conclusion always is...there is NO “noticeable” benefit for either from a electrical point of view.
There are exceptions. there are advantages for a both the site of w8ji describes such a situation for a quad.
But there are also equal as many advantages for yagi's..depending on your situation and what you are expecting from a directional antenna.
Ill give you one right now: It is difficult (if it can be done at all) to lower the first sidelobs in the E plane of a long boom quad compared to a long boom yagi. Now, if you connect your antenna to your transceiver the noise level rises. The antenna picks up ‘noise”. So, if we can lower those first sidelobs the noise will be less aswell. There are some Yagi types famous for this. You will have a lower noise floor compared to a quad …
It is also fair to say...that overall (not always) that on the same boomlength a yagi with one element more compared to a quad the yagi can have overall better performance.
A quad can have a front to back of 40dB but say if you drop 2 procent from the design frequency and it severly drops where the Yagi with the additional element still keep a relative high front to back...Which one would be best? (and although that is what most find important it is not always the case),..what is it what we are searching for ...?
In all my live I keep hearing about the quad versus yagi story. So I actually have had the same boomlength yagi/quad up in the air for a long time. (opposite to moste “writers”). NEVER could i give a advantege to any.
It is also fair to say as Cebik (SK) has done that most “known” benefits for a quad are those discovered in the early days. But since the introduction of modeling and with todays present knowledge MOM/SWAMP etc…it is possible to design Yagi’s which are at least equal or better.
We are also forgetting the “high Mercedes” attitude here. Since it is always more difficult to put up a quad compared to a yagi (as a quad is a 3 dimensional antenna and a yagi is flat) people have a mind set in which they believe it must be better since they have put more effort in it…
But how many have actually compared with present day knowledge both ?
I know I have.
The “excuse” most use for not giving a honest comperisment is the large area a quad will need.. Oke, I can live with that..But just ask yourself: how is that then on VHF/UHF ? How does that go for the big gun EME stations?, Guys who do nothing else but searching for a better antenna …always searching for that lower noise level etc…I havnt seen quads being used by them though.
Quads are primarily seen on HF, which is strange due to the mechanical aspect. In my believe the reason is cause people still believe and hold on to the stories originally made in the 60’s. Though im also confident the guys who actually do there research will find there are other aspects which will give them more benefit.
There is one situation where i would favour a quad instead of a (well designed!) Yagi on CB.
And thats in a vertical polarisation. The quad will have less influence from the mast and coax cable.
And yes ill state again: There are some boomlengths and some number of elements where a quad model migth be better. But that also can be true for the Yagi.
It is more the poor modeling that one has done which gives either a advantage.
And actually i tend to believe that on almost all boomlengths they can be atleast equal, It is not black and white.
Kind regards,
Henry HPSD 19SD348
All about antennas
