[TowerTalk] Quad vs. yagi

[K3BU@aol.com]

W8JI writes:
> 
>  Most of the benefits of quads are far over-rated. They do not, 
>  contrary to folklore, have "2 dB gain over a yagi".
>  
>  A single loop has the maximum advantage over a dipole, and even 
>  that idea case favoring the quad almost always produces much 
>  less than the proclaimed "2 dB advantage". 
>  
>  In actuality the gain of a full wave loop over a dipole can be 
>  anywhere from zero to two dB, depending on height and position. 
>  For example, contestors often use horizontal full-wave loops on 80 
>  meters  to "get gain" at high angles, when in reality there is no gain 
>  advantage over a dipole at low heights!
>  
>  We can eliminate the hyperbole about gain, because it doesn't 
>  happen.
>  

(Somebody has to defend "poor" quads :-)

I wouldn't be so sure! 
    It appears that some of the "new wisdom" is coming from the software 
modeling "facts." 
    I just quickly modeled single Quad 1/4 wave/side loop vs. dipole and I 
can get paper advantage of over 2 dB. So no folklore there. (My 3 el. Quad 
beat 7 el. KLM Log Yagi on almost twice the boom on 2m.)
    Quad (circular or delta) loops have larger aperture than dipole, they 
have fatter vertical lobe and there is suspicion that they pick up some of 
the "other" polarization too. 
    Quad loop has lower Q, wider frequency response, flatter SWR curve, wider 
bandwidth.
    Quad loops provide more efficient match and RF transfer between coax and 
antennas.
    Quad loops are less prone to precipitation arcing and take all the power 
you (coax) can supply, no "matches" to burn.
    Quads can be build to withstand what Yagis do. You can build lousy quad 
as you can build lousy Yagi. I had Quad elements survive ice storms in 
Toronto area, and had commercial Yagis folded. There are now some super 
materials and with proper design there is no problem. I for example designed 
my Razors, using quad elements, so if really bad storm came, I'd rather have 
quad elements fly away (cheap wire and spreaders) rather than have boom or 
tower damaged (major expense and danger).
Antennas using quad elements will outperform Yagis up to about 4 el. Beyond 
that it is better to use Yagi parasitic elements, having higher Q they couple 
better in the array. Examples of Quad/Yagi combination are Quagis and my 
Razor beams. 
see http://members.aol.com/ve3bmv/Razors.htm
Single Razor would consistently beat 6 el. KLM by about 10 dB in real life 
tests.
    Some notable contesters use(d) loop antennas to cream competition (W2PV, 
K6UA, VE3BMV, K3ZO, KC1XX, VK3MO) and their experience confirms the benefits 
of loop antennas. Those who know ....
    As far as cost goes, one can build quads for peanuts using bamboo and 
spider spreader holder, up to bullet proof fiberglass or carbon filament 
spreaders for extra bucks. (BTW the best preserver for the bamboo is the 
latex driveway coating!)
    As far as "difficult" assembly goes, I had no problem with 20m elements. 
I would suspend the boom at my waist level, assemble top and side spreaders 
and wires. Then lift the boom for enough clearance for the bottom spreaders, 
get up on the ladder, and fasten the spreaders to the crosses with two hose 
clamps and lift the sucker up. (Had Big Bertha tower with no guy wires). You 
can have it ride on the carrier cable just like Yagis too.
    I am just now "investigating" loops with vertical polarization for the 
salty beaches, see what comes out. I am already getting 2 dB from single loop 
over "mighty" dipole.

Yuri, K3BU
da Quad defender

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