[VHFcontesting] Quagi

[Darryl J. Holman]

Hi Cal,

   I use a 5 element 2m quagi for one of my rovers.  It works quite well 
for its intended purpose.  Mine is built to be quick to assemble and 
disassemble, and the boom is hinged in the middle to stow in a small 
airplane.

   I've used a 6 element WA5VJB “cheap yagi” on 2m during the same 
contests out of a car, where the antenna can be permanently mounted. 
(You can see photos of both of them in action in different 
configurations in the same contest here: 
http://tinyurl.com/ww7dJunVHF12R ).   The 5 ele quagi and 6 ele "cheap 
yagi" have similar boom lengths--the Quagi is 7' and the yagi is 6'.

   I've set-up both the 5 ele Quagi and 6 ele cheap yagi in my back yard 
on separate 20' masts and done A/B comparisons during a weekly 2m SSB 
net.  I was hoping to learn that one substantially outperformed the 
other.  It wasn't the case...they performed identically.

   Both antennas use wood booms, and I would rate them as equally easy 
to build.   The LFA array, mentioned by G0BSU, uses a metal boom with 
the elements insulated from the booms by plastic insulators, so 
construction is a bit more complicated.

   Quagi construction hints: Use bare bronze brazing rod for the loops. 
  Avoid using copper wire. It isn't stiff enough and the resulting loops 
look like hell and deform easily.    I use 3/32 rod for a lightweight 
quagi that isn't subjected to 70 MPH winds.  1/8" rod would work for 
beefier loops that must endure highway speeds.   (If you insist on using 
copper wire, work-harden it by chucking it in a drill, anchor the other 
end in a vice and aggressively twist the wire.)   The welding rods are 
not long enough to form the entire loop.  One way to complete the loops 
is use high quality electrical butt crimp connectors to form the 
corners. Remove the plastic, bend to 90 degrees, insert the welding 
rods, use a punch to mechanically crimp and then solder the connector to 
the rods.  I prefer 3/16th aluminum rod for the directors.

   LFA arrays:  For the recent UHF contest I built a shortened (8') 432 
MHz LFA array for my street rover.   I used spruce blocks instead of 
plastic insulators.  A single machine screw with a washer and a Nylock 
nut (all stainless steel) holds the insulator to the boom.  The nut is 
tightened enough to hold the elements in place at highway speeds, but 
the reflectors and directors will rotate (instead of bending) when hit 
by tree branches and whatnot.  That is an extremely useful feature for a 
street rover.  I've not done A/B comparisons to the cheap yagi it 
replaced.  I intend to eventually build 222 MHz and 2 meter LFA arrays 
for the street rover, perhaps one by September and the other by January.

   In conclusion: All three designs have been successfully used for 
roving. The LFA yagi is the newest and sexiest design but, without 
additional design work, requires a metal boom, is heavier, and a bit 
more complicated to build.  But the antenna is expected to perform 
better for some useful characteristics.  The 5 ele quagi and 6 ele cheap 
yagi have similar performance, and are both extremely simple to build. 
If vertical mast space is a limitation, the cheap yagi is best.   The 
quagi's vertical loops make it more susceptible to getting snagged on 
trees.


Best,
   Darryl
   ww7d




On 08/19/2013 06:23 AM, Cal Zethmayr wrote:
> Has anyone on this forum built or used a Quagi on 2 meters?  Anyone currently using a Quagi?
> Any comments welcome.
>
> Cal Z
> W4GMH
> Crestview,Florida
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