The one advantage of the Quad vs Yagi that no one has mentioned
is turning radius. When I was going to school, our club station was
saddled with a small tower stuck between two flag poles. The only
way to get a rotary gain antenna on 20 meters was to go with a 2
element Quad. As to whether or not it was better than a yagi, I don't
know since we never made any direct comparisons (there was no room
to put up a rotary yagi). The antenna worked very well (disclaimer - this
is an unscientific subjective claim based upon the emotions of young
men who drank too much and liked to break DX pileups), and we felt
reasonable competitive on 20. Of course, now that we had a decent
antenna on 20, we spent all of are time fretting about our lack of a
competitive antenna for 40. And now that I have access to good
antennas on 40, I spend all of my time fretting about lack of good
antennas on 80 and 160 - and the beat goes on.........
73 de Mike, W4EF.........................
----- Original Message -----
From: <K3BU@aol.com>
To: <towertalk@contesting.com>
Sent: Wednesday, February 07, 2001 8:33 AM
Subject: Re: [TowerTalk] Quad vs. yagi
> 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
>
> --
> FAQ on WWW: http://www.contesting.com/FAQ/towertalk
> Submissions: towertalk@contesting.com
> Administrative requests: towertalk-REQUEST@contesting.com
> Problems: owner-towertalk@contesting.com
>
>
--
FAQ on WWW: http://www.contesting.com/FAQ/towertalk
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
|