[NLRS] Halo/Big Wheel Antennas

[John P. Toscano]

Eric Shook (KT8O) wrote:

> Just one quick question.  When stacking these, what
> spacing should be used (2m)?  Do they have to have a
> power divider on them also?

When I put up my stacked pair of M-Squared SQLOOP antennas (the
predecessor of the current HO-LOOP), I was advised that the
vertical stacking distance should be 36 - 50 inches, and that
36 inches was a compromise usually reserved for mobile operation
where you may not have a lot of vertical space available for the
stack.  They said 48" was optimum, so that's what I did at home.

The Big Wheel is obviously not the same antenna, so the best
stacking distance may be somewhat different.  But hopefully this
will be at least a fair approximation.

Two 50 ohm impedances in parallel should give you 25 ohms, which in
turn, should make your radio and/or amplifier UNhappy.  So yes, you
will want impedance transformation of one sort or another.  There are
(at least) two ways to go.

M-Squared said that for mobile use, many folks stacking a pair
of 2 meter SQLOOPS opted for the low-buck approach, using two
equal-length (odd number of quarter-wavelengths x velocity factor)
runs of 75 ohm coax, which steps up the impedance from 50 ohms at
the antenna end to 100 ohms at the other cable end, and two of these
into an ordinary TEE gives you 100/2=50 ohms.  Then you run any
sort of 50 ohm feedline from there to the radio/amp that you wish.
They also said that for a bit more performance, I could opt for a
2-port power divider, 50 ohm phasing lines, and then naturally my
choice of 50 ohm feedline.  This is the route I went, since at the
time I did this, I was anxious to get the best signal I could with
the setup, having just blown up an expensive rotator that was going
to take many months to repair, and being "beamless" for several
contests.  They made me two phasing lines of 1/2 and 3/2 wavelengths
(to keep the two antennas in phase, but allow for the 4 foot vertical
separation) and a 2-port power divider.  And they were even polite
enough to refrain from laughing at me over the phone when I called
them up in my then, much more highly ignorant state of mind, not
even knowing what cables hooked to which ports of the device.  At the
time, I had no idea at all of why this funny-looking device acted any
different than a simple TEE connector.  Thank goodness I've learned a
few more things since then!

If you are handy working with metal, you can build a very good PD for
a lot less money than it costs to buy one.  Donn has drawn up plans
for a 2M version before.  A square aluminum tube, a round brass tube
(at the correct length and diameters, of course), and 3 N connectors
will do it, plus the screws to secure the N's to the square aluminum
tube, and a touch of solder to connect the center conductors of the
N's to the brass tube that is nested inside the aluminum tube.

John (W0JT)