I use my Iwatsu SS5711 4 ch. 100mhz scope for tuning the 4 sqr antennas I
have built. I have 4 equal length coaxes carrying the signal from current
xfmrs at the tower bases to the scope amp inputs. All 4 current xfmrs are
first placed on the same tower base to assure that the 4 channels are
identical in phase and amplitude at the CRT screen. I found that they were
extremely closely matched.
My first 4 sqr used 4 Hytowers with the stubs for 20 meters and up
removed. I used a homemade hybrid coupler for the 90 deg shifted signal and
1/2 wave of coax for the 180 deg. on 80m. Two of the towers were relay
selected for broadside operation on 40m in one direction and another pair
for the other direction.
The current phase and amplitude values on 80 were less than the desired
values and really suffered when going from SSB to CW. After several years of
use, the 40m option was disabled and the stingers were strapped to the top
of the tower. The stingers were lengthened by extending the 2 inch portion
with sleeved tubing. This greatly improved the bandwidth of the system and
it was used that way for a while even though the currents were not as close
as desired in amplitude and phase.
Ultimately I abandoned the hybrid coupler and built a W7EL type LC 90 deg
phase shifter. This was easily tunable to the correct phase shift but the
amplitude was not right. A tapped auto xfmr allowed the amplitude to be
tweaked to the desired value. This put all of the amplitudes and phases at
the desired value. Unfortunately, this solution is quite frequency
sensitive. I tuned it for the CW band and had plans to relay select a
similar circuit for SSB but left Dallas to move to Spokane before that
happened. The towers were sold at the time of the move That system worked 39
zones from Dallas and the other (z23) was picked up from Spokane. 73, Dan,
----- Original Message -----
From: "Michael Tope" <W4EF@dellroy.com>
To: "Tom Rauch" <email@example.com>; "Jim Lux" <firstname.lastname@example.org>;
"Dan Levin" <email@example.com>; <firstname.lastname@example.org>
Sent: Saturday, May 08, 2004 8:11 PM
Subject: Re: [TowerTalk] 4 Square phase line length question
> From: "Tom Rauch" <email@example.com>
> To: "Jim Lux" <firstname.lastname@example.org>; "Dan Levin" <email@example.com>;
> Sent: Saturday, May 08, 2004 7:23 PM
> Subject: Re: [TowerTalk] 4 Square phase line length question
> > > Here's the interesting thing..I assume you're using some
> > scheme where you
> > > use 1/4 wavelength lines for current forcing, right? so
> > the element current
> > > will be what it should be, regardless of the element
> > impedance. The
> > > mismatch at the feed eventually winds up back at the
> > hybrid/phasing network,
> > > where you can take it out by changing the L or C of the
> > phasing network (or,
> > > just ignore it, and take it out at the array feed point).
> > Forcing equal currents requires equal input voltages and
> > correct input voltage phase. 1/4 wl away that becomes equal
> > currents and with correct current phase.
> I hadn't thought about it before, but since the 1/4 wave lines
> force equal feed currents for equal input voltages, one could
> use a dual-trace oscilloscope at the phasing network/power
> splitter to set the relative amplitude and phase of the element
> currents. Seems like that would make it really easy to get
> the array currents dead nuts on.
> 73 de Mike, W4EF..................
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
> TowerTalk mailing list
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
TowerTalk mailing list