Autek Research WM-1 SWR Instructions Manual page 4

3 .
SWR Rli:ADING TOO HIGH /PO\vER TOO
liT Gil
a. Be suro input and output on RF head arc not
reversed .
b. Especially lf this occurs only at high power
nnd
is more apparent ln PEP position, it could be
arcin& (spark) in your transmitter, linear, or
antenna.
c . RFT .See below . Could also cause low readings .
This may indicate RF flowing in cables or power
connected to the main meter box, or direct RF
pi ckup . The IVMI ls extensively tested in a high
POWer
RF
envi ronment . However, ex treme or
unusual
cond i tions might e xist in some shacks which could
cause a problem.
(lve
test at I
KW
with the antenna
only 15 feet away with no problem .)
Be sure the meter . is not near unshielded feedlines
or coils carrying power . The top of the antenna
tuner or linear may not be the best location. If
readings vary as the main meter cabinet is moved
around , the problem is probabl y direct radiation
into the unit . Find a good location or reduce the
radiation
fro~
the source.
More likely ls a ground loop . If the ~eter reading
does not vary when the mecer is moved several feet ,
suspect ground loops . Typicall y, transmitted power
could be picked up by the house wiring and flow from
the AC adaptor through the WHl chassis and back to
the remote RF head.(Using a small battery would
eliminate this possibil ity . ) Unplug the AC adaptor
from the wall
·~cket.
The WHl will continue to
operate for a second or two . If the reading instantly
cl>anges when unplugged , you proba bly have a ground loop .
Try o I )Plug the AC adaptor into an out l et away from
t he transmitter. 2)Connect a good earth ground to
your transmitter or linear. 3) Move the
WM L
to
a
different location.
Note that sending the unit back to "checkout" ls
useless, since we will
f~nd
nothing wrong with Lt .
I f
you experience persistent RF pickup with
any
Autek equipment . send a 9" + wide
SASE
for
a
~re
detailed discussion. We reali ze it can be quite
frustrating at first lf yeu have this proble~.
Forcunately, thlo problem is r are, and we know of
no one who has not been able to solve it •
)
}
)
)
5 . MEIER "STICKS" liT ONC READCNG OR Ci\>II'IOT GO BEYOND
A
CERTAIN
READI"lG
This could
be
caused by low B+ or batt ery voltage. See
Section
foo.
On at least one occasion a microscoplc ptccc of the
~eter plastic ~lding
has
broken off and lodged itself
in the meter ~vement . The solution ls simple. Turn
the
WMl
upside down
and
shake the obstruction out of
the 1110vement . If problem reoccurs, ren10ve the two
screws Whlch hold the front panel of the meter , remove
the clear front panel , and shake the obstruction out.
\~e believe thls problem is eliminated and would
appreciate a postcard if
you
experience lt so we can
tighten quality control further .
6 . OTHER PROBLEMS
See our ongoing "late not es" for reports of common
problems , if
any,
as well as tips from owners .
G. THEORY Of OPERATION
See schematic/block diagram . The RF head operates as
follows• Capacitors Cl and C5 form a voltage divider
for Rf voltag~ at the head output. Toroid Ll measures
the current flowing into the load and
l~presses
a
voltage across the 33 ohm resistors proportional to
this current . Voltage at the left of Rl ls proportional
to voltage across the load ~ current into the
load . Voltage at the right of R2 is proportional to
voltage across the load minus current into the load.
(Voltages at opposite ends of the torold are 180
degroes out of phase , as with all transformers . )
These Rf voltages are r ect ified by the diodes and
converted to DC values . \Vith a 50 ohm load , Cl is
adjusted to null out t he vol tage between 02 and the
5V reference-- this voltage is proportional co the
square root of "reflected power . " Similarly the
voltage between Dl and the 5 V reference ls proportional
to "forward+ reflected" pewer, cheoretlcally. With
any
load ocher than 50 ohms r es istive, the reflected pewer
ls non-zero and SWR is above l ol .
Note chat all voltages in che RF head are referenced
to a regulated 5 volts from the matn circuit board,
not ground.
The dravins shows a block diagram of the main circult
board. Forward and r everse voltages are scaled for
the power range selected, and peak detected by active
peak detectors , not just diodes . The peak detectors
have negligible error (less than 0.1%). The forward
and reverse voltages are then divided ln a wide range
electronic divider ci r cuit accurate to 0 .2% or better,
and drift - free due to the precision resistors and
voltaee regulator used .