Autek Research WM-1 SWR Instructions Manual page 3

PEP is generally used on SSB, and AV i s used for
tuneup. Switching to AVon SSB produces a noisy, low
SSB power and SWR reading. The
PEP
feature also allows
you to comply wl.th latest FCC rules allowing 1500
watts PEP QUTPVT on many bands and for moat classes
of llcensees.
The SWR reading in the
PEP
position will be accurate
for reasona~ly conti~JOus speech, but is designed to
decay much faster than the
PEP
power reading. This
allows almost instant response to antenna tuner
adjustments when talking on SSB.
Incidentally , try this• Transmit
a
continous carrier
on CW (key down . ) . Note the power reading in the
AV position. Then switch the WM1 to PEP . You ' ll
probably notice a slight i ncrease in PEP. No, the
PEP
detector isn ' t wrong! you're measuring the increase
in PEP power caused by the tiny ripple on your power
supply voltage!
Occasionally, you may want the met ers to decay faster
when switching to a lower r ange scale. Simply switch
monentarlly to AV , which discharges the PEP circuit.
D. CALI BRAII!li
Your WM1 is calibrated using an air-cooled I KW 50
oM % 0.1 OM "driftless" load and a special technique
to measure power which is accurate to less than 1/2
percent. It is unlikely you have equipment of this
accuracy. (Two ~4 instrument s can disagree by as much
as 10%.) For example dummy l oads commonly used by hams
can vary from 3g to 63 oMs in our experience, even
though specified as accura t e t o
5%.
Worse yet, most
drift 10 or more ohms when heat ed!
The complete calibration pr ocedur e is shown below.
(Note • steps 1,,3 , and 4 may be done without fear of
degrading factorT accur acy, Ste p 1 , especially, m ay
have to be performed occa sionally. )
1. W i th DC power appl ied t o the WM1 (!.ED lit) , but
your transmitter off, mechani call y zero both meters
with the front - panel meter screws using a screwdriver.
2. Connect the remote head to your transmitter and a
load known to be 50 ohms r esistive at the frequency
tranemitted.(lf you use, say, a 40 ohm load,which is
off by 20~,your power calibr ation would be off by
201. at 50 oMs , and SWR would not read correctly.)
YaJ should preferably transm1c on 40 meters (7 mHz) .
While tranamittl.ng CW ad just the trinvt~er capacitor in
the remote RF head until SWR reads 1•1 or as close as
possible . Use 20-200 waccs i f possible.
3. Reverse coax connecti ons to Che RF head , so chat
your transmitter is connected to the output and
the load is connected to che i nput. Disconnect one
wire going to che SWR meter to avoid pegging this
meter . You ' re now reading r eflected power , which
is much more sensitive than SWR . Touch up the trimmer
to yield lowest power reading .
'• . Reverse coax connections to the
Rf
he!ld agaln so
that the transmitter i.s connected normally to the
input. Reconnect the wire to the SWR meter . Disconnect
the load from the Rr head output, leavlng XOTHING
connected co che RF head ou~put coax connecto~ , not
even a short length of coax. Transmit less than
200
watts
CW
(no linear) and adjust the SWR trimpot on the
circuit board (see drawing) so that the SWR meter
reads infinity (full scale. ) Do this on 40 meters
if possible , for best accuracy.
s.
Connect your accurate 50 ohm load ns in seep 2.
Nith a power meter of known accuracy in series with
the WHI, adlust the PWR trimpot on the circuit board
(see <Jra••ing) until the lvH1 reading agrees with the
reference power meter . Be sure SWR is \ol .
E.
OPERATING CAUTIONS
Never run the
WI-ll
at all
SIVR
greater than '"
l
with
power greater than 300 watts. This could possibl y
burn out the RF head , which is not covered by
warranty. These limits are quite conservative. Your
linear is likely to arc-over before the
WML
is
damaged. However, to be safe, check SWR before
switching on your linear. Never short the WMI Rf
head output. This could melt the Rf wire in the head .
F. W
CASE OF TROUBLE
1 • HEIER DAtlACED
This is extremely rare . Damage is not always visible
by looking at the unopened box . All shipments are
insured. Keep the original box and packing material
and report damage to the shipper (usually UPS) .
Once you do this , you will not have any problems
collecting. We do this for you, and wlll slllp a
.. r eplr.cement upon r eceipt of the damaged equlpment .
2. MEJE:R
!lEAD .
POWER OR S1VR
READING TOO LOI~
Check pow er source. Be sur e meter has a DC suppl y
attached as ln section A, and that voltage is pr oper .
NoteoAC adaptors are tested by the manufacturer , not
by us . Shoul d you receive a bad AC adaptor , write or
call and we'll get you out a good one lmmed lately.
Examine the RF head . tf you ' ve shorted the head output
the wire through the toroid cay have overheated . Simply
replace the wire. If vou ' ve subjected the head to
high SWR at high power, the white portion of the
trimmer capacitor may be cracked or singed . We can
send you a replacement for $5 ppd USA . If you ' ve
shorted any RF head board component to either coax
connector, say whil e adluscing the trimmer , you ' ve
probably blown both diodes . Replace these wlth any
GERMAI'IIUM dlode , available at Radio Shack . li\I34,1N270 ,
and others are su itable.
llamaga to the RF head, especially the trlmmer capacitor
cnn a l so be caused by lightning . A direct strlke ls
not necessary. Thi s ls also not covered by w arranty .
Again, note that slmply replacing thcdamagecl component
and a minor recalibrati on is sufficient. (Unless the
toroid or 33 ohm resistors are damaged.)