The Washington herald., 1922-10-03
WAVE METER EASY
TO MAKE AT Home
Can Be Constructed at Cost
OF Little More Than Var
liable Condenser.

when wave meters are mentioned
an amateur thinks Of the CONNER
cisl type, which cost quite a sum.
This article will deal with a home-
made type that can be made for
little more than the price OF a good
variable condenser.
A wave meter can be used for
number of things. the most impor-
tant being to cslibrste q receiving
set so as to be able TO set 1t at any
desired wave length without a lot
of preliminary tuning-can be used
to measure the wave length OF your
transmitting station and to meas
ure the wave length OF a distant
transmitting station.
The essential parts are a variable
condenser. hxed induetance and an
indicating device. which can be
either a small flashlight bulb or q
crystal detector and telephone. The
accessorie5 to measure OF calibrate
your receiving set are key and
buzzer to excite the wave meter.
How to Make IL.
The 'tnductance can be MADE UP
on a cardboard tube AZ inches In
diameter. Wind "a turns OF No. 20
double silk covered magnet wire on
the tube. This will give you a tube
about two inches long as you do not
want the wire to come to the edge
Of the tube. Allow seven inches of
wire at the beginning and end OF
the coil for connections to the va
riable condenser. A miniature
socket and flash-iight bulb can be
connected in one lead from the coil
TO condenser This is TO be used
when measuring the transmitting
station.
This is done as follows: DiscOn-
meet the aerial and ground and
loosen the coupling between the
primary and secondary OF the oscl-
Iation transformer. Start your set
up and bring the wave-meter near
the Inductance. vary the condenser
Of the wave-meter until the bulb
lights up. II il burns too brightly
it may burn out. SO be careful and
move the meter further away. Re
fer to your wave length chart
for your wave length II IL be
above 200 reduce the turns OF wire
in the primary OF the oscillation
transformer and take another -eal-
ing. If-below 200 add more wire
until the correct wave length IS OBJ
tained. II you have an aerial am
meter the circuits can be brought
to resonance by adjusting the aeria'
inductances until maximum rafia-
tion is obtained with loose coup
ling. II you haven't such a meter.
il will be necessary to Calibrate 'he
serial or open circuit similar to the
closed as follows:
Connect your aerial and ground
to set. dlsconnect your condenser
and take the leads from the trans
former secondary and connect one
to ground and the other to secon-
dairy Of Oscillation transformer.
Start your transmitting set and
take a reading with wave metsr-
When you have the desired wave
length. the set can be hooked up
for sending in the usual manner.
Sending Two Wave Lengths.
when both the open and closed
circuits are adjusted to the same
wave length and then coupled to-
eether IL will be found that you
are sending out two wave lengths.
One lower and the other longer
than the one measured. This can
be overcome by loosening the coup
ling until only one wave length Is
shown on the wave meter when
connected up as a receiving set by
short-circuitins the flsshlight lamp
and putting a crystal detector and
a pair of telephones in shunt to
the condenser.
To measure the wave length OF
the transmitting station when your
set Is not calibrsted. you first tune
in the station on your receiving
set and when you have been prop
erly tuned in. you start your wave
meter buzzer and move the con-
denser until the maximum sound
is heard in the telephones. As you
had adjusted your receiving set to
the sending stations wave. you
now have the same wave length
being sent out by the wavemeter.
You then look II up on your chart.
To calibrate your receiving set
you simply start your wave meter
buzzer and put your condenser at
its lowest reading. adjust your re-
ceivlng set until maximum sound
is heard and take notes Of the di:-
ferent adjustments OF your Undue
tance and condenser on the recalv-
ing set. mark them down and move
your condenser five degrees and
take another reading. etc. until
you have covered the entire scale
of the meter. For higher wave
lengths you will need a larger coil.
A wave meter can also he made
from a honeycomb coil and a va
riable condenser. This Is more
compact but will have to be call
brated for wave length scale.
The figures given below will be
near enough for any wave meter
built along the aforegoing lines.
but IL you desire an accurate scale
1t Ia suggested that you have IL
calibrated by radio inspector. or
send II to the Bureau of tandards.
Washington, .. c.. which makes
nominal charges for celebrating
your wave meter.
Following is the wave length ta-
BILE which can he made up on a
piece of paper and carried with the
meter
Condenser Deprees waye Ianufhs