The Challis messenger. (Challis, Idaho) 1912-current, 1924-11-19
BY LEWIS L. ELLIOTT


A perplexing problem facing the
radio fan of today Is the elimination
of interference from broadcast sta
lions In and about great metropolis.
With Its six or seven powerful stations
In operation and whose wave lengths
are somewhat close together, 1t is
quite difficult to tune in to a given
station without hearing the side bands
from the other transmltters. This
can be more related to the operation
of WEAF on 492 meters and the new
station WNYC on 526 meters would
show only "a meters In difference.
combination wavemeter and filter
consisting Of precision vernier con-
denser and tapped coil or inductance
has been available to radio expert
mentors for some time. With this in
strument the broadcasting listener can
readily check the wave lengths of
broadcasting stations or of the dot
and dash telegraphlc signals which
may be Interfering with his programs.
The device may also be employed eff
fectively as radio filter to reduce
interference from undesirable stations
The use of the instrument as a
filter Is shown In the accompanying
diagrams. This device will improve
the selectivity of any receiving set.
This Improvement Is more noticeable
when used with the single circuit type
of receiver than with the inductively
coupled type. Its use with crystal
receiver Is quite simple.
There are two particular methods
OF using this instrument as a filter;
one Is called the series method. the
other the parallel filter. In Figure l
Is shown the proper connections for
use as series filter. When troubled
by interference from q nearby broad
casting station. break the antenna lead
to your receiver and insert the coup
ling coll as shown In Figure 1.
Setting the Coil.
Set the switch on tap 8 (eight turns |
in the coupling cold and slowly rotate |
the condenser knob until the desired I
signal decreases, vnnishes and again
increases Using the small knob pass
slowly back and forth over this point
until the position for minimum inter-
fering signal Is located. The filter is
now set for this one interfering station
(ts wave length In meters Gun be read
from the condenser scale). Both the
Interference and the filter may now be
forgotten and the receiving set tuned
to distance stations in the usual
manner.
The parallel filter Is used to reduce
from spark transmitters,
static, A. c.. hum and similar sources.
1t will also allow you to tune OUT sew
ernl local stations broadcastng stimuli
and receive from a broad-
casting station of wave length differ
ing by only a few meters from the
nearest interfering wave
Connect the parallel filter as shown
In Figure .. Sci the switch on open
and tune your receiver to the desired
station. Then move the litter switch
to contact and all signals will dis
appear until the filter condenser is ad-
justed TO exactly the wave length of
the desired station. The wave length
on the dial are a help II the
desired wave length is known. Listen
closely for your station while slowly
moving the filter condenser back and
'orth over the approximate wave
cngth OF the station. Use the small
lnob and tune carefully. because one
,alf of one degree on the condenser
iial is enough to tune the desired sta
ion in or out.
How to Get Results.
Most people are not accustomed to 9
he highly desirable sharp tuning t
Which Is obtained from this radio fl q
err, and therefore pass over the proper b
citing without noticing the signal. '
'ractice first on tuning in loud 1
II oadcasting station. After the filter
his been carefully adjusted for maxi Il
mum signal strength slightly retune q
he receiver, making change In the ]
mount of regeneration, If necessary. n
Use Of the switch: Place switch t
n "open" TO entirely disconnect alter. 7
rom receiver. on IS" or IS" for mod I
rate Interference and on 80" for I
trong Interference. r
It II often desirable when listening /
NJ = certain hroa dca sting. station to r