Belt Valley times. [volume] (Armington, Mont.) 1894-1977, 1926-10-07
wave Traps That VIII Be Of Interest to Fans

Many radio fans complain OF their
sets lacking selectivity. The sets have
not the power to separate stations
sufficiently and their operators are al
loss TO know what to do A wave
trap Is the only solution II one does
not want to pull his set apart again,
so here is some data that will be OF
Interest to fans troubled In that re-
spect:
Wave traps and blocking devices are
becoming more and more essential TO
operators OF none too selective re-
eefvers, especially In congested dis
tricts where not only does one have
to contend with % or more STATIONS
separated by the smallest possible
margin. but with annoying proximity
to many which are brOadcasting on
high power.
The better-designed receivers are
not affected hut a great many Of the
sets built In the days before so many
stations were on the air, as well as
many of the less selective creations OF
more recent months. find It expedlent
to use auxiliary apparatus In the form
Of wave traps.
Here is a commercial trap and 9TH
ers just as effective that can be con
structed very cheaply by the listener
who finds need for one IN reducing to
a minimum the interference Of sta.
tions operating on waves too nearly
the same for the unselectlve receiver
to separate. II Is sometimes necessary
to use more than one trap to bring to
an unobjectionable point the Interior
ing stations. This Is especially true
where high power is the source OF I'M
noyance.
Series and shunt Traps.
The simplest form OF traps which
are effective are series and shunt traps
as we'll as few variations Of absorb
ton and rejection traps.
The circuit Is that given In Fig. i
and~consists OF two 13-plate variable
condensers. one Of which is connected
In series with on inductance OF 65
turns Of No. 20 single cotton-covered
copper wire. wound on az Inch
cardboard tube. This is the left-hand
dial in the commercial unit and tunes
the reflector circuit The other con-
denser. adjusted by the right-hand |
dial. is shunted across a coll OF SINH
lar dimensions. 65 turns. over whlcltlfs
wound n primary OF p turns OF No. p !
gauge wire. and forms the absorption
side Of the circuit
The theory of operation OF this cir
cult Is very simple. The undesirable
station is tuned to maximum intensity
On the receiver The reflector or left
dIaI is then turned until the signal IS
to the lowest audiblllty pos
sible. The absorption trap is then adj
Iusted until all perceptlble reception
II the undesirable station IS absolute
y eliminated or reduced to negligible
~. The receiver proper can then be
.uned to any other station that Is
wanted without further interference
rom the heretofore offending station
Where more than one station causes
rouble It would be we'll for the opera
or to log the interfering stations and
he proper dial settings for their elm
nation so as to facilitate the proper
unIng Of the receiver. This trap. as
veil as the other traps to.be described.
no change OF wiring IN
he sets to which they are attached,
urther than connecting the antenna q
nd ground to the proper binding pegts
n the trap and connecting the output
the trap or traps to the ground and
erial posts OF the receiver.
Connected In Series.
Fig. 2 shows a simple trap that may
e connected in series with the an
snna or ground as shown. It can be
lada-N-ith co turns Of No "a nee. I
ire on a 1k-Inch cardboard tubing Z
lpped at the 9Th. 10th. 18th and Both .
rms and shunted by a 0O5 mid. vari- y
bic condenser.
Fig. 3 Is a diagram Of trap In
lunt that can be made by winding a
III Of the same dimensions and val
3 az that IN Fig. 2, leaving out the
piping arrangement and shunting II d
ith a variable condenser OF COOS $
I'd. capacity. In addition fixed o
OF .OOO1 MID capacity Is In 4
rted IN the connection that goes 10 .
e antenna binding post Of the set r
shown IN the diagram. d
Fig. 4 gives another arrangement Of a
shunt trap that consists Of an Undue v
nee coil ~ No. "a DEC. wire wound e
tubs "a inches In diameter until ~
ere IL a coil OF wire AZ inches long e
series with this q variable con II