The Washington herald., 1922-04-11
Simple Crystal Receiver.

S"Phc SEyhtat EheCctNt''
Q. l have a set consisting of 1000
ohm phone, fixed condense-, crystal
detector and an aerial 100 feet long.
What are the next steps in improv-
ing upon this? F. w.
A. With the equipment you have
you could make only the simplest
set-up. Even your phones are of
low resistance. They should be at
least 1000 ohms. To improve on
what you have. purchase or make
a tuning coil. If you buy a loose
coupler you will be able to vary
both your coupling between primary
and secondary circuits and also the
inductance OF either primary or sec
ondary, depe nding on the number
of movable contacts you have on
the coils. II you shunt your second
ary coil with a variable condenser
you will have an inductively cou-
pied receiver, which has given good
results. You can, however. use one
coil. with double contacts; one on
aerial lead. the other on detector
lead, thus giving you a directly cou-
pied circuit. This could be done
with the equipment you have. with
the addition of single coil No. "a,
No. % or cotton covered copper wi.e.
Herald. March IS, gives a diagram
similar to equipment you now have.
Loose Coupler.
Q. (a) What size should the loose
coupler receiving coils be2
(b) How far should they be sep
arated for receiving distant trans
mitting? c. C.
A (a) The size OF the loose cou-
pier governs the amount of induct-
ance in the circuit. Six to eight
inches long and four, five or six
inches in diameter is a fair size for
the primary. The secondary can
be just the size to comfortably slide
within this. / assume by size that
you may mean the size of wire. This
should be No. 90 double cotton COW
cred copper wire for primary and
No. "a or No. &c for secondary.
CD Probably loose coupling with
large capacity in your secondary
circuit will be most effective for the
signals you want. The maximum
sensitiveness of your set can be told
only by trial Tuning is dependent
on the wavelength received. power
of the transmitting station and
interference. Separating primary
from secondary is only one opera
tion in bringing your set into reson-
ance with the incoming wave trains.
The othe1 operations are varying
inductanceN by moving the sliding
contacts on your coil. varying your
capacity by your secondary con-
denser and by sensitive detector ad-
justment. These operations must
sometimes be made simultaneously.
A Battery-AcrinL
Q. (a) Is it possible to use the same
A battery with two different makes
of vacuum tubes. l want to use the
same filament battery with an au-
diotron for detecto- and a radiotron
U. V. pol as amplifier?
(b) How many turns of wire
would be required on an indoor loop
aerial for elimination of local in
reference? J. c. w.
a. (a) You may use the same A
tb5 For the short wavelengths
(2O0 to 500 meters) a loop four feet
on a side with six or seven turns
of No. Is wire. or larger, spaced
about one inch apart. 1t will be
necessary to use a variable con-
denser across the loop fo- tuning.
Most Effective Results.
Q. (a) To the east of my house
are two trees spaced $50 feet apaT,
on each of which l can Obtain Il
height of 20 feet for attaching
aerial. wish to get signals pri-
marily from NNE. but this would
mean that a slanting lead-in would
be required in order to have open
end of aerial away from the send
ing station. Which is preferable.
to have above e-mentioned slanting
lead-in. which would necessarily
be about 100 feet long, or have a
longer fat top and very nearly
perpendicular lead-ln, but with
open end facins sending station?
Thought possibly the height of Ct
to 20 feet obtainable would almost
eliminate any directional effect.
(b) Have the following set: De-
tector and two-step and regenera-
tive. consisting of two variometers
and variocouplers. Bearing In mind
the aerial mentioned in question
(a), its capacity. etc. where in the
circuit could place to best ad-
vantage two .001 condensers Zone
Connecticut and the other a Mu:-
dock) in order to get more selec-
tive results?
A. Yu state NNE. This Is a
ship. Vertical antenna is better.
II you meant NAA you should have
no difficulty with set-up as ex-
planned
CD will have to see your. hook