Evening star., 1925-11-22

Mysterious interferences in the
ether never cease, 1t seems.
Radio Supervisor T.. A. Beane of
the Chicago district reports a form
OF radio interference in the broad
casting band which may require
reallocation of channels. When two
hish-powered broadcasting stations,
using either modulated or unmodu-
lated continuous waves, are operated
simultaneously on widely separated
frequencieS, they produce a third fire.
quency in the air. which is quite
sharply defined. They actually hetero-
dyne each other, Mr.. Beane points
| out. This. of course, interferes with
any stations on the wave produced
and broadcast by the two operating
stations
Explaining the, phenomenal to the
interference committee. Mr.. Beane
said: THE principle of heterodyna-
ton is quite well known, of course.
For instance. an oscillator functioning
on given frequency can beat with
another oscillator located in close
| proximity to it, which produces a
/ third frequency. This frequency is
the difference between the frequencies
at which the two oScillators are func-
| tioning. Another frequency equal to
! their sum is also created. Similarly,
| a radio station operating on $50 kilo-
| cycles and another station operating
ON a frequency of 1.200 kilocycles
| will actually heterodyne at radio fire.
| quencieS and produce a third frequen-
cy of $40 kilocycles in the air. AS
this third frequency created by the
two stations may already be assigned
| TO third, on q continuous wave,
| broadcaster, modulated or unmodu-
| lated, Il SO-called beat note is pro.
| duced, running transmission of a third
| station operating on $40 kilocycles.' -
! The reaSSignment of new waves or
| frequencieS should be so arra nged, ac.
| cordinS to Mr.. Beane, that this phe.
nomenon will not take place. It Is
| actually taking place, he has ascer-
| tanned, between broa sting stations
| using continuous waves. Fortunately
| he states, the field strength of the
! third wave or frequency created by
| the two stations on their proper fire..
| quenCleS, Is considerably less than the
| strengths of the original fre1uencies
| so that the use of frequencieS which
may cause such interference need only
be considered within a small radius OF
! two stations which may produce a
third frequency. The third frequency
| created by two 500-watt transmitters
Is reported as only Objectionable for u
! distance of about 5 miles. Two 5000
! watt stations, however, cause this
| difficulty over d radius of approx
| mately 90 miles. If practical the log
| ical assignment of frequencies In the
| future is 10 be made, 1t IS, believed
absolutely necessary that the results
| OF radio frequencieS heterodyning
| each other must be considered.
! Officers Of the Navy point out tha,
| they have taken this phenomenon into
! consideration for some time and use
| frequencies ending in >: any new fre
| quency created by beat notes is there
| fore not an assigned frequency and
| cannot interfere with regular chan
| neis; since their sum or difference
| would necessarily be a frequency end
| ing In 0. 4 reaSsignment by the De
! partment of Commerce to prevent
this form Of interference may he
| undertaken on this basis-that is. In,
| creaSing all assignments by FIVE kiIo.
| cycles, or reducing them that much
| Mr.. Reane's tests in Chicago in.
| cluded several stations, among them
; kiW on $50 kilocycles. and WGY and
WOR on 1.200 kilocycIes. They pro.
| duced Il frequency of $40 kilocycles
| which was unassigned, yet Chicago
| listeners got the beat note created
| Tuning below and above this fre
| quency showed that the adjacent sta.
| lions in the band We're on their prop
| er assignments and were not involved
| In the interference reported