Radar System Engineering

SEC. 16.15] THE STABLE LOCAL OSCILLATOR 661
quencies and different oscillators. If this coupling is too loose, frequency
instability will result. If the coupling is too tight, tuning will be difficult
and the power output from the local oscillator will be reduced. It must
be possible to obtain two to three times the mixer current that will
actually be used. When restarting a correctly tuned oscillator, it maybe
necessary to vary the reflector voltage slightly up and down to cause the
echo box to lock in.
A microwave discriminator circuit developed by R. V. Pound’ gives
promise of overcoming many of the difficulties of the simple echo-box
stabilizing arrangement. Measurements of local-oscillator stability at
3 cm, as reported below, show that this system of stabilization might be
adapted to MT1.
TABLE 16.5.—TYPIcAL LOCAGOSCILLATOR STABILITIES
(
Descriptionof oscillators compared. (cf. Sec.
Frequency average
Frequency band
16.21) of ~, (Kc/secZ) to half-power, cps
Two identically shock-mounted type 417 re- 79 1300
flex klystrons (10 cm) without stabilizing 61 250
cavities 50 140
Two identical type 2K28 reflex klystrons (10 168
I
1300
cm), without stabilizing cavities, in a quiet 100 250
room
I I
Same tubes as above, one stabilized
1
I
137
1300
6S 250
Same tubes, both stabilized 1.4 250
1.4 140
TWO other stabilized tubes of same type in a 3 250
quiet room (more typical value)
Two such oscillators; 60 cps a-c heater power 36
used for one
I
250
Two such oscillators operating in an SCR- 10
584 truck
Two such oscillators operating in the radio 70
compartment of a B-17 aircraft after somewhat
improved shock mounting
Two type 2K25 reflex klystrons (3 cm) in the 20
laboratory with echo-box frequency control
: Described in detail in Chap. 2 of Vol. 11 of the series,