------ELECTRONICS ------SSB-FilterS (PART 4)
ELECTRONICS This is the fourth article of a tivity and stability characteristics, with mtmaturization of equipment.
This is the fourth article of a series from a training course written but their large size makes them Also to the advantage of the me series from a training course written by Collins Radio Company for per subject to shock or vibration de· chanical filter is a Q in the order by Collins Radio Company for per- sonnel concerned with single side terioration. Also, their cost is of 10,000 which is about 100 times sonnel concerned with single side- band communications. quite high. the Q obtainable with electrical band communications. Both SSB transmitters and SSB Newer crystal filters are being elements. Both SSB transmitters and SSB developed that have extended fre receivers require very selective receivers require very selective Although the commercial use of bandpass filters in the region of bandpass filters in the region of quency range and are smaller. These mechanical filters is relatively
100 to 500 kilocycles. 100 to 500 kilocycles. newer crystal filters are more ac new, the basic principles on which In receivers, a high order of ad- In receivers, a high order of ad ceptable for use in SSB equipment. they are based is well established. jacent channel rejection is required jacent channel rejection is required LC Filters The mechanical filter is a me if channels are to be closely spaced if channels are to be closely spaced LC filters have been used at IF chanically resonant device that re to conserve spectrum space. In to conserve spectrum space. In frequencies in the region of 20 kilo· ceives electrical energy, converts SSB transmitters, the signal band- SSB transmitters, the signal band it into mechanical vibration, then width must be limited sharply in cycles. However, generation of the
order to pass the desired sideband width must be limited sharply in SS B signal at this frequency re converts the mechanical energy back and reject the other sideband. The order to pass the desired sideband quires an additional mixing stage into the electrical energy at the out filter used, therefore, must have and reject the other sideband. The to obtain a transmitting fr equency put. The mechanical filter consists very steep skirt characteristics and filter used, therefore, must have in the high-frequency range. For basically of four elements: a flat bandpass characteristic. very steep skirt characteristics and this reason LC f i 1 t e r s are not 1. An input transducer that con
These filter requirements are met a flat bandpass characteristic. widely used. verts the electrical input into me by LC filters, crystal filters, and These filter requirements are met Mechanical Filters chanical oscillations. mechanical filters. 2. Metal disks that are mechani Crystal Filters by LC filters, crystal filters, and The recent advancements in the
Until recently crystal filters, mechanical filters. development of the mechanical fil cally resonant. used in commercial SSB equipments, Crystal Filters ter have led to its acceptance in 3. Coupling rods that couple the were in the 100-kilocycle range. Until recently crystal filters, SSB equipment. Mechanical filters metal disks. Such filters have excellent selec- used in commercial SSB equipments, have excellent rejection character 4. An output transducer that con SSB-Filters were in the 100-kilocycle range. istics, are extremely rugged, and verts the mechanical oscillations
(PART 4) Such filters have excellent selec· are small enough to be compatible back into electrical oscillations. tivity and stability characteristics, Figure 1 shows the elements of but their large size makes them
subject to shock or vibration de- the mechanical filter. Figure 2 ONE SUPPORTING DISK AT EACH [NO....._..,·,,. terioration. Also, their cost is -BIAS WAGNET shows the electrical analogy of the quite high. mechanical filter. In.the electrical Newer crystal filters are being analogy, the series resonant cir developed that have extended fre- cuits L1C1 represent the metal quency range and are smaller. These disks, the coupling capacitors cl newer crystal filters are more ac- represent the coupling rods, and ceptable for use in SSB equipment.
' the input and output resistances R LC Filters '
LC filters have been used at IF WAGNETOSTRICTIV[ _/ represent the matching mechanical - {INPUT OR OUTPUT l ORIVI"G ROO frequencies in the region of 20 kilo- loads. cycles. However, generation of the Transducers
SSB signal at this frequency re- The transducer, which converts Figure I. Elements of mechanical filter. quires an additional mixing stage electrical energy into mechanica1 to obtain a transmitting frequency in the high-frequency range. For Figure 2. F.leclrical analo� of a mechanical filter.
this reason LC filters are not
widely used.
Mechanical Filters
The recent advancements in the
development of the mechanical fil-
ter have led to its acceptance in
SSB equipment. Mechanical filters
have excellent rejection character-
istics, are extremely rugged, and
are small enough to be compatible
ONE SUPPORTING
DISK AT EACH END
COUPLING RODS
BIAS MAGNET
TRANSDUCER
COIL
ELECTRICAL SIGNAL
(INPUT OR OUTPUT ) UNIVERSITY 0 F CALl FORN lA 30 MAGNETOSTRICTIVE BuShips Journal
DRIVING ROD
ELECTRICAL SIGNAL
(INPUT OR OUTPUT)
Figure 1. Elements of mechanical filter.
Figure 2. Electrical analogy of a mechanical filter.
with miniaturization of equipment.
Also to the advantage of the me-
chanical filter is a Q in the order
of 10,000 which is about 100 times
the Q obtainable with electrical
elements.
Although the commercial use of
mechanical filters is relatively
new, the basic principles on which
they are based is well established.
The mechanical filter is a me-
chanically resonant device that re-
ceives electrical energy, converts
it into mechanical vibration, then
converts the mechanical energy back
into the electrical energy at the out-
put. The mechanical filter consists
basically of four elements:
1. An input transducer that con-
verts the electrical input into me-
chanical oscillations.
2. Metal disks that are mechani-
cally resonant.
3. Coupling rods that couple the
metal disks.
4. An output transducer that con-
verts the mechanical oscillations
back into electrical oscillations.
Figure 1 shows the elements of
the mechanical filter. Figure 2
shows the electrical analogy of the
mechanical filter. In.the electrical
analogy, the series resonant cir-
cuits L,C, represent the metal
disks, the coupling capacitors C,
represent the coupling rods, and
the input and output resistances R
represent the matching mechanical
loads.
Transducers
The transducer, which converts
electrical energy into mechanical
30
BuShips Journal ELECTRONICS ------energy and vice versa, may be ical filters will without doubt bring impedances are largely resistive either a magnetostrictive device or an even faster rate of cutoff. and range between 1,000 ohms and an electrostrictive device. Coupling 50,000 ohms. The magnetostrictive transducer In the equivalent circuit, the The insertion loss is measured is based on the principle that cer coupling capacitors cl represent with both the source and load im ELECTRONICS tain materials elongate or shorten the rods that couple the disks. By energy and vice versa, may be pedance matched to the input and either a magnetostrictive device or when in the presence of a magnetic varying the mechanical coupling output impedance of the filter. The an electrostrictive device. field. Therefore, if an electrical between the disks, that is, by mak value of insertion loss ranges be·
The magnetostrictive transducer signal is sent through a coil, which ing the coupling rods larger or tween 2 decibels and 16 decibels, is based on the principle that cer- contains the magnetostrictive ma smaller, the bandwidth of the filter depending on the type of transducer. tain materials elongate or shorten terial as the core, the electrical is varied. The transmission loss is an in when in the presence of a magnetic oscillation will be converted into Because the bandwidth varies dication of the filter loss with field. Therefore, if an electrical mechanical oscillation. The me approximately as the total area of source and load impedances mis signal is sent through a coil, which chanical oscillation can then be the coupling wires, the bandwidth matched. The transmission loss is contains the magnetostrictive ma-
terial as the core, the electrical used to drive the mechanical ele can be increased by using either of importance when using a mechan oscillation will be converted into ments of the filter. larger or more coupling rods. Me ical filter in pentode IF amplifiers mechanical oscillation. The me- The electrostrictive transducer chanical filters with bandwidths where both source and load imped· chanical oscillation can then be is based on the principle that cer as narrow as 0.5 kilocycle and as ance are much greater than the fil used to drive the mechanical ele- tain materials, such as piezo wide as 35 kilocycles are practical ter impedances. ments of the filter. electric crystals, will compress in the 100- to 500-kilocycle range. The transfer impedance is useful The electrostrictive transducer when subjected to an electric Passband is based on the principle that cer- to determine the overall gain of a
tain materials, such as piezo- current. Although an ideal filter would pentode amplifier stage that makes electric crystals, will compress In practice, the magnetostrictive have a flat "nose" or passband, use of a mechanical filter. The when subjected to an electric transducer is more commonly used. practical limitations prevent the transfer impedance of the filter mul current. The transducer not only converts ideal from being attained. The tiplied by the transconductance of In practice, the magnetostrictive electrical energy into mechanical term "ripple amplitude" or "peak the pentode gives the gain of the transducer is more commonly used. energy an d vice versa; it also pro to-valley ratio" is used to specify amplifier stage.
The transducer not only converts vides proper termination for the the nose characteristic of the filter. The physical size of the mechan electrical energy into mechanical mechanical network. Both of these The peak-to-valley ratio is the ical filter makes it especially use energy and vice versa; it also pro- functions must be considered in vides proper termination for the ratio of ma ximum to minimum output ful for modular and miniaturized mechanical network. Both of these transducer design. level across the useful frequency construction. Recent developments functions must be considered in From the electrical equivalent range of the filter (figure 3). A have resulted in a tubular filter transducer design. circuit, it is seen that the center peak-to-valley ratio of 3 decibels that is about 14 inch in diameter by From the electrical equivalent frequency of the mechanical filter can be obtained on a production 1 3;� inches long. circuit, it is seen that the center is determined by the metal disks basis by automatic control of ma Types frequency of the mechanical filter which represent the series resonant terials and ass embly. Mechanical Types of mechanical filters other is determined by the metal disks circuit L1C1• filters with a peak-to-valley ratio which represent the series resonant than the disk type are being used. Skirt Selectivity circuit L,C,. of 1 decibel can be produced with One, the plate type, is a series of
Skirt Selectivity In practice, filters between 50 accurate adjustment of filter ele flat plates assembled in a ladder In practice, filters between 50 and 600 kilocycles can be manu ments. arrangement. and 600 kilocycles can be manu- factured. This by no means indi Spurious responses occur in me Another type that has recently factured. This by no means indi- cates mechanical filter limitations, chanical filters because of mechan
cates mechanical filter limitations, but is merely the area of design ical resonances other than the de Fi�re 3. Mechanical filter character· but is merely the area of design concentration in a relatively new sired resonance. By proper design, istic curve. concentration in a relatively new field. Since each disk represents spurious resonances can be kept field. Since each disk represents
a series resonant circuit, it follows a series resonant circuit, it follows far enough from the passband to ! 1�81_� f �- fl that increasing the number of disks that increasing the number of disks permit other tuned circuits in the • :1.2KCAT·608 ! �-� will increase skirt selectivity of will increase skirt selectivity of system to attenu ate the spurious 101-- j ' ' I PEAK TO ' t ' t VALLEY the filter. the filter. responses. RATie lOB. ' Skirt selectivity is specified as Skirt selectivity is specified as Other Characteristics z : 20� shape factor which is the ratio - . [___j_j g.. ' shape factor which is the ratio Other mechanical filter charac :> S>
ical filters will without doubt bring shape factor of approximately 1. 5. filter frequency. With such capaci
an even faster rate of cutoff. The future development of mechan- tors added, the input and o�.r-put. •Yigma rom Coupling
In the equivalent circuit, the June 1958 UNIVERSITY 0 F CALl FORN lA 31
coupling capacitors C, represent
the rods that couple the disks. By
varying the mechanical coupling
between the disks, that is, by mak-
ing the coupling rods larger or
smaller, the bandwidth of the filter
is varied.
Because the bandwidth varies
approximately as the total area of
the coupling wires, the bandwidth
can be increased by using either
larger or more coupling rods. Me-
chanical filters with bandwidths
as narrow as 0.5 kilocycle and as
wide as 35 kilocycles are practical
in the 100- to 500-kilocycle range.
Passband
Although an ideal filter would
have a flat "nose" or passband,
practical limitations prevent the
ideal from being attained. The
term "ripple amplitude" or "peak-
to-valley ratio" is used to specify
the nose characteristic of the filter.
The peak-to-valley ratio is the
ratio of maximum to minimum output
level across the useful frequency
range of the filter (figure 3). A
peak-to-valley ratio of 3 decibels
can be obtained on a production
basis by automatic control of ma-
terials and assembly. Mechanical
filters with a peak-to-valley ratio
of 1 decibel can be produced with
accurate adjustment of filter ele-
ments.
Spurious responses occur in me-
chanical filters because of mechan-
ical resonances other than the de-
sired resonance. By proper design,
spurious resonances can be kept
far enough from the passband to
permit other tuned circuits in the
system to attenuate the spurious
responses.
Other Characteristics
Other mechanical filter charac-
teristics of importance include in-
sertion loss, transmission loss,
transfer impedance, input imped-
ance, and output impedance.
Since the input and output trans-
ducers of the mechanical filter are
inductive, parallel external capaci-
tors must be used to resonate the
input and output impedances at the
filter frequency. With such capaci-
tors added, the input and output
impedances are largely resistive
and range between 1,000 ohms and
50,000 ohms.
The insertion loss is measured
with both the source and load im-
pedance matched to the input and
output impedance of the filter. The
value of insertion loss ranges be-
tween 2 decibels and 16 decibels,
depending on the type of transducer.
The transmission loss is an in-
dication of the filter loss with
source and load impedances mis-
matched. The transmission loss is
of importance when using a mechan-
ical filter in pentode IF amplifiers
where both source and load imped-
ance are much greater than the fil-
ter impedances.
The transfer impedance is useful
to determine the overall gain of a
pentode amplifier stage that makes
use of a mechanical filter. The
transfer impedance of the filter mul-
tiplied by the transconductance of
the pentode gives the gain of the
amplifier stage.
The physical size of the mechan-
ical filter makes it especially use-
ful for modular and miniaturized
construction. Recent developments
have resulted in a tubular filter
that is about % inch in diameter by
1% inches long.
Types
Types of mechanical filters other
than the disk type are being used.
One, the plate type, is a series of
flat plates assembled in a ladder
arrangement.
Another type that has recently
Figure 3. Mechanical filter character-
istic curve.
*
3rTTTl
30
D6 1 1 1 9t, IK T 0 I VA R LLEY »TI» z ⢠1 k JOB 1 1 o k 20 SHAPE FACTOR < D Z / Ul ZOKC t J.2KC-22 5 jo (/» W 1 a G«o w o I \ / \ 50 \ \ -5 -4 -3 -2 -1 0 tl *2 *3 t4 + 701 c t T-6 ODB i KILOCYCLES FROM RESONANCE June 1958 31 ------ELECTRONICS ------ been developed is the neck-and All mechanical filters are similar They may also have different types slug type. This type of filter con in that they have mechanical reso of transducers. sists of a long cylinder that is nance. They differ in that they The next subject to be taken up turned down to form the necks that have various modes of mechanical by the series on SSB communication couple the remaining slugs. oscillation to gain their purpose. systems is exciters. ELECTRONICS been developed is the neck-and- All mechanical filters are similar They may also have different types slug type. This type of filter con- in that they have mechanical reso- of transducers. sists of a long cylinder that is nance. They differ in that they The next subject to be taken up turned down to form the necks that have various modes of mechanical by the series on SSB communication Operating Controls and Terminals of a Basic Oscilloscope couple the remaining slugs. oscillation to gain their purpose, systems is exciters. Operating Controls and Terminals of a Basic Oscilloscope The following reference symbols are shown in the accompanying schematic diagram of a basic oscilloscope: reference symbols are shown in the accompanying schematic diagram of a basic oscilloscope: Function Home of Reference Changes the d.c. potential of the vertical-deflection plate, and thus controls Function the vertical position of the trace. Control Symbol Changes the d.c. potential of the horizontal-deflection plate, and thus controls the horizontal position of the trace. Vertical R3 Changes the d.c. potential of the vertical-deflection plate, and thus controls Changes the voltage of the grid of the cathode-ray tube, and thus controls position the vertical position of the trace. the intensity of the trace. Changes the voltage of the focusing electrode of the cathode-ray tube, and Horizontal R4 Changes the d.c. potential of the horizontal-deflection plate, and thus controls thus adjusts the focal point of the beam. position the horizontal position of the trace. Changes the voltage of the input signal applied to the grid of the vertical amplifier, thus controlling the amplitude of the vertical signal. Changes the voltage of the input signal applied to the grid of the horizontal Intensity Rl Changes the voltage of the grid of the cathode-ray tube, and thus controls amplifier, thus controlling the amplitude of the horizontal signal. (Input signal the intensity of the trace. is produced by the time-base generator or by an external signal source.) Selects the various sweep capacitors. This switch provides a rough adjustment Focus R2 Changes the voltage of the focusing electrode of the cathode-ray tube, and of the sawtooth oscillator frequency. thus adjusts the focal point of the beam. Provides a fine adjustment of the sweep frequency by controlling the rate at which the selected sweep capacitor is charged. Vertical R5 Changes the voltage of the input signal applied to the grid of the vertical Varies the amplitude of the synchronizing voltage applied to the time-base gain generator, thus enabling the operator to "lock-in" the signal being viewed. amplifier, thus controlling the amplitude of the vertical signal. Provides a means for the operator to select a synchronizing signal from either an internal or an external source. Horizontal R6 Changes the voltage of the input signal applied to the grid of the horizontal Provides a terminal for the connection of an external signal source to the vertical gam amplifier, thus controlling the amplitude of the horizontal signal. (Input signal amplifier. is produced by the time-base generator or by an external signal source.) Provides a terminal for the connection of an external signal source to the hori- zontal amplifier. Coarse S4 Selects the various sweep capacitors. This switch provides a rough adjustment Provides a voltage of stated amplitude for testing amplifier sensitivity. frequency of the sawtooth oscillator frequency. Provides a terminal for connecting the external synchronizing-signal source. These binding posts are used to ground the chassis of the oscilloscope to the at ground of any input signal source. Fine R7 Provides a fine adjustment of the sweep frequency by controlling the rate Allows either an external signal or the internally generated sawtooth sweep frequency which the selected sweep capacitor is charged. signal to be applied to the horizontal-amplifier grid. The following Sync. amp. R8 Varies the amplitude of the synchronizing voltage applied to the time-base reference s generator, thus enabling the operator to "lock-in" the signal being viewed. Name of Control Sync. S3 Provides a means for the operator to select a synchronizing signal from either Reference selector an internal or an external source. Symbol Vertical R3 Vertical Tl Provides a terminal for the connection of an external signal source to the vertical position mput amplifier. Horizontal R4 Horizontal T2 Provides a terminal for the connection of an external signal source to the hon· position Input zontal amplifier. Intensity Rl Test signal T3 Provides a voltage of stated amplitude for testing amplifier sensitivity. Focus R2 Vertical Ext. sync. T4 Provides a terminal for connecting the external synchronizing-signal source. R5 gain Ground T5 These binding posts are used to ground the chassis of the oscilloscope to the Horizontal T6 ground of any input signal source. R6 gain Horizontal S2 Allows either an external signal or the internally generated sawtooth swef'F' Coarse mput signal to be applied to the horizontal-amplifier grid. frequency S4 selector Original from Fine D1g ize b frequency 32 UNIVERSITY OF CALIFORNIA BuShips Journal R7 Sync. amp. R8 Sync, selector S3 Vertical Tl input Horizontal T2 input Test signal T3 Ext. sync. T4 Ground T5 T6 Horizontal S2 input selector 32 BuShips Journal