Boonton 59 Megacycle Meter Instruction Manual

OPERATING INSTRUCTIONS
for
MEASUREMENTS MODEL 59

GENERAL DESCRIPTION

INTRODUCTION

The Megacycle Meter is:
A grid d1p meter
A variable frequency oscillator
An absorption wavemeter
An oscillating detector
A tuned circuit absorption detector
It consists of a compact oscillator corinected to 1ts power sup- ply by a small flexible cord. The tuned circuit coil is mounted externally so that it will be convenlent for coupling to other cir- cuits.
In series with the grid leak are a d-c microammeter and a Jack for insertion of a telephone headset in the circuit.
A switch is provided to remove the plate voltage from the oscillator tube, changing the tube from a triode oscillator to a diode detector. The Model 59 is promptly accepted as a most useful tool.
It is a simple, accurate, and versatile instrument capable of saving much valuable engineering time.

SPECIFICATIONS

Frequency Range:
2.2 Mc. to 400 Mc. with seven plug-in coils.
Modulation:
CW or 120 cycles fixed at approximately 30% or external.
Dimensions:
Power Unit 5-1/8″ wide; 6-1/8″ high; 7-1/2″ deep, wt. 6-1/2 1bs.
Oscillator Unit 3<3/4″ dia.; 2″ deep; wt. 1 1b.
Power Supply:
117 volts, 50-60 cycles, 20 watts.
Tubes:
One type 955 oscillator
One type VR-150/30 regulator
One type SY3GT rectifier

OPERATING INSTRUCTIONS

a. Setting up:
The Megacycle Meter consists of three units: The power supply, coil set, and oscillator unit.
It is convenlent to remove the coil set from 1ts storage space in rear of the power supply and clip 1t in place as shown in Figure 1A. This permits free access to the coils and provides a definite place for unused coils.
Do not allow unused coils to lie scattered about on the work bench. They are easily lost or camaged. These coils are individually calibrated for each oscillator unit and serially numbered; therefore replacement usually involves re-calibra- tion. For storage position of coils see Figure 1B.
Check power supply voltage and frequency.
411 standard Model 59’s are designed for operation on 117 volt, S0-60 cycle power.
If the supply is correct, plug in the power cord and switch on by £11pping up the power switch at the right side of the power unit.
After 30 seconds warm up period the meter should ndicate to the left 1f switch 1s on DIODE, or up scale if a coil is plugged into the oscilla- tor unit and switch is set on CW or MOD.
Adjustment of the SENSITIVITY knobd will sel the osclllating grid current to some conveni- ent value on the 0 to 100 scale.

b. Selection of Cotle:
Frequency ranges are mérked on each coil except for the two highest frequency coils. Fre- quency limits of the corresponding scales are marked on the osciliator unit. After insertion of the cestred coil, it 1s advisable to set ‘the tun- ing knob to mid-scale, and then ad‘tust tne sensi- tivity knob to approximately 50 on the grid cur- rent meter. Normal variation of the grid current with tuning will then usually remain on scale over the entire range of that particular coil. (Note: on some low frequency coils it may be necessary to readjust the sensitivity knob at the extremes of the tuning range. )
c. Adjustment of Coupling
Either inductive or capacitive coupling of the 59 can be made to circuit under test.
For most tuned circuits it may be more convenient to utilize inductive coupling. A simple 1llustration of a typical circult is  shovn in Fig- ure 2. This represents a comucn by-pass difficulty which glves rise to cead spots in high freguency receivers and transmitters. Maximum coupling (and largest dip in grid current) wtll result with the axis of the oscillator coil at right angles to the current flow. For accurate checking of the reson- ant circult frequency, the coupling should be loosened by increasing the separation between the oscillator coil and the circuit under test until only a moderate dip in grid current (10 to 20%) results when tuning through resonance Some types of tuned circuits are well shielded magnetically, so that’it is difficult to utilize inductive coupling. Figure 3 illustrates such a circuit. This co-axial line resonant cir- cuit is self shielding and of sufficiently high  This 11lustrates the arrangement of the oscillator coil at right angles Lo the currenl flow for maximw coupling to the resonant circuit.
“Q” to permit the use of the capacitative coupling obtained by placing the open or “hot” end of the circult near one coil terminal of the Model 9.
This stray capacitance coupling may not be suffi- clent for loaded circuits, such as might be used in television pre-selectors, etc. For these ap- plications, 1t may be necessary Lo use a one or two micromicrofarad coupling capacitor. This can be obtained by twisting together an inch or two of hook-up wire. This capacitance should be kept as small as possible, since 1t will affect the frequency calibration accuracy of the Model 59.
Fortunately 1t 1s not usually required that loaded (low “Q”) circuits be located as accurately in frequency as higher “Q” ones.
Completely enclosed resonant cavities usually have some type of coupling loop which can be utilized with the aid of an auxiliary ex- ternal transmission line and coupling loop as a 1ink coupling arrangement for coupling inductive- 1y to the Model 59.* This 1llustrates capacitive eoupling to a quarter wave co-axial stub.
d. Modulation:
Intemms) 120 cycle modulation can be ap- plied ty turning the switch to MOD. This may help ifentify the signal from the S9 in the vresence of cther siznels when working on receivers, etc.
External meculation can be applied dy a standard phone plug in the jack marked “EXT. MOD.”. About 20 volt (r.m.s.) are required for 30%.
e. Use of Phones:
Phones can be plugged into the PHONE jack for indication of the dip. A sharp click accom-
Panties the dip in gric current fcr conventional eacplication.
If indication of frequency of an ogcilia- tor {s required, the phones will permit use as a high sensitivity oscillating detector with its resultant zero beat method of accurate frequency determination. For some types of “Q” measure- ment, this may be useful in measuring 4 f (see Section V(d).). AS a nen-oscillating, diode detector (switch on DIODE) the identification of modulated signals, oscillator harmonics, sound of parasitics of blocking character, etc. will be found very useful.

USE IN RECEIVER DESIGN AND ALIGNMENT

As a typical application of the Model 59, its use in the construction of a television receiver is presented herewith. This application involves the construction of video amplifiers with their peaking coils, low pass filters, high pass filters bandpass filters, discriminators, traps, oscilla- tors, etc.
a. Video Output Design:
In order to select a suitable peaking ar- rangement for the video amplifier the actual input and output capacitances should first be measured (as described in Section V(a).) with the Model 59 Next by reference to a suitable handbook, a peaking circuit can be selected and the values of peaking coils calculated. These coils can be measured with the Model 59 (as described in Sec- tion V(b).) Their lowest self-resonant frequency can also be measured directly.
It is desirable in most instances that this self-resonant frequency be considerably higher than the highest frequency to be transmitted through the video amplifier.
1t carrier difference type of sound is de- sired, the circuit shown in Figure 4 may be useful.
This utilizes series-shunt type of peaking with an inductively coupled 4.5 megacycle trap for sound take off. The 4.5 megacycle trap circuit should be resonated by means of the Model 59. The fm discriminator should be aligned by means of a Sweep generator with the 59 serving as a trace marker. This can be accomplished by merely coup- 1ing in the 59 to secure a beat note superimposed on the oscilloscope trace as shown in Figure S.
If a sweep generator 1is not avallable, the 59 can be used by fixing the coupling to Lz and Lg at a satisfactory value to permit taking a d.c. dis- criminator characteristic with the aild of a high resistance d.c. voltmeter (such as our Model 62).
The secondary of the discriminator should be tuned for cross over at 4.5 megacycles, while the pri- mary should be tuned for symmetry of the positive and negative peaks.
If necessary, the coupling between the primary and secondary should be ad- Justed to separate the peaks by at least 200 kilo- cycles or more.
Figure 4 indicates the use of d.c. trans- mission with negative polarity input video signal as would be obtained from a detector shown in Figure 6. The use of this arrangement has several advantages: such as, economy of tubes since high level video of the correct polarity 1s available for sync clipping without extra tubes, no extra d.c. restorer and its time constant, absence of grid current in presence of strong signal, so that all interference is essentially black, etc.
b. Video Detector Filter Design:
Improved detection efficiency and overall stability can be obtained through the use of a simple “constant K” low pass filter between the  video cetector and the video amplifier stage as shown in Figure 6. The design of this filter involves first a determination of the input and output capacitances with the Model 59 (Section V(a);) then a calculation of the load resist- ance frem the desired bandwidth.
An examination of thé equations for this filter shows that the resonant frequency of the series coil in parallel with the sum of the in- put and output capacitances should be twice the cutoff frequency of the filter. This relation 15 quite useful In remembering the design for- mula for low pass filters; for thus, the product of L and C (inductance and capacitance) are de- termined. The other relation with regard to impedance level is given In Figure 6.
It 1s usually necessary to add about S mmfd. input capacity when using IN34 type video detectors, in order to secure proper operation of the filter. The lowest self-resonant fre- quency of the series coil should be at least as high as the 1.f. pass band in order to obtain good 1.f. rejection. If the self- resonance does occur at the 1.f. frequency, a rejection peak will occur at this frequency. This type of filter then resembles the “m-derived” type rather than the simple “constant-k” as shown in Figure 6.
The video detector is polarized for nega- tive output in order to operate properly with the single video stage shown in Figure 4. Obviously the detector polarity does not affect the opera- tion of the filter, however.-
c. Video I.F. Bandpass amplifier Design and Alignment:

1. Stagger tuned (single tuned circuit) amplifiers can be very successfully used for tele- vision 1..’s; however, it has been pointed out by Wallman* and others that the distribution of stag- gered frequencies and correct loading for each circuit can best be calculated by attention to mininun phase non-linearity. After the correct frequencies have been determined, each tuned cir- cult can be easily adjusted by means of the Model 59; then the correct load resistors can be placed across each circuit and the resultant comdination checked for uniformity of amplitude response by means of a sweep generator and the Model 59 as the sweep marker. Some sacrifice in stage gain results from the use of stagger tuned circuits.
   A hopeless phase characteristic will result, if choice of staggered frequencles and loading is based only on observation of the resultant amplitude response.

2. Stagger tuned amplifiers can also be made by alternating single and double tuned cir- cuits with proper choice of load and peak separa- tion.** Again the location of resonant frequencies can be determined by the Model 59, and the separa- tion of the double tuned peaks can be adjusted by a temporary reduction in loading for more accurate indication on the Model 59.

3. Double tuned circuit amplifiers! can be adjusted by first loading down one of the circuits and setting the unloaded circuit to approximately the correct center frequency; then loading it and removing the load from the other circuit to permit setting 1t to the correct center frequency also.
   Then both loads can be applied and the coupling in- creased, 1f necessary to secure proper bandwith.
   The location and separation between peaks can bde also measured with the 59. After loading and *Wallman, B., “Stagger Tuned I.P. Amplifiers”, Radiation Laboratory Report #524, Pebruary, 1944.
   Baum, R.F., “Design of Broad Band I.P. Amplifiers”, Journal of Applied Physics, Volume 17, Pages 519-721.
   Wight, A., “Telaviaion Receivers”, RCA Review, March, 1947, Page 10.
   **Terman’s “Radlo Englineer’s Handbook”, Page 172.
   Trerman’s “Radio Engineer’s Handbook”, Pages 154-162.
   Lersen, M.J. and Merrill, L.L., “Capacitance-Coupled Intermediate Prequency Amplifiers”, Proceedings of the I.R.E., Page 71, January, 1947.
   coupling aajusuwnt nas been wuyleted, a slight retuning will usually be necessary. In checking such heavily loaded circuits, it is necessary to uee rather tight coupling to the Model 59; this should be clone in such a manner as to avoid seri- owly shlrting the callbrated rrequency or the 59.

4. Triple tuned circuits’ and cther topes of 1.f. dand-pass amplifiers cam usually te ad- gusted in a manner similar to that outlined etove for dcuble tuned circuits.

5. Traps for sound rejection and adjacent channel rejection can be resonated to the correct frequency by the Model 59. Care shculd be taken not to couple too tightly to trap circuits, since their high °Q” will result in freguency reaction on the calibrated frequency of the Model 59. (This effect is sometimes referred to as “frequency pulling”).

6. Sound 1.f. circuits can also be adjust- ed to the proper frequency, if the frequency dif- ference method of sound detection 1s not to be used as previously mentioned under Section II c.(3) above.
   Overall 1.f. sweep characteristics are usually checked with a suitable sweep generator. The Model S59 can be loosely coupled to the 1.f. input and thus serve aS a convenient beat type marker for accurate frequency identification.

d. Input Circuit Design and Alignment:
The Model 59 can be used to adjust the re-celver local oscillator to the correct frequenciesSome input systems may utilize harmonic (usually 1.f. plus carrier). Then the carrier circuits can be adjusted to the correct carrier frequency, and the separation between peaks of the bandpass measured.
When grid mixing circuits are employed with too.much coupling to the oscillator, some oscilla- tor pulling will be apparent. The circuits should, of course, be adjusted with loose coupling, and the coupling then increased just surriciently to pro- duce saturation of the converter. Without the aid or the Model 59, it is possible to obtain rather misleading apparent increases ln converslon gain when the carrier circuits are badly mlstuned. Wch valuable time can be saved by proper setting of the various circuits to the correct frequency first berore use of the signal generator for rlnal adjustment of coupllng for optimum conversion gain.
Some input systems may utlllze harmonic operation or push-pull input, parallel output con- verters, etc. All or these more complex circuit arrangements can be readily aligned with the aid of the Model 59. In many cases it is not neces- sary to apply plate voltage to the amplifiers, etc.; thus reducing the shock hazard when making connections and peeling turns. This also saves the usual wait ror the tubes to warm up ror test agaln between adjustments.
Some types of co-axial cavity tuned circuits may require a small. capacity coupling or the use of link coupling because of their inherent shielded construetion. Fortunately most or these circuits are usually very high “Qn and require only slight coupling for adequate meter dip.
Since there my be many radio services operating in the i.r. pas’sLband or the average television receiver, it is rrequently deslrable to make use or auxiliary rejection filters to re- move this interference rrom the picture. One or the simplest such rilters consists or three or rour “constant K” high pass sections between the transmission line and the input or the receiver.
This type of rilter is the inverse of that men- tioned under Section II(b). An examination or the equations ror the high pass rilter shows that the resonant frequency or the shunt coil and series capacitance Should be one halr the cutorr rrequency or the rilter. Thus the product or L and c are determined, while the other relation with regard to impedance level can be obtained rrom Figure 7. The lowest selr-resonant frequency or the shunt coil should be rather high, and the lowest series reson- ant rrequency (as determlhed by shorting the coil) should be well above the carrier rrequency range to be transmitted. All these selfrescnant fre-quencies can be determined by the Model 59. It will be round that sbple spaced solenoids or small diameter or spiral wound coils will give low values or distributed capacitance with resultant high selr-resonant rrequenc lea. some sell-reson- ant rrequencles will be round in a pie-wound r.i.
coil which are independent or whether its termin- als are open circuited or shorted, 1.e. neither series or parallel resonances. resonances to be avoided in the operating rrequency range ror most applications in filters.
These are internal Of course, absorption type traps can be used to remove unwanted interference not in the carrier pass band or tha receiver; and these can be adjusted approximately by the Megacycle Mcter.
A rinal exact adjustmnt for minimum interference under actual operating con4itions will usually be helpful, since such a trap must be high Q to be errective, and thus necessarily somewhat critical or tuning.

USE IN TRANSMITTER DESIGN AND ADJUSTMENT

The Model 59 orrers considerable time saving and reduction or electrical shock hazard, since it is possible to make many transmitter measurements and adjustments with the power turned off. In the final power stages neutralization and pre-tuning by use of the Model 59 berore application of plate power will reduce rireworks and damage to tubes.
a. Application toAudio Modulstors:
Most modern audio ampliriers employ high mutual conductance triodes and pentodes. Long cabled leads, stray mutual coupling, etc. combine to produce undesired spurious oscillations out or the range or audlbility. Sometimes these errects can be seen on an oscilloscope connected to the audio output, but orten the :requency or spurious oscillation may be too high to be transmitted through the oscilloscope amplirierp. The Model 59 may be coupled to the output or the audio ampli- fier and used as an oscillating detector with a pair or headphones to locate the spurious oscilla- tion by tuning slowly thfough the high frequency spectrum. tone to the amplifier in order to produce tb spur 1 ous osclllation.
It may be necessary to apply a steady These spurious oscillations can usually be eliminated by inserting a small non-inductive damp- ing resistor or 10 to 100 ohms in the grid and plate Leads or the orrending tubes. In general, it is good practice to always use such resistors with high s, tubes in audio amplirlers.
ally it may be necessary to put these damping re- Occaelon- sistors in the screen leads or beam tetrodes as well.
The oscillation can be localized by use or the Model 59 as an exploring probe to lochte the region or most intense oscillation. The senaitl- vity bi the Model 59 can be conveniently reduced, if necessary, by use in the non- oscillating or ‘DIODE’ condition.
D.C. amplifiers sometimes used in voltage regulated power suppl’ies, television transmitters, test equipment, etc. may exhibit erratic performance which can be Cracea, through application or the Model 59, to spurious oscillation and rensdied by proper application of damping resistors as pointed out above.
b. Use in Master Oscillator Stages:
The transmitter master oscillator circuit can be tuned up berore power is applied by coup- ling the Megacycle Meter (‘CW” position) to the oscillator “tank” circuit, then the Model 59 is tuned ‘&rough the appropriate range until a maxi- mum dip or the meter is found with as little coup- ling between the Megacycle Meter and oscillator tank circuit as possible.
two tuned circuits, such as the tuned-plate tuned- grid circuit, each circuit is tuned separately.
When an electron coupled oscillator is used, and the plate circuit is operated on a harmonic, the If the oscillator has plate circuit is readily tuned to the hannonlc with the Megacycle Meter in the same way.
Crystal oscillator circuits are tuned in the same manner. After power is applied to the crystal oscillator, it may be necessary to slight- ly detune the crystal tank circuit ror maximum stability in accordance with well known crystal requirements.
wlll usually require application or power for Pierce crystal osc illator c ircuits proper adjustment.
c. Use in lZlnipg Butler Amplirler Stages:
Interstage burrer amplirier circuits are tuned with the Model 59 in the “CW” pOSitlOn. All tubes should be connected in place. The tuning can be done with no power on the tubes. If double tuned circuits are used, the circuits should be tuned berore coupling together or the circuit coupled to the one being tuned should be heavily loaded so that its tuning is very broad and it does not arsect the tuning of the circuit under test very much.
Tuning the ampllrier interstage coupling clrcults with power orr is an approximate method, When the amplirier tube is put in operation the capacitance or the grid circuit may change rrom that or the “power oft” condition. Slight retun- ing may be necessary, depending on the relation of the change in capacitance to the total capaci- tance or the circuit and also depending on the Q of the circuit, or broadness or tuning.
Harmonic mpllriers can also be readlly adjusted by use or the Model 59 prior to the ap- plication of power. Arter application or power, the Model 59 can be used as a wavemter in the non-oscillating condition marked “DIODE” to kcl- just grid drive and other circuit parameters (such as bias, screen voltage, etc.) for maximum harmon- ic rrequency output.
Ir the burrer amplirier is to work into an appreciable load, optimum coupling to the load can be determined when the “DIODE” reading drops to one hair on connection or the load. or course, it wlll be necessary to keep the Coupling of the Model 59 to the output tank constant during the deter- mination of this optimum halr voltage loading ad- justment. NUTE: The meter adjustment knob should be set all or the way to the right (clockwise), and coupling of the Model 59 to the amplifier tank loosened, if necessary to keep the meter on scale; othemise the meter bucking circuit will spoil ac- curate determination of the .half voltage point.
NOTE: Either pure mutual inductance or pure capa- citance coupling, must be used. A combination or both will yield erroneous results.
d. Final Power Amplirler Tuning:
The rinal power amplirier can be tuned without application or power as suggested above under Sectlon III(c).
neutralization can be errected through the proper 11 necessary (as in triodes), use or the Model 59 as outlined below in Section III(e).
Determination or optimum output loading can be made by the use or the Model 59 ror halr voltage determination as’suggested above in Sectlon III(c), except that more care is required in re- tuning arter connection or antenna load, since most antenna circuits will exhibit some reactive component which must be tuned out.
CAUTION:
on high power transmitters, care must be taken not to damage the Model 59 by coupling too closely when ruii plate power is applied. Ir any doubt exists as to the posslbllity or damage, it is well to either remove the instrument rrom the inmediate vicinity or detune the 59 sufrlciently when power is applied for the flrst time.
Caution must be exercised to avoid accidental contact with high voltage parts or the circuit during “hot.” measurements. Fortunately the sen- sitivity or the Model 59 is sufficient to permit ample distance separation in most normal transmlt- ter circuits. If close coupling.ls necessary, a sheet of polystyrene or other suitable insulatlon should be kept as a guard between ‘hot” circuits and the Model 59 probe assembly.
The Model 59 can be used to indicate the hannonic or sub-harmonic content present in the output or the transmitter by simply tuning to the various possible rrequencies and comparing the “DIODE” readings, while keeping the coupling con- stant. The presence of appreciable hannotfics not only re?resents a waste of power, but a nuisance to other services and a violation or the law.
Suitable filters should be installed between the transmitter and the antenna to remove tbse ex- traneous rrequencies. The errectiveness or such rilters can be checked, ir surricient power is available, by proper use or the Model 59 when bandwidth (in the case of broadband circuits), There are several-methods or using the Me1 50 to indicate nedxallzation or the various stag68 in a transmltter. Figure 8 illustrates the reaction method which is userul where it is dangerous or impractical to apply driver power to the stage to
be neutralized, as is required in the method or Fim 9,
Feedback can occur in many ways, but the one most frequently encountered (in properly con- structed circuits) occurs in the internal plate to grid capacitance or triode type ampiiriers,* Most tetrode and pentode type tubes of proper design in suitable circuits should not require neutraliza- ti0n.t coupled to the antenna. Care should be exercised not to couple too closely and damage the instru- ment. Readings taken at the harmonic rrequencies with and without the rilters in place will indi- cate their relative errectiveness. Of course the power lnput to the rinal should remain about the same, and the coupling or the Model 59 to the antenna should be constant during the tests.
e. Neutralization:
The purpose of neutralization is to pre- vent feedback in an mplirier which would tend to produce oecillation or instability in gain or There are various well bown methods tor neutralizing or balancing out the undesirable coupling between plate and grid circuits.”
general it can be seen that when the tube is not operating, it should not be possible to transrer energy rrom the input to the output circuit or In vice versa. The procedure in the case of the method or Figure 8 is to rirst tune the input and output circuits to the proper rrequency with the neutralizing control set for minimum; then slight- ly detune the input circuit and couple the mega- cycle meter to thls circuit, until only a slight decrease in grid current (“CW”) remains when the Model 59 is set to the frequency of the output
Oramr, Oeorge, “Keeping Your Earrnonlcs at HOM” Q.s.T., NOV. 1946, Pager 13-19.
*”The Rad10 Amateur’s Randbook”, 1947, pages 101-104.
tmh, Donald, “Operating the 80?”, Q.S.T., Hay, 1946, Page 53.
“No Meutrellsation~On Required”, Q.S.T., June, 1946, Page 40.
circuit (the proper aperatihg’ Ire- quency). Then swing the output tuning through resonance and note the reaction on the grid current.
Next slowly increase the neutral- izing control while the output tun- ing is swung back and forth through resonance, It will probably be ne- cessary to couple more closely to the input circuit after a rough ad- justment of the neutralization has been made to obtain improved lndi- cation sensitivity on the Model 59.
It may also be necessary to further detune the input circuit when this is done. After finding the setting which reduces the reaction to a minimum retune the input Circuit with the aid of the Model 59 and the amplifier should be well enough neutralized to prevent self-oscil- latlon. For more complete neutral- ization it may be nesessary to use the method of Figure 9. In Figure 9, driving power to the amplirier stage to be neutralized is applled, and the Model 59 is employed In the “DIODE” position a8 a tuned deteator to indicate the presence or signal in the output circuit. Of course no plate voltage is ap- plied to the amplifier, so that any drlvlng power present in the output is preslupably there as a re- sult of grid plate capacity of the amplifier tube. Obviously, poor circuit layout and lack of shield- ing will also contribute to coupling between these two circuits with resultant difriculty or complete neutralization.
There is some interaction of plate tuning and adjustment or the neutralizing capacitor in Figure 9. It is necessary to retune the plate tank for maximum and then readjust the neutralizing Control for another minlmup. It may be necessary to COUDh the Model 59 more closely to the output circuit for greater sensitivity of indication after partial neutralization has been completed.
f. Parasitics:
If the circuit conditions in an r.f. oscil- lator or amplifier are such that self-oscillation exists at some rrequency other than that desired, the spurious oscillation is termed a parasitic.
Such spurious erfects In audio modulators have been previously mentioned in Section I11 (a) above.
If parasitics &re present, the Model 59 can be used as a tuned detector to detect thir approximate rrequency by the use or headphones or “diode” current indications. After their approx- imate frequency has been located (usually non- harmonically related to the desired frequency) , the power to the amplifier or oscillator can be turned off, and the Model 59 used as a grid dip meter to locate the exact tuned circuit causing the parasitic.
sorption (inductive coupling) are places where a small resistor can be inserted in series to damp out the parasitic. Or lr series damping is not feasible, the points or maximum voltage absorp- tion (capacitive coupling) are places where a high resistance Can be shunted across to damp out the paras it IC.

USE IN ANTENNA ADJUSTMENT

Since most antennas are relatively high “Q” circuits with distributed constants, only very loose coupling to the Model 59 need be used. It will be necessary to couple inductively to the cur- rent maxima or capacltlvely to the voltage maxima.
Most antennas have harmonic mode responses which can also be located and measured by the Model 59. Both harmonic and fundamental rrequency mea- surements can be made with the swiqch In the “CW” position, and no power applied to the antenna under est. This lessens the possibility or interrer- ence to others during antenna adjustment.
The shift or antenna resonant rrequency with addition of rerlectors and directors can be observed with the Model 59. Loading coils and other shorten- ing devices can also be adjusted with the Model 59.
The Model 59 can be used as a field strength indlcator in the “DIODE” position, and when placed at a suitable distance from transmitter antenna arrays, it can be used to indicate proper adjust- ment of the array spacing for maximum output sig- nal. Alternatively it can be used as a signal source (in the “MOD” position) ror the adjustment of antenna arrays with the aid of a receiver as a signal strength indicator connected to the antenna.
The Model 59 can .be used to determine whether a transmisslon llne is properly matched at a par- ticular frequency, by operating in the “DIODE” po- sition and coupling to the transmission line as shown in Figure 10. surricient coupling should be used ror a reliable readlng with power applied to the transmissioh line, then the coupling should be held constant as the Model 59 probe is mo?d at least 1/4 wavelength along the line. If no appre- ciable variation in indication can be noticed, the line does not have standing waves and is correctly terminated at that particular rrequency.
The above method cannot be applied to coaxial lines; hence it is usualfy customary to adjust the load and matching network ror maximum output; since under conditions of maximum output, the line must be matched. For determining maximum output the Model 59 can be used in the “DIODE” condltlon as a rleld strength indicator suitably coupled to the radiating antenna.
Matching stubs can be pre-adjusted to tb proper rrequency by observation or their resonant rPequenCY with the aid of the Model 59. Quarter- wave stubs should be shorted at one end and coupled inductively to the Model 59. (See Figure 11) It will be possible to locate several odd-harmonic modes also.
Hair wave stubs should be iert open and in- ductive coupling to their center utilized ror checklng natural resonance. For coaxial half wave stubs capacitative coupling to one end can be used.
In this case several even harmonic modes may also be located.

MEASUREMENT OF C, L, M, AND Q

a. Heasurement of Capacitance:
The Mcdel 59 can be used for measuring capacitance, if a standard inductance is available.
The coils of the 59 can be used as standards, and reference to Figure 12 indicates directly the shunt capacity which must be used to resonate each coil to a particular frequency. In order to mea- sure capacitances between 10 mUd. and 50 mmf., it will be necessary to purchase a spare 5 to 10 mc.
coil. Figure 13 shows the use of standard meller #SRS cllps and one of the Model 59 coils in the measurement of input capacitance of a vacuum tube and its associated socket.
NOTE: Some Circuits may involve Capacitance shunted by resistance; therefore the approximate minimum permissible shunt resistance for each coll is indicated on Figure 12. Higher values of shunt resistance will permit more accurate measuremente.
In the case of large capacitancss in the range of 200 to lo00 mnfd., it may be necessary to take precautions in securing good contact and thus avoid high series resistance, which would have the same detrimental effect on accuracy of indication as low shunt resistance. It is also well to bear in mind the possibility of internal series induc- tance of the capacitor under test. This internal inductance may alter the apparent capacitance con- siderably.
b. Measurement of Inductance:
The Model 59 can be used for the measur- ment of inductance with the aid of a standard capacitor. Close tolerance silver mica and cera- mic capacitors are generally available over a wide range or values. Only the small units should be used to reduce the self lndpctance of the Capacitor standard. If necessary, the value of unknown capacitors can be determined as outlined above in Section V(a) so that they can be used as standards for the measurement of inductance. It is well to avoid the use of large air dielectric type capacitors because of their high inherent self inductance. It is only necessary to connect the induc- tor to be measured to the standard capacitor with the shortest possible leads wd manure the re- sultant resonant Srequency with the Model 59 as a grid dip meter. Then the actual total Circuit inductance can be read Srm! t.b chart OS Figure 14.
For maximum accuracy the inductor should be re- placed. with a short copper strap (about 1/2 inch wide,) and the new resonant Srequency or this com- bination determined with the Model 59. Then rind the inductance OS this latter combination from the chart OS Figure 14 and subtract this value Srom that: previously measured. he dirserence IS the true inductance of the inductor.
Since the presence of shields, tuning slugs, etc. may seriously armt the value or an inductor which is to be measured, it lpay be neces- sary to leave the coil in place tor msasuremsnt.
In this case, it will.be necessary to disconnect any tuning capacitor, tubeg,.and other capacitors associated With the coil to be measured, besore connecting the standard capacitor across the in- ductor.
c. Measurement OS Mutual Inductance:
Mutual inductance OS two coils can be mea- sured by Sirst connecting the coils in series ald- ing and measuring the resultant inductance as described above in Section V(b), and then connect- ing the two coils in series bucking and again mea- suring the resultant inductance. The disterence in inductance divided by rour is the mutual ln- ductance.
Figure 15 outlines the above procedure step by step. The use or the ~odel 59 permits mutual inductance measurements to be made near the actual operating Srequencies. In some circuits this may be or considerable advantage over lower Srequency measurements. Lower valu~s OS mutual inductance can be measured with the Model 59 than those possible on most low Srequency bridges. d. Measurement of Q:
The. Q of a tuned circuit is a measure of its rigwe of merit.
the ratio of energy stored to energy lost per cycle; the ratio of shunt resonart to series It is defined variously as resonant induced voltage; the measure of the se- lectivity or a tuned circuit at 0.707 down from resonance , e tc.
Frequently one also speaks of the Q of a coil or a capacltor. This is merely the recipro- cal of the power factor (for values larger than 10) or dlssipatlon factor.’
A relative measurement of ‘Qn can be made by observing the sharpness of the dip in grid cur- rent when the Model 59 ls tuned through resonance.
This procedure is very simple and speedy in appll- cations where an approximate determination of “Q” by the comparative method is sufficient.
At the higher frequencies it becomes dlffi- cult to separate the inductive and capacitive com- ponents of a circuit. Therefore a method of ma- suring clrcult Q is shown in Figure 16A by measur- lng the selectivity or a tuned circuit. Alternate methods of reducing error due to vacuum tube volt- meter input loading are shown in Figures 169 and 16C. This measurement requires the use of awll- iary equipment which can be simply constmcted, since only relative calibration of amplitude is required of the vacuum tube voltmeter. In some cases the circuit will have associated with it a vacuua tube amplifier which can itself be made tc function as a voltmeter by suitable biaslng of its grid circuit and the insertion of a meter for reading d.c. plate current. Its relative cali- bration can be made at audio frequency if neces- sary.
For high Q circuits it may be difficult to read the bandwidth closely enough on the tuning dial of the Model 59. In this case an auxiliary unit such as a frequency meter may be used for accurate measurement of the two “.71” rrequencies.

SERVICE AND MAINTENANCE

a. Replacement of Tubes:
The vacuum tubes in the Model 59 ere con-servatively operated and should provide long ser- vice life unless tie instrument is abused by rough handling.
tion; however, the 955 oscillator tube may show Aiter several hundred hours of opera-signs of reduced output by lower readqgs or grid current on the highest frequency coil. When this occurs it may be necessary tomplace the 955 in the probe.
To replace the 955, remove the tuning knob and the three screw8 around the edge of the probe assembly. Then lift the dial cover from the probe; thus exposing the calibrated tuning dial, etc.
Next remove this calibrated dial, taking care not to touch and mar the calibration numbers. (This dial should be kept face up and covered during the time it remains out of the probe to prevent dam- age). The cathode Clip must be slipped loose radi- ally ffrst. The 955 can then be removed by a Ellght twisting, counter-clockwise motion, after disen- gaging the cathode clip. Next insert the new 955 and twist slightly into place. Take care to see that all four pins line up properly. Do NOT FORCE into place. Forcing is not necessary, if the radial tube pins are properly lined up with their respective clips; application of excessive force wlll probably damage the alignment of the tuning condenser. After twisting the new tube into place properly, slide the cathode (center pin) contact clip into place. Next replace the tun- dial and three mounting screws, again exercising care not to smear the printed numbers. Replace the dtal cover and knob and leave the three cover screws slightly loose, 80 that it will be possible to rotate the dial cover (permitted by the three slots around the fastening screws). Turn the tuning knob as far as it will go clockwise and adjust the po- sition of the fiducial so that it falls over the long end mark on the dial. Tighten the three case SC rews .
During the above procedure, care should be exercised to prevent placing the probe and oscil- lator coil too close to any metal object which mlght seriously affect the frequency or the oscil- lator.
It 11 not necessary to couple closely to the receiver or frequency meter for zero beat against the standard frequency source. Replacement or the rectifier and voltage regulator tube will seldom be required. Aged regu- lator tubes sometimes become erratic and their out- put voltage will fluctuate, resulting In erratic grid current. Occasionally new regulator tube: may also be erratic. Any tube which exhibits jitter or unstable operation should be replaced.
b. Circuit Failure:
Most circuit failures wlll be evident from indications of the grid current meter and reference to the schematic diagram, Figure 17. Failure to oscillate will usually result, if the probe ha6 been dropped and one of the ceramic variable tunlng eapacltor supports has been broken. It is advisable to return the instrument to the factory for repair in this event. Replacement of the ceramic is a major repair and will require re-callbratJon of the frequency dial. If return is not possible, after replacement of the ceramic support, it wlll be necessary to center the stator approximately and then set the frequency callbration as closely as possible by the roiiowlng process. Put the lowest frequency coil in position (with the serial numbered side UP tmard the tULng dial side of the probe). Be sure it is fully inserted or bottomed in the jacks. Then allow about 5 minutes for the instrument to warm up.
dial until it reads approxlmately 5 mc. and locate exact zero beat note with W. Then turn dial down to 2.5 mc. and note displacement of beat note from the calibration mark. Rotate cover and fidu- cial to registration, if the displacement is about the same as at 5 mc. If the amount is more or Rotate the tuning less than that at 5 mc., split the difference by rotating the cover and fiducial.. Tighten the three screws so this adjustment will not slip.
A slight readjustment of the dlal cover md ilh- cia1 may be required.
A delted coil ‘can be ascertained by visoal inspection and use of an ohmeter.
mechanical manuracturing limits are maintained for Close the coils used with the Model 59, but re-cali- bration is always recommended when coil repiace- ment is necessary. This re-calibration is best done at the ractory where specialized equiPment IS available ror this purpose.
A damaged meter can be temporarily re-placed w ith any suitable 200 microampere movement.
It is suggested that a derective meter be re-turned ror replacement. my other railures should be reported to us promptly, since our study of such derects is helpful in the improvement or our instruments.

ACCURACY

Maximum accuracy or rrequency callbration can be secured by placing the coil into position with the serial numbered side up toward the tuning dial side of the probe. On the highest frequency coil a red dot is used to identiry the upper side, since it is not reasible to stamp tb serial number there.
It is always well to see that the coil is rully bottomed in the contact posts. Ir the probe dial ccver has been removed, the rrequency callbration should be rechecked as outlined above in Section VI(a). Under favorable conditions (loose coup- ling, etc.) the frequency accuracy or the Model 59 should be within 2%. Replacement of oscillator tubes or damage or the com, or course, will al- ter the above accuracy.
llaximum accuracy of frequency measurement is dependent to some extent upon the Q of the circuit under test. The more tightly tM Model 59 has to be coupled to a circuit, the greater the pulling or rrequency, etc. When checking rrequency or an oscillating circuit, the use or headphones and the Model 59 as an oscillating detector is recommended tor greater accuracy.
This method can also be used together with an accurate frequency meter ror accurate setting of the Model 59 to a particular rrequency. Use or the Model 59 as an oscillating detector permits loose coupling to the oscillating circuit under test.
Accuracy of capacitance determination depends on Q anq on accuracy or the coil standards. Under most conditions capacitance measurements should be reliable to within 1s. Under favorable condi- tions, it la possible to masure to Sg with the technique outlined In Figure 13.
Accuracy or inductance maasurement depends on the accuracy or the capacitance standard and pro- per correction for lead inductance as outllned in Sec tion V(b). Mutual inductance measurements de- pend ror accuracy on the dirrerence between two inductance measurements.
The accuracy of Q measurement depends on the relative calibration or the auxiliary vacuum tube voltmeter and the alccurace measurement of the rre- quency increment (ai). The use or a frequency meter or audio oscillator and beat note methods will greatly improve the overall accuracy. It is possible to measure actual circuit Q under opera- ting conditions, something which is rather import- ant at high rrequencies, because of dynamic input loading, etc.
And last of all the Model 59, like a line watch, must be handled wlth some care. The probe and the coils must not be dropped or given rough treatment, ir the accuracy or the original ractory calibration is to be preserved.

Boonton 59 Megacycle Meter.max

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