Marconi Instruments TF 2005R User manual

' '
marcon1
· Instruments
TF 2005R
AF TWO-TONE SIGNAL SOURCE
Instruction Manual

~ - ~ - -- -- -~---
MARCONI INSTRUMENTS LIMITED
SERVICE DIVISION
HOME and EXPORT
SALES OFFICES
u.s.A.
BUNDESREPUBLIK
DEUTSCHLAND
FRANCE
THE AIRPORT, LUTON,
BEDFORDSHIRE LU2 9NS
Telephone: [phone]
Telex: 825248
LONGACRES, ST. ALBANS,
HERTFORDSHIRE AL4 OJN
Telephone: [phone]
Telegrams: Measuretest, St. Albans
Telex: 23350
MARCONI I~STRUMENTS DIVISION,
MARCONI ELECTRONICS INC.,
100 STONEHURST COURT, NORTHVALE,
NEW JERSEY 07647
Telephone: [phone]
Telex: 710-991-9752
MARCONI MESSTECHNIK G.m.b.H.,
P.O. BOX NO. 210330
JOERGSTRASSE 74
8 MUNICH 21
Telephone: 582041
Telex: 05 24642
MARCONI INSTRUMENTS,
3 AVENUE DU MARECHAL DEVAUX,
91550 PARAY-VIEILLE-POSTE
Telephone: [phone]
Telex: 203882
A GEC-MARCONI ELECTRONICS COMPANY

Nov . 79
AF Two-tone Signal Source
·rF 2005R
Code No : 52 005 -3 0 1D
©
1979
MARCONI INSTRUMENTS LIMITED
ST. ALBANS HERTFORDSHIRE ENGLAND
P art No. 4 68 81- 381L P rint code: A- 11 /79 M. I. 0. 5c
Ine t ru ct l on Ma nual
H 52005-301 D
Page (i)

H 52005 -30 1D
Note ...
CONTENTS
PRELIMINARIES
Title page
Co ntents
Notes and cautions
CHAPTE RS
1
Gener al information
2
Inst allation
3 Operation
4 Technical description
5 Ma~ ntenance
6 Replaceable parts
7
Circuit di agrams
Each page bears the date of the original i ssue or the code number and date of the
l atest amendment (Am .l , Am. 2 etc.). New or amended material of technical importance
introduced by t he latest ame ndmen t is indica t ed by triangles positioned thu s ~ .. ... ~
to show the extent of the chan ge . When a ch apter is re-issued the triangles do not
appear.
Any ch anges subsequent to the latest amendment state of the man ual ar e included
on inserted sheets coded Cl, C2 etc .
Page (ii) Nov. 79

H 52005-3010
NOTES AND CAUTIONS
ELE CTRICAL SAFETY PRECAUTI ONS
Th is equipment i s pr otected in a ccor dan ce w ith IE C Safety Class l. I t has been
designed and t est ed according to IEC Publicatio n 348 , 'Safet y Requi rements for Electr o nic
Me as uring Apparatus', and has bee n s upplied in a sa f e conditi on. The followin g pre-
c autions must be obse rved by the u se r to ensu re safe operation and to retain the equip-
me nt in a sa fe c ondition.
Def ec t s and ab normal stre sse s
Whenever
it is likely th at protection has been impaired, f or example as a result of
damage caused by sev ere c ondi tions of transp ort or storag e, th e e quipment shall be made
in op erative and be secu red against a ny uninte nded o peration.
Removal of c overs
Removal of the covers i s likely to ex pose live part s a lthough reason able precautions
have been ta ken in th e design of the equipment to shield su ch parts. Th e equipment
shall be disconnected fro m the supply bef ore carry ing o ut an y adjustme nt, r e pl ac e me nt or
maintenance and repa "ir durin g which the equipm ent sha ll be op ened, If any adjustment ,
ma
intenance or repai r under v oltage is inevitabl e it s hall only be car ried out by a
s
kill ed pers on who is aware of th e hazard inv olved,
Note that capa citors inside the equipment may still be charged wh en t he equipment
has been disco nnected from th e suppl y . Befo re carryin g ou t any work in s ide the equip-
ment, capacitors connected to high vo lt age points shou ld be discharged; to discharge
mains filt er capac it o rs, if fitted , s hort together the L (live) and N (neutral) pins of
the mains plu g .
Mains plug
The mains plug shall onl y be ins erted in a socket o utl et provided with a protective
earth co nta ct. The protective actio n shal l not be negated by the use of an extens ion
lead without protective con ductor . Any inte r ruption of th e protective conductor inside
or outside th e eq uipment is lik e ly to make the eq uipment dang er ous .
Fu
ses
Note that there i s a suppl y fus e in both t he li ve and n eu tr al 1-1ires of th e supply
lead. If only one of th ese fuses sh ou ld rupt ure, c ertain parts of t he equipr . 1e nt could
remain at suppl y potential.
To provi de protect ion again s t br ea kdo vm of the sup ply lead, it s co nnect ors , and
fi lt er where fi t ted, an exter nal su pply fuse (e . g . fitted in t he connec ting plu g) shoul d
be used in th e li ve l ead. Th e fuse shou ld have a conti nuous ratin g not exceeding 6 A.
Ma ke su re that on l y fuses wi th th e r eq uired rated cur rent and of the spec ifie d type
are us ed f or r ep lacemen t. Th e use of mended fuses and the s hort-circuiting of fuse
ho lders sh all be avoi ded.
· Nov . 79
Page (lU/lv)

H 52005-301D
Chapter 1
GENERAL INFORMATIO N
C
ONTE NTS
Para.
1 Introduction
1 Purp o se
2 De sc ription
3 Electrical data
3 Composite instrum e nt
4 Oscillator (TF 2100)
5 A ttenuator (part of TF 2160/1)
6 Input voltmeter (pa rt of TF 21 60/ 1)
7 Power requirements
8 Dimensions and weight
9 Safety
10 Radio frequenc y interf e rence
11 Accessories
Fig.
1 AF Two- to ne Si gna l Source TF 2005R P
age
1
INTRODUCTION
1. Purpo se
2. Description
To provide low distortion s ignals for det e rminin g the in ter -
modulation d istortion in amplifiers, or (using o ne o sc ill ator
only) for ge neral purpose testing .
(1)
An AF Two-tone Signal Source TF 2005R co nsi sts of
two
AF Oscillators TF 2100 ( les s case) a nd one AF Monitored
Atte nu a tor TF 21 60/ 1 (l es s case), all fitted in a case s uit ab le
for rack mounting.
Fig . 1 AF Two-tone Signal Source TF 2005R
C hap. 1
Nov. 79 Pag e 1

ELECTRICAL D ATA
H 52005-301D
(2) Ea ch oscillator has its frequency indicated on a cali-
brated dial which covers a r an ge of 3 to 1. The s ix frequenc y
ranges b etwe en 20 Hz and 20 kHz are se l ected by means of a
rang e switch. There is al so a fine tune control. The output
le vel is adjusted by means of coarse a nd fine cont rols . Each
osc ill ato r is isolated by means of a switch when the output
level of the other oscillator is being adjusted.
(3) The two oscillators are connected in para llel to the
attenuator which has three switches having steps of 10 dB,
1 dB and 0 .1 dB. Various output load conditions a re selected
by means of two switches. The input is moni tored by means
of an elect ronic voltmeter. The four voltage ranges from
1. 5 V f . s. d. to 25 V are selected by means of a range sw itch.
3. Co mposite in strume nt (TF 2005R)
Frequen cy range
20 Hz to 20 kHz in s ix bands.
(Eac h oscillator can be ad justed independently.)
Amp li tude Referenc e l eve l : Up to +1 0 dBm from each osc illator.
Attenua . tor range : 111 dB in 0.1 dB steps.
Harmonic distortion Less than 0. 05% between 63Hz and 6 kHz wh en using un-
balanced output .
Genera~ l y les s than 0 .1 % under o ther conditions.
lntermodulation Below -80 dB with respect to the wanted signal.
Hum Be low -80 dB with respect to t he wanted s i gnal.
4. Oscilla tor (TF 2100)
Frequency range 20Hz to 20 kHz in six ba n ds .
Auxiliary fin e co ntr o l.
Frequency accura cy ±1% ± 0. 2 H z.
Output power +15 dBm (31. 6 mW) int o 600 r..
Over 8. 5 V open c ircuit.
Output co n tro l At l east 40 dB range of atte n uation, by continuousl y varia ble
T-networ k.
Output impeda n ce 600 r. ±20% unb a lanced.
Frequency response Over the freq u ency r a ng e, the change in output level is le ss
than ±0.4 dB.
Distort ion Le ss than 0.05 % from 63Hz to 6.3 kHz;
less th an 0.1 % from 20Hz to 20kHz.
Hum Le ss than 0. 01 % (- 80 dB) of outpu t si gnal, or -10 0 dBm,
whichever is the greater .
5.
Attenuator (p ar t of T F 216 0/ 1)
Frequency ra n ge
Attenuation range
Chap . 1
Page 2
20 Hz to 20 kHz with ba l anced output.
DC to 550 kHz with unbal anced output.
0 to 111 dB in 0. 1 dB steps.
Nov. 79

H 52005-301D
Residual loss
Unbalanced: Less than 0.01 dB at d.c.
Balanced : Varies with frequency and impedance as follows
"" .:~111111111111111111111111!111111111 !IIIII k::
20 50 100 200 500 lk 2k 5k 10k 20k
"''"'• FREQUENCY "z
Attenuation accuracy 20 Hz to 20 kHz : ±1% of dB setting ±0. 2 dB;
at d. c. : ±1% of dB setting ±0. 01 dB;
20 Hz to 550 kHz : ±2% of dB setting ±0. 2 dB.
Input impedance (W it h 600 ~ load.) 600 r, unbalanced.
Output impeda.nce
Power input
Frequency response
Distortion
When input voltmeter is switched in, varies with frequency
and impedance as follows :-
600--- -
,--,-,- --:- l
,00 ~..-.~~.-..-~ --- .... ~- ~~::::t=t=tt1m~~~~t=t=t==jl
:"-.: ...... ~TTEN
I? SOOt-------·-- -1- - - · - - ...... ~ >IOd&
-- - -- -- · -- -
~0+-------- __ -t- -t- -t-t-+++1+---+--+-+-+1' Od8
--- -- ---
520 - - - - - - - - - - - - -+---+---'-_J_+-'-...J...I..I..l---+-L-L+...L.l.""---1
0 IOk 20k 50k lOOk 200k 500k lM
~REOUEHCY Hl
(With input voltmeter switched out, the lmear part rises to
600ft.)
(With 600 Q source . ) Balanced : 600 0, 150 Q and 75 r, via
transformer.
Unbalanced : 600 0. When input voltmeter is switched in,
varies with frequency and attenuation as follows :-
600-- --------- --
-
-..I..
..........
' I
"-
'"
~TTEN.
>10d8
ATTEN.
"\ OdB
I I
5ZO -------------·
I I
0 10~ 20k 50k lOOk 200k
500k IM
FR£QUEPICY Nz
(With input voltmeter switched out, both linear parts are at
600 Q.)
1 W (25 V maximum), continuous a. c. or d. c.
Output is flat within ±0 .2 dB from 20Hz to 20kHz, and within
±1 dB from 20 Hz to 550 kHz at any attenuator setting, with
input voltmeter re ad ing held constant.
At balanced output with matched load with +15 dBm (31.6 roW)
pure input, output distortion factor does not exceed 0. 1%
from 50 Hz to 20 kHz and 0. 3% from 30 Hz to 50 kHz.
6. Input voltmeter (part of TF 2160/1)
Ranges
Accuracy
7. Power requirements
AC supply
Nov, 79
1. 5, 5, 15 and 25 V full-scale ; a lso marked - 6 dBm to
+30 dBm.
±5% of full-scale from 20Hz to 550kHz.
45 Hz to 500 Hz : 95 V to 130 V or 190 V to 260 V.
500H z to 1000Hz : 105 V to 130 V or 210 V to 260 V.
C hap. 1
Page 3

F 52005-301D
Power consumption
· Dc supply
14 VA.
65 Vto 90 V; 60 rnA.
DIMENSIONS AND WEIGHT
8.
Height :
Width :
Depth:
Weight :
SAFETY
200 mm (7 3/ 4 in)
475 mm (18 31 / 4 in)
270 mm 101 /2 in}
16.5 kg (36. 3 lb)
9. Designed to meet the requirements of IEC 348.
RADIO FREQUENCY INTERFERENCE
10. This equipment conforms with the requirements of EEC Directive 76 /88 9 as to
limits of r. f. interference.
ACCESSORIES
11. The instrument includes the following supplied accessories :-
Mains lead TM 7052. Code 43122-017.
HT lead (supplies power to m~mitored attenuator) TM 7053. Code 43125-029 .
Two
coaxial leads (connect each oscillator to the monitored attenuator) TM 6958.
Code 43125-028.
Coaxial free plug, type BNC. Code 23443-305B.
Shielded adaptor (provides BNC outlet from terminals) CE 51003. Code 43168-008.
Instruction Manual. Code 46881-381L
C hap. 1
Page 4 Nov . 79

H 52005-301D
Chapter 2
INSTALLATION
CONTENTS
Para.
1 Unpacking and repacking
UNPACKING AND REPACKING
1. Retain the packing materials and the packing instruction note (if included) in case it
is necessary to reship the instrument.
2. If the instrument is to be returned for servicing attach a label indicating the service
required, type or model number (on rear label), serial number and your return address.
Pack the instrument in accordance with the general instructions below or with the more
detailed information in the packing instruction note.
(1) Place the plywood/felt cap (without finger holes) in the bottom of the inner
(fibreboard) carton.
(2) Lower the instrument into the carton with the feet facing the cut-outs in the
bottom cap surround.
(3) Place the top plywood/felt cap (with finger holes) in position, with the cut-outs
facing the feet .
(4) Fold down and seal the inner carton with tape.
(5) Fit the foam cushion pads in the outer (wooden) case.
(6) Wrap the instruction manual and accessories in a pa dded parcel a nd
lay it in the bottom of the case.
(7) Lower the packed inner carton into the outer case and fold over the cushion
pads to obtain a snug fit.
(8) Fit the top lid and secure with wood screws.
(9) Mark the case FRAGILE to encourage careful handling.
Note . . .
If the original container or materials are not available, use a strong double-wall
carton packed with a 7 to 10 em layer of shock absorbing material around all sides
of the instrument to hold it firmly. Protect the front panel controls with a plywood
or cardboard load spreader; if the rear panel has guard plates or other projections
a r ear load spreader is also advisable.
Nov. 79 C
hap. 2
Page 1/ 2

H 52005-301D
Para.
1
5
5
8
10
12
15
22
25
30
32
35
37
Controls and connectors
Preparation for use
Power supply
Interconnections
Switching on
Setting frequency
Oscillator output
Monitored attenuator input
Reading input signal level
Setting output impedance
600 Q, 150 Q or 75 Q balanced
600 Q unbalanced
150 Wor 75 Q unbalanced
39 37.5Qor18.75Q
42 R ea ding attenuation and output
42 Attenuation
47 Power output
48 Voltage output
51 Output to a mismatched load
Chapter 3
OPERATION
CONTENTS
54 Using the ou tput matching transformer to obtain a voltage step-up
Table
1
Decibel conversion
2
3
Fig.
1
2
3
4
5
Transformer vo ltage step-down ratios
Transformer voltage step-up ratios
Controls and connectors on front panel of oscillator
Controls and connectors on front panel of monitored attenuator
Output v oltage corresponding to dBm when output impedance and load are 600 Q
Mismatch loss with external load .. .
Mismatch loss with internal load . .
CONTROLS AND CONNECTORS
1. The controls and connectors on the front panel of the oscillators (Fig. 1) are as
follows ·-
( 1) SUPP LY s wit c h. For sw itchin g on t he a. c . or th e d. c. supply .
N ov . 79
Page
9
11
14
2
3
12
13
13
Ch
ap. 3
Page 1

H 52005-301D
(3)
(1) ------l...._r
Tuli<t"A-~:"1.
(7)
(5)
{2) (8)
T~C59!1
Fig. 1 Contro ls and connectors on front panel of oscillator
(2) FREQUENCY RANGE switch . For selecting the appropriate range for the frequency
required .
(3) FREQUENCY control and dial. For setting the frequency using the outer sca le A or
the inner sca le B according to the setting of th e FREQUENCY RANGE switch.
(4) FINE TUNE control. For fine adjustment of the frequency.
(5) SET OUTPUT contro l. For setting the output l evel required up to a maximum le, · el
of +15 dBm into 600 n.
(6) FINE OUTPUT control. For fine adjustment up to 0. 7 dB.
(7) OUTPUT switch. For switching the output to the OUTPUT terminals on the front
panel or to the OUTPUT socket on the rear panel.
(8) OUTPUT terminals. For connecting apparatus directly to the oscillator.
2. The controls and connectors on the rear panel of the oscillator s are as follows :-
( 1) MAINS inlet. For connecting the a. c . supply by mean s of mains lead TM 7053.
(2) BATTERY termina ls. For con n ect in g the d. c. supply.
(3) BATTERY /MAINS switch. For se lecting the appropr i ate supp l y.
{4) HT outlet. For co nn ecting the monitored attenuator by means of h.t. leact TI\I 70 5 :L
(5) OUTPUT s ocket. For co nnectin g th e monitored att e nuator by mean s of eoaxia l kact
TM 6958 .
Ch~p. 3
Pag-e 2 Nov. 79

H 52005-301D
(7)
(9)
(11)
(10)
AF MONIT OR ED
MTENUAT OR
Bol 20t /s- 20k tf s
Unbal DC - 55 0 ktfs
TPC91
Fig . 2 Controls and connectors on front panel of moni tored attenuator
(1)
(2)
(5)
(6)
3. The contro ls and connectors on the front panel of the monitored attenuator (Fig. 2) a re as
follows :-
(1) INPUT socket. For connecting apparatus to the monitored attenuator (in parallel
with the oscillators connected at th e rear) .
(2) METER RANGE switch . For switching on the h.t. supply and selecting the required
voltmeter sensitivity, and also for checking the h.t. level.
(3) METER. For indicating the input level according to the setting of t he METER RANGE
switch , and also for checking the h. t. level.
(4) 10 dB switch . For setting the attenuation up to 100 dB.
(5) 1 dB switch. For setting the attenuation up to 10 dB.
(6) 0.1 dB switch. For setting the attenuation up to 1 dB.
(7) O UTPUT IMPEDANCE switch. For selecting the appropr iat e output impedance,
balanced or unbalanced .
(8) WAD switch . For switching in a matched internal lo ad across the attenu a tor output.
(9) UNBAlANCED terminals. For connecting appara tus of GOO n impedance unbalanced.
(10) BALANCED terminals. For connecting a pparatus of 600, 150 or 75 ~ impedance
balanced .
(11) CENTRE TAP termina l.
Nov. 79
For connecting the earth of balanced apparatus .
Chap. 3
Pag e 3

H S2 005 -301D
4. The controls and connectors on the rear panel of the m onito red attenuator are as follows :-
(1) HT inlet. For cormecting one of the attenu a tors by means of h.t. lead TM 705:3.
(2) INPUT sockets. For connecting the oscillators by means of coa xial leads TM (j95R.
PREPARATION FOR USE
Power supply
5. The instrument can be operated f rom an a.c. supply or a d.c. source, according to the
setting of the BATT ER Y/ MAINS switches at the rear of the oscillators .
6. The instrument is adju sted for an a . c. supply of 95 V to 1 30 V or 190 V to 260 V (Chap. 5 ).
After che cking that the m ains voltage adjustm ent is correct, connect to the mains by means of
lead TM 7052. When fitting a supply plug e nsure that the conductors are connected as follow s:-
Earth- green/yellow, Neutral- blue . Live -brown .
7. A d.c. source can be between 65 V and 90 V. It must be floating. Dry batteries can be
used, but it should be noted that the drain is about 60 rnA. Connect leads from the source to the
appropriate te rminals marked + and - at the r ea r of the oscillators.
Interconnections
8. DC is required by the monitored attenuator. This is fed from one of the oscillators by
means of le ad TM 7053.
9. It is usu a lly most convenient to use the instrument with the OUTPUT sockets on the rear
panel s of the oscillators linked to the INPUT sockets on the rear panel of the monitored att e nu a-
t or by means of le ads TM 6958.
Switching on
10. Switch on o ne oscill ator a nd the monitor ed attenuator by turning the appropriate SUPPLY
switch clockwise. Switch on the other oscill ato r, if required, by turning its SUPPLY switch
clockwise. The instrum e nt is read y for use almost immediately; the time taken to reach a
hi gh degree of stability depends on the frequency rang e, but is normally less than ! min.
11. If a lo ad is already con ne cte d, and is sensitive, it may be advisable to turn the SET OUT-
PUT con trols counter-clockwise before switching on. Initially, the generated signal may rise
to approximately 50% above normal amplitude before stabilization takes place. Also -when
th e lo ad imp e dan ce is high an d the SET OUTPUT control is fully clockwise- a d.c. pulse of
several volts app ears briefly when t he instrument is switched on and switched off, the pulse
being positive and negative respe ctiv ely .
SETTIN G FREQUENCY
12. S et an o scilla tor to a part icular frequency as follows :-
(1) Set the FREQUENCY RANGE switch to the range which includes the required fre -
quen cy. On the front panel, each position of the switch falls between two figures, which
indicate in Hz the frequency limits of the range obtained in th at p os it i on. Ea ch position
is also marked with a l et ter, A orB, indicating wheth er sca le A orB must be read on th e
frequency dial.
(2) Turn the FREQUENCY co ntrol so that the dial indicates the required frequency,
reading scale A or B according to the setting of the FREQUENCY RANGE switch.
Readin gs on the scales are eithe r direct re ading or requir e to be multiplied by 10 or 100
according to the range selected.
Chap . 3
Page -!
Nov. 79

H 52005-301D
(3) Set the FINE TUNE control to the mark on the pa nel, i.e. the centre of its range of
adjustment.
13. The tuning elements are ganged wire wound re sis tors. As a result of the contacts passing
over the discrete turns of wire, some fluctuation of output may occur. Stabilization of the output
level will take place after any adjustment.
14. The FINE TUNE control gives gradual and precise frequency adjustment over a limited
range in the region of the setting of the main FREQUENCY control. It can be used to minimize
the frequency calibration error of the main dial at a particular frequency and its vicinity; by
adjusting the FINE TUNE control, the reading of the main dial can be standardized against the
indication of a counter connected to the output . The FINE TUNE control also facilitates setting
the instrument exactly to the optimum pass or rejection frequency of a highly selective circuit,
such as a filter having a narrow frequency response.
OSCILLATOR OUTPUT
15 . Before connecting a sensitive load to the instrument, turn the SET OU TPUT controls fully
counter-clockwise to avoid applying too mu ch output.
16 . Output from an oscillator can be t aken from the front panel OUTPUT terminals, or from
the OUTPUT coaxial socket at the re~r, depending on the setting of the OUTPUT switch above
the terminals on the front panel. Set this to the right for front terminals output, or to the left
for use of the rear coaxial socket. The fro nt terminals contain sockets for 4 mm plugs and
will accept a twin plug having 19 mm pin spacing.
Note .•.
The 'live' front panel terminals and the centre socket of the rear coaxia l outlet are fed
internally through a reversible electrolytic capacitor. Damage may result if the l oad
applies more than ±25 V d. c . back to the instrument.
17. The OUTPUT switches situated above the front panel terminal s of each oscillator ca n be
used to bring the oscillators into c ircuit independently when they are both connected to the moni-
tored attenuator. As the two oscillators are co nnected si mp ly in parallel it is necessary when
setting the output level of one to sim ulate the shunt impedance of the other . This is done by
making use of the fact that the attenuator internal load resistor when switc h ed in with zero
attenuation appears directly across the attenuator input.
18 . To set output level proceed as follows :-
(1) Connect the load to the appropriate attenuator OUTPUT terminals.
(2) Turn the LOAD switch to INT.
(3)
Turn the a ttenuator switches to 0 dB.
(4) Connect one oscillator only to the attenuator by pressing the OUTPUT switch of one
oscillator to the left (REAR) and the other OUTPUT sw itch to the r ight.
(5) The oscillator that is connected may now be brought up to the desired le ve l, as in-
dicated by the input vo ltm eter of the attenuator.
(6) Interchange the oscillators by reversing the settings of both the OUTPUT switches
and adjust the output level of the other oscillator.
(7) Now connect both oscillators by pressing both OUTPUT switches to the left (REAR)
and disconn ec t the internal l oad by turning th e LOAD sw i tch to EXT .
19. When the SET OUTPUT control ha s been rotat ed through a sma ll ang le from the ex treme
Nov . 79 Cha
p. 3
Page 5

H 52005-301D
counter-clockwise position, it enters upon an approximately linear range of at least 40 dB adjust-
ment. Maximum output, when the control is fully clockwise, is at least +15 dBm into a 600 fl
load, or up to more than 8.5 V acrcss a high impedance load. Make small adjustments to the
level with the FINE OUTPUT control. This control has a range of approximately 0. 7 dB.
20. The output impedance of the signal source with no attenuation will be that of the two oscil-
lators in parallel, i.e . 300 0. If, however, 10 dB or more of attenuation is used, the effective
output impedance will rise to 600 fl.
21. If it is desired to use the instrument as a single tone signal source the osc illator not in use
should be disconnected; either by pressing the OUTPUT switch to the right, or by breaking the
plug and socket connection at the rear . If this precaution is not taken, and the unwanted oscil-
lator simply switched off, it will remain as a non-linear load across the output of the oscillator
in use, giving rise to distortion.
MONITORED ATTENUATOR INPUT
22. Set the METER RANGE switch to a position suitable for the input to be applied; set it to
OFF if the input will not be a sine wave. The input should not exceed 25 V a. c . or d. c.
23. The INPUT socket on the front panel is a type BNC. Cover this socket with the ca p pro-
vided when the INPUT soc~ets on the rear panel are being used. All the sockets are in parallel.
24. The input impedance is 600 fl , providing th at the output impedance is matched by the load.
H the output is mismatched, the input impedance is still 600 fl provided that a substantial amou nt
of attenuation is in use; if the load has a very high or a very low impe dance rel ative to the
matching value, the attenuation can be reduced to abo ut 13 dB or less before a 1O% variat ion
arises in the input impedance. When the load has a very high impedance, the internal termi-
nation should normally be used, and the output will then be approximately matched .
READING INPUT SIGNAL LEVEL
25 . Turn the METER RANGE switch clockwise to the most sensitive range that can be used
without the meter deflection exceeding full-scale. Read the app ropriate scale on the meter
according to the setting of the switch . Readings on the scales for the lower two ranges are
direct reading and for the higher two ranges require to be multiplied by 10 and 5. The meter
reading is the :r.m.s. value of the input voltage, assuming that the signa l is a sine wave. The
reading may be inaccurate if the signal is not sinusoidal, or if its frequency is less than 20 Hz .
26. The meter also has a scale calibrated -6 dBm to +6 dBm . The 0 dBm m ark on this scale
corresponds to the voltage, on the 0 to 1. 5 V scale, that will produce 1 mW input to the attenua-
tor. When the voltmeter is used on higher voltage ranges, the dBm scale is effectively exten-
ded by addition of the dBm increments marked at the range switch positions.
27. When the OUTPUT IMPEDANCE switch is set to one of the BAL positions, if the wanted
output is such that less than 10 dB of attenuation is required, first switch in 10 dB a nd terminate
the attenuator internally or externally before setting the input and reading the meter. Then
reduce the attenuation as required, and do not compensate for any rise in meter reading.
28. The dBm reading indicates the power fed into the attenuator networks assuming that th e
input impedance is 600 fl. This will not be so if the instrument is mismatched at its outlet and
the value of attenuation is low (para . 24) .
29. The dBm scale and the dBm markings on the METER RANGE switch ca n be used to relate in
dB different levels of applied signal without regard to the actual values of power concerned .
Chap. 3
Page 6 Nov. 79

H 52005-301D
SETTING OUTPUT IMPEDANCE
30. The different o utput impedances available as follows arc only obtained providinl{ the input
to the attenuator comes from a GOO n generator. or providing a substantial amount of attenuation
is in use (o\·er 13 dB ensures an o utput impedance close to the selected nominal va lue).
31 . The OUTPUT terminals conta in sockets for 4 mm plugs and any pair of adjacent terminals
will accept a twin plug having 19 mm pin spaci ng . Carrying a BNC socket, the shielded adaptor
can be plugged into the two UNBAL terminals to provide good shielding and facilitate employing
coaxia l l eads.
600 n, 150 nor 75 n balanced
32. Set the controls and connect the load as follows ·-
(1) Set the OUTPUT IMPEDANCE switch to whichever of the BAL positions indicates the
required source impedance.
(2) Set the LOAD switch to EXT.
(3) Connect the load to the two BAL terminals.
33. If the BAL terminals alone are used, a floating source is obtained. To balance the source
relative to earth, connect the CENTRE TAP terminal to earth. The left-hand UNBAL terminal,
which is connected internally to case and chassis, serves as an earth point assuming that the
outer of the coaxial inlet socket on the attenuator is earthed by the input le ad.
34. Under these conditions the matching transformer is in use and the frequency range of the
instrument is 20 Hz to 20 kHz.
600 n unbalanced
35. Set the controls and connect the load as follows
(1) Set the OUTPUT IMPEDANCE switch to 600 Q UNBAL.
(2) Set the WAD switch to EXT.
(3) Connect the load to th e two UNBAL terminals. The left-h and one, which is connected
internally to case and chassis, se rv es as an eart h point assuming that the outer of the co-
axial inlet socket on the a ttenuator is eart h ed by the input le ad .
36. Un der these conditions the output is obtained directly from the attenua tin g networks and the
frequency range ofthe instrument extends fro m d. c. to 550 kHz (except that the input voltme ter
becomes inaccurate below 20 Hz).
150 nor 75 Q unbalanced
37. Set the controls and connect the load as follows :-
(1) Set the OUTPUT IMPEDANCE switch to BAL 150 Q or BAL 75 n , according to th e
required value of source impedance.
(2) Set the LOAD switch to EXT.
(3) Connect the l oad to the two BAL terminals . Connect one of these terminals to earth,
as required . The left-hand UNBAL termina l, which is connected intern ally to case and
chas si s, se r ves as an earth point assumi ng that the outer of the coaxia l inlet s ocket on the
a tt e nuator is eart h ed by the inp ut l ea d. Leave the CENTRE TAP terminal disconnected.
Nov. 79 Ch
ap . 3
Page 7

H 52005 - 301 D
three dia ls from the dBm v al ue of i nput power indica t ed by the inp ut meter and its ran~c sw i tch .
Vo lt age ou tp ut
48. When the output impedance is arranged to be GOO nan d the load matches th is val ue , the
output vo l tage developed across the l oad is the in put volt age reduced by the tota l attenuation
reading . The out put v olt age is therefore t he input vo l tage mul tip l ied by the app rop riate factor
(Table 1) . Alterna tivel y, the output vo l tage across a GOO n l oad ca n be d etermi n ed fro m the
dBm value of the ou t put read from the meter and dials (F i g. :l).
Ra t io down
Voltage Power
1·0 1·0
·9886 ·9772
·9772 ·9550
·
9661 ·9333
·9550 ·9120
·
9441 ·8913
·9333 ·8710
·9226 ·
8511
·9120 ·8318
·9016 ·8128
·8913 ·7943
·871 0 ·7586
·
8511 ·7244
·83
18 ·6918
·8128 ·6607
·7943 ·6310
·7762 ·6026
·7586 ·57
54
·7413 ·5495
·7244 ·5248
·7079 ·5012
-6683 ·4467
·6310 ·
3981
·5957 ·3548
·5623 ·3162
·5309 ·2818
·5012 ·
251 2
-4467 ·1 995
·3981
·1 585
·3548 ·1
25 9
·3162 ·1000
·2818 ·07943
·2512 ·06310
·2239 ·05012
·1995 ·
03981
·1778 ·03162
Nov. 79
TAB LE 1
Decibel convers io n
Dec i be ls
0
·1
·2
·3
·4
·5
·6
·1
·8
·9
1·0
1·2
1·4
1·6
1·8
2·0
2·2
2·4
2·6
2·8
3-0
3·5
4·0
4·5
S·O
S·S
6
7
8
9
1(1
11
12
13
14
tS
R atio up
Voltage
1·0
1·012
1·023
1·035
1·047
1·059
1·072
1·084
1·096
1·109
1·122
1·148
1·175
1·202
1·230
1·259
1·288
1·318
1
·3 49
1·380
1·413
1·496
1·585
1·679
1·778
1·884
1·995
2·239
2·512
2·
81 8
3
·1 62
3·548
3·
981
4·467
5·012
5·623
Power
1·0
1·023
1·047
1·072
1·096
1·122
1·148
1·175
1·202
1·230
1·259
1·318
1·380
1·445
1·514
1·585
1· 660
1·738
1·820
1-905
1·995
2·239
2·512
2·818
3·162
3·548
3·
981
5·012
6·310
7·943
10·000
12·59
15·85
19·95
25·12
31 ·62
Chap . 3
Pa~e 9