Racal Instruments RA-117 User manual

Racal RA-117
Radio Receiver

1. Contents
1. Contents ............................. 2
2. List of Illustrations ........................ 3
3. Technical Specification ...................... 4
4. Introduction ........................... 7
5. Installation ............................ 8
6. Operation ............................ 10
7. Brief Technical Description ................... 14
8. Detailed Circuit Description ................... 16
9. Maintenance ........................... 25
10. Spurious Responses ....................... 26
11. Fault Diagnosis ......................... 28
12. Representative Test Data .................... 30
13. General Servicing and Aligment Procedures .......... 32
13.1. General Servicing . . . . . . . . . . . . . . . . . . . . . . 33
13.2.ReceiverTests........................ 33
14. Alignment Procedures ..................... 37
14.1.Introduction ........................ 37
14.2. 100 kc/s I.F. Amplifier . . . . . . . . . . . . . . . . . . . . 37
14.3. 100 kc/s (L-C) Filter . . . . . . . . . . . . . . . . . . . . . 37
14.4.SecondV.F.O. ....................... 39
15. Dismantling ........................... 44
16. Component List 1. ....................... 49
17. Component List 2 ........................ 63
18. Valve Data ........................... 67
19. Illustrations ........................... 69
[2]

2. List of Illustrations
Fig.
Rear View of Receiver Chassis 1
Front Panel, RA.117 2
RA.117 Block Diagram 3
Simplified Balancing Circuit 4
Noise Limiter Circuit 5
Typical Selectivity Curves 6
Terminal Tag Strip 7
Top View of Receiver 8
First V.F.O. - top view 9
First V.F.O. - underside 10
Second V.F.O. 11
1.7 Mc/s Oscillator/Amplifier and Mixer Unit 12
B.F.O. Unit 13
Crystal Calibrator Unit 14
Key to Under-chassis Layout 15
R.F. Attenuator 16
Supply Filters 17
Crystal Oscillator/Amplifier and Harmonic Filter System 18
Second Mixer 19
Band-Pass Filter 20
100 Kc/s I.F. amplifier - right side 21
100 Kc/s I.F. amplifier - left side 22
Power Supply and Audio Stages 23
[3]

3. Technical Specification
Frequency range: 1 – 30 Mc/s
Stability: Afterwarm-up, overall drift is less than 50 c/s per hour
under conditions of constant supply voltage and ambient
temperature.
Input impedance: (1) Wideband 2000-ohms approx.
(2) Wideband 75 ohms.
(3) 5 double-tuned circuits, 75 ohms.
(a) 1 – 2 Mc/s
(b) 2 – 4 Mc/s
(c) 4 – 8 Mc/s
(d) 8 – 16 Mc/s
(e) 16 – 30 Mc/s
Tuning: Effective scale lenght of approximately 145 feet, i.e. 6
inches of scale lenght corresponds to 100 kc/s Frequency
increments remain constant over the entire range.
Calibration: A 100 kc/s signal derived from a 1 Mc/s crystal oscillator
having an accuracy of 5 parts in 106provides check points
at 100 kc/s intervals.
Sensitivity: A1 reception, bandwidth 3 Kc/s; 1µV for 18dB signal-to-
noise ratio. A2 reception, 30% modulated, bandwidth 3
Kc/s; 3µV for 18dB signal-to-noise ratio.
Intermodulation: More than 100dB down for interfering signals at least
10% removed from the wanted signal.
Cross modulation: For wanted signal levels between 3µV and 1mV, an inter-
fering signal 10 Kc/s removed and modulated 30% must
have a level greater than 50dB above that of the wanted
signal to produce a cross modulation of 3%. The ratio
of wanted to unwanted signal is improved up to 10% off
tune, at the rate of 3dB per cent.
Blocking: With similar conditions to those for cross modulation an
unwanted signal f2must be 60dB greater before the audio
output of the wanted signal f1is reduced by 3dB due to
blocking.
Selectivity: Six alternative I.F. bandwitchs are obtained by means of
a selector switch. Filter details are:
-6dB -66dB
(1) 13 kc/s 35 kc/s
(2) 6.5 kc/s 22 kc/s
(3) 3.0 kc/s 15 kc/s
(4) 1.2 kc/s 8 kc/s
(5) 0.3 kc/s Less than 2 kc/s
(6) 0.1 kc/s Less than 1.5 kc/s
[4]

Technical Specification 5
Bandwidths 5 and 6 are obtained with crystal-lattice fil-
ters; differences in centre frequencies of these bandwitdth
settings do not exceed 50c/s.
I.F. Output: 100 kc/s at 75-ohms impedance. Level 0.2 V approx, with
A.V.C. in operation. Two outlets in parallel are provided.
Image and Spurious Responses: With wideband or tuned input, external image signals
are at least 60dB down. Internally generated spurious re-
sponses are less than 2dB above noise level in all cases.
Noise Factor: Better than 7dB throughout entire range.
B.F.O. Range: ±8 kc/s
B.F.O. Stability: With constant ambient temperature and supply voltage,
drift after warm-up does not exceed 50 c/s. For input level
variations from 10µV to 1mV, B.F.O. drift is negligible.
Automatic Volume Control: An increase in signal level of 20dB above 1µV improves
the signal-to-noise ratio by 18dB. An increase in signal
level of 100dB above 1µV increases the A.F. output by
less than 7dB.
A.V.C. Time Constants: Short: Charge 25 milliseconds
Discharge 200 milliseconds
Long: Charge 200 milliseconds
Discharge 1 second
A.F. Response: With 13 kc/s bandwidth, response remains within ±4dB
from 250 c/s to 600 c/s.
A.F. Output: 1. 2.5-in. loudspeaker on front panel (switched).
2. Two headphone sockets in parallel on front panel.
(see Note)
3. Three independent outputs of 3mW at 600-ohms
at rear of chassis.
4. One output of 10mW at 600-ohms. Preset level
is independent of A.F.GAIN control setting.
5. One output of 1W at 3-ohms. Note: The two
headphone sockets are connected across one of
the 600-ohms, 3mW outlets.
Distortion: Not greater than 5% at 1W output.
Hum Level: With A.F.GAIN control at maximum, the hum level is
never worse than 40dB below rated output (1W)
Noise Limiter: A series noise limiter circuit van be switched into oper-
ation to provide limiting at modulation levels exceeding
30%.
Meter Indication: Alternative switching for indication of signal carrier level,
A.F. output level or ”S” meter indication.
Power Supply: 100-125V and 200-250V, 45-65 c/s. Power consumption
100W approx.

Technical Specification 6
Dimensions: Height Width Depth
For rack mounting 10.5in 19in 20.125in
(fitted dust cover) 26.7cm 48.25cm 51cm.
Fitted cabinet 12in 20.5in 21.875in
30.5 cm 52cm 55.6cm
Weight: Rack mounted 62 lb (28 kg)
In cabinet 92 lb (42 kg)

4. Introduction
General Description
1. The Communications Receiver Type RA.117 has been designed for use as a general
purpose receiver which will provide a high order of selectivity and stability. The re-
ceiver covers a frequency range from 1.0 to 30.0 Mc/s.
2. A built-in crystal-controlled calibrator provides reference signals at each 100 kc/s
division to permit exact alignment of the scale pointer. Two independent I.F. outputs,
in parallel, at 100 kc/s are provided for external use if required. A number of audio
outputs are available providing flexibility during operation; a small loudspeaker is
fitted for monitoring purposes.
3. The receiver is designed to operate from 100-125 volts and 200-250 volts, 45-65 c/s
main supply. The power consumtion is approximately 100 watts.
Constructional Details
4. The receiver is designed for both bench (table) and rack mounting. The front panel is
painted Light Battleship Grey (British Standard Specification 381C, colour 697) and
has been carefully designed to minimize operator fatigue.
5. The dimensions of the 1/8 in. thick front panel conform with the requirements for
mounting in a standard 19 in. rack.
6. For bench mounting, the receiver is fitted in a robust steel cabinet which has a rear
opening to enable the operator to gain easy access to the fuses and the termination
strips.
7. A dust cover is provided with both models. This may be removed from cabinet-
mounted receivers in conditions of high ambient temperature.
8. The chassis and major modules are of cast construction thus ensuring maximum rigid-
ity and effective electrical screening. Each receiver is supplied with three keys to facil-
itate removal of the control knobs, insulated trimming tool and coaxial terminations
for aerial and I.F. connections. Extra sleeves can be provided with the terminations
for alternative coaxial cable sizes.
[7]

5. Installation
1. After carefully unpacking the receiver, remove the dust cover and make sure that all
valves and screening cans are firmly in place and that no packing material remains
within the tuning mechanism.
POWER SUPPLY.
2. Ascertain that the mains transformator is set to the appropriate voltage tapping. This
is carried out by means of soldered connections to the transformer. A power lead is
permanently fitted to the receiver which can be connected directly to the power supply.
Check that the terminals HT1 and HT2 situated on the main chassis are linked (unless
the L.F. Converter is in use).
FUSES.
3. Ensure that the rating of the supply fuse and the H.T. fuse correct wiz:
Supply fuse 2A
H.T. fuse 350mA, anti surge.
AERIAL.
4. The impedance at the aerial (antenna) input plug is designed to match into a 75-ohms
unbalanced transmission line. The cable termination supplied with the receiver can
bee provided with alternative sleeves to enable it to be used with a type UR.18 or
UR.70 cable or similar cables of nominal diameter 1/2-in or 1/4-in. respectively.
AUDIO OUTPUTS.
5. A number of audio outputs are available to give the following facilities.
(1) The two telephone jack sockets situated on the front panel are connected across
one of the 600 Ohms, 3mW outlets.
(2) The following outputs are connected to the terminal strip at the rear of the
receiver:-
(a) Three 600-ohms outlets at 3mW.
(b) One 3-ohm outlet at 1W.
(c) One 600-ohms outlet at 10mW. This output is controlled by a preset A.F.
LEVEL control on the front panel and is independent of the outputs previ-
ously described.
100 kc/s I.F. OUTPUT.
6. The connection consists of two coaxial plugs connected in parallel to the 100 kc/s
output. The total load should not be less than 75-ohms (e.g. with outlet loaded by
75-ohms, the other can be can used as a high impedance source).
EXTERNAL INPUT/OUTPUT CONNECTIONS.
7. The following input and output connections are available on a panel at the rear of the
receiver (fig.1):-
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Installation 9
1 Mc/s input/output: May be used diversity operation.
2nd V. F. O. output/input(3.6 – 4.6 Mc/s) For diversity operation and external chan-
nelizer crystal oscillator output.
1.7 Mc/s input/output For diversity operation and fine tuning unit
input.
R.F. (2 – 3 Mc/s) input: Input from an L.F. converter.
The above input/output connections are selected by internal linkage, the connections
should be made as follows:-
1 Mc/s input Remove “T” adaptor and place in clip pro-
vided on side of gusset plate. Connect the
free plugs PL12 to SKT3 and connect the
free plug PL2 to SKT2.
1 Mc/s output Disconnect plugs PL12 and PL2 and con-
nect “T” adaptor to socket SKT2. Connect
plugs PL12 and PL2 to the “T” adaptor.
2nd V.F.O. input Connect the free plug PL302 to SKT302.
2nd V.F.O. output Connect the free plug PL303A to SKT304.
1.7 Mc/s input Connect the free plug PL303A to SKT303.
1.7 Mc/s output Connect the free plug PL303A to SKT306.
(blue)
Note 1 When using the internal oscillators with crystals, the connections should be made
for outputs since the cable capacity will pull the internal crystal off frequency.
Note 2 The 1 Mc/s and 1.7 Mc/s crystal must be removed if an external source is applied
to the input socket. Stowage space is provided on the chassis for the crystals when
they are not in use.
AUTOMATIC VOLUME CONTROL.
8. The A.V.C. line is brought out to the terminal strip at the rear of the chassis for such
applications as diversity reception.

6. Operation
1. References to the controls are in capitals and are in accordance with the panel titles
adjacent to them (fig.2).
2. It should be noted that the method of operation of the receiver extremely simple,
depens largerly upon the purpose for which the receiver is being embloyed.
FUNCTION OF CONTROLS.
3. The front panel controls are described in the order in which they could be used for
setting-up prior to use.
POWER Makes and breaks the power supply to the mains transformer.
R.F. RANGE MC/S This control enables the selection of one any of five antenna ranges
plus two WIDEBAND positions, one of 75-ohms input impedance
and other a high impedance input of 2000-ohms.
R.F. ATTENUATOR This control enables the operator to reduce the level of all incoming
signals when strong unwanted signals are present which cannot be
rejected sufficiently by tuning the antenna.
MEGACYCLES This control selects the desired Mc/s frequency. The dial should be
checked periodically to ensure that its setting is reasonably central
with respect to the band in use. This is indicated by a reduction
of signal or noise on either side of the correct setting.
SYSTEM This switch provides facilities for STANDBY, MANUAL, A.V.C.,
CALIBRATION and CHECK B.F.O.
BANDWIDTH The two crystal filters determining the band- width are adjusted
to ensure that their centre frequencies are all within 50 c/s, thus
any bandwidth can be selected without retuning the receiver. Six
bandwidths are provided as follows:-
13 kc/s, 6.5 kc/s, 3 kc/s and 1.2 kc/s (L-C) 300 c/s and 100 c/s
(crystal)
A.F. GAIN The A.F. GAIN control adjusts the audio output.
KILOCYCLES This control selects the desired kc/s frequency. The calibration of
this scale may be checked at 100 kc/s intervals by setting the system
switch to the CAL. position and V.F.O. switch set to INT.
B.F.O. The B.F.O. ON/OFF switch makes or breaks H.T. to the beat
frequency oscillator.
B.F.O. NOTE KC/S The B.F.O. is exatly tuned to a central point on the I.F. ampli-
fier response when B.F.O. NOTE KC/S control is st to zero-beat
with the calibrator. Having standardized the B.F.O. frequency, the
frequency of an incoming signal may be accurately measured by set-
ting the KILOCYCLES control to a zero-beat position; the B.F.O.
should de detuned in order to produce an acceptaple note for c.w.
reception.
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