Eddystone EC10 Transistorised Communication Receiver Instruction Manual

Eddystone EC10 Transistorised Communication Receiver Instruction Manual

The EDDYSTONE Model EC10 is a fully transistorised single conversion communi- cation receiver covering the frequency band 550 ke/s to 30 Mc/s in five ranges. Provision is made for AM and CW reception and the unit is powered by a self-contained battery pack.

A total of ten transistors is employed together with five diodes one of which is a zener type which serves to stabilise the supply for the RF section of the receiver. This arrangement helps to maintain a sensibly constant per- formance with falling battery voltage. Current drain has been kept to a minimum to prolong battery life.

A wide variety of aerials can be accommodated including a small telescopic rod aerial for portable operation. An internal five inch loudspeaker is fitted and arrangements are made for using low impedance telephones where this is more convenient. A push-pull audio output stage is employed and a selective audio filter can be introduced for CW reception under conditions of severe adjacent channel interference.

Independent RF and AF Gain controls are fitted and the other controls include separate BFO and AGC switches and a variable BFO pitch control. The tuning drive is a geared type and is flywheel-loaded for ease of operation. Tuning scales are some nine inches in length and are calibrated directly in terms of frequency. Dial illumination is provided for use when necessary and is controlled by a switch on the panel.

The receiver is light in weight, has contem- porary styling with compact dimensions and is housed in a strong metal cabinet. High quality components are used in all parts of the circuit and reliable operation is assured throughout the world.

TECHNICAL DATA

Frequency Coverage
550 kc/s to 30 Mc/s in 5 ranges :—

Range 1: 18-0 — 30:0 Mc/s
Range 2: 8-5 — 18-0 Mc/s
Range 3: 3-5 — 8-5 Mc/s
Range 4: 15 — 3-5 Mc/s
Range 5: 550 — 1500 kc/s

Intermediate Frequency
465 ke/s.

Semiconductor Complement

TRI: OC171 RF Amplifier.
TR2: OC171 Mixer.
TR3: OC 171Local Oscillator.
TR4: OC 1711st IF Amplifier.
TRS: OC 171 2nd IF Amplifier.
TRO: OC 171Beat Oscillator.
ERY: OC 171 Audio Amplifier.
TR8: OC83 Audio Driver.
TRO: 2X Audio Output.
TRIG: OC83
D1: OA7 AGC Attenuator.
D2: OA90 Detector/AGC.
D3: OAZ203 Voltage Stabiliser.
D4/5: 2xDDO006 Aerial Protection Diodes.

Power Supply
9V from 6 x 1-5V leak-proof dry cells, external supplies of 12V or 24V DC (positive earth) using Voltage Converter Type 945° or standard AC mains supplies using AC Power Unit Type 924.

Consumption
36mA quiescent, 77mA at 50mW and 180mA at 500mW output.
Dial lamps when in use add 90mA to the normal current drain.

Aerial Input Impedance
Ranges 1: — 4 iy 75Ω2 (nom) balanced or unbalanced.
Range 5: Re sie 400Ω (nom) balanced or unbalanced.

A high impedance input connection is provided for use on all ranges and is suitable for use with short rod aerials.

Sensitivity
Better than 5uV for 15dB s/n ratio on Ranges 1—4.
Better than 15uV on Range 5.

IF Selectivity
Typical overall bandwidths at 6dB and 40dB down are 5 kc/s and
25 kc/s respectively.

IF Breakthrough
Ranges 1 — 4 : greater than 85dB down.
Range 5  : greater than 65dB down.

Image Rejection
20dB at 18-0 Mc/s and 50dB at 2:0 Mc/s.

Calibration Accuracy
1% on all ranges.

Frequency Stability
Drift does not exceed 1 part in 104 per °C change in ambient temperature.

AGC Characteristic
An 80dB increase in signal produces less than 12dB change in output. Taken from 6uV at 2-0 Mc/s on Range 4.

Audio Output and Response
The maximum audio output exceeds | watt and 800mW is available at 10% distortion.

Frequency response is level within 6dB over the range 300 c/s to 8 kc/s except when using the audio filter. The filter is resonant at approximately 1,000 c/s and can be brought into circuit for selective CW reception. 6dB bandwidth is of the order 180 c/s.

Dimensions and Weight

CIRCUIT DESCRIPTION

The RF Section of the receiver comprises TRI, TR2, and TR3 @ x OCI71). TRI is a grounded-base amplifier with signal input applied to the emitter from a tap on the appropriate tuned circuit which is selected by Sla, b and c. L1/C2 is introduced on Range 5 and serves as an IF rejector circuit to limit IF breakthrough when using this band. AGC can be applied to the RF Stage and manual gain control is effected by RV1 which also controls the Ist IF Amplifier TR4. The RF Stage is coupled tothe Mixer by-L7-L11 which have low impedance secondaries to match the base imped- ance. Oscillator injection is to the emitter and IF output is taken from the collector to the Ist IF transformer IFTI.

A tuned collector circuit is employed in the Local Oscillator Stage (TR3) which tracks above the signal frequency on all ranges. Injection for the Mixer is taken from a low impedance link winding on the appropriate oscillator coil.

A\ll three stages in the RF Section are operated from the stabilised supply provided by the zener diode D3 (OAZ203). This gives a nominal 6:5V and maintains sensibly constant performance with falling battery voltage. All tuned circuits associated with TRI-TR3 employ precision wound coils and have individual trimming adjustments. The circuits are arranged in such a manner that the coils which are not in use are shorted out to prevent absorption and dead spots in the tuning.

IF amplification is provided by TR4 and TRS (2 x OC171) which operate at 465 ke/s with a total of five tuned circuits to ensure a high degree of adjacent channel selectivity. AGC and manual gain control are applied to the first stage while the second operates at constant gain, Improved operation under strong signal conditions is given by the diode switch (D1 : OA70) which introduces a damping resistor (R19) across the primary of IFT1 when the signal exceeds a certain level. This action assists the AGC circuit and prevents overloading of the Detector and TRS.

The diode (D2 : OA90) which serves as the Detector is housed in the IFT3 screening can and also provides the AGC voltage which is applied to TRI and TR4 via’ the filter circuit C63/R28. Audio output from the Detector is coupled through C74 to the base of the Audio Amplifier which is an OC71 (TR7).

TR6 is introduced for CW reception and provides a locally gen- erated carrier which is amplified by TRS and applied to the Detector along with the normal signal. The beat frequency obtained can be adjusted by means of the pitch control C70. TR6 derives its supply from the zener diode D3.

An audio filter (L18/C76) is included in the coupling between TR7 and the Audio Driver Stage TR8 (OC83). The filter is resonated at approximately 1,000 c/s and will be found most useful for CW reception when interference is severe. The filter can be switched out by S4 when receiving AM signals.

The push-pull Output Stage operates in Class “B” and provides a 3Q output to feed the internal loudspeaker. Low impedance telephones can be plugged into a socket on the panel and the circuit is arranged so that the speaker output is interrupted when telephones are in use,

INSTALLATION

Batteries

The EC10 receiver is supplied without batteries. Six standard 1-5V dry cells are required and these are of a type which is available in all parts of the world. It is recommended that leak-proof types are used wherever possible, the Ever Ready HP2 being suggested as the most suitable battery for this receiver. Other batteries which can be used are as follows:

N.A.T.O. Stock No. 6135-99-910-1101.

To fit the batteries, first unscrew the two knurled screws which retain the battery box at the rear of the receiver. Lift the box clear and free from the receiver by disengaging the four-way connector at the right-hand end. Now remove the inner cover from the box, sort the batteries into two groups of three and slide them into the battery troughs.

Use the diagram printed on the battery container as a guide when fitting the batteries and make absolutely sure that they are in the correct positions before switching on the receiver. Switching on with the batteries connected the wrong way round will damage the transistors. Replace the inner cover, re- connect the four-way plug and then re-fit the battery container in the rear of the set. It should be noted that the plug is a non-reversible type so that there is no chance of the battery polarity being reversed at this point.

Aerial Connections

Sockets are provided for connecting short rod aerials, normal single wire aerials and either balanced or unbalanced transmission line feeders. Single wire aerials are connected to the “A1” socket with the special shorting plug in position between the “AE” socket and the “EARTH” terminal. This same shorting plug is also used when the receiver is fed with coaxial line or when using a short rod aerial. In the case of a coaxial feeder the outer braid is attached to the “EARTH” terminal and the inner conductor to the “Al” socket.

If a balanced feeder (twin transmission line) is employed, the shorting plug is removed and the feeder wires are connected to “AE” and “A1”. The shorting plug can be pushed temporarily into the “A2” socket to avoid loss. This latter socket is used only for connecting short rod aerials when a full size aerial is not available.
The socket is not suitable for connection of resonant loaded whip aerials which should be connected at the “A1” socket with the link in place between “AE” and “EARTH.”

In some cases a good earth will give improved results and it is well worth taking the trouble to install one. Reduction in the level of locally generated noise will be one of the advantages gained from proper earthing of the receiver.

Telephones

Telephones or an external loudspeaker can be connected to the socket on the panel. The output is matched to 3&2 and will give satisfactory results with telephones of up to 60082 impedance. Higher impedance can be used but with some reduction in output and slightly inferior quality.

OPERATION

Operation of the receiver is quite straightforward and a few minutes spent in manipulating the various controls will quickly familiarise the user with their functions.

The SUPPLY switch is ganged to the RF GAIN control and is moved to the “‘on”’ position by rotating the RF GAIN ina clockwise direction. Tuning is with the large knob at the right-hand side of the panel, the drive mechanism being a precision unit employing spring-loaded split-gears giving a reduction ratio of the order 110-1.
This facilitates accurate tuning on the HF ranges while flywheel- loading allows the control to be “spun” to permit rapid movement from one part of the dial to another. The dial calibration is in Mc/s on all ranges except Range 5 where the scale is marked in ke/s. Range numbering appears at the left-hand end of the dial and is repeated on the WAVECHANGE switch which is located immed- iately to the left of the TUNING control.

The calibrated vernier which appears in the window above the TUNING control is used in conjuction with the bottom logging scale on the main dial. Combining the two readings will give an arbitrary figure which corresponds to the actual frequency to which the receiver is tuned. The readings can be recorded to allow rapid re-setting to specific frequencies.

Independent RF and AF GAIN controls are provided, the former being a combined RF and IF control. Four push-button switches control the following functions :—

AF FILTER IN/OUT, BFO ON/OFF, AGC ON/OFF and DIAL LIGHTS ON/OFF. The DIAL LIGHT switch is mechanically biased to the “off” position and must be held in the “on” position to obtain scale lighting. Illumination of the dial will not normally be required and since the scale light consumption doubles the average current drawn from the supply, this facility should be used only when absolutely essential. The other switches are of the press- to-operate press- to-release type and lock in the “‘on”’ position.

The remaining control is the BFO PITCH control which is function- al only when receiving CW signals. It allows the BFO to be set to either side of the incoming signal and when using the audio filter it provides a means of setting the beat note to coincide with the resonant frequency of the filter (1,000 c/s).

The AGC will normally be switched “off” when receiving CW signals (BFO “on”) and under this condition of operation it is usual to reduce the setting of the RF GAIN to prevent overloading of the pre-detector stages. When receiving AM signals the AGC should be in use and the RF GAIN is then advanced to maximum to secure optimum AGC action.

ERRATA

R24 should read: 1.5K, R35: 47K.
C10 should read 20pF.
Add C23a. 10pF Tubular Ceramic across tuned winding of L9.
D1 is shown reversed.
Add two DD006 diodes (parallel- connected with reverse polarity) across the “Al” and “AE” terminals. Alloc- ate Reference D4 and DS.

Layout of  IF Printed Board

LIST OF COMPONENT VALUES

CAPACITORS

72, 73, 76 : O-luF Polyester+20% 250V DC wkg.
C17| 0-0015uF Tubular Ceramic+50%—25 % 750V DC wkg.
C20| 34 : 70pF Tubular Ceramic+10% 750V DC wkg.
C29| 0-005uF Tubular Ceramic+10% 750V DC wkg.

15V DC wkg.
C67| 1pF Tubular Ceramic–0-5pF 750V DC wkg.
C68| 0-001uF Polystyrene+5% 125V DC wkg.
C69| 470pF Polystyrene +5°% 125V DC wkg.
C70| 5-60pF Air-Spaced variable.
C78| 1-25uF Tubular Electrolytic+ 100°%—10 % 16V DC wkg.
C80| 0-25uF Metallised Paper +20% 150V DC wkg.
C81| 350uF Tubular Electrolytic+ 100 %—20% 12V DC wkg.

MAINTENANCE

General

The EC10 receiver should require very little in the way of routine maintenance apart from replacement of the batteries. If a fault should develop, the cabinet can be removed by carrying out the procedure detailed below :

1. Remove the battery container by unscrewing the two knurled retaining screws and disengaging the four-way battery connector at the right-hand end.
2. Remove the four cabinet retaining screws.
3. Free the cabinet from the panel by applying pressure with the fingers between the rear inner edge of the cabinet and the ends of the strip which supports the IF printed board near the top of the cabinet.
4. Slide the cabinet away from the panel.

Dial Bulbs

Faulty dial bulbs can be changed by levering the holders free from the rubber mounting grommets at the extreme ends of the dial.
Replacement bulbs should be of the L.E.S. type rated at 6V, SOA.

Instructions for re-stringing the drive cord

In the unlikely event of the pointer drive cord either breaking or slipping out of the pulley grooves, replacement will present no real problems if the instructions given below are followed carefully. If the cord is broken, a new length should be obtained and this can be  made longer than the length actually required (32” : 82cm.) to make it easier to handle. Right-hand and left-hand in the instructions given below are as viewed from the rear of the receiver.

1. Remove the existing cord and then set the tuning gang to full mesh,
2. Tie a double knot in one end of the replacement cord and feed the cord through the hole provided in the left-hand drive pulley with the knot on the inside of the rim. The hole should lie at approximately “4 o’clock.
3. Wind approximately one and a half turns anti-clockwise round the drive pulley and then pass the cord under and over the left-hand guide pulley.
4. Pass the cord across the dial from left to right and then, while holding the free end of the cord in tension, rotate the tuning  control to fully unmesh the tuning gang. This operation will wind just over three complete turns of cord onto the left-hand drive pulley and tension must now be maintained to prevent the cord from slipping out of the pulley groove.
5. Pass the cord clockwise round the jockey pulley (right-hand side of the receiver) and then back across to the right-hand drive pulley. Feed the cord into the pulley groove and then through the hole in the rim (hole lies at about “10 o’clock) Increase the tension on the cord until the outer rim of the jockey pulley takes up a position level with the nearest edge of the panel handle retaining screw, Mark the cord with a pencil at the point where the retaining knot must be tied.
6. Free the cord from the jockey pulley and while maintaining tension, draw the cord through the hole in the right-hand drive pulley until the cord tightens on the left-hand guide pulley.
7. Tie a double knot in the position marked in (5) above and cut off any surplus cord. Feed the cord back through the hole and replace in position round the jockey pulley.
8. Set the tuning gang to full mesh and slide the pointer to ‘O” on the logging scale. Attach the pointer to the cord (when viewed from above the cord should pass under the two outer prongs at the rear of the pointer carrier) and then check the drive for free and normal operation.

Re-alignment

The initial factory alignment of the receiver should hold for a long period of time and re-alignment should not be carried out unlessthere is a clear indication that it is in fact necessary. Alignment  should be carried out only by individuals with a sound knowledgeof the procedures involved and the test equipment listed below must be available if the task is to be completed satisfactorily. It should be noted that any figures quoted for sensitivity etc., are based on the assumption that a new set of batteries is in use. It is further assumed that the receiver cabinet has been taken off as described earlier.

The following items of test equipment are required for re-alignment

Signal generator(s) covering 465 kc/s and the range 550 ke/s to 30 Me/s with provision for modulation at 30°% (400 c/s) and with an output impedance of 50/7592.

Crystal controlled harmonic generator providing 100 ke/s markers up to 7-5 Mc/s and 1 Mc/s markers up to 30 Me/s.

Output meter matched to 32 with plug to mate with telephone socket.

Trimming tools :
Miniature insulated screwdriver with 7” blade, small metal-tipped insulated screw- driver and a Neosid Type H.S.1. hexagonal core adjuster.

Re-alignment of the IF Stages and BFO

First locate and remove the four screws which retain the IF printed wiring board. Turn the board through 90° into a vertical position and replace two of the screws to keep the board in this position. All trimming adjustments are now accessible and there is no need to unsolder connections to the board.

Now stand the receiver on one end to allow connection of the generator output lead to the Range 5 Mixer coil L11 (see underside view of receiver). The generator should be arranged to provide a 508 source and the earth lead can be clipped to the screen adjacent to the coil. Disable the Local Oscillator by shorting out the forward section of the tuning gang (C48) and then plug the lead from the output meter into the telephone socket on the panel. The speaker is automatically disconnected on insertion of the plug and the meter will therefore indicate true output power.

Switch on the generator, allow it adequate time to stabilise against drift and then set the receiver controls as follows :

Tune the generator to 465 ke/s (with modulation 30% at 400 c/s) and then set the attenuator to give a reading of approximately S0mW on the output meter. Peak the cores in IFT1, IFT2 and IFT3 formaximum output, all cores being set on the “outer” peak. Re- check each adjustment several times to ensure accurate alignment and then set the attenuator for an output reading of SOmW. The input should be of the order 4uV at 465 kc/s. If the IF sensitivity appears to be on the low side investigation can commence with a check on the AF sensitivity. At 1,000 c/s an input of 12mV across RV2 should result in an output of SOmW.

Leave the generator tuned to the intermediate frequency, switch off the modulation and unplug the output meter. Set the BFO pitch control to mid- travel (index on knob at 12 o’clock) and check that the mid position corresponds to the half-capacity setting of the capacitor and that clockwise rotation of the control results in an increase in capacity. If necessary, slacken the grub screw and re-set the knob before proceeding. With the control at mid-travel, switch  on the BFO and adjust the core in L17 for zero-beat. Check fornormal operation of the BFO control and then disconnect the generator and the shorting link across C48.

Re-alignment of the RF Section

The first step in this part of the procedure is a check on the overall calibration accuracy. Proceed as follows :

Connect the output of the harmonic generator to the “AI” and “AE” sockets with the shorting link in place between “AE” and “EARTH.” Set the generator to provide 1 Mc/s markers and then with the BFO switched on, tune across Range 1, checking the scale accuracy at each megacycle point. The scale accuracy should be within 1% (ie. 300 kc/s at 30 Mc/s, 180 ke/s at 18 Mc/s etc.) and re- alignment of the Local Oscillator should not be attempted unless the error observed is greater than this.

Repeat the check on Ranges 2 and 3, again using the | Mc/s markers and then check Range 4. The 100 kc/s markers can be introduced

on this range so that checks can be made at the half-megacycle points. Finally use the 100 kc/s markers to check Range 5.

If errors in excess of 1 % are noted, carry out normal tracking procedure using the alignment frequencies and adjustments listed in the preceding Table. Adjustment should be restricted to the ranges on which excessive error is noted and care should be taken to repeat the adjustment of trimmer and core until interaction between the two adjustments is nullified.

Alignment of the RF (Aerial) and Mixer circuits can now be commenced. Disconnect the harmonic generator and connect the standard signal generator (modulation 30% at 400 c/s) and arrange the output impedance to match 7512 for Ranges 1-4 and 400S2 for Range 5. Re-connect the output meter and switch off the BFO.

Adjustments are made at the same frequencies employed for oscillator alignment but using the trimmers and cores listed in the second Table. As with oscillator alignment each adjustment should be repeated several times to cancel the interaction between core and trimmer.

L7L8L9L I 0LI I

On completion of the adjustments on Range 5, tune the receiver to the low frequency alignment point (560 kc/s) and the generator to 465 kc/s. Increase the generator output until an indication is obtained on the output meter and then adjust the IF rejector coil L1 for minimum output. Re-tune the generator to 560 ke/s, reduce its output and check the alignment of L6 for maximum signal. Repeat the checks once more at both 465 kc/s and 560 ke/s and then carry  out a sensitivity check on all ranges.

Plan View of Model EC 10 Recieiver

Underside View of Model EC 10 Receiver

VOLTAGE ANALYSIS

The voltage readings given in the Table will prove useful in the event of the receiver developing a fault which makes it necessary to carry out voltage checks. All readings are typical and were taken with a meter having a sensitivity of 20,000 Q/V. The batteries were in new condition and a tolerance of 10 V, will apply to all readings taken with a meter of the sensitivity quoted. The tolerance should be increased if a meter of lower sensitivity is employed and allowance must be made for the state of the batteries.

Readings should be taken under “no-signal” conditions with the controls set as follows : All readings are NEGATIVE with respect to chassis and the stabilised supply should lie in the range 6.4-6.6V.

* Readings become 6-5V, 0-1V and OV with RF Gain at min.
** Readings become 7.35V, 0.35V and 0.16V with RF Gain at min.

SPARES

The following list details all major spares for the ECIO receiver.
The Serial No. of the receiver must be quoted in all correspondence and enquiries should be directed to the “Sales and Service Dept.”

Inducators, Transformers etc.

Miscellaneous

Range Switch

Telephone; 021-475 2231
Cables: EDDYSTONE, BIRMINGHAM
Telex: 33708

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