ETALDOC 370/4

Page 1 of 3

January 2001

PRODUCT DATA SHEET

UNIVERSAL 12kHz METERING

P2895

SIGNAL FILTER

Features

∗

  Miniature construction

∗

  >30dB attenuation at 12kHz

∗

  Matches 600

Ω

 and complex impedances

∗

  Minimal in-band attenuation

 

 

DESCRIPTION

Many telephone networks bear 12kHz  metering
signals at amplitudes sufficient to operate simple
relay-type apparatus without amplification on
customers' premises. Modems containing
semiconductor line-hold circuits are easily upset by
these large signals because the voltage swing may
exceed the standing DC level. The P2695 filter

deals effectively with this by problem suppressing
the metering signals, its attenuation ensuring that,
in the worst case, their level is reduced to less
than 0.25Vrms across the line-hold. The claimed
performance is maintained even when the drive is
the greatest of which the network is capable and
with simultaneous maximum DC superimposed.

CONSTRUCTION

to Electronic Techniques

(Anglia) Limited

P2895

ETALDOC 370/4

Page 2 of 3

January 2001

Safety

Worst-Case Drive

A non-safety-critical component.

Line to Line

Maximum:
Supports:

200V DC.
75V DC plus maximum ringing
voltage.

This is determined by the Swiss test  conditions
which are the most stringent. In Switzerland the
most unfavourable level of 12kHz meter pulses is
10Vrms at the subscriber's equipment.

(ETS 300 001 para. 1.7.8)

TEST CONDITIONS

Attenuation Test*

See circuit Fig. 1 Note that C1 etc. need not be
present.

Frequency

12kHz ±150Hz

Input voltage

up to 10Vrms

DC

up to 100mA

Temperature

-10ºC to +70ºC

*IN and OUT terminals MUST be respected but the
filter may be inverted because the transformer
interwinding  impedances are very high, so avoiding
imbalance effects.

PERFORMANCE CLAIMS

Attenuation

Exceeds 32dB.

NOTE:  Further attenuation at the load may be
provided by roll-off in the transformer.

P1200 and P2001

approx 6.0dB

P1165

approx 0.5dB

P2781

negligible

Input Impedance (11.88 – 12.12kHz)

With 15nF input capacitor C3, >800

Ω

 (almost pure

capacitance).
Without 15nF input capacitor, >1k

Ω

Line loading due to shunt impedance at 12kHz
±1%<1dB (600

Ω

 source, 600

Ω

 measuring set).

DC Resistance

Pins 1-2:   12.5-14.5

Ω

The Attenuation is defined as A =20 log          dB

Vx
Vy

430

Ω

200

Ω

DUMMY
FEEDER
BRIDGE

CURRENT

SINK

P2781

1

e

B

A

X

Y

P2895

ETALDOC 370/4

Page 3 of 3

January 2001

For matching to transformers and reference
impedances not specified below, please contact
Profec Technologies.

Z ref

Transformer

C1

C2

C3*

R1

Return Loss, dB

µ

F

nF

nF

ohms

300Hz

500Hz

2500Hz

3400Hz

220

Ω

+

P1200

2.2

27 ± 5%

15 ± 5%

910   2%

15

26

26

26

(820

Ω

//115nF)

P2001

2.2

27 ± 5%

15 ± 5%

910   2%

15

26

26

26

P1165

2.2

15 ± 5%

15 ± 5%

910   2%

14

24

26

20

P2781

2.2

15 ± 5%

15 ± 5%

820   2%

16

26

22

20

600

Ω

P1200

3.3

33 ± 5%

Not fitted 560   2%

16

21

21

19

P2001

3.3

33 ± 5%

Not fitted 560   2%

16

21

21

19

P1165

3.3

Not fitted

Not fitted 470   2%

15

21

22

18

P2781

3.3

Not fitted

Not fitted 470   2%

16

22

19

14

400

Ω

+

(500

Ω

//330nF)

P1165

2.2

27 ± 5%

Not fitted 620   2%

14

21

23

20

*To obviate the need for C3, ETAL® product P2622 is available.

COPYRIGHT

CAUTION

This signal filter has been designed and
characterized for use with ETAL line isolating
transformers only.  Satisfactory performance
cannot be guaranteed with other components.

ETAL and P2692 are  Trade Marks of Profec
Technologies Ltd.
The  Trade Mark ETAL is registered at the UK
Trade Marks Registry.

Profec Technologies Ltd. is the owner of the design
right under the Copyright Designs and Patents Act
1988 and no rights or licences are hereby granted
or implied to any third party.

© 1977, 2000 Profec Technologies Ltd.
Reproduction prohibited.

T R A N S F O R M I N G    T H E         F U T U R E

Profec Technologies Ltd., 10 Betts Avenue, Martlesham Heath, Ipswich, IP5 3RH, England

                           Telephone: +44 (0) 1473 611422

Fax:  +44 (0) 1473 611919

Websites: www.etal.ltd.uk

www.profec.com

Email:

info@etal.ltd.uk

sales@profec.com

ISO 9001

FM 25326

TRANSFORMER

C 2

2

R1

C 1

C 3

1

CURRENT

SINK

–

Z ref