Delta Electronics CPB-1, CPB-1A & CPB-1B Common Point Impedance Bridge

Delta electronics Logo



The Delta Electronics Model CPB-1, CPB-1A and CPB-1B Common Point Impedance Bridges are operating impedance bridges similar to the Model OIB-1 and Model OIB-3, but are designed for permanent installation in the phasing equipment at the antenna common point. The CPB-1 operates with common point power up to 5 kW with 100% amplitude modulation on a continuous basis. The CPB-1A operates with common point power up to 50 kW and the CPB-1B operates with common point power up to 100 kW. These instruments have two 4″ dials calibrated directly in resistance and reactance. A front panel meter operates as a null detector. The R and X dials are manipulated as a normal bridge to give a null indication on the panel meter while the transmitter is operating at full or reduced power. The value of the common point resistance and reactance are then read directly from the two dials.
Many directional antennas have common point impedances which vary from time to time due to seasonal drift of the antenna parameters. On many occasions, remeasurement of the common point impedance indicates that the station had been transmitting with less than full power for some time because of these changes. The Common Point Bridge permits the station operator to determine the common point impedance at all times, even during normal operating hours. By minor adjustment of the common point resistance control, the station can maintain radiated power at the full license value at all times. Changes in the antenna system which affect the common point impedance are easily detected with the Common Point Bridge. This alerts the station to equipment faults and prevents citations for antenna misadjustment. The CPB-1, CPB-1A and CPB-1B thus satisfy a critical test equipment requirement of consulting and broadcast station engineers. Application Bulletin 2, available on request, describes the operation and additional uses of the Common Point Bridge.


Each Common Point Bridge may be supplied with a Delta TCA RF Ammeter System factory installed. The complete series of 5, 10, 20, 40, 80 and 160 Ampere single scale and dual scale RF Ammeters with appropriate sampling transformer are available. With the RF Ammeter mounted on the bridge panel, the total RF power is easily determined from the load current and measured resistance. Consult the factory with your requirements.

The Common Point Bridges are available mounted on a standard 7″ high by 19″ wide equipment rack mounting panel. They are also available with a custom front panel with special dimensions, finish paint and legend to mount in the phasor cabinet. Consult the factory with your requirements for mounting.

Technical Specification

Technical Specification

Frequency Range:
500 kHz to 1.65 MHz

Power Rating:
at 100% amplitude modulation continuous

CPB-1: 5 kW
CPB-1A: 50 kW
CPB-1B: 100 kW

Resistance Range:
30 to 100 ohms

Reactance Range:
±50 ohms at 1 MHz


±2% ±1 ohm

±2% ±1 ohm
(Provision is made for your consultant to adjust the calibration to agree exactly with your licensed resistance value)

RF Source:
Transmitter operating at normal or reduced power acts as source, no generator is required.

Tuned internal detector with 25 µA panel meter. BNC output connector for use with external detector.


No. 10-32 Screw Terminals

1/2″ Copper Straps

1/2″ Diameter Rod with 1/4-20 Mounting Holes

Standard 7″ high x 19″ wide equipment rack panel.
Optional 8-3/4″ high or 10-1/2″ high rack panel when supplied with integral TCA RF Ammeter System.

Optionally available with custom size and finish front panel for mounting in the phasor cabinet. Also available without panel for mounting directly on the phasor panel (drill template supplied).


Bridge with standard front panel:

7″ high x 19″ wide x 10″ deep.

CPB-1 or CPB-1A with TCA RF Ammeter System:
8-3/4″ high x 19″ wide x 10″ deep

CPB-1B with TCA RF Ammeter:
10-1/2″ high x 19″ wide x 11-1/4″ deep

Bridge without front panel:
7″ high x 9″ wide x 9-1/4″ deep

Comments are closed.