A simple means of checking whether Transmitters and Antennas were working properly was required. For outside broadcasts in particular there is always the question as to whether the Antenna is resonant.

A commercial Power/VSWR meter is the obvious solution here but not everyone understands VSWR and I wanted to explore something different.

The ‘Stockton’ Power Meter is well known in the industry, named after David Stockton who popularized the concept through Amateur Radio Press. This Meter consists of a true 4 Port Hybrid which allows the simultaneous measurement of Transmitted and Reflected Power.

The Hybrid is seen the picture below, it is made up with two transformers consisting of some Semi-Rigid cable, Enameled copper wire and a couple of Ferrite cores.

The performance of the Hybrid over 100MHz is shown in the graph below. The isolation is about 30dB with respect to the coupled path at 50MHz which is good enough for this application.

The coupling is not far off what is expected by the 12:1 transformer ratio chosen. I am only operating at 50MHz but if calibrated at this point the error over 1.5-75MHz is only ±0.02dB.

The outputs of the Hybrid are Rectified and applied to two meter's which are calibrated with a Power scale up to 10W.

The complete unit uses N type connectors for the RF in and out and also has BNC outputs from the Detector’s. These can be connected to a Voltmeter for accurate measurements or they could be used to automatically detect a high level of reflected power – this could be used to switch the PA off in a Transmitter for example.