Instruments required

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  1. Two (3) Signal generators
  2. Hybird combiner
  3. Audio AC voltmeter
  4. Distortion meter (FM Only)
  5. Noise figure meter (for noise figure measurements only)
  6. Two (2) step attenuators with 10dB and 1dB steps
Top to bottom, HP 3406A Broadband Sampling voltmeter, Tektronics TAS 465 Two Channel 100MHz Oscilloscope, HP 3586B Selective Level Meter, and HP 8656B Signal Generator

The signal generators at the W9KFB lab are as follows:

  1. HP 3586B Selective Level Meter (dBm measurements are calibrated for 75 Ohm characteristic impedance, signal is 0 dBm out only at the level measurement frequency)
  2. HP 8656B Signal Generator 0.1-990 MHz (dBm measurements are calibrated for 50 Ohm characteristic impedance)
  3. HP 10544A Crystal Oscillator
Formulas and Values for a 45 Ohm Hybrid Combiner
Homebrew 45 Ohm Hybrid Combiner

The Hybird combiner was made from an old PC network splitter. The device was found in an used PC warehouse. It was a four port device with 4 BNC jacks on it. On inspection of the device, we found that it was a resistive splitter with four 39 Ohm resistors connected to each BNC center contact and a common point. These were removed and replaced with 15 Ohm 2 Watt 2% resistors metal film resistors (NTE 2W015 Flameproof Resistors).

To design you own splitter/combiner see this web site for a calculator[1]