# How to test an RF attenuator with limited tools

I have an RF attenuator with the specification:

• Freq DC to 3 GHz
• 30dB attenuation
• 2W avg power rated
• VSWR = 1.2 max
• Imp = $50\Omega$

How can I test this attenuator without a spectrum analyzer?

I have an oscilloscope which has a 1kHZ, 5V output. Can I use this signal to check the attenuator and observe the attenuator output with the scope?

Will 5V is too high for this attenuator?

• You cannot verify any of these specifications without RF test equipment.!! I see you have never done this before. – Tony Stewart Sunnyskyguy EE75 Oct 14 '16 at 6:50

I have a RF attenuator with spec (Freq DC to3 Ghz, 30dB attenuation, 2W avg power rated, VSWR=1.2max. Imp= 50ohms , how can i test this attenuator without spectrum analyzer.

If you want to test its attenuation characteristics, you could use a signal generator and an rf power meter instead of a spectrum analyzer.

If you want to test its VSWR (impedance matching characteristic), you'll also need a directional coupler. Or else a slotted airline probe. At which point you're well on your way to trying to build your own network analyzer.

I have scope which has 1kHZ 5V output, can I use this signal to check the attenuator, and observe the atternuator output at scope.

Along with a 1 kHz signal generator, you could test the attenuator up to 1 kHz. But that won't tell you whether it works at 3 GHz as specified. Any deviations from specification are most likely to happen at the high end of the device's frequency range.

Will 5V is too high for this attenuator?

5 V into 50 50 ohms is 0.5 W, well below the rating for this attenuator.

• About 5V 1Khz signal from scope, with the Peak-to-Peak value equal to or greater than 1MΩ of load. – Transformer Oct 14 '16 at 10:34

Yes you can use any signal from DC to 3 GHz to test the pad. 5V is not too much for a 50 Ohm, 2 Watt pad.

It might be easiest to test it with DC. Connect a 50 Ohm resistor to the output of the pad. Apply a voltage. Measure input voltage and input current accurately. Use Ohm's law (V = IR) to calculate input resistance. Should be 50 Ohms.

Measure output voltage and input voltage. Calculate attenuation. If it is 30dB, then a 5V input will generate a 158 mV output, so use a good mV meter.

Attenuation (in dB) = 20 * log (Vin/Vout). Should be 30.

You can use your 1kHz signal, too, if you want. But make sure the pad output is terminated in 50 Ohms. Best to measure input and output voltage simultaneously.

Good luck.