How do I test for mixing products. - Page 1
Forum section: electronics / rf-microwave

author: Qmavam
author_rank: Regular Contributor
timestamp: August 25, 2019, 01:11:06 pm
content: I'm working on a variable inductor, it is varied by going up the B curve towards saturation,that is achieved by increasing the amplitude of an external magnetic field.It has been mentioned that when in this region it is non-linear and will create mixing products.How would I test this?I don't have a spectrum analyzer, could I just use my receiver to listen for the mixing products?How would a implement the two signals to drive the inductor?I mean a physical layout, I know I need two signal generators, how do I add the two signalsto drive the inductor?I only have one generator that can be modulated, I expect that I can just listen for that modulationat the mixed frequency. Does that sound right?Thanks, Mikek

author: David Hess
author_rank: Super Contributor
timestamp: August 25, 2019, 02:39:10 pm
content: Search for how to do a two tone intermodulation test.With two closely spaced tones combined from the two signal generators, the receiver can be set to monitor the various intermodulation products.

author: kg4arn
author_rank: Unknown
timestamp: August 25, 2019, 03:19:53 pm
content: What frequency range are you looking at?

author: Qmavam
author_rank: Regular Contributor
timestamp: August 25, 2019, 03:22:45 pm
content: Thanks David, I have a signal combiner, if I can find it!AM broadcast band up to 4 MHz Frequency range.Mikek

author: fourfathom
author_rank: Super Contributor
timestamp: August 25, 2019, 04:58:53 pm
content: Quote from: Qmavam on August 25, 2019, 03:22:45 pmMake sure your combiner has good port-isolation. Using a simple resistive combiner will send the output of one sig gen to the output of the other sig gen, which can cause the sig gens to generate their own intermod. This of course depends on the sig gen.

author: Qmavam
author_rank: Regular Contributor
timestamp: August 25, 2019, 10:57:14 pm
content: I think it was called a hybrid combiner, built from directions in the ARRL Handbook.It's probably 25 or thirty years old.Mikek

author: fourfathom
author_rank: Super Contributor
timestamp: August 25, 2019, 11:29:03 pm
content: Quote from: Qmavam on August 25, 2019, 10:57:14 pmGood. A hybrid combiner is what you want.

author: kg4arn
author_rank: Unknown
timestamp: August 26, 2019, 01:27:27 am
content: This app note explains how to do it. You can build a hybrid combiner for those frequencies yourself.You can use a receiver instead of the spectrum analyzer. A spectrum analyzer is just a receiver that sweeps and graphs for you.https://www.minicircuits.com/app/AN00-008.pdf

author: David Hess
author_rank: Super Contributor
timestamp: August 26, 2019, 04:56:34 am
content: Another option for combining the signal generator outputs is a simple resistive combiner with additional attenuators between the signal generators and combiner. The increased isolation between the signal generator outputs provided by the attenuators is almost always sufficient and the attenuation of the combined signal outputs may even be desirable.If you are up on your low distortion feedback amplifier design, then a summing amplifier can provide considerable isolation between its inputs.