Passive Matching Network

[Skillet]

resistive matching network

For a class I was asked to design the insides of a 'black box' matching network.

It is a very simple problem, but I am having some trouble with it.

I have a 600 Ohm generator load, and a 50 Ohm terminating load.
When looking into the box on either side the impedance has to be matched.

The 'box' has an attenuation of 3 dB and all of the elements have to be passive. The voltage source is a sine wave with an frequency that theoretically can range from 0 Hz to infinity.

We are supposed to make the innards of the box to these specifications. To me it looks like a matching network for a phone system, but I don't understand exactly how I am supposed to make the matching system. I thought about using a isolated transformer approach, but I'm pretty sure that their is a simpler way to solve the problem.

Thanks for the help

 

[biff44]

low pass t matching network

You can not make a passive attenuator, using resistors alone, that simultaneously has 600 ohm inpedance at one port, 50 ohms at the other port, and only 3 dB of loss. You can, using series and shunt resistors, get the two impedances to match, but the loss will be much greater than 3 dB.

So you are going to have to use some sort of reactive matching, which would be narrow band, or a 600ohm to 50 ohm transformer and a resistive 3 db pad, or something like that. Unfortunately, you can not buy a transformer that works from ohz to infinity!.

Good luck

Added after 2 minutes:

A passive (resistor only) matching attenuator apparently will have at least 16.63 dB of loss:
https://chemandy.com/calculators/matching-t-attenuator-calculator.htm

 

[flatulent]

passive matching

Many companies, such as minicircuits, make transformers that go between these two impedances.

 

[Skillet]

matching network resistor

Thanks for the responses!

I worked out some of the numbers on the purely resistive attenuator and you are right in order to achieve a match between 600 and 50 ohms you need have at least a loss of 16 dB.

 

[kspalla]

passive resistive attenuator

I think it just impedance transformer like the balun in TV etc.
You better use inductive transformers for this application

 

[Phytech]

t attenuator network calculator

How big is the size of your "black box"? you can easily use a low pass filter (LC for example) to make the transformation.