Learning about Amplitude Modulation using a EMRS-1 double balanced Mixer

Thread Starter


Joined Sep 14, 2008
I am trying to learn about AM by doing some experiments with a 555 timer producing a square wave at say 3Khz and a old Levell transistor Oscillator (TG668) at say 10khz.

I want to produce a full AM output signal from an EMRS-1 mixer.

I am having some trouble doing this.

I don’t know how to impedance match the two signals for driving the mixer.

Also I want the output to have some carrier with it, so I believe I need to add some DC bais to the IF siganal.

Carrier sine wave on the RF port and the square wave modulating signal with dc bias on the IF port.

Output from the LO port.

Is this correct configuration for AM ?

How much bias and how to apply it, and impedance match the two input signals to the EMRS Mixers input impedance requirements. What ratio do the input signal need to have to each other?

The RF port has low input impedance. The output impedance of the Level Oscillator is unknown.

How do I figure out the output impedance characteristics of the oscillator?
The IF port goes into the diode ring via the two secondary windings, i don’t know what it’s input impedance characterises would be.

I have seen 555 circuit driving 64ohm speakers coupled with 100uf capacitor, is this appropriate for driving the IF port?

Can anyone help with these questions or point me to some simple literature so I can work it out.

Many thanks


Thread Starter


Joined Sep 14, 2008

A couple of things I have found out.

EMRS mixer has grounds on pins 2,3 and 6 and they are not common to one another, ie the all need to be taken to ground individually.

The RF and LO ports are low impedance transformer inputs and conseqently require a minimium input freq of 0.5Mhz to produce enough
input impedance not to short out the source supply.?

I will try again with this configuration

I now think I want the square carrier at say 1mhz (can a 555 do this?)
on the RF port pin 4 and the 3khz modulation on the IF port pin 5 and output on LO pin 1