Coupling/Mixing transformer

Discussion in 'General Electronics Chat' started by KCHARROIS, Aug 10, 2012.


    Thread Starter Active Member

    Jun 29, 2012
    I'm having problems selecting a transformer for the following circuit below. The circuit does do what I want it to do but what kind a transformer would I need to mix 2 signals together when I actualy build the circuit? I've been looking on digikey and I see transformer with different unductance values?

    The incoming signal is 5MHz going on to a 10KHz signal.

    Thanks in advance
  2. vk6zgo

    Active Member

    Jul 21, 2012
    I'm a bit confused about what you are trying to do.
    "Mixing" in the Electronic sense,normally means to feed both signals into a non-linear device,so that in your case,you would end up with the 10KHz signal,the 5000kHz signal,plus two new signals at 5010KHz & 4090kHz.
    Normally,the 10kHz signal would be filtered out,leaving you with an Amplitude modulated signal,where 5000kHz is the carrier,& the other two signals the upper sideband (USB) & lower sideband (LSB) respectively.
    In your circuit, Q1 would be the non-linear device,& you would be using "gate modulation".

    The other meaning of "mixing" which is mainly confined to the music,PA & Broadcast industries is where two signals are added together without the process described above taking place.They should really be called an "ADDER".
    I think that this may be what you want to do.
    If so,to make sure that the signals do not combine to produce sidebands as in the earlier case,the operating conditions of Q1 must be such that it is linear.
    In the real world,some "intermodulation"will occur,but it is usually at such a low level that it may be ignored.