Do I use a wrong type of rf-mixer?

Hi,

I am new to RF-mixers, and i read that RF mixers should maintain the amplitude and phase relationship from the RF-input signal (Linearity).

Do I use a wrong type of mixer, ore are there other ways of doing this. I can not get phase alignment. Maybe I am missing a fundamental issue.

If anyone can enlighten me on this subject, I wold appreciate it so much.

Data:

I am using the mixer “ADL5801”. My RF-in signal is 0dbm, 440Mhz.

My LO-inn signal is 0dbm 485Mhz.

My IF-out signal is filtered thru a 45Mhz crystal-filter.

I am not able to get any phase lock between RF-in and the 45Mhz.

Best Regards

Richard

Top Replies

  • Actually, what does it mean 

    phase lock between RF-in and the 45Mhz

    ?

    RF and IF are both in different frequency domain, the phase is not defined. Or IF=45MHz is an input of PLL?

  • Hi,

    I will try to explain a little clearer.

    I am trying to get a phase relationship between the RF-input and IF-output signal, although these are to different frequencies my belief was that this was how it would work.

    In some ways like a PLL, if I measure the two signals with a scope, it wouldn't matter witch of the two I was triggering on, both would show clearly. The signals would not drift from Itch-other.


    My project is to receive a radio signal at one frequency converting it to another, and sending it out again. The two signals must not drift opposite Itch-other. On the output I am using a PLL, for the uppconverting, but on the input because of filtering I was hoping to use a RF- mixer.


    I hope I can get to the bottom of this problem.

    Best Regards
    Richard

  • RF-input and IF-output signal, although these are to different frequencies my belief was that this was how it would work

    I afraid, it is not true. Result of division 485MHz/45MHz is not integer number, but 10 7/9 thus you cannot think about phase relation if you trigger in principle at random edge of RF (or IF) signal. Even if the both frequencies are in integer relationship there are other conditions to see on the oscilloscope non-drifting signals. First, IF must be filtered, otherwise you measure not only e.g. LO-RF (in case LO is above RF) but also LO+RF signals and probably LO (and its harmonics) leakage. Second, the LO signal of the mixer shall use the same freq. reference as the RF signal, otherwise small frequency offset may cause slow drift in phase. 

  • Thank you so much, this was exactly the information I was looking for

    Best Regards

    Richard