How to apply a crystal oscillator to a mixer?

[Circuit_seller]

Hi

I want to apply a crystall oscillator to a mixer, and want to filter unwanted harmonics. What is the best solution?

Regards

 

[DJ]

Depend on the mixerfrequency range.
In some cases you can design a subharmonic mixer so the Cristal Oscillator is the LO.
If the LO is too high in the frequencyrange, check if you can modulat it by the data and then use the Cristal as the IF.

D.J

 

[djalli]

Oscillator will have harmonics true but what worsen things is the mixer. All harmonics can be eliminated in either cases using filters.

 

[flatulent]

If this is very important to you, first filter the output of the oscillator and then put in a power amplifier that is capable of an output 10 dB or so more than needed to drive the mixer. This "back off" should make the amplifier highly linear.

 

[DJ]

Did you simulate the circuit and found a problem with the harmonics?
Are you going to design the mixer? If so you can design a parallel or antiparallel couple diodes to reduce the even or odd harmoics. If not you can use a narrow band BPF at the Cristal output.
D.J

 

[crystalguy]

alot depends on the type of crystal oscillator you are intending to use. in the case of a Pierce type oscillator, you should take the signal from the input side of the active device. at this point the signal should be a pure sinwave with very little harmonic content. If you have the choice, use AGC rather than selflimiting design to keep the harmonics to a minimum. use a design that allows you take the signal after it has been filtered by the crystal good ones would be: emmiter coupled, pierce, Butler. Hope this helps.

 

[Circuit_seller]

Hi

I want a 21.4MHz - 455KHz LO Signal to an Active mixer using a crystall oscllator. I want to design a BPF after the crystall oscillator to remove harmonics, So my quetsion is "What is the best configuration".
LO Drive power is -10dBm.

Best Regards

 

[crystalguy]

if you are looking for a good performance filter than i would recomend that you just buy an inexpensive monolithic crystal filter centered at 21.4MHz. i think you can buy these off the shelf from digikey. in volume, these filters are very inexpensive.

 

[sergio mariotti]

Are you sure the harmonics generated by the Xtal oscillator are "bad" for your conversion mixer?
Since the mixer is a non linear device, it generate inside an high level of harmonics, so the harmonics generated by the oscillator may be a NON problem.

 

[DJ]

As I understand it you made your mind and came to a conclusion that for a specific cristal oscillator you have to filter harmonics.
You can find MURATA LPF normaly used for DC. Or a cristal or LC LPF.
If you know the most problematic harmoinc think to have BSF instead.