[SOLVED] Issue regarding the multipliers

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shashy.br

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Dear all,

I am using an input of 30MHz to generate a frequency of 60MHz and 240Mhz utilizing individual multipliers,
while testing the module it was found that there multiple spurious components at the output,

at the 240MHz output i observed a 270MHz signal at 27dBc from carrier along with harmonics of the fundamental component.


i always thought the multipliers will produce only harmonics!!!! (Is there any other factor that i should take into account?)
 

This is caused by parametric pumping of the semiconductor material. It is quite common. It is good engineering practice to follow such circuits with filters.
 
As I can see, 270 MHz is 9th harmonic of your 30 MHz input. For a good spur rejection, you need a good filter of the harmonic output. I do not see any parametric effect that may be\ non-harmonic.
 
Thanq for replying to my quiery,
also i need clarification on the RF amplifier output,
i am getting harmonics at the output of the amplifier eventhough the input to the amplifier is pure,

The 1dB compression point of the amplifier is 5 dB away from the maximum operational output.
is there any other factor i shouls take into account ???
 

For harmonics, it's usually easiest to add a simple lowpass filter. Take a look at Mini-Circuits LTCC LPF. You can also reduce the harmonics by lowering the input to the amplifier. For second harmonics they will fall 2 dB for each 1 dB reduction in fundamental, third harmonics fall 3 dB for each 1 dB reduction of fundamental. Or if you have extra DC power, you can go with a more powerful amplifier.
 
Many RF amplifiers do generate harmonics even with more than 5 dB back-off from P-1 dB. If you use one frequency, use a low-pass filter as above indicated, or, combine a low-pass and band-pass filter for best results.
 
Dear all,

thanx for your help ...

the amplifiers used are producing harmonics even though the 1dB compression point a 5dB away from the output power generated.

also the 270MHZ component is due to the inability of the filter used to remove the harmonics..i replaced the filter and got a proper output.
 

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