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Topic: Mismatch&power leakage with port of mixers..attenuators solution (Read 326 times) previous topic - next topic

Fovakis

Hi ! I am making an RF Transmitter and i have a problem with power leakage for LO port to IF port and RF port. I don't know what to do and i am little confused about how can i fix this.


Source(-10 or -20dBm) 10KHz --------->MIxer conv.loss=8db--------->RF port

and

L.O=30.01MHz and 7dbm

I put an oscilloscope to mixers input IF and i don't see a sin wave from my Source. I is a sine wave with a lot of phase noice and amplitude variations..when i decrease the L.O power the sine becomes better.:o

I have heard about attenuators but i cannot understand how they will solve the problem. They attenuate maybe the standing waves that maybe create ?Also and my signal right?
I don't understand...
http://i1284.photobucket.com/albums/a578/fovos1/P5181092_zps5ee33fa8.jpg

MarkT

Can't read anything on those thumbnails, too small...
[ I won't respond to messages, use the forum please ]


pito

Quote
They attenuate maybe the standing waves that maybe create ?Also and my signal right?

A mixer (especially a diode ring mixer) must "see" the 50ohm impedance on all its ports, otherwise it will leak..
Pi or T attenuators may do it as they "match" to 50ohm (while they do attenuate a little bit..). You may match with other matching networks as well.. The resistive attenuators are easy to design and they are broadband, with L/C matching networks you have to match at specific frequency of interest.
On that ring mixer you cannot expect to see clean sine wave on any port as the isolation is not too big, and, the signals will be full of sums and differences of the LO and RF signals (plus sums and differences of all combinations of their harmonics).
Your crystal filter must be matched (50ohm input) to the mixer's 50ohms output, and when well designed you may see on its output a "clean" signal (which fits in its bandwidth)..

Fovakis

So an attenuator if it has got 50 ohm input and 50 ohm output match with the components that are in the input and the output right?

Can you propose me an attenuator before the first mixer ZAD 6+ from mini circuits menu:

http://217.34.103.131/products/Attenuators.shtml

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