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Saturday, December 20, 2014

Pete Tries Baluns on the DBM


A couple of weeks ago I ran a post about an old 73 Magazine article that extolled the virtues of putting baluns at the RF input and IF output of diode ring mixers.   Dedicated experimenter that he is, Pete Juliano gave it a try: 


Hi Bill,
I did the modification and used 20 bifilar turns of #26 on a FT-50-43 core for each transformer.
The most important observation is that I did not see any degradation of performance and in fact I think has helped an overloading situation I was seeing on some extremely strong signals.
The photo is of a DBM that is behind a bilateral stage that on Rx is the RF amplifier and on Tx is the Tx pre-driver. I do have another single transistor RF amp ahead of this. In normal operation the next stage would be the Band Pass Filter.
The back end is an IF amplifier, AGC, Product Detector, balanced modulator and mic amp stage all on a board that came out of a Hallicrafters FPM-300 SSB/CW transceiver. There is a you tube video of this prototype project.
73’s
Pete N6QW 

Thanks Pete! 

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1 comment:

  1. "The most important observation is that I did not see any degradation of performance and in fact I think has helped an overloading situation I was seeing on some extremely strong signals."

    That's good to know, but the advantage of using the input/output baluns is supposedly better balance, which should result in lower RF and LO pass-through in the receive case. So was that observed and measured?

    What about the increase in insertion loss and any change in return loss? If the baluns are introducing loss, this might explain the overload problem improvement, which implies an overall gain distribution issue. I hope to hear more about this subject.

    Tnx & 73's, David WB4ONA

    ReplyDelete

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