Space Varmint
New Member
Hi, I would like to have a discussion about this subject, signal-to-noise. I got some questions and I would like to report some of my findings as well that may be informative to others. Some of it may be speculative because I am using crude equipment to the best of my ability. Here is what I think:
I got a 40 watt transistor that I am using as a transmitter final amplifier into the antenna. I have had as much as 25 watts output but my signal to noise ratio went up to 2-to-1 ratio or 1 to 2:1 commonly refered to as 2:1 ratio.
Unfortunately I was probing around in the mixer section and made some changes in the filtering and I cannot achieve the same results now. That's OK I'm not done yet. My output signal is derived from two different frequencies combined in a mixer. So from there I am amplifying and filtering all the way to the output.
So my questions and apparent observations are this. I believe that spectral purity is paramount and directly proportional to the amount of signal that will be received by the antenna. Does this sound right? What I have noticed is that some frequency components such as parasitics and harmonic energy will be reflected by the antenna impedance. This can be seen as spurious radiation being kicked back onto the scope probe when reaching the maximum acceptable output.
In building power amps, I have more experience with class C type power amps where allot of the signal can actually be produced by the amplifier itself, triggered by an input signal, and so spectral purity is not that hard to achieve because we are not interested in bringing forth linear modulation intelligence from lower stages where in class A operation we wish to preserve and amplify all necessary intelligence which can bring forth other undesired parasitics.
Your thoughts and inputs are greatly appreciated.
Thanks, Frank
I got a 40 watt transistor that I am using as a transmitter final amplifier into the antenna. I have had as much as 25 watts output but my signal to noise ratio went up to 2-to-1 ratio or 1 to 2:1 commonly refered to as 2:1 ratio.
Unfortunately I was probing around in the mixer section and made some changes in the filtering and I cannot achieve the same results now. That's OK I'm not done yet. My output signal is derived from two different frequencies combined in a mixer. So from there I am amplifying and filtering all the way to the output.
So my questions and apparent observations are this. I believe that spectral purity is paramount and directly proportional to the amount of signal that will be received by the antenna. Does this sound right? What I have noticed is that some frequency components such as parasitics and harmonic energy will be reflected by the antenna impedance. This can be seen as spurious radiation being kicked back onto the scope probe when reaching the maximum acceptable output.
In building power amps, I have more experience with class C type power amps where allot of the signal can actually be produced by the amplifier itself, triggered by an input signal, and so spectral purity is not that hard to achieve because we are not interested in bringing forth linear modulation intelligence from lower stages where in class A operation we wish to preserve and amplify all necessary intelligence which can bring forth other undesired parasitics.
Your thoughts and inputs are greatly appreciated.
Thanks, Frank