Well,
Following my total confusion over the KISS mixer, I decided to go back to basics and make certain my very little brain:
http://en.wikipedia.org/wiki/Winnie-the-Pooh
was up to speed and understanding the diode ring mixer as a starting point.
So, I made one of these:
Please accept my apologies for the simply appalling quality of the image above.
Now, the LO looks like this into 50R:
I make that 1.25V peak to peak which is 5.85dBm.
The RF input looks like this into 50R:
thats a whopping 2.36V peak to peak which is 11.44dBm (that's way too big!).
The output of the mixer looks like this (after a lot of fiddling with the 'scope):
So hopefully it's clear that ever time the LO (we could call it a switching signal) is negative the RF input is inverted on the IF output. If you then apply a filter to the IF output we can find a nice clean signal at the wanted frequency.
Now, if I keep the amplitudes as they are above, this is the output of the diode mixer on the SA:
I've put some markers on some notable signals; the 5.85dBm LO signal is visible at the output port at -32dBm. The RF input signal at 11.44dBm is at the output port at -20dBm and my wanted signals are at 1.7dBm. I also placed a marker on the harmonic at 40MHz - that's at -38.5dBm.
If I now add 30dB of attenuation to the RF signal, the output looks like this:
So now, the 5.85dBm LO signal is visible at the output port at -32dBm (no change), but my RF input signal now at -18.5dBm is visible at the output at -42dBm. My wanted signals are at -23dBm and my random harmonic is at -50dBm.
So, back to the KISS mixer confusion:
Let's look at exactly the same input conditions with the KISS mixer configured as per the schematic:
So, here we have the LO signal at 5.85dBm, the RF at 11.44dBm, with these input signals the bias pot has no effect at all that I can see:
and here, the LO signal remains at 5.85dBm but the RF signal is at -18.5dBm, with these signal levels I can make a slight change to the amplitude of the LO signal in the output with the bias pot - I have set it for minimum LO:
What does all this tell me? Primarily that I need to go out more!
I'm going to let those far cleverer than I draw the conclusions.
Interesting, egh?
Following my total confusion over the KISS mixer, I decided to go back to basics and make certain my very little brain:
http://en.wikipedia.org/wiki/Winnie-the-Pooh
was up to speed and understanding the diode ring mixer as a starting point.
So, I made one of these:
Please accept my apologies for the simply appalling quality of the image above.
Now, the LO looks like this into 50R:
I make that 1.25V peak to peak which is 5.85dBm.
The RF input looks like this into 50R:
The output of the mixer looks like this (after a lot of fiddling with the 'scope):
So hopefully it's clear that ever time the LO (we could call it a switching signal) is negative the RF input is inverted on the IF output. If you then apply a filter to the IF output we can find a nice clean signal at the wanted frequency.
Now, if I keep the amplitudes as they are above, this is the output of the diode mixer on the SA:
I've put some markers on some notable signals; the 5.85dBm LO signal is visible at the output port at -32dBm. The RF input signal at 11.44dBm is at the output port at -20dBm and my wanted signals are at 1.7dBm. I also placed a marker on the harmonic at 40MHz - that's at -38.5dBm.
If I now add 30dB of attenuation to the RF signal, the output looks like this:
So now, the 5.85dBm LO signal is visible at the output port at -32dBm (no change), but my RF input signal now at -18.5dBm is visible at the output at -42dBm. My wanted signals are at -23dBm and my random harmonic is at -50dBm.
So, back to the KISS mixer confusion:
Let's look at exactly the same input conditions with the KISS mixer configured as per the schematic:
So, here we have the LO signal at 5.85dBm, the RF at 11.44dBm, with these input signals the bias pot has no effect at all that I can see:
and here, the LO signal remains at 5.85dBm but the RF signal is at -18.5dBm, with these signal levels I can make a slight change to the amplitude of the LO signal in the output with the bias pot - I have set it for minimum LO:
What does all this tell me? Primarily that I need to go out more!
I'm going to let those far cleverer than I draw the conclusions.
Interesting, egh?
