"Pete KE9OA" wrote in message
...
That is correct. Another thing that can cause that (2 X 2nd I.F.) image is
2nd LO leakage coming back into the input of the 1st mixer. Once the
concept of mixer theory is understood, things become clear. I know that
many, if not most of the folks on this group understand this, but for the
new folks, I will repeat it.
A mixer is a three port device. It doesn't matter if it is used as an SSB
detector or as the first stage in a superheterodyne receiver; the concepts
are the same. In the first stage of a receiver, the antenna input is
applied to the RF port of the mixer, the tuning oscillator is applied to
the LO port, and and the resultant signal is taken from the IF output
port. Here is where it gets a little tricky (not really!). If you could
see the IF output of the mixer on a spectrum analyzer, you would see three
distinct signals. You would see a lower sideband signal, the LO signal
(suppressed by a certain amount, depending on the LO feedthrough), and an
upper sideband signal. Both the lower sideband and the upper sideband will
be separated from the LO feedthrough signal by the intermidiate frequency.
This means that if you have a 455kHz I.F., the lower sideband will be
455kHz BELOW the LO signal, while the upper sideband will be 455kHz ABOVE
the LO signal. If you have now preselection ahead of the mixer,

Sorry folks, that should be "if you have NO preselection ahead of the mixer"

Pete