Hi,

My objective is to homebrew a 10khz to 60Mhz software defined radio; one
that uses the power of the PC for all modulation and demodulation functions.
There are several references for a direct conversion receiver that uses a
sample and hold detector or Tayloe detector which seems to provide
remarkable performance. If possible I would like to use this detector; it
embraces the KISS approach ;-). The problem I find however, is that the
detector responds to odd harmonics of the receiving frequency, for a doubly
balanced configuration. ;-( As an example, if the receiver is tuned to 10
Mhz, a signal of 30Mhz will also be received. Using Linear Technology
LTspice (which is a free spice type simulator) to simulate the detector, the
30Mhz signal is about 10db lower then the 10Mhz desired signal. Looking for
140db or better difference; have a long way to go. Possibly there is an
error in the simulation; but I think, unfortunately, it is correct. After
all, the switch function is not linear. A Fourier analysis of the switch
pulse closely agrees with the detected result; the third harmonic is about
10db lower then fundamental. Does anyone have experience with this type of
detector?
Thank You.