"w9gb" wrote in message
. ..
"numeric" wrote in message
...
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.

Personally, I would put that effort into the HPSDR project -- which
benefits
all (open source) and expands your total education.

http://hpsdr.org/


Checked out your link, while interesting this is not my project's direction.
The fun is designing the entire project from concept to the finished
product.