"Pete KE9OA" wrote in message
...
Hi Brian,
What you can use is low-side injection at 36.7125MHz.
Normally, high-side injection is used since it has fewer in-band spurs. A
freeware program such as AppCad will generate spur charts for you, and you
can see what happens. Because you are only interested in one frequency, it
is pretty unlikely that you will have any problems.
The circuit topology can be like this: your I.F. output will feed into the
RF port of the NE602 mixer. Because this mixer has an IP3 of only -10dBm
or
so, your 1dB compression point will be at around -24dBm. Your RF level
should be at least 10dB below that point.......................-40dBm is a
good figure to shoot for. This corresponds to a 2.24mV level into 50 ohms.
It is a good idea to have a "pi" type of resistive attenuator ahead of
that
NE602............this way, you can adjust the input level as needed. The
50
ohm figure is good to shoot for, but there are always imaginary terms
(reactance) at the mixer input so calculations are only a starting point.
You can use the on-board oscillator of the NE602 for you LO. A 3rd
overtone
crystal would do the trick. You can actually use a Colpitts scheme,
adjusting the feedback capacitor values so that they have a high reactance
at the fundamental frequency of the crystal; this way, only the harmonic
will be generated. Over the years, I would use a 4:1 ratio of the top cap
vs
the grounded cap. An example is 120 over 30pF for a 10.7MHz oscillator,
but
your mileage may vary.
Your I.F. output really should go through some type of 21.4MHz tuned
filter,
because you are going to have two sidebands coming out of that mixer. The
lower sideband (the desired one) will be a 21.4MHz, while the upper
sideband
(the image) will be at 94.82MHz. You don't want to have this response.
Since the NE602 has a good NF and has gain, you shouldn't need a buffer
amp,
unless the WJ unit presents a 50 ohm load. You need to know what level the
WJ unit requires, so that you can provide the proper level from your
translater.
I hope this helps.
Pete
Thanks Pete. Would it be possible to fabricate the design in such a way as
to acomodate differant IFs. Maybe some type of switchable or multiport setup
so it can be used on differant receivers?
--
73 and good DXing.
Brian
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