It's a superheterodyne receiver thus
avoiding opposite sideband interference that occurs with Direct
Conversion receiver.
The IF is 4.096MHz, approx. 600Hz wide IF filter. You could
probably fiddle with the capacitors in the filter to make it narrower,
but I felt that anything much narrower that 600Hz would be difficult to
tune to. VFO is at 10.003 Adjustable. (Note that my
first attempt was a 10MHz IF, with a 4.096 VFO, this worked but there
was so much feed though from 10MHz WWV I decided to switch the IF and
VFO frequencies)
There is a very nice high pass filter on the input which starts to roll
off below 10MHz and does an excellent job of suppressing the image (at
5.9MHz) by 50db and AM broadcast stations by 100db. I am also
using a lightly coupled broad band input transformer that minimizes
capacitive coupling and favors higher frequencies.
KIT $35.00 plus S/H (computed by Paypal)
PCBs are all sold out, will resume shipping this kit in July-Aug 2011
Antenna: You will need an
outside antenna. I use a 50 ft long wire about 15 feet off the
ground. From my Nevada QTH I have heard the following beacons at
various times: 4U1UN, W6WX, KH6WO, ZL8B, VK6RBP, JA2IGY, ZS6DN,
OH2B, CS3B, LU4AA, OA4B, YV5B
NCDXR Beacons
schedule & status
Audio output: The audio output comes out on a 3.5mm stereo
The
output level is not huge. Generally I recommend amplified
computer
speakers, but you can also feed it into the audio input of your
computer sound card. If you want to have a stand alone setup (no
computer) go to your local computer store, or swap meat and buy the
cheapest pair of amplified computer speakers. Plan on spending $5
to
$10. Don't get stuck with the old non amplified ones, if they
don't
come with a wall wart for power, then they are not amplified.
DC Power. It draws
about 70mA and needs a supply with no AC ripple, so
a cheap wall wart probably won't work. The audio and IF amps are
simple class A amps, so any ripple on the power supply with feed right
through to the audio output. It's not real picky about the
voltage,
anything from 10 to 18 volts is OK, so filtered but unregulated supply
is OK. If you want to use a wall wart, try it, and just add
a big ~1000uF filter cap on the output if you hear AC hum.