Fixed Frequency Receiver
for 14.100 DX Beacons
This is a simplified version of my general coverage receiver kit, using a crystal as a VFO.
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)
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.
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, YV5BNCDXR 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.