The Neophyte receiver is an easy-to-build receiver, already built by lots of people. Many radio clubs used it as a project for starting builders. It was developed by John WA3RNC and first published in QST, February 1988. The circuit can be used to create either a 80m or a 40m receiver, depending on a few capacitors. The 60m band is just in between, therefore I decided to find out the correct caps for this new amateur radio band (well… at least new in the Netherlands, from December 2015).
Based on the given values for 40m and 80m and recommendations in the NE602 datasheet I determined proper values for C7, C8 and C9. I calculated the required values for C9-C11 to obtain a VFO tuning range from 5350 to 5450 kHz. Finally I found the correct value for C1 by simply trying. Table 1 in the article would now look like this:
Based on the article you should be able to build the 60m version now. The VFO circuit for the 60m version is equal to the one in the 80m version.
12 Volt powerThe receiver is originally powered by a 6 volt battery supply (e.g. 4 penlites). In most radioshacks 12 or 13.8 volt DC is plenty available and therefore the preferred voltage. To allow your receiver to run on these voltages there are two things to do:
- The NE602 mixer does not allow 12 volt, so add a zener diode (5V6 ~ 8V2) with anode to ground and cathode to pin 8 of the NE602. Also increase the value of resistor R2 to 220 ohm.
- The maximum allowed voltage for your 386 audio amp depends on the subtype, e.g. the LM386N-1 has a 12 volt limit, while the LM386N-4 goes up to 18 volt (and gives a bit more LF power output). I recommend using the 18 volt version.
IF transformer alternativesThe circuit contains two IF-transformers (Mouser 42IF123-RC) which are outdated nowadays and probably hard to find. These are 1:7 transformers for 10.7 MHz (green core). There are several ways to replace them.
- T1 is used as a real transformer. Compatible models include the KANK3334 (also outdated) and the A1210 (did I say it is outdated?). I made my own transformer; I put two windings (5 turns and 28 turns) on an adjustable 5mm core. Since the original transformer included a 47 pF parallel capacitor I used a 150 pF capacitor for C1, which is about the sum of the given 100 pF (see table above) and 47 pF. Yet another option is to put the windings on a toroid core, as described in the article Making a toroidal KANK by David G4COE, although you can’t tune the coil now so you have to add a trimmer (e.g. replace C1 with 120 pF and a parallel 50 pF trimmer).
- T2 is used as a single coil of 4.5 uH, which can be easily made on a toroidal core. Again, don’t forget you’re missing 47 pF, so increase the value of C11 (e.g. use 150 pF instead of 100 pF for the 60 meter version). I would not use those resistor-look-alike coils, their Q is too low for a steady oscillator.
VFO alternative (not tested)The original circuit includes a 365 pF variable capacitor to set the receiver’s frequency, often found in old analog AM/FM radios. I initially used a 200 pF capacitor, which I found in my junkbox. Both have the same issue: 100+ kHz tuning range on a half turn is not convenient. For a more precise tuning you may replace it with the circuit below, based on a BB112 varicap diode. The variable resistor turns about 270-300 degrees. You may even use a 10-turn potmeter for more comfort.
Down here you see some pictures of my final Neophyte-60. This one is based on the original circuit, except for the different capacitors for 60m and the homebrew IF coils.
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