A SIMPLE 10MHZ WWV RECEIVER BY MCKEAN
This board was somewhat hard to build. The coil forms are obsolete (the article was written in 1995), so I used toroids instead: The biggest problem for the builder is T2, the diode mixer transformer. 7mm 10.7Mhz IF transformers are obsolete. They used to be in every FM portable radio, but got replaced by ceramic filters. The holes on the PC board seem to be poorly positioned for the pins on a 7mm IF transformer anyway. The author re-wound the bobbin to make essentially a tri-filar broadband transformer. I used a FT23-43 toroid, but the more common FT37-43 toroid (FAR Circuits has available) will also work (it's harder to fit over the PC board holes though). I wound AWG30 enameled wire with 5 tri-filar turns. (Use this URL for info winding a tri-filar transformer: http://www.qrp.pops.net/xmfr.asp.) The coil form for T1 the author used had a base with holes on the bottom to thread the wires, likely salvaged from a junk TV. These are no more. I used a T37-2 toroid (FAR Circuits has available) and reduced all the coil turns by 25%. Then, C11+C12=~45pf. One feature of a toroid is it self-shielding, so I omitted the foil shield described in the article except for a short length between C1 and C12.
The CA3240 is hard to find (still available from Mouser, but over $2) so I used a MC4558 from my junk box. The MC4558 is fairly low-noise, and the band noise overshadows the IC noise anyway. But I first tried a NE5532: This is a wide bandwidth IC and the 10Mhz oscillator signal ran straight through causing problems. The MC4558 has a 2.5Mhz bandwidth, the CA3240 4Mhz. A commonly used op-amp like the TL082/TL072 will work fine. Don’t use a LM358/LM2904.
The 10Mhz crystal that I bought surplus was 3Khz high and it took major effort to get it to zero-beat WWV. (FAR Circuits has 10Mhz crystals available). I used a 4.7v Zener for D3 and jockeyed R1 and R2 to make Q1 oscillate after adding capacitance and inductance to the circuit. I couldn’t maintain the oscillator within 10Hz of zero-beat with temperature changes, even using NPO and air-variable capacitors. A diode mixer expects to be driven with a symmetrical waveform for good balance, but the oscillator output is not so. The diodes must be at DC ground; add a small molded choke (~4.7uH+) from the T2/C8 junction to ground.
My transistors had more gain than those used by the author, so I chose higher (220K–470K) values for R1, R4, and R8 to re-bias the circuits and conserve current.
The LM386 audio amp was unstable due to inadequate bypassing, and also lacked the RC network at the output to kill a 5Mhz oscillation. I set C16=470uF to stop the motor-boating. This cap ideally is connected directly between pins 6 and 4, so instead I added a 0.1uF ceramic cap with short leads to these pins. The RC network is 0.05uf in series with 10 ohms per the LM386 datasheet, connected from pin 5 to 4 with short leads:
Reduce C20 and C24 to 1/3rd their values for a 3Khz audio cut-off freq: Thus C20=220pF and C24=330pF. The author chose values that cut-off below 1Khz, likely to compensate for the tinny sound of a small speaker.
The finished product works as typically a direct conversion receiver would. A 3ft whip antenna is enough to hear WWV/WWVH 10hrs a day from CA, better than most AM radios. Due to the high audio gain (or poorly balanced mixer?), hum is a problem unless the receiver is battery powered. The PC board should be placed atop a metal plate to minimize the hum. The author suggests connecting the board ground to an "earthy" ground: This is also probably needed. Any direct-conversion radio that doesn't use a doubly-balanced mixer (examples: SA602/NE602, diode ring) will probably have hum. Thank you Chris
Description: This is the companion receiver to the Micronaut QRPp transmitter that is designed for the low end of 40 Meters. The receiver is a single stage direct conversion using a 7.048 MHz crystal, NE612, and LM380 on a 42 by 22 pc board.
Description: The receiver is built around a MC13135 IC with a PLL LO SYNTHESIZER using MC145170P2. The computer interface and control is done with a PIC16C73 uP which also drives a 16 character 2 line LCD display, an Optrex DMC16207N-B. The PC program to run Windows 95/98 and the source code for the PIC uP is available under hag2mrx.zip from ARRL http:/www.arrl.org/files/. Other ICs required: LM2931AZ and LM386.
Description: This is a well designed double conversion AM/CW/SSB receiver that covers 6.5 to 7.5 Mhz. The design uses an SBL-L for the two mixers, an MAR-1 for the front end amplifier, two MC1350 IC's, an NE602 for the detector and three stages of MC1458 for the audio. The project is built on two boards. If you are looking for a good receiver to build, this is the one
Description: See http://www.electronics-tutorials.com/receivers/regen-radio-receiver.htm for complete details.
Description: Check out this site for the details to build a DGPS pocket receiver. http://home1.gte.net/clseng/dgps/dgps3.htm. THE P C BOARD COMES WITH THE MC145157P2 PLL IC.
Description: This app note shows how a receiver can be made with a SA602 and a SA604, from antenna to low level audio. The board is 3"x3" double sided, non plated-thru holes. If you like playing with receiver designs, this is the board to build this double conversion receiver.
QST SEPT 00
Description: HF regen receiver that uses 2N2222 and LM386.
Description: see home.att.net/~wb8wfk/foxfinder80.htm
QEX Sep/Oct 00
Description: The board can be used to make a 38-54 MHz, 88-180 MHz, or a 118-136 MHz AM or FM receiver. The receiver design contains a squelch circuit. Project uses 2 J310 FETs, a 2N2222 transistor, and a LM386N audio amplifier. This is another quality project from Charles Kitchin.
73's Nov 00
Description: This is the ARDF receiver for 3.5 Mhz fox hunting. Circuit uses (2) NE602A, MPF102, MC1350, AND LM386. See home.att.net/~wb8wfk/foxfinder80.htm for more details.
QST Mar 01
Description: this is a simple TRF receiver for tracking the source of HF RFI and operates around 136 MHz. The circuit consist of MRF901, J310,and LM358 and operates from a 9 v battery.
Description: This is the Colpitts regenerative receiver. The circuit uses 2N3904, MPF102 78L05 and LM386 IC. The receiver covers 5 to 15 Mhz.
Description: The project is assembled on a 3.125" x 2.5" PC board. The circuit uses 2N4416 FET and a TL431CPL Voltage controlled Zener. The radio tunes the FM broadcast band. http://www.somerset.net/arm/fm_only_one_transistor_radio.html
Customer Comment: I built the Armstrong Update regenerative receiver from Dave Cripe's article. As promised, the 1496 detector produced uncommonly smooth regeneration control and his use of a 324 op amp as both an audio filter and a push-pull gives adequate, clean audio. Like other regenerative circuits, this one is sensitive to its surroundings and benefits from good shielding and layout after the board is working. The Far Circuits board worked the first time but care should be used to avoid control wires crossing each other as they leave it.