40 meter NE602 DC RX -- 2023 version

 At the request of KA5VZE, AKA "my big brother", I am going to make a replica of my original 1987 "NE602 40 meter RX".   I covered the back story for my 1987 version in the immediately preceding blog post. 

I have transferred the original design into a KiCad project and produced a new PCB layout on the same size 1.5" by 2" board. The details are shown below.  I will order the boards from PCBWAY this week.

The original schematic is shown below.  Except for the trimmer capacitors, all parts can still be obtained for the RX.  (I guess from 1987 to 2023 makes the original project 35 years ago.  Where did the time go?) 

click to enlarge

For the 2023 version, I've added connectors to facilitate working with the board for testing and mounting in the cabinet.   The new schematic, entered into KiCad is shown below: 

click to enlarge.

The layout for the PCB, shown below is done on a two sided board, with the bottom side serving as the ground plane. The ground plane is cleared out underneath the oscillator circuit in the lower left and under the tuned antenna circuit in the upper left. 

click to enlarge

The KiCad generated 3D view is shown below, with my added annotation.  

click to enlarge

Compare this to the original layout from the 1987 version and you can see both PCBs are similar. 

click to enlarge

40 meter DC NE602 RX (2): Background

Link to first post about 40m NE602 DC RX 

The original 40m DC RX was built to evaluate the NE602 mixer circuit. This was 1987 and I received a free sample of the NE602 on a blister card.  It looked very useful, because it had the oscillator and double balance mixer all in one chip.  I quickly learned that NE602 overloaded very easily but I still built a receiver up just for fun. draft article submission from 1987

Here's a photo of the original 1987 NE602 RX.  It was housed in a Radio Shack cabinet, using a vernier dial for tuning,  and volume and phone connections on the front panel.  The 9V battery was inside the cabinet, and the antenna connection was through an RCA phono connector through the back panel.

Below is a photo of the interior of the RX.  Click to enlarge.

The original circuit board was single sided, as shown below in a view from the component side.  Click to enlarge. 

Building The 40M Direct Conversion Rcvr

I've decided to start the build on Steve's (formerly N5JBB) direct conversion receiver.  My goal is to build a replica to the original in his article.  (The first post of this blog)  The procuring of parts has been a very time consuming task.  I managed to find everything through ebay and various other sources, including the project box and vernier dial and so it will at least look the same as the original.  As of now I'm waiting for all the parts to arrive so that I can start on the printed circuit board layout and component location.

Here is the original description of the Receiver that is more legible than the photo copied one posted before on Box.net:

An Experimental Receiver Using the NE602 Oscillator Mixer

Steven Morris, N5JBB

4913 Rustic Rd

Sand Springs, OK 74102

719-245-0582

          The NE602 is an 8 pin oscillator/mixer chip made by Signetics which was meant for use in battery powered receiver circuits.  I was intrigued by the possibility of a very simple direct conversion portable receiver based on this chip and was able to get a fairly good 40 meter receiver onto only 3 square inches of board space.

          The NE602 contains an active mixer circuit optimized for best performance at 6 volts.  Biasing of the mixer is taken care of on the chip, making it simple to use.  An oscillator/buffer stage is also provided on the chip.  The base and emitter of the oscillator transistor are brought out on pins 6 & 7 respectively, where the frequency determining components can be attached.  The signal input is into pins 1 & 2 while the outputs are from pins 4 & 5.  Fig. 1 shows a block diagram of the NE602.

          This chip has several advantages over some of the active and passive mixers currently in use.  Since this chip provides about 20 dB of signal gain from the input to the output, there is not as much gain needed in the audio strip as that needed for a receiver using a passive mixer.  Its small size and on-chip oscillator and biasing eliminate much board space and many of the components that would be needed if another active mixer such as the LM1496 were used.  The chip has very good sensitivity but mediocre dynamic range, potentially a problem when working on the 40 meter band.  Nevertheless a good receiver can be built based on this chip, giving a very small, low power set good for portable operation.

           Looking at Fig. 2, the receiver is split into two sections, the oscillator/mixer and the audio strip.  In the first section T1 is used to match the 50 Ω antenna impedance to the 3 kΩ input impedance of the mixer.  It is tuned to reject out of band signals.  R1 is used to drop the 9 V supply down to 6 V.  The oscillator circuit is of the Colpitts type with C2 used as the bandset and C1 used for main tuning.  Output from the circuit is single ended, being taken off pin 4.  C8 R2 and C16 are used to filter RF before the audio signal is sent to preamp Q1.

          The audio strip contains a 2ND5210 preamp and an LM386 power amplifier.  The preamp is designed to have a gain of 10 although more gain can be had by bypassing R6 with a 10 µf capacitor.  R7 is the receiver volume control.  The LM386 is designed to have a gain of 20 but that can be increased to 200 by adding a 10 µF capacitor between pins 1 & 8.  The LM386 tended to oscillate when using 4 Ω headphones so I rewired the headphones for 16 Ω operation which cured the problem.

          I laid out a circuit board just to see how small I could make it.  The circuit board is 1.5 X 2 in., occupying 3 sq. in. of space.  The layout is shown in Fig. 3 and the component location is shown in Fig. 4.  The completed receiver was built in a metal cabinet purchased from Radio Shack and is shown in Fig. 5.  The cabinet was modified to make the cover more easily removable when replacing the battery.  This was done by using #6-32 knurled thumbscrews instead of the sheet metal screws supplied and cutting slots in the cover so it can slide under the thumbscrews.  Fig. 6 shows the internal layout of the box.

          I believe this receiver would make a good portable set because of its small size and low power drain.  There is much room for experimentation too.  The antenna circuit could be reqorked to eliminate the input attenuator and raise the Q of the input tank.  The oscillator circuite could be reworked to obtain better frequency stability.  I think that some improvement in dynamic range could be gotten by using an audio transformer across pins 4 & 5 of the NE602 for balanced output from the chip.  Some experimentation with gain in the audio strip is called for.  The headphones I use are very sensitive, other headphones might require more gain.  By increasing the gain in the LM386 enough ti might be possible to eliminate the preamp.

          You may have to go through a Signetics distributor to get the NE602.  I have not seen them for sale in any of the common mail order outfits.  I bought mine from Schweber Electronics, a nationwide distributor which handles Signetics.\

References:

Signetics 1987 Linear Data Manual, Vol. 1:  Communication, pp 4-60 to 4-74

Signetics application note AN198, “Designing With the SA/NE602”

Signetics application note AN1982, “Applying the Oscillator of the NE602 to Low Power Mixer Pllications:

Here is the parts list:

PARTS LIST

J1                BNC Connector

J2                1/8 in. phone jack

T1                T50-2 toroid

 L1               T68-6 toriod

C1                15 pF variable cap

C2, C6            75 pF trimmer

C3                 100 pF

C4, C5           680 pF

C7                .1 µF

C8, C9, C10     .047 µF
C11               .068 µF

C12               .01 µF

C13, C14        10 µF

C15               .05 µF

C16               .22 µF

C17               1000 µF

R1                120 Ω

R2                1.5 kΩ

R3                100 kΩ

R4                2.2 kΩ

R5                12 kΩ

R6                220 Ω

R7                10 kΩ Pot

R8                10 Ω

U1                NE602

U2                LM386

SW1             SPST Miniature Switch

Vernier dial

Head phones

Circuit board

Stand offs

Machine screws

Project box

9V Battery

Battery connector

Enamel wire

Hook up wire

Thumb screws

Labels

Foot pads

I'm working on the schematic.  The original can be viewed from the link below:

(deleted link)

15 Mar 13:  Today I'm starting the Regen project.  I've gathered all the major components and onto the proto board they will go.

I scanned the old article I wrote on the NE602 40 meter receiver.  The link is below.

1987 40m NE602 RX file

Here's a grainy photo of my sons Harvey, 9, and Sam, 7, posing with the little rig.  Last month Harvey turned 35, Sam is 32.

 

Below is a shot of the interior of the rig.

Sorting old stuff

I have been going through my files to find old ham radio projects.  I am looking for the cardbox trans-receiver that I built, as well as a couple of other projects. 

I found a lot of the old files at the bottom of box, everything except the cardbox rig.  I have a very nice article that I wrote concerning the small NE602  40 rx that I built. I guess I wrote it up and didn't submit the article to anywhere.  At any rate I think we should use that rx for another carbox rig, rather than the 1496 rx.  It's much smaller.  When the NE602 first came out in the late 80's I ordered samples through my company and built that little rx.  It would have been one of the first NE602 rigs.  There's a zillion of them out there now.  

I am thinking of modernizing this circuit and producing about 10 of them. The circuit board is 1.5 inches by 2 inches.  

First post. 40 meters cardbox

Okay,

I've created a new blog called "QRP Brothers" for sharing stuff and commenting and other stuff. 

I scanned the Cardbox Trans-receiver article and posted it in the QRP Brothers folder on my box.net account.

Here's the link.