Thursday, May 21, 2020

Radio Shack DX-398 / Sangean ATS-909 Mods Part 4 - IF Out Panadapter

This modification is similar to the DX390 panadapter tutorial that I posted HERE. I encourage you to check it out for more detailed information on panadapters, software, SDR dongles, and configuration.


What You Need

  • SDR


  • Female MCX bulkhead connector



  •  MCX male to SMA female cable
  • 24ga insulated copper wire
  • Additional cables or adapters to connect the SDR to your radio available on Amazon.
  • 1k ohm, 5 watt resistor
  • 1 nf to 2.2 nf non-polarized capacitor (I used a 2.2nf film capacitor)
  • Drill bits. Cordless drill
  • Soldering iron. Heat shrink tubing
  • SDR software
  • Drivers for your RTL-SDR

  

The Radio


The DX-398/ATS-909 is a dual conversion, superhetrodyne receiver.. The first IF is 55.845 MHz and the second IF is 450 kHz. We want to use the 1st IF stage for our panadapter for maximum bandwidth.


Connecting your SDR directly to the radio could alter the signal of the IF stages and cause poor reception. It could also transfer unwanted DC voltage between the radio and your SDR. We will use a small value capacitor for blocking spurious voltage and resistor to prevent receiver sensitivity drain. Connect them in series to your radio.


Identifying the correct tap point for a strong IF signal in this radio is fairly simple. We could tap between Q3 and Q4 near the filters. The Sangean service manual indicates TP11 is used to measure the 1st IF frequency. We can use this for our panadapter.



 

Connecting the Cable to the Radio

Disassemble the receiver case and remove the large circuit board. It is much easier to remove the speaker and control pcb before drilling holes and soldering. 

Drill your holes in the plastic case near the external antenna jack. Watch out for the two inductors. You can gently separate the rear pcb from the plastic housing to prevent damage to the components.

Make your cable assembly and add heat shrink.


 

Secure the cable assembly with the connector nut.




 Route the wire through the top hole and solder to TP11.


 

 Reassemble the radio and test.




73,

W9JES

Monday, May 4, 2020

Radio Shack DX-398 / Sangean ATS-909 Mods Part 3 - Tuning Knob

The next part of this series covers the rotary tuning knob. The DX-398 has a good tuning knob, but it has an unwanted feature causing it to stop or "click" in small increments. It is hard to spin the dial freely while tuning for DX. This is due to the plastic notches or detents in the tning shaft that mate up with a half-circle in the metal retainer/spring assembly.

Arthur Hollingsworth  created a video on how to perform this mod - You can view it here https://youtu.be/53VKmO8mqTc?t=1172



Steps

  • Locate 6 solder pads on the circuit board near the LCD display light
  • Remove the solder from the 6 pad connections
  • Remove the tuning control from the board


  • Gently pry up the 4 metal tabs on the back of the tuning control with a small, flat bade screwdriver. Use a pair of needle nose pliers to remove any bends
    Copyright Arthur Hollingsworth
  • Gently separate the metal case and plastic control housing.



  • Remove the copper section from the 4 plastic retaining posts

  • Using needle nose pliers, gently flatten the notch that sticks up on one side of the ring.

  •  
  • Reassemble the tuning knob in reverse order noting correct orientation (note the "detent" is now removed, but is shown here for reassembly reasons)
  • After the control has been put back together gently flatten the 4 tabs back into place using the needle nose pliers
  • Resolder the control into place on the PCB
  • Check your work and power up the radio
  • You should now be able to tune much easier now


73,
Jesse W9JES

Radio Shack DX-398 / Sangean ATS-909 Mods Part 2 - LED Replacement

This is one of the easiest mods you can do to a 909. Replace those dim, lime green LEDs with white ones!

All you need to do is desolder the old ones and replace them. Be sure to note polarity as seen on the PCB.






73,
Jesse W9JES

Radio Shack DX-398 / Sangean ATS-909 Mods Part 1 - Disable Mute


This radio design was sold under several brands including Radio Shack and Sangean. Radio Shack's model DX-398 and Sangean ATS-909.


Disable muting while tuning aka "chuffing"


This radio has a similar design to the ATS-818 where the PLL muting circuit is processed by the controller chip.


Steps


  • Disassemble the radio
  • Locate  CNT2
  • Find the Black Wire connected to PIN 10 and gently pry out with a small screwdriver
  • Use some heat shrink tubing and cover up the exposed pin and tuck neatly behind radio
  • Reassemble radio and enjoy!