SoftRock Lite - RF filter

Description

This filters the RF coming from the antenna, runs it through a transformer and sends it on to the QSD. This stage will complete the Softrock receiver.

Components - gray on schematic

filterSchematic.jpg

  • L1 - on T25-2 38 turns of #30
  • T1 - on T25-2 10 turns of #30, 5 turns of #30 bifilar
  • C20 - 0.1uF smt, bottom near pin 1 of U4
  • C21 - 100pF
  • C22 - 1500pF

filterBack.jpg

The back of the board has had the last smt capacitor, C20, added to it, and is now fully populated.

filterFront.jpg

You can see the toroids in the lower right corner, wound as an inductor, L1, and a transformer, T1, along with the two capacitors, C21 and C22. You can also see the antenna wires that are attached to a BNC connection.

Test

All you need to do is attach the antenna wires (BNC) to an antenna, connect the stereo output to the stereo input of your sound card, and plug in the battery. You've already tested all the other stages, now it's just, did you wind the toroids correctly?

I first connected it to a P4 grade computer (Athalon 2800+) with a Delta 44 sound card running the Rocky software. It had great image rejection with very little center frequency noise. I switched it to PSK mode, clicked on a railroad track signal and saw perfect text on the bottom. I next installed Linrad on a "dumpster grade" P3 Optiplex GX110, hooked up the Softrock Lite and it worked, but no image rejection. So the SoftRock Lite works well, but Linrad is probably not set up right.

srLiteRockyPSK.jpg

Here is a screen shot of the Softrock Lite using Rocky on 40m between 9 and 10 in the evening. The PSK mode is selected and it is tuned to a PSK transmission. You can see the translation of the PSK along the bottom. You can easily see many CW QSOs going on and around 7053 there is an SSB QSO.