Archive for July, 2011

Arduino IRLP Simplex Node Controller

Monday, July 25th, 2011

One of my first Arduino projects was this IRLP Simplex Node Controller.  This
controller provides several functions:

  • CW ID
  • FAN Control
  • Courtesy Tone

This controller is for simplex IRLP nodes which which controls ID, fan, courtesy tone and a PTT lock (transmit hang) funciton. The CW ID’er  allows the audio to be mixed with the controllers CW ID so that it will only ID when some one is speaking accross the link or when the node is idle.  The controller  frees up the node for extra process scripts for ID’s, Fan Control, and courtesy tones.  With the  PTT Lock (Transmit hang) timer,  the transmitter will be protected by a “hung” transmitter and will force an unkey of the transmitter when a timeout has occured. This PTT Lock will also send an LOCK tone and UNLOCK tone when the PTT line is unkeyed.

The controller is interfaced to the irlp/transmitter via a “breakout board” which allows the user to customize the radio interface.

I have included a breakout board schematic for a GM300 that I use for both simplex node and repeater control even thought I have only tested the controller in simplex operation.

Construction of the controller was done with a proto-boards from Radio Shack.  When building the controller board,  keep in mind that you want to have access to the adjustment resistors,  which was an oversight when I built my original boards.

Some of the modules can be obtain in kit form from the following online stores:

Two boards will need to be built, one for the IRLP audio breakout board which interfaces the audio, PTT, and COS signals to the IRLP Controller board and  another board which contains the interfaces to the Arduino Bare Boards Board.

  Schematic Diagrams


  Board Images



SB-200 Modifications

Monday, July 25th, 2011

The Heathkit SB-200 amplifier has been around for years and many are still in use.

I rebuilt my Heathkit SB-200 that I obtain from e-bay.  This one was in bad shape but the price was right.  It was dropped, bad tubes, and definitely been used.  I slowly rebuilt the amp and got it fully functional. Initially I rebuilt the power supply using  Harbach Electronics PM-200 Replacement Power Supply Module. Refer to their website.

I came across a web site,, which PA0FRI explains in detail on how to modify the sb200. I went ahead and modified my SB-200 according to his website and followed most of his recommendations. The following items are what I wanted to accomplish with these modifications:

  • Tube Protection. Fuse the high voltage to reduce catastrophic failures.
  • Soft Start to limit the primary in-rush of current and slow the rise of anode voltage. This protects the filaments and rectifier diodes and permits the use of a lower current primary fuse.
  • Stability
  • Change amplifier key to support modern radios.
  • Reduced filament voltage. On my SB-200,  I had almost 7 Volts on the Filaments.  I ended up using a loop of 18 gauge Teflon wire to drop the voltage until the filament voltage was in an acceptable range.
  • ALC Adjustments is now easily adjusted.  This is nice when I use it with my Drake transmitter which I can easily overdrive.  The amplifier is very stable and is well protected.
  • Faster QSK Operation.  I  wanted a faster transmit/receive transition, by  updating  the input and output relays did the trick.


SB-200Modified Amplifier

SB-200 Modified, Schematic Diagram

These modifications are based upon PA0FRI’s modifications.  I give him all the credit. I am impressed with the stability of the amp and have not had any issues.  Please refer to his  website:,

The modified SB-200 schematic diagram is shown below.  This uses a “Key-All” circuit board for keying the amplifier. This board may still be available from Jackson Press.  I also incorporated a “soft-start” from Harbach Electronics.

Here is the meter switch wafer detail.  This needs to be modified per the schematic above.



Input/antenna relay uses a reed relay for the input and a VAC relay for the output side. I had to had a 24V power supply for these relays since the original used 117V.




SB-200 Modified Amplifier Gallery:








W0ANM IRLP Node Information

Saturday, July 16th, 2011

Welcome to the W0ANM IRLP node 3106 blog. This site was created to provide  reference material for this nodes  usage and operation. I may also include some useful  IRLP scripts for other node owners.  Basic information about Node 3106. This node has been in service since February 4, 2006.

Location and Frequency:

  • Saint Michael, MN (next to the Crow River)
  • 446.050 Mhz 131.8Hz CTCCS Tone

RF Equipment:

  • Motorola GM300  ~30W
  • Node simplex link antenna, home made 5/8 wave vertical.


Mobile coverage is limited due to the stations location and antenna height. The coverage for typical mobile operation is approximately 10-15 miles.

This node is open to all.  Please check the status of the node by using DTMF tones and  enter  “*0” .  The node will respond if the node is connected to a reflector, cleared, disabled.  Please review the node guidelines before using this node.


Latest Kit – SDR Cube

Thursday, July 7th, 2011

This is a really cute QRP rig.   I am in the last test phase and RF functional testing.  I did have one issue with the 40 pin cable that I made.  I have made many of these cables in the past but for some reason there was a short in the 3.3V power section.  At first, I thought it was the DSP board since this was were the main PIC processor resides and the display was unresponsive.  After doing some checks, I discovered the fault resided in the ribbon cable connecting the I/O board and the DSP board.  Lucky the DSP board was fine.

Overall the kit took about 2 weeks to build.  Keep in mind, I was not able to work on this kit everyday, and when I did work on the kit, it was for short periods. The hardest part of the build was the RxAmp Module; the parts are truly tiny.  For more information, visit the SDR Cube Site.

I’ve added the following circuit to allow keying of my external amplifier.  The circuit was build on a proto board that is “piggy backed” on the Soft Rock RxTx 6.3 board.

Here’s the schematic of the board:

Mounting of the board is shown here: