Saturday, April 7, 2012

Web SDR - HF Propagation

Observing the HF bands during contests can reveal some very interesting statistics about overall propagation spectrum usage, and especially during the start and end of contests.

At higher FFT resolutions, one can inspect the quality of signals such as this digital transmission on 20m.  This snapshot was taken running my experimental web sdr
View live SDR here :

Digital mode on 20m (using 8k FFT) using websdr

When observing digital signals, where transmitter energy is evenly distributed across the 2.8KHz transmitter bandwidth, the effects of rapid path fading, as a result of ionospheric conditions between the transmitter and receiver stations, become very visible.

This received digital signal to the right clearly shows the effects of fading - which would have had less impact on SSB voice transmission (left) , but because the even energy distribution, clearly shows the differential signal strength, for frequencies across the 2.8KHz pass-band.   
By comparison, the SSB signal shows very little signs of fading.  This could be a result of the different origin of the SSB signal (and of course the fact the the energy distribution of SSB makes it less obvious for casual observation)

Rapid fading visible in the 2.8KHz digital signal.  (Using websdr

Monday, March 19, 2012

WWW-SDR - Intro Video

I've always thought that SDR had good promise for visuals and demonstrating the fun side of Amateur Radio today.  I put together a quick intro video, using content from my www-sdr client, running in a www browser with a link to the live wwwSDR. (requires Browser + Java add-on)

Please leave your comments on quality of audio, UI ease of use, or any other thoughts.

73, happy hf watching - as the solar cycle picks up.
Fun Side of SDR.

Sunday, March 18, 2012


Improved network bandwidth usage by using loss-less compression for both data and audio streams.
Audio streaming compression using AAC is in progress.  Audio streaming ~ avg 48kbs.

Improved some of the colormaps - although not a priority at this time.  Server-side performance improvements are ongoing, especially the DSP section. (BPF, Demod)

Feel free to connect to the live server.  Any comments/feedback are always appreciated.

Tuesday, January 17, 2012

How to replace the Icom IC-725 LCD lights

I used this method for replacing LCD backlight bulbs on the Icom IC-725.  The LCD backlighting is provided by 3 x miniature 12V bulbs (not LEDs).  Each lamp is help in place in a hole behind the display.
The limited access behind the front panel is the main constraint in replacing the bulbs.

Ensure to follow the standard safety precautions - ie. the radio is disconnected, and remove any connected devices, Mic, CW Key, data connectors, etc.

NOTE:  This procedure does NOT require the removal of the front-plastic panel.  

  1. Follow the instructions found in the user manual for removing the top/bottom covers.
  2. Remove 2 x the screws on top which holds the front-panel connected to the heat sink.
  3. Remove the 2 x Left and 2 x Right side screws holding the front panel in place.
  4. With the 6 x screw removed, the front panel should be free to be tilted down (away from the heatsink) See pic below.  Be careful not to tilt too far.  The connecting wires between front panel and the bottom (circuit board side of the radio) is short, and only allows for a little play.
Left View

Left/Top View - showing the access gap, after rotating the front panel down.

  1. The top side of the front panel can be rotated away from the heatsink, allowing about 1 inch space between the heatsink and front panel assembly.  This is the gap through which you will access replace the lamps.
Top view
 There are 3 x 12V mini lamps (backlights to the LCD panel) which can be access via the gap between the heatsink, and the front panel when it's in the rotated state.

The image below indicates the locations of each of the 3 x lamps.

Relative Lamp Locations when viewing from the heat-sink side.
Left lamp (meter backlight) is clearly visible here:
This lamp is easy to reach, and replace. See below.

Meter Backlight (Leads visible, with light bulb inserted into socket and yellow sleeve)

Middle Lamp (LCD left backlight)

The middle lamp is the trickiest to replace, due to the placement behind the mounting bracket, which leaves very little space for a soldering iron, and tweezers to grab the lamp leads and maneuver the new one into place.  To complicate matters, the soldered connected wires, are sort of in the way.  Be careful not to sever these connections while working on this lamp.

Middle Lamp (trickiest to get to, since it's behind the mounting bracket)

Right Lamp (LCD right backlight)
This lamp is also easy to reach and replaceIt is also clear of the mounting plate.

Right Lamp (LCD right side backlight)

The process for replacing the bulbs, simply involves unsoldering, and replacing with equiv 12V lamps.  You can re-use the yellow sleeve.  (This is what gives the backlight the yellow tint).  You can experiment with other colors, for a different effect.  I chose to re-use the sleeves, for the original effect.

Front panel view
This view shows the relative locations of each of the lamps, and their back-light effect on the meter and LCD panel when the radio is powered on.
Front panel view - indicating relative lamp location.

Good luck on replacing the bulbs to give your IC725 a new look again.
Please send comments if you think this was helpful.

73 and happy maintenance.