One of the problems with the Yahoo group is that we lost the facility to search through the posts. I'm going through my email to find some of the replies I sent to questions about the SDR-4+ receiver and other products.
When we test the SDR-4 the frequency calibration is checked against a
GPS disciplined oscillator or on-air standard which has an accuracy
measured in parts per billion. The calibration correction for the Si570
oscillator is stored in a microcontroller in the SDR-4.
If the correction data gets changed or corrupted then the Si570 reverts
to a factory default figure which may be several kHz from the true value.
I've devised a method for SDR-4 users to check the calibration using off
air frequency standard signals using HDSDR.
First connect the SDR-4 to the PC and an antenna. Open HDSDR and tune
the LO to 10.010 MHz. In the UK a time signal beacon should appear on
9.996 MHz. This is the frequency of the frequency standard station RWM.
If the receiver is in calibration the time signal or morse transmission
will be seen exactly on the 9996 kHz line on the waterfall.
If the frequency is offset by any significant amount then in the HDSDR
program, left click on the ExtIO button just to the right of the Tune
frequency display. Click on Open to start the program.
This will bring up the SoftRock Configuration Tool. Click on the
In this window enter the frequency that RWM appears on the waterfall in
the Tuned box.
In the Real box enter the actual transmitted frequency of RWM (in this
case 9.996 MHz.
If the frequency was out by several kHz you may have to retune the
receiver to 9.996 MHz to find RWM again. It should now be on frequency.
As a final check set the receiver to USB and put the red line in the
centre display on 9.995 MHz so that RWM appears as a 1 kHz audio tone in
the speakers. In the bottom waterfall RWM should be on the 1 kHz line.
If not repeat the calibration process again to correct any small errors
When the calibration process is completed click on Close on the SoftRock
Calibration Tool and close it completely by clicking on the X at the top
right hand corner.
I've suggested the use of RWM as it's usually a strong signal in the UK.
Here's a link to a list of other frequency standard stations that may be
Regards and 73,