9kHz Frequency Stability Test 2 - 15th January 2011. Well tonight I ran a second stability test using a PC sound card generated frequency source. I used a free downloaded software application called "SG102 PC Oscillator". The 8.971kHz audio was generated and output from the PC sound card was used to drive my audio amplifier. The amplifier produced 2 to 3 watts into a 50 ohm dummy load, I ran this for a while without any major interruption and the stability was quite good. My next test was to generate QRS mode. In the audio feed line from the PC sound card I fitted a simple relay to switch the signal which was triggered from the RS232 port using qrs.exe a popular QRS and DFCW application by Rik Strobbe ON7YD. The qrs.exe software was programmed to send "WGT" at a keying speed of QRS500, this means that a single dot would be 500 seconds long. The complete sequence took 233 minutes to send. Although the PC oscillator software worked OK I did find that the frequency accuracy was difficult to set up and I had to create an offset in the selected frequency to get the signal within my narrow Spectrum Laboratory configuration. Although not at my ideal frequency of 8.971kHz I got it near enough to enable the tests to be run. The accompanying pictures will be self explanatory.
Displayed at QRS 120
Displayed at QRS 600
14th January 2011 - 9kHz Frequency Stability Test 1.
Last night I ran my DDS VFO (with no amplifier) fed into a 50 ohm dummy load in the shack and the signal was received by my VLF loop receiving system. The test was started from cold at 2130utc until just after midnight. I believe that the stability of this device is perfectly adequate for VLF transmissions. The frequency selected was 8.971kHz and as you can see from the screen capture the DDS VFO is very very close to the correct output. This SpecLab configuration is locked to GBZ. I will also be testing a PC sound card generated output and compare the frequency stability.