[Today’s run: none – yesterday 6.8 miles]
I’ve been playing around with this half-baked receiver that I picked up for $5 at the Jackson, MS hamfest a couple of weeks ago. Learning quite a bit, and enjoying it. It has opened a whole world of homebrew tube receiver projects from the 1960’s like the HBR series and the DCS-500.
But it occurred to me on the run yesterday that I should get my 2 year old GPSDO project wrapped up, then I could focus on the receiver if I want to.
So I spent all of Saturday afternoon and some of today getting it “done”, or close anyway. I have everything in the box and I have the parts talking to each other. My GPS was able to lock ok. The 10 Mhz oscillator is still drifting, after about 8 hours now. I don’t know if that is good or bad. It seems to be going at a steady pace in one direction. So I will just let it run and see where it ends up.
I have a few wrap-up things I could do: There’s a multi-colored LED that is supposed to show whether the thing is in “lock”. I need to run that to the front panel. I also need to wire up the power on/off LED. And my antenna system could use some improvement. I need to acquire some 50 ohm BNC terminators so that I can terminate any open outputs. That is supposed to help with overall stability.
But I have it working in a general way. Power goes where power is meant to go, and it is producing a 10 Mhz signal of limited quality. If it ever locks on the GPS system it will be a pretty cool gizmo.
The GPS puts out a 1 pulse per second (pps) signal. The 10 mHz ovenized oscillator is a high stability gadget which allows small adjustments using a controlling voltage between -5 and +5 volts. The controller card has a processor on it. It compares the signal from the GPS with the 10 mHz oscillator and does some statistical smoothing, deciding if the control voltage needs to go up or down to make things sync up. So the oscillator is “disciplined” by the GPS signal. And they call it a GPS disciplined oscillator – GPSDO. If I get it working right I can use it as a frequency standard for my counter and o-scope, with an accuracy close to the atomic clocks used on the GPS system.
Both the GPS and the controller card will talk to me via serial port and I have that working ok. I can see if the control voltage is going up or down and whether the GPS is seeing enough satellites to work correctly.