To continue debugging my problems with CC1, I needed a signal source that I could feed into the transciever. Jason/NT7S sketched out a simple crystal based Colpitts oscillator circuit for me to try.
Colpitts oscillator schematic
Fortunately I was able to find everything I needed in my parts bin to breadboard the circuit. I used a 7.030 MHz crystal and a 10 pF capacitor at the output.
Colpitts oscillator
Colpitts oscillator
Will give it another examination tomorrow to make sure I have all the right components and that everything is laid out properly on the breadboard, then give it some power and see if I get anything out of it.
After digging a bit into the manual and figuring out what buttons I should be pressing, I was finally able to get the oscilloscope to give me some waveforms at some of the test points on CC1. No indication of what the time base is (have to figure out what buttons to press to make the text display again) but it’s progress at least. I’m just tickled that I’m able to get any kind of waveforms at all.
This is the nice sine wave out of the U6 50 MHz oscillator chip
CC1 oscillator waveform
At the BFO test point, this is what I got
CC1 BFO waveform
Based on this, the BFO would seem to be in good shape.
At the VFO test point, the trace looks like this
CC1 VFO waveform
It was tough to get a stable trace out of this, and I had to wiggle the probe around a bit before I could get the waveform. I wonder if that could be an indication of any kind of problem.
Diagnostic work continues on CC1 and now I have another tool I can use on my workbench. There’s still a bunch of stuff I need to learn about this scope, so I’ll be spending more time with the manual. There’s supposed to be some text on the display as well which I think I made go away in my earlier attempts at playing with the scope. Need to figure out how to bring those back.
Using Audacity, I was able to finally get a decent recording of the whining noise that my CC1 is making (the recording isn’t very loud so you might have to turn the volume up).
The audio clip starts with CC1’s startup message (“CC1”) followed by the whining noise, and then the Morse code readout of the frequency and then more whining. Of interest I think is that the whining is muted when CC1 is playing the dits and dahs. Not sure if that says anything about where the source might be.
Using Audacity’s frequency analysis tells me the main frequency of the whine is around 1300 Hz with second and third harmonics at around 2600 and 3900.
CC1 whine spectrum
Still haven’t had much luck figuring out what’s making it, although Jason/NT7S has given me a few helpful tips. I need to check and make sure the BFO is oscillating and check to make sure there are no open circuits in the toroids. Haven’t found anything yet. Need to put CC1 back on the bench and have a closer look at everything.
While I was checking the signal paths through the toroids, I decided to go ahead and make some modifications to the IF filter suggested by Jason to improve the signal leakage. Didn’t expect them to have any effect on the whining, but I figured I’d make them anyway.
I’m enjoying this detective work trying to figure out what I did wrong with CC1. It’s almost as fun as putting it together.
CC1 seems to work, but all is not well I think. Attached a 50 Ω BNC terminator and applied power, but I was hearing this whining noise that I didn’t remember hearing before. Apparently it’s normal and is a result of clock in the DDS part of the radio. It’s supposed to be fixed by a firmware update, but applying it didn’t help with my radio. Since there are 4 other CC1s completed that don’t seem to be doing this, it’s probably something wrong with mine. Not sure what the problem is yet. I think I might have to find someone with a working oscilloscope to do some probing around with. Whiny.
Finally found a BNC/SO-239 adapter at Hurricane Electronics/Radio Shack up in Summerville. Used it to connect CC1 to the antenna and was hoping to hear something, but if there was anything, I couldn’t hear it over the whining noise. Tried tuning around to some frequencies where I could hear CW activity on the big radio, but wasn’t able to hear anything when I tuned to the same frequency on CC1. Deaf, or at least hard of hearing.
Was hoping I’d be able to get CC1 operational, but it looks like it needs some troubleshooting. In the meantime, there are a couple of hardware modifications that need to be made to T1 and L5, which I’ll try to get to soon.
