Yes, the channel C input is a little bit of a lesson for me
I assumed it had it because the connector was there, but it wasn't. That in in line with the manual, and the seller didn't say it was fitted when I bought it on eBay. But no matter I got it reasonably cheaply because there was an error with the unit where it wouldn't read correctly. Turned out the PLL that takes the 10MHz and converts to 500MHz (on the 6030, not sure about the 6010) was broken - the first divider was dead. I was able to source a replacement and was all good. I also took the precaution of replacing the electrolytics..
As for the External/Internal switching, I'm not sure about the 6010, but if the 6030 is anything to go my, it is a manual switch - you need to move jumpers around inside the instrument. These are located on the left side of the module.. There is no auto switching
In my case the instrument runs at 500MHz derived from a PLL, so the external 10Mhz would have to be constant..
On my long list of "projects to do when I get a chance" is to break out the jumpers to either a small relay daughter board or even add a toggle switch on the back..
marginal at 10MHz tho.
I also intend to make or re-purpose a divider board to bring the C channel up. I'm reasonably sure there is the ability to go to higher frequencies as some of the pins to the daughter board set the divide ratio so the firmware can correctly display the frequency. the 6030 is labelled at 2.4GHz..
If you have a GPSDO, just setup as an input, and you will be more accurate than me
I don't know what the differences are between the models, but if they share common hardware, I have a copy of the 6030 EPROM if you want to play with it..
Ash.