Teardown !
I have received my 25MHz unit and it is pretty much the same as in the photo. The architecture seems to be an STM8 micro (small TQFP on the right) handling the coms & display, CH340G (upper right TSOP) usb uart bridge deals with the USB part. The signals are produced by a Lattice MachXO2 CPLD/FPGA (large QFT in the center) with 2 8bit resistor DACs (left of it) with some opamps (immediately left of the DAC ladders) and AD603ARs (left from the opams). I didn't remove the heatsink, so not sure what is under it - perhaps some power transistors.
The rest is not very interesting - there are relays to switch the outputs on and off, standard 2 line LCD, encoder knob on a separate board and a boatload of passives. The bottom right of the board is a switching PSU.
It looks fairly well built, actually, especially for the price. I have seen much much worse already.
However, what I would love to get is an English manual. The original is in Chinese, unfortunately. I still haven't figured how to actually use the counter functionality the unit is supposed to have nor how to use the various synchronization inputs, including the TTL inputs and outputs on header in the back.
the specs I found on ebay list only higher than 6MHz for “sine wave” in the 3 “top” models (12/20/25 MHz),
all other wave forms are speced at 6MHz
Care to open up and have a look if the difference is pure in firmware or they add in the more expensive ones some kind of additional ( hardware?) sine wave generator.
?
There isn't any separate gen for 25MHz and 6MHz square wave. I have checked the signal on my scope and when set to square wave, the signal starts getting distorted around 1-2MHz and the higher you go, the more sine-like it looks, until you get basically straight sine wave above around 4-5MHz (it might do 6MHz, but I didn't probe it correctly). On the scope it looks like as if there was a heavy low pass filter and the higher harmonics were getting progressively cut from the signal as the frequency was increased. Not sure whether there is a physical low pass filter on the output or whether it is an artifact of the sampling.