Interesting that they have put all 9 FPGA versions in that folder. Wonder why ...
For 50 ohm, even that the switch can be "moved", that need to be compensated as a value, along the signal path.
If is just a relay that route the signal to a passive limiter (impedance adapter), it will be lower as amplitude.
The 50 Ohm in put is not with a resistgor in to ground at the input. There are different signal paths to the front-end chips.
It very much looks like the lower relay switched between 50 Ohm and 1 M ohm mode.
The upper relay looks like it switches between 2 attenuators for the 50 Ohm version and likely also for the 1 M version.
The 50 ohm paths are to the left side, with 2 clearliy visible dividers in the 50 ohm range, going to 2 pins of the front end chip.
Between the 2 realys there is also some attenuator that is too low in impedance to be used with the 1 M signal.
The 50 Ohm termination is thus likely split over multiple resistors: the 3 between the realys, one of the 2 attenuators on the left and to a small part the termination at the front end chip.
The 50 ohm front end looks essentially the same, so it should really be only a SW question of enabling a suitable inputs at the front end chip.
In the high frequency range the 50 ohm part may have a subtile effect on the 1 M path - so instead of redicigning the PCB they may have decided to populate the extra realy and few resistors for the 50 ohm part too.
There may however be a catch: It looks like that in the HDO4000 there are 2 differential signals from each front end to the ADCs. With the HDO1000 only 1 differential signal per front end goes to the ADC.
So the 50 ohm path may just be a dead end at the output of the front end chips with no free ADC inputs to go to. Even the developers at Rigol may not have an easy way to add the 50 ohm option for the 4 channel 1 ADC combination. With the 2 channel version there would be enough inputs.
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The front end chip definitely chooses between the different inputs. It looks like 2 x for 50 Ohm and 4 x for 1 M mode + an additional DC input that also has to be somehow combined with the AC part !
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The front end chip definitely chooses between the different inputs. It looks like 2 x for 50 Ohm and 4 x for 1 M mode + an additional DC input that also has to be somehow combined with the AC part !
-snipSo the simple answer to my question is : Yes, we do not need a double path to ADC to provide 50 ohms input capability.
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There may be a good reason in no enobeling it with the cheaper version: the 50 ohm inputs are somewhat prone to overload. With this scope this could mean damaging the front end chip and not just burning a 51 ohm resistor.
There not seem to have much choices. For HDO1K with A100T, only S2 bit2 can be used, as S4 need two ADC's, bit1 is for testing and bit3 is maybe for a future version with AWG.
Also in the frontend is a little difference that can be a filter to limit the bandwith of the frontend amplifier to 2-300 MHz. Tho I wish I'm wrong ...
For all this debate about how the product might work.... has there ever been a "hack" on this forum that actually extended functionality by adding new code? As I recall it has always been enabling of already existing code by overriding/bypassing software lockouts.
Interesting that the PCBs are in fact not identical. I wonder if it's just a different revision for the same PCB or there's slight differences between the HDO1k and HDO4k models.
For the SDM3055/3045 there is something around for a more or less new firmware (not sure if this is for the inbound or outbound part or manybe both). AFAIK this came with additions and parts still missing.
Changing focus, has any HDO4K/1K's owner changed the FANs ?
I noticed that they are controlled in speed, i wonder if it is under software control.
if there's any GPIO's available you could probably build a small pcb to control the fans.
temp information should be available in sys/class/thermal/ I think, so you could build a script for it. how many thermal zones are there?
edit: but you'd have to open it up, so you'd lose your warranty.
ls /sys/class/thermal
there should be folders for each thermal zone. go in each and cat the "temp" file. hope it has this structure
Changing focus, has any HDO4K/1K's owner changed the FANs ?
I noticed that they are controlled in speed, i wonder if it is under software control.
It´s possible to control fans which got only 2-wire connections, but kinda uncommon today.
I looked at the photos for the backside of the PCB and to me those look like 2 SO8 MOSFETs and maybe a smaller sot23 one to drive their gates. It may be available in software. There may be clues in the dtb file.