The analog front end probably isn't that hard. On the digital side,
you really want a single-shot sample rate of at least 10x your analog
bandwidth (20x is nicer). For a "typical" 100 MHz scope that means 1 G
Sa/sec, with (hopefully) sub-nsec jitter.
Picoscope seems to have the best numbers. Their prices look like
they're close to comparable desktop DSOs from Instek or Rigol.
Yeah, but Pico units are really pricey. I forget the details, but I
think they want $2K for a 300 MHz unit although that may be a 500 MHz BW
unit and it may include some digital inputs. I just remember I didn't
go any further than their price page.
I did a little searching over the last half hour and found a hand held
unit with the Hantek name on it. I don't see it at the Hantek site, but
that doesn't surprise me. The DSO1202B claims 200 MHz BW and 1 GHz
sample rate. The main difference with the DSO1200 seems to be the
DSO1200 has a 500 MHz sample rate and 32 KSample buffer while the 1202B
has a 1 MSample buffer.
I found a couple of reviews on the 1200 where folks seem to recommend a
Rigol desktop unit over this, but not because they have used it. I
think a handheld might be a great combination of small size on the desk
along with full functionality for stand alone operation. It even runs 6
hours on batteries, well, the 1200 does, I haven't found this spec for
the 1202B yet.
I would like digital inputs too, but just haven't found anything decent
at a "reasonable" price. Obviously if everyone is charging more than I
want to pay that makes their price UNreasonable... lol