Electronics > Projects, Designs, and Technical Stuff
Homebrew spectrum analyser high-impedance probe
branadic:
Here is another FET probe based on TI's JFET OpAmps from DC to 500MHz:
http://www.mikrocontroller.net/topic/188227#new
and another AC FET probe (page 112):
http://www.bartelsos.de/index.php?dl_file=3TNJFF9YR3
philpem:
--- Quote from: KJDS on April 06, 2013, 12:32:07 pm ---How stressed is that 78L05.
7V across it, and at a guess 40mA? A quick check suggests it'll get warm enough to worry me enough to either lower the supply voltage if practical or if you're going to mount it away from the probe then use a 7805 instead.
--- End quote ---
I'll probably use a normal 7805 anyway - I don't tend to keep 78L05s in stock.
Exceeding voltage regulator specs seems to be Elektor's SOP - I've seen them do it in a few designs. That and using solder pads barely larger than the component pins...
Just patching together an EAGLE library for the Minicircuits MAR-6, then modifying the Elektor design and etching a PCB!
philpem:
Well, this is what I've got so far -- schematic and PCB attached. Would be interested in any comments, criticisms or suggestions for improvement you might have :)
Dimensions of the board: around 14 x 50 mm. In old money, a whisker over half an inch wide by two inches long.
My eventual plan is to (hopefully!) build up some form of shielded case for the thing. That's still on the drawing board, though.
fpliuzzi:
Thanks for posting the schematic and board layout (I'm assuming that you're using Elektor's original bottom layer layout as is). Nice job on the PCB layout. I also like your idea of moving the 5V regulator off of the probe board to minimize the probe's dimensions.
I am happy that I held off building Elektor's original probe board design. I like your implementation much better. I'm sure that you cannot wait to test drive your new probe.
Regards,
Frank
vk6zgo:
--- Quote from: philpem on April 07, 2013, 11:27:53 am ---
Exceeding voltage regulator specs seems to be Elektor's SOP - I've seen them do it in a few designs. That and using solder pads barely larger than the component pins...
--- End quote ---
I thought that was just a generic European thing,like through holes barely larger than component leads.
Great for flow soldering,but a nightmare to rework!
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