Hello Roelof,
Is there some progress on your side? I may have some useful
informations for you.
In the last test i found that i need more gain and in the end i want to
have a fiber optic antenna that covers LF and MF, maybe even VLF.
Furthermore a resonated antenna is not suitable when the antenna is
sometimes grounded or floating in the tests.
In my circuit the problem is the low rise- and fall- time of the
SFH350V. I saw the problem years ago and ordered a few SFH250V photo
diodes which should work well. The LED transmitter is suitable i think,
although the SFH757 is faster of course. But i'm always looking below 1
MHz.
Now i seareched for some additional ideas for a the optical/electrical
converter. Some time ago i built a transimpedance converter but i was
sceptic about OP AMPs at 475 kHz. But i think i learned something and
got some new ideas on these pages:
http://circuits.linear.com/all--Photodiode_Interface_*_Transimpedance_Amps-53
Seems that these frequencies are no problem at all, even if a high gain
is desired. The LT6200
is available at RS, 4.56 EUR here. Quite expensive but worth to play
with :-) OK, some may say it is overkill and the device can cause VHF
oscillations, but anyway...
I guess it will be no problem to get the needed gain to go on with the
experiments, even if no resonated antenna is used... BTW the output
current of the device is even 60 mA. So maybe it is even suitable to
drive the LED...
What do you think?
73, Stefan/DK7FC
Am 13.07.2013 12:55, schrieb Roelof Bakker:
Hello
Edgar,
I don't know how linear these devices are, but that will show up in
actual use.
The SFH756V and SFH350V are housed in a moulded plastic casing with a
cable clamp:
http://www.avagotech.com/pages/en/fiber_optics/general_purpose_industrial_control_data_link_650nm/sfh756v/
I also found that for a wider bandwidth the SFH 757V / SFH 250V are
more suitable.
These are rated at 100 MBd.
I will order them in the near future.
73,
Roelof Bakker, pa0rdt
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