[NLRS] BPW43 vs BPW34 vs OPT101 for Daylight Optical Communications

[Rob Jahnke]

*Why Does the Ronja Optical Transceiver work so well in the daylight?*

*The BPW43 Radiant sensitive area is 0.78 mm^2  - Used on the Ronja
Receiver ( 0 dB)*
*The BPW34 Radiant sensitive area is 7.5 mm^2  - Used on the KA7OEI
Receiver  ( +9.8 dB in area)*
*The OPT101 Radiant sensitive area is 5.24 mm^2 - Used on the K0THZ
Receiver ( +8.3 dB in area)*

*So the BPW43 is MUCH LESS sensitive to light (and much faster) than either
the BPW34 or OPT101. Which may be one of the reasons they are able to
operate in daylight. They only transmit with 17 Mw of output power but the
range was limited to 1.4 km. So they were able to achieve an adequate SNR
in daylight over that short distance.*

*So the "Secret" to successful daylight operation for our system might be
to use a Bandpass Optical Filter on the receiver (which Ronja did not use),
but also use a restricted aperture on the receiver (or a smaller lens) for
daylight to help avoid saturation of the receiver. We can also use a
negative bias voltage on the OPT101 to reduce the offset voltage at the
input of the amplifier and thus extend the ambient light range. *

*AND use a high power transmitter. I don't know what the **radiated **output
power is for our LED flashlights, but the input power dissipated by the LED
is around 3 Watts. Multiply that by the radiometric efficiency of the LED
and you still get WAY more than 17 Mw.*

*If the efficiency of the LED is 50% (hypothetical - I have seen numbers
between 25% and 80% for Red LED's) then our transmitter would be about 20
db more powerful. Each 6db doubles the range, so 20dB would theoretically
increase our range by 2^(20/6) or 2^3.33 or 10 times the distance. 10 x 1.4
km = 14 km (8+ miles). We only need audio bandwidth instead of Mhz
bandwidth so that should help as well.*

*These are VERY ROUGH calculations but they give us a VERY ROUGH estimate
of what might be achievable with our current transmitter and receiver and
give us a direction for further experiments. We are struggling to find 5
mile LOS paths here in central MN so 8+ miles is probably good enough.*

*Rob - K0XL / K0THZ*
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/nlrs/attachments/20251214/ccbce488/attachment.html>