Calculating range from known technical parameters
- First clarify your technical parameters:
- Transmitter LED (choice: HSDL4230, HSDL4220, HPWT-BD00-F4000,
HPWT-BD00-E4000, HPWT-BH00-H4000, HPWT-BH00-G4000, HPWT-BD00-D4000,
HPWT-BH00-F4000, HPWT-BD00(-0000), HPWT-BH00-E4000,
- Transmitter lens (choice: loupe with diameter 60, 75, 80, 90, 100, 130).
Based on real measurement of these common Chinese loupes:
- Receiver lens. (choice: loupe with diameter 60, 75, 80, 90, 100, 130).
- If the transmitter is multiple, number of parallel transmitters
- In how dense fog (visibility) you want the link to surely run. Choice: 4km
visibility, 2km, 1km, 500m, 200m, 100m, 50m.
- Then determine Launch intensity (dBTq*sym^-1*sr^-1) of your setup
from these graphs (Fig. 10, 11, 12): PostScript or
PDF. Launch intensity is a quantity that says how
many photons is emitted per spatial angle unit during one bit time slot. This
number is expressed in decibels above tera-photon (10^12 photons) for
- Then determine from this PostScript or PDF the range of your link.
There are 72 combinations how to set up a single Ronja transmitter. Some of
them are very efficient, some not so much. Four of them have been selected as
recommended. See PostScript or PDF, Fig. 17
Calculating required lens diameter from range
Guess some transmitter and receiver lens diameter and perform range
calculation according to the above. Then adjust your guess according to the
Nevertheless it's recommended to have the lenses as big as conveniently
possible, i. e. the best recommended combination. It is always handy to have
extra reliability during fog. However in some situation big optical heads are
not welcome, in which a reasonable compromise must be made.
Additional interesting numbers
The lenses are for Ronja like antennae for microwaves (WiFi). Gain in
decibels can be assigned to them as well as to the WiFi antennae. Antenna
(lens) gain is defined firly simply: it's how many times the density of the
energy beam becomes bigger when you start with isotropic radiator and suddenly
put the antenna over the radiator.
The gain is dependent also on LED geometry (smaller LED's are sensitive to
lens' aberration which blurs them out and lowers the gain) and the wavelength
(the glass of lens absorbs different wavelengths differently).
Therefore gains were measured for 3 families: red diodes (HPWT-B family),
HSDL4220 infra diode and HSDL4230 infra diode. See PostScript or PDF, Fig.
Source codes of the calculations