[Ronja] Distance between multiple Tx beams

[Gullik Webjörn]

Hello Cecilia,

What this all comes down to is that if you want to use
multiple transmitters, you have to make sure that each transmitter hits
the receiver photodiode through the receiver lens.

Look up the lens equation in a physics book, it will show you
the "small image" converted through the lens to the "large image"
in the relation to front focal length(FFR) to back focal length(BFR)

If you have an object the size of the receiver PIN diode, ( 5 mm)
you can figure out a circle far away, which will reach the detector

As Karel says, as long as you keep your transmitters within a distance
from each other of approximately 1 m / 200 m, both transmitters will
hit the photodiode more or less right on.

In practice, if you have a distance of, say, 1 km, you cannot place
your transmitters more than 5 m apart, because then the projected image
might not be entirely on the PIN diode, some part might spill over.

>From your question I understand that you want to bridge more than 1.5 km
with Ronja. If that is the case, just place the two (or four or...)
transmitters less than 5 m apart, and all transmitters will project all
their energy on the photo diode.

Last, if the light was coherent, i.e. single wavelength, you would have
to worry about interference between the different beams, luckily, the
LED light is so broadband that these effects will not show with these
distances and transmitters.

Bottom line:

Place your transmitters closer than 1m / 200 m -- 5m / 1 km and you will
gain the full 3 dB (x2) of gain for each doubling  of the transmitters.

Best regards

Gullik


On Sat, 2009-11-21 at 10:02 -0600, Cecilia Puon wrote:
> El sáb, 21-11-2009 a las 13:22 +0100, Karel Kulhavy escribió: 
> > ---- Cecilia Puon <cpuon at fsomexico.com> schrieb:
> > > I have read this pages and I understand that I win intensity if I use
> > > two Transmitters but I do not know which is the maximum distance that I
> > > can separate these Tx if I do not want to distorsion the signal. 
> > > 
> > > Do I have to direct the two Tx's beams through the same point in the
> > > len?Because I dont want to distorsion the signal.
> > 
> > The longer the link the more you can separate the TX's and still fit into the field
> > of view of the receiver.
> > 
> > The photosensitive area extends over the whole diameter of the RX diode in SFH 203, as
> > can be seen by naked eye. Not sure how it is with BPW 43. The RX diode is 5mm in diameter and focal length about 30cm. This gives ratio of 5:300 or 1:60. For every 600 meters of track you can theoretically separate the TX 10 meters
> 
> 
> I am a little confused, what exactly do you mean with "For every 600
> meters of track you can theoretically separate the TX 10 meters". I
> understand that the distance between Tx and Rx is the link lenght and
> is equal than the word "Track" for you, am I right? So, how can I have
> a track(link) of 600m? and also I can separate Tx from Rx 10 meters, I
> dont understand the point.
> 
> Thank you, regards.
> 
> Cecilia Puón 
> 
> 
> > In practice, since the images of the transmitters in the receivers are not points but
> > blotches, the separation should be kept less, I would guess one third of that, i.e. 1
> > meter every 200 meters.
> > 
> > Regards,
> > 
> > Karel
> > > 
> > > Thank you for your help. 
> > > 
> > > Cecilia Puon.
> > > 
> > > 
> > > El jue, 19-11-2009 a las 12:05 -0600, Russell Valentine escribió:
> > > 
> > > > http://ronja.twibright.com/metropolis/dist.php
> > > > 
> > > > Get your intensity number from (notice the dual TX table):
> > > > http://ronja.twibright.com/msmt/gains.pdf
> > > > 
> > > > Then find the range from here:
> > > > http://ronja.twibright.com/drawings/dist.pdf
> > > > 
> > > > 
> > > > Cecilia Puon wrote:
> > > > > Hello, I have a question. What is the distance between two Tx beams
> > > > > which are used to transmit the same signal to one Rx?, with the proposal
> > > > > to improve the range. 
> > > > > 
> > > > > Thank you for your answer.
> > > > > 
> > > > > Cecilia Puón.
> > > > > 
> > > > > 
> > > > 
> > > > 
> > > > _______________________________________________
> > > > Ronja mailing list
> > > > Ronja at lists.pointless.net
> > > > http://pointless.net/mailman/listinfo/ronja
> > 
> _______________________________________________
> Ronja mailing list
> Ronja at lists.pointless.net
> http://pointless.net/mailman/listinfo/ronja