groups and chanels

[tim10243]

hi,
after studying the hard- and softwarediscussions here for a while i am
missing the option to choose between several "chanels". normaly a
radiotrigger (like pocketwizard, radiopopper, etc) has a fixed
frequency but the option to coose between several chanels in case
there a more than one photographer and each wants to build up his own
speedlight system with radiotriggers. within this chanel there are
several groups to adlust mainlight, backlight, filllight, etc.as far
as i understand the SPOT has no chanels, right?
regards
tim

[Till Seyfarth]

Hi,

 

the SPOT has 8 channels, called "IDs". It's limited to 8 because I don't really see the need for more... ;-)  and 8 channels already cost three bits in the protocol. There's a tradeoff between number of channels and x-synch.

 

Cheers

Till

[Konstantin]

Well, to be perfectly clear here, it depends on what you really mean
by "channel". RFM12 works in a fairly simple manner - it a specific
frequency for "0" and a specific frequency for "1". These can vary -
AFAIR by hundrends of KHz around the main band (i.e. 433 or 868 MHz).
These frequencies are filtered out by the receiver. If they are apart
far enough for two transmitter-receiver pairs, there's a pretty good
chance of them being able to work simultaneously.

Now, there are the "IDs" incorporated in the protocol. They occupy the
3 bits mentioned. These you use to adjust your lights separately.

So, I would say, no, SPOT works on 1 radio channel. If two SPOTs were
used simultaneously, there would be a good deal of interference, even
if they would be using different IDs.



P.S.: I didn't develop the SPOT system, but that's what it looks like.
I may be wrong though :)

[Till Seyfarth]

Let's not confuse ids and groups... ids are exactly what i've said before (what was called channels). They are not used for adjusting your lights separately. This is what groups are for. There are four groups (A, B, C, D - two bits in the protocol) for which the flash power is adjustable, each receiver chooses a group to which it listens.

 

So up to 8 SPOTs could work in the same area without much interference. There's of course still the issue of bandwidth occupation - but that's unavoidable. Because of the wide use of the free frequencies even radio controlled garage door openers interfere with the SPOT by competing for air time. They do not however misfire the flashes. If they send at the same time and cancel out the SPOTs signal they can probably prevent it from triggering.