Hi John,
Comments inserted:
Jon Stone wrote:
Simon wrote:
I find it hard to imagine both system protocols working harmoniously as the local field.
Why would they not work in harmony on the same field? Existing radios are on 72 Mhz. Existing SS radios use 900 Mhz and 2.4 Ghz. Are you assuming the powers that be might grant spread spectrum on the same 72 Mhz?
No, it would have to be the ISM band (900MHz/2.4MHz and up), chances of dedicated bandwidth is slim to none given the current FCC agreement.
To be able to comment requires a firm understanding of the technology, bandwidth requirements versus numbers of channels per TX, and the fact it varies (protocol), effective range because the carrier frequency (to get the bandwidth) would have to be at least a magnitude higher than 72MHz. Does everyone "just turn on" ( actually impossible), or does your TX use blue-tooth (eg: 802.11), and a central hub takes care of the communications protocol (which one...FHS, DSS, how about FSK or FDM). More B/W means a higher carrier, which equates to less effective range.
Theoretical maximum bandwidth is proportionol to center frequency. Classic
channel theory. Range is primarily determined by radiated power. Smart
radios can exchange bandwidth for power if required, by changing the amount
of redundant information (error correction codes) transmitted.
Sure range is affected by frequency, but with enough power that is easily overcome. Just look at TV satelites broadcasting 200 channels of video at the same time.
Agreed, but as you elude to below the maximum in the ISM band is a pultry 100mW. This will be a factor.
Go talk to the inovators using spread spectrum, you will learn that not only is their particular application limited by range, but also bandwidth, and more importantly a protocol that is limited to real-time commands of a rate which is in the stone age compared to what we are used to right now.
Again. Power is their real limit (FCC), which in turn limits range and/or bandwidth, as you mentioned.
There seems to be a general misnomer that Dave Jones:
http://www.auav.net/spread_spectrum_radio.htm
..has perfected a workable SS system as we modelers would understand it, unfortunately this is not true.
Dave's system (pretty neat) sends commands for data receipt like lat/long, waypoint changes, etc as it relates to changing values within an autonomous system which is utilizing GPS to course-navigate. He can request specific preset values, but does not actually move a transmitter stick to affect a positional change as we need it.
A regular TX is used to get the aircraft airborne, then command/control switches over to onboard pre-set conditions to navigate a pre-described course. The closest the SS system comes to real-time control is a command to gain or loose GPS (non-corrected) meters.
The fact that he can be 10 miles from the circling aircraft is because it was pre-launched by a normal TX, and he can uplink "after" this. Noteworthy, at an elevated signal strength "more" than ISM band regulations.
I'll take a wild-ass guess the JR offering at present is 3 channels, ground use only, and has not succeeded reliably in a sorta busy (let alone 79 channel saturation), at visual distance on airborne aircraft...
I hope someone comes forth and proves me wrong <grin>
-- Simon Van Leeuwen RADIUS SYSTEMS PnP SYSTEMS - The E-Harness of Choice Cogito Ergo Zooom
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