Replies to This Discussion

Permalink Reply by Hein du Plessis on February 6, 2012 at 3:30am

1 Watt was just an example, but surely 300mW is still in line with most regulations.

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Permalink Reply by Michael Pursifull on February 6, 2012 at 3:40am

heh, famous last words ... I'm sure 2Amps is safe ... it's only 2 feet deep ... the door is not that hot, I'll just open it ... I'm sure the laws allow me to do this ...

I don't know the EU regs for this, so I cannot offer an opinion. But it is my impression that many people unwittingly break local regulations and laws all the time, and are surprised to learn it ... because "everyone else is doing it"

Permalink Reply by Hein du Plessis on February 6, 2012 at 3:30am

Sorry for that.... I was confident that I havent seen any 868 posts.

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Permalink Reply by Michael Pursifull on February 6, 2012 at 2:04am

Underpowered? That is relative, I suppose. Depends on what you need, what frequency you are transmitting on, what form of modulation, sensitivity of the receiver, etc.

See http://en.wikipedia.org/wiki/DBm

50mW is quite good for local communications. If the system is well tuned, you might get several miles very reliably, depending on frequency, modulation, sensitivity of the receiver, antenna performance, etc. 

However, under ideal conditions, you can go quite a lot farther with a lot less. See http://www.e-discounter.net/qrparci/messages/6063.html as an example of what ham radio folks call QRP or low power. He communicated 1536 miles using just 0.72 microwatts. Yes, that is a decimal (0 point 72) and micro (not milli) watts....  Of course, he was using CW, not a spread spectrum high speed serial burst for telemetry.... 

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ModeratorPermalink Reply by Gary Mortimer on February 6, 2012 at 2:31am

You have it Mike, with decent low loss coax and connectors and well tuned antennas lots can happen. 

Just stuffing something into a fuse and hoping just does not cut it.

Hein the FPV community are in for a big shock when the WRC finally rules. Again another one of the I did'nt know it was happening for most. Which will then turn into its not fair.

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Permalink Reply by Michael Pursifull on February 6, 2012 at 2:40am

We're all in for shocks it in some way or another.

I've been meaning to chat with you and Patrick about some very minor wordsmithing that might allow RCAPA to attract and retain more of this community, especially the highly ethical (often more politically active/fiscially active than the less self-restrictive enthusiasts) but I've never gotten around to it.

Banding togeather to ensure the interests of our communities, non-business, small business, anything other than military industrial complex and established well resourced businesses...is long overdue, and I'm not doing my part because of a single wording issue which Patrick has publicly clarified, but has not integrated into the RCAPA guidelines...

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Permalink Reply by Hein du Plessis on February 6, 2012 at 3:10am

I say 50mW is underpowered because there is very little cost and weight penalty to ramp it up to 300mW which should give us 10km+ ranges without using directional antennas.

Very Interesting article re. the QRP - but translating that to something usable for the APM is not going to happen, we're still having trouble implementing a well-documented technology such as GSM Data.

There are other ways of increasing range, but none easier and cheaper than simply boosting power a little higher, while amplifying results of alternate methods such as focussed antennas, alterative modulation, etc.

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Permalink Reply by Michael Pursifull on February 6, 2012 at 3:26am

boosting power might be easiest, but it is not usually best. It increases the power requirements significantly, increases heat waste and heat issues, adds weight (larger power budget required) increases radio interference, larger risk of inductance and other signal problems in other components, etc. Oh, and it might be illegal, too.

If you can do it, increasing the sensitivity of the ground station equipment is preferred. 

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Permalink Reply by Hein du Plessis on February 6, 2012 at 3:57am

Seing that most systems run with 2200mAh +, 60mAh usage increase per hours will fall well within budget ;) Very little heat increase, especially since most XBees are outboard. At around 500mW one should start adding ferrite cores to prevent induction.

Legality, I hear you, depends on the local law, which I try to adhere to.

Permalink Reply by Michael Pursifull on February 6, 2012 at 2:30am

Be sure to read over this summary. You should look into getting your HAM license. ;)

http://fpv-community.com/forum/showthread.php?tid=952

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Permalink Reply by Hein du Plessis on February 6, 2012 at 3:34am

Thanks Mike, Gary

I'm not based in Europe or US, so the legalities are different and trying to match one solution to all rulings will be almost impossible. Either way, 2.4ghz is "legal" almost everywhere, I as hoping for a 300mW 2.4ghz XBee which will give us enough power to stay connected even in noisy areas.

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Permalink Reply by Michael Pursifull on February 6, 2012 at 3:43am

oh, wow. Sorry about that. I knew you were in SA, I just got confused while talking to another guy in Europe. I guess it's past my bed time, the brain isn't working right. :) 

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