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Old Jan 07, 2013, 04:05 PM
Stuart
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Quote:
Originally Posted by dave1993 View Post
i suspect the silabs rf chip does have programmable output like all the si44xx series but the class c amp does not reflect this change in level.
Yes.
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Old Jan 08, 2013, 12:26 PM
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United States, ID
Joined Sep 2011
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Quote:
And it would be inevitable that the vast majority of RC users would leave the higher power on, even when its clearly not needed, 'just in case'.
It wouldn't be hard to put a momentary switch on it that you would have to hold down. Or it could emit annoying warning beeps to remind you it was in high power mode.

Using high power all the time would defeat the purpose of having a safety margin in your range, so I don't think people would abuse it very often. The whole point is to have a little extra power available when you loose signal.

Quote:
Anyway, if your planning for the system to use 100mW to 1W in the 433Mhz band, what disruption would you expect this to cause to other devices that are legal users of that band ?
I would be using the 915 band where I'm allowed to transmit that power level. But if I were using 433, I don't really see a problem there either. Ham transmitters use that band and a FHSS system isn't going to disrupt their conversations.

Amateur video also uses the 433 band I think. FHSS systems don't cause any major disruption to video either. Most users in the 433 band are also using multi-watt transmitters, so the real issue is if there is enough clear frequencies to get a good link.

Quote:
i suspect the silabs rf chip does have programmable output like all the si44xx series but the class c amp does not reflect this change in level.
If the gain on the PA stays the same and you vary the input power you should get different output power. If that's not happening then there's problems with the module design.
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Old Jan 08, 2013, 01:21 PM
Stuart
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Quote:
Originally Posted by jakestew View Post
But if I were using 433, I don't really see a problem there either. Ham transmitters use that band and a FHSS system isn't going to disrupt their conversations.

Amateur video also uses the 433 band I think. FHSS systems don't cause any major disruption to video either. Most users in the 433 band are also using multi-watt transmitters, so the real issue is if there is enough clear frequencies to get a good link..
Glad you are not a regulator.

Would it not be an idea to implement such a device on frequencies and with powers that the intended market can legally use ?

Quote:
Originally Posted by jakestew View Post
If the gain on the PA stays the same and you vary the input power you should get different output power. If that's not happening then there's problems with the module design.
Its a class C design and operating as it should, its not a linear amplifier. It does have a very good efficiency level, which is good, but the trade off is that you have very little control over power level.
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Old Jan 08, 2013, 03:11 PM
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United States, ID
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> Glad you are not a regulator.

Me too! It would certainly put me into an early grave.

> Would it not be an idea to implement such a device on frequencies and with powers that the intended market can legally use?

There are lots of markets, and it seems like they all have their own regulations. Even in the same market different rules apply to different types of devices and different types of users. We can't control how people use the hardware, and in the end it's really up to the user to make sure they're compliant with whatever laws and regulations apply to them.

For example, someone with a ham license in the US could transmit up to 500 watts in the 433 band, and there are other licenses that allow other higher power levels.

From what I can tell we're allowed to transmit "24000/f(kHz) ÁV/m @ 30 m" on the 433 band here in the US. Whatever that means? Like I mentioned earlier, the regulations are so confusing and poorly written that I don't see how most people could even understand them enough to comply if they tried!

Cable locating equipment is allowed up to 1W in the 433 band, and I think there's some sort of a "biomedical telemetry" exception also. Maybe someone will program in a cable locating feature and they'll get to use more power. Maybe somebody else will use some sort of biomedical telemetry feature, who knows? Perhaps remote telemetry of "fine motor muscle contraction force" is a perfectly legitimate biomedical telemetry application. Who am I to make that call? I certainly don't know the regulations well enough, or have the test gear to verify, if someone is operating in compliance with the regulations.

I think the most rational solution is to do what WiFi makers do. They have international versions which you load with the proper firmware for your countries regulations, or simply have a firmware setting for region. Ultimately it's how the firmware operates the radio that will determine if it is transmitting legally.

I'm much more interested in the 915mhz band, as I think it's a good compromise between range and antenna length.

For frequencies of 902-928 MHz "Spread Spectrum Transmitters" are allowed up to 1 watt output power under 15.247.

For the 433mhz band "24000/f(kHz) ÁV/m @ 30 m" works out to 92mW if I'm doing the calculations right.

If that's correct it works out perfectly. 433mhz band users can set their radio to put out 92mW and still have 8mW worth of extra emergency power.

As far as I've seen, the FCC usually only gives warnings except in cases of fairly major violations by commercial players. I highly doubt that you'd even get an official warning if you tell them that you "used an extra 8mW of TX power for a minute or two in order to avoid endangering people." Does anyone really think that you'd actually be fined for that?
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Old Jan 08, 2013, 03:25 PM
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Some further info on the FCC rules...

Quote:
Home-Built Transmitters that are Not for Sale

Hobbyists, inventors and other parties that design and build Part 15 transmitters with no intention of ever marketing them may construct and operate up to five such transmitters for their own personal use without having to obtain FCC equipment authorization. If possible, these transmitters should be tested for compliance with the Commission's rules. If such testing is not practicable, their designers and builders are required to employ good engineering practices in order to ensure compliance with the Part 15 standards.
[Section 15.23]

Home-built transmitters, like all Part 15 transmitters, are not allowed to cause interference to licensed radio communications and must accept any interference that they receive. If a home-built Part 15 transmitter does cause interference to licensed radio communications, the Commission will require its operator to cease operation until the interference problem is corrected. Furthermore, if the Commission determines that the operator of such a transmitter has not attempted to ensure compliance with the Part 15 technical standards by employing good engineering practices then that operator may be fined up to $10,000 for each violation and $75,000 for a repeat or continuing violation.
[Section 15.5 47 U.S.C. 503]

Operating a prototype of a product that is ultimately intended for market is not considered "personal use." Thus, a party that designs and builds a transmitter with plans to mass produce and market a future version of it must obtain an experimental license from the FCC in order to operate the transmitter for any purpose other than testing for compliance with the Part 15 technical standards. Information on experimental licenses may be obtained from the contact point listed in the Additional Information section of this bulletin. FCC authorization is not required in order to test a transmitter for compliance with the Part 15 technical standards.
[Section 15.7 47 CFR Part 5]
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Old Jan 08, 2013, 04:59 PM
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so assuming you are not the author of those quotes, looks like you have a green light to blast those annoying 10mw and 100mw guys right out of the sky.
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Old Jan 09, 2013, 12:17 AM
Stuart
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UK, Cardiff
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Quote:
Originally Posted by jakestew View Post
For the 433mhz band "24000/f(kHz) ÁV/m @ 30 m" works out to 92mW if I'm doing the calculations right.

If that's correct it works out perfectly. 433mhz band users can set their radio to put out 92mW and still have 8mW worth of extra emergency power.

As far as I've seen, the FCC usually only gives warnings except in cases of fairly major violations by commercial players. I highly doubt that you'd even get an official warning if you tell them that you "used an extra 8mW of TX power for a minute or two in order to avoid endangering people." Does anyone really think that you'd actually be fined for that?
I doubt you would get a warning or be fined either for such a transgression.

For the UK, and I guess most of Europe too, the equivalent limit is 10mW.

So the 1W you propose in the first post is legal where exactly ?

And do you really expect anyone to believe that the intention for an 'emergency' power button is to add a mere 9% to the power output ?
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Old Jan 09, 2013, 12:22 AM
Stuart
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Quote:
Originally Posted by dave1993 View Post
so assuming you are not the author of those quotes, looks like you have a green light to blast those annoying 10mw and 100mw guys right out of the sky.
And run the risk of having legal users of the frequency chosen blast you out of the sky.
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Old Jan 09, 2013, 09:46 AM
Stuart
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I dont think I would want to use a RFM22B for a critical application such as Airborne RC model control.

I discovered in my many experiments with the RFM42\22 that the devices POR circuit is a bit too sensitive to power supply glitches. The POR can cause the device to clears its registers when TX is turned on, the higher the power the worse it is, but rarely seen below 25mW. With careful layout and good supply regulation, problems are fortunately minimal.

However what would be safer would be to turn off the POR detection after the device is initialised, you can (sort of) but only after TX is turned on.

For my 'mission' critical satellite the work around is to re-load all the RFM22 registers just before the TX is turned on (every time) and run a check on the frequency setting registers after TX is turned off. This is no great hardship for the satellite, all transmissions are fairly slow, but for a fast running RC application it could be a problem.
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Old Jan 09, 2013, 12:23 PM
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Columbus Ohio.
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I totally agree with Jake's observations.

Today's radios and receivers are not utilizing their full digital potential. We're stuck in the past with methods akin to holding down and releasing a Morse Code ticker switch in correctly timed patterns. Then sending these square-waves over the air to be picked up by the receiver...which takes this clunky pattern, and tries to decode it, and spit it out down the correct servo wires.

Is this digital???
Really???

Well yes...in a manner of speaking. It's 1s and 0's...On and Off.
But it's also a very primitive way of doing things. We can do much better by utilizing the full capabilities of the MCU and RF chips that reside at both ends.

Instead of transmitting square waves, we should be gathering the analog data from the sticks and rotary pots, and immediately converting each reading into a full 2-byte digital number. So a 6-channel radio would require a string of 12 bytes(6 two-byte fields) to hold the channel information. Besides the sticks and rotary pots, we also need to collect the positions of the toggle switches. An additional 2-byte field could hold the on/off position of 16 two-position switches(or 8 three-position switches). Is there a radio made today that would need more than 16 readings? If so...just add another one-byte field to give you 8 more buckets.

So now our 6-channel radio uses a 14-byte packet of data to hold all the information to be transmitted into the air. So the Radio's MCU streams the entire 14-byte packet to the Radio's RF chip Transmit FIFO at a bit rate of 4Mhz over the SPI bus. Once that happens the Radio's MCU is done with the communications task and can move on to other things until the next transmit cycle is required.

In the meantime the radio's RF chip has been waiting for its Transmit FIFO to fill based on a predetermined "fixed packet size". As soon as the FIFO is filled, but before the RF chip sends the information up into the air, the RF chip automatically adds a Preamble, Sync Word, Header, and Packet Length to the front of the data packet. It also automatically calculates and appends a CRC to end. All this is done in the RF chip's silicon...no MCU processing overhead is involved.

Now the chip transmits the data over the air at a settable baud rate. 50-60K is a common range.

Up in the air the Receiver's RF chip captures the message into its Receive FIFO, strips off all the extraneous leading fields. Does the CRC checking and sets a CRC Pass/Fail Register Bit as well as a Message Received Register Bit. Remember now all this is happening in the RF chip's silicon. There are no MCU cycles being burned.

All this time the Receiver's MCU is simply monitoring the RF chip's Message Received Register Bit, and when the MCU sees that a Message has arrived, it checks the CRC bit to see if the message was valid, and if so, it can pull the 14 byte data packet from the Receive FIFO over the SPI bus and into its memory. Then it can take the numeric data from each channel and generate the proper square wave to send out over the proper servo signal wires. This can be done using timer based interrupts to raise and lower the voltage on the signal output pins.

My apologies for the length of this explanation, but this is how an efficient digital method would operate. And yes, I've left out a lot. Obviously, there would be more data fields. A GUID is obviously a field that I've left out. This was meant to be a simple conceptual example. The main objective was to point out all the silicon based goodies provided in today's chips. This cuts down on software coding complexities and MCU processing overhead. Today I'm fairly certain most of these advanced capabilities are being ignored.

Yes unfortunately today it seems that backward compatibility (keying in Morse code) is the name of the game. And when someone has 10 airplanes and has invested in 10 dedicated receivers adhering to a specific brand's protocol nuances, then it's hard to advance the state of the art. When cassette tapes displaced 8-Tracks, there was naturally some hesitation. Here too, we need to be willing to scrap our 8-track collections.

In addition, these digital methods make the task of adding more and more channels a breeze. Just lengthen the data packet by 2-bytes per channel...clone a few lines of code to service each additional channel...and add a few more physical 3-pin servo channels to the receiver. Going digital makes this task trivial.

Also, the PPM methods and protocols used today promote lock-in and have become a marketing boom for the manufacturers. They take a 4-channel system then add an extra toggle switch or pot and call it a channel...bump up the price up by 75 bucks...and voila...5-channels. Each channel jump becomes a large jump in Radio and Receiver price. When you see how easy adding channels can be...you see what suckers we have become.

This also facilitates telemetry and autopilot. Sending digital packets down is as easy as sending them up.

I laugh when the topic of "failsafe" comes up. Today's failsafe means that the control surfaces will revert to straight and level flight, and your plane will fly away in straight and level direction. How wonderful to see you plane disappear in a straight and level manner. I also hear a lot of guys poo-pooing telemetry and autopilot.

In three years everything will have telemetry and autopilot. In fact, you won't know how you ever got along without it. In three years "failsafe" will actually be an autopilot function of last resort. It means that if you puposfully switch off your radio, or accidently loose radio contact, the MCU on our plane's receiver will switch into a "Failsafe Return Home and Land Mode". A few pre-programmed autopilot waypoints will guide your plane downwind...then the autopilot will make a turn into final approach....followed by a level touchdown somewhere within a 25x75 foot rectangle in the center of the field...that's what "failsafe" will eventually mean.
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Old Jan 09, 2013, 12:49 PM
RC beginner
New York
Joined Oct 2008
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you basically complained current systems are no dam good at all then describe a "new improved" system which works exactly the same way. w-t-f

as far as default failsafe behavior most radios in use today (spektrum) remove throttle pulse and set all others to the bind position. this aint too bad if your throttle happens to be is on their queer ch1 but if its the standard ch3 or any other channel you got problems.

most other radios simply hold all channels (aka flyaway mode) which i agree is the most stupid method imaginable. many have user settable failsafe procedures but the problem there is most hobbyists dont bother with them.

if one actually stops and thinks about it the most reasonable default failsafe is to simply remove all pulses on all channels. this cuts throttle and holds all servos. your plane typically spirals in nearby safely w/o prop spinning. afaik flysky is the only maker who have adopted this.
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Old Jan 09, 2013, 12:51 PM
Stuart
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UK, Cardiff
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Quote:
Originally Posted by RJKIRK View Post
In three years everything will have telemetry and autopilot
Well it wont of course, as I am sure you realise.

I have no intention of dumping my current radios, mainly aging RD6000s, and a couple of small and very cheap 2.4Ghz sets. They fly my planes well enough and are reliable. There is a good range of cheap and light RXs for the FM sets because the protocols are not proprietary. The range is as far as I need, I just cant see more than a couple of thousand feet anyway, and no need for that so called emergency 1W power (fixed of course) switch either.

I have tried the FRSky telemetry, its not expensive, but I dont see the particular need for it, so I dont use it.

Its the nature of those proposing new developments to completely rubbish everything that has gone before, but it needs to be appreciated that the vast majority of people are perfectly happy with their lot. Thats not to say they would not be tempted by new features, but its the new features that would attract them, not the false claim that all current RC sets are inadequate for the job.
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Old Jan 09, 2013, 12:57 PM
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Columbus Ohio.
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[QUOTE=srnet;23760175]I dont think I would want to use a RFM22B for a critical application such as Airborne RC model control.

I discovered in my many experiments with the RFM42\22 that the devices POR circuit is a bit too sensitive to power supply glitches.

Yikes srnet...
That doesn't sound too good. The RFM22B is the module I want to use. Can you give us some more details on your power setup.

The data sheet says 85mA current requirement for Transmit. Do you think there is some sort of unstated current requirement when the transmitter mode is turned on?

I plan to run my configuration off of 4-AA batteries run through a linear LDO that will bring the voltage down to 3.3v 1000mA capable. I wonder if I will experience issues? I plan to use Enloop NiMh rechargables and would recharge between flying sessions...and the batteries are 2000mAHour capacity, so there should be plenty of juice before things start to drain.
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Old Jan 09, 2013, 12:58 PM
Stuart
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Quote:
Originally Posted by dave1993 View Post
if one actually stops and thinks about it the most reasonable default failsafe is to simply remove all pulses on all channels. this cuts throttle and holds all servos. your plane typically spirals in nearby safely w/o prop spinning. afaik flysky is the only maker who have adopted this.
The coronas allow you to set the failsafe. I normally trim my plane for a power off gentle glide with a soft left turn. So hopefully the plane wont crater hard into the deck destroying itself or injuring someone in the process. If its trimmed for a turn, at least it should not dissapear over the horizon.

And if you have at least some altitude you at least have time to warn others that you have a flyaway.
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Old Jan 09, 2013, 01:09 PM
Radio? Screwdriver!
United Kingdom, England, Bristol
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Quote:
Originally Posted by RJKIRK View Post
So now our 6-channel radio uses a 14-byte packet of data to hold all the information to be transmitted into the air. So the Radio's MCU streams the entire 14-byte packet to the Radio's RF chip Transmit FIFO at a bit rate of 4Mhz over the SPI bus. Once that happens the Radio's MCU is done with the communications task and can move on to other things until the next transmit cycle is required.

In the meantime the radio's RF chip has been waiting for its Transmit FIFO to fill based on a predetermined "fixed packet size". As soon as the FIFO is filled, but before the RF chip sends the information up into the air, the RF chip automatically adds a Preamble, Sync Word, Header, and Packet Length to the front of the data packet. It also automatically calculates and appends a CRC to end. All this is done in the RF chip's silicon...no MCU processing overhead is involved.

Now the chip transmits the data over the air at a settable baud rate. 50-60K is a common range.

Up in the air the Receiver's RF chip captures the message into its Receive FIFO, strips off all the extraneous leading fields. Does the CRC checking and sets a CRC Pass/Fail Register Bit as well as a Message Received Register Bit. Remember now all this is happening in the RF chip's silicon. There are no MCU cycles being burned.

All this time the Receiver's MCU is simply monitoring the RF chip's Message Received Register Bit, and when the MCU sees that a Message has arrived, it checks the CRC bit to see if the message was valid, and if so, it can pull the 14 byte data packet from the Receive FIFO over the SPI bus and into its memory. Then it can take the numeric data from each channel and generate the proper square wave to send out over the proper servo signal wires. This can be done using timer based interrupts to raise and lower the voltage on the signal output pins.

My apologies for the length of this explanation, but this is how an efficient digital method would operate. And yes, I've left out a lot. Obviously, there would be more data fields. A GUID is obviously a field that I've left out. This was meant to be a simple conceptual example. The main objective was to point out all the silicon based goodies provided in today's chips. This cuts down on software coding complexities and MCU processing overhead. Today I'm fairly certain most of these advanced capabilities are being ignored.
Most new systems don't use modules. One of the last that does, the Aurora 9, uses a async UART to send and receive servo and telemetry data. I can tell you that the systems I have looked at (hitec, Futaba and frsky), all do what you've described above... No doubt every other system does similar.

The Frsky modules only use PPM as their input as the module bays output that. Iirc their new radio will internally use a UART to send data between the tx section and the main radio.

Si.
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