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Devo7e work

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20 Jan 2013 19:21 - 20 Jan 2013 19:32 #5281 by Xermalk
Xermalk replied the topic: Devo7e work

quique65 wrote: Hello,
I've just installed Deviation on my 7E (last build posted by PB) and I've tested it with the Walkera SuperFP and Ladybird models. With both, after the binding, the TX and RX appear to constantly connect and disconnect. The led on the RX is blinking and impedes the flight. The same config on Devo10, with a build before the 7E code, works fine.
Please, can you ckeck it? Thank you.

Regards,
Enrique.


Check what Tx power your using, for me to reproduce that blinking i have to lower my tx power to below 10mw that is the standard devo 7E transmit power.

Edit, actually i just noticed it at 10 mw.

The 10 mW in Deviation is much lower then walkeras 10mW, as you go out of range within ~2m.
Last Edit: 20 Jan 2013 19:32 by Xermalk.

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20 Jan 2013 20:24 #5283 by PhracturedBlue
PhracturedBlue replied the topic: Devo7e work
What is the power output set to?
I'm seeing the same thing on mine. at '10mW' it can barely work over 5 ft. It is better at '100mW' but it does appear something is wrong with the power output. I'm not sure how it could be different than the other radios but I'll dig in some more

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20 Jan 2013 20:41 #5284 by PhracturedBlue
PhracturedBlue replied the topic: Devo7e work
I wonder if the code isn't turning on the power amp. The range we're seeing is similar to what I'd expect if there was no amp at all.

I'll investigate more

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20 Jan 2013 21:41 #5286 by quique65
quique65 replied the topic: Devo7e work
Ok, thanks. I wait for your results. I'll try to test tomorrow with more power on mine. It was on 10mW, same as Devo10.

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20 Jan 2013 23:42 #5288 by PhracturedBlue
PhracturedBlue replied the topic: Devo7e work
Well, bad news I think. I removed the shield from the CYRF board, and took a look. There appears to be a diode between the transceiver chip and the power-amp on pin SWPA. I don't believe this diode is there on the other Devo modules. This results in the PASW having a voltage of 2.5V, whereas the threshold is documented as being 2.8V. The documentation is very slim, but it appears this may be a way of reducing the gain of the RDAT212. Additionally, I think the Devo7e runs the CYRF at max power all the time. This would correlate with having reduced gain on the power-amp.

So it looks like the power needs to be set at 100mW or 150mW in Deviation in order to match the Devo7e's default range (which is probably actually only 10mW). I'm not set up to measure the actual output gain of the system, so the only way to verify for sure is to do a range test. It is still possible I'm missing something, but I've confirmed that the power-amp and transceiver do seem to be configured correctly.

You could probably short-out the diode to get full gain back, but it requires pulling the shield off which requires a really beefy soldering iron, and then some delicate soldering to short the pins

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21 Jan 2013 07:40 - 21 Jan 2013 07:42 #5296 by Xermalk
Xermalk replied the topic: Devo7e work

PhracturedBlue wrote: Well, bad news I think. I removed the shield from the CYRF board, and took a look. There appears to be a diode between the transceiver chip and the power-amp on pin SWPA. I don't believe this diode is there on the other Devo modules. This results in the PASW having a voltage of 2.5V, whereas the threshold is documented as being 2.8V. The documentation is very slim, but it appears this may be a way of reducing the gain of the RDAT212. Additionally, I think the Devo7e runs the CYRF at max power all the time. This would correlate with having reduced gain on the power-amp.

So it looks like the power needs to be set at 100mW or 150mW in Deviation in order to match the Devo7e's default range (which is probably actually only 10mW). I'm not set up to measure the actual output gain of the system, so the only way to verify for sure is to do a range test. It is still possible I'm missing something, but I've confirmed that the power-amp and transceiver do seem to be configured correctly.

You could probably short-out the diode to get full gain back, but it requires pulling the shield off which requires a really beefy soldering iron, and then some delicate soldering to short the pins


Guessing a 50w 350c iron is out of the question. To bad for walkera now I'm forced to change tx when I go up to a 450/500 size. Will likly end up with a 9X.

Now I'm going to have to look into a antenna mod now as the range of the 7E just isn't enough to be comfortable with for a Master CP.
Iv almost lost my night kitted master 3 times now due to range limitation.

Wonder if the restricting diode is a result of deviation or its just the module manufacturer beeing a douche. Normally you would not hardware limit something if it means additional components.
Last Edit: 21 Jan 2013 07:42 by Xermalk.

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21 Jan 2013 07:46 #5297 by SadSack
SadSack replied the topic: Devo7e work
Would it be doable to swap module out for one used in 8s ?
Maybe easier to change than mod module...

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21 Jan 2013 07:51 #5298 by Xermalk
Xermalk replied the topic: Devo7e work

SadSack wrote: Would it be doable to swap module out for one used in 8s ?
Maybe easier to change than mod module...


If one is going that far one might as well just sell a 7e and get a devo 10. And get better stick, more buttons/switches and more power.

Though the size of the 7e makes it perfect for the sub 200 size helis.

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21 Jan 2013 13:23 #5304 by PhracturedBlue
PhracturedBlue replied the topic: Devo7e work
FYI, I used a cheap 'gun' style soldering iron (100/150W to remove the shield. my 40W irons wouldn't cut it.
I'll ask over at RCGroups, maybe someone there has experience with the RDAT212.

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21 Jan 2013 13:59 #5306 by PhracturedBlue
PhracturedBlue replied the topic: Devo7e work

SadSack wrote: Would it be doable to swap module out for one used in 8s ?
Maybe easier to change than mod module...

Yes it probably would be easier.
Butthe antenna is soldered onto the devo7e as opposed to using a standard plug. So you need to replace that too, and the 8S module doesn't come with the wire.

I'm still a bit confused. assuming they reduced the gain to ~10dBm, we still should get better than 5ft with the range set at '10mW' in deviation. It is still possible I'm missing something here.

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21 Jan 2013 14:09 - 21 Jan 2013 14:10 #5307 by Xermalk
Xermalk replied the topic: Devo7e work
Darn guess a 48w 450c soldering iron wont cut it. Ill just lie low then.
Btw while your poking around the insides, can you check what pins need soldering for the flysky module?

Ps could the 5 feet range be explained by a subpar antenna?
Last Edit: 21 Jan 2013 14:10 by Xermalk.

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21 Jan 2013 14:16 #5308 by vlad_vy
vlad_vy replied the topic: Devo7e work
I see at datasheet RDAT212, Test Circuit for RDAT212 - SPWA connected R1 0Ω (Tuning PA gain). Possible it's not a diode between the transceiver chip and the power-amp on pin SWPA, but a resistor.

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21 Jan 2013 14:27 #5309 by PhracturedBlue
PhracturedBlue replied the topic: Devo7e work
I actually checked it and it does appear to be a diode. I can only measure current though it in one direction. It drops about 0.7V when actually running (as measured by my DSO) which is what a diode would do.
That said, the only reason I think it is used to affect gain is:
(a) those words 'Tuning PA Gain' attached as a description to one resistor on a test circuit
(b) the spec for the SWPA says '>= 2.8V' and it is only seeing 2.54V
(c) SPI traces indicate that they do use max power settings on the CYRF chip all the time and it is believed that this is ~10mW

Nothing else in the document indicates you can control gain this way though, so I'm just guessing.

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21 Jan 2013 14:32 - 21 Jan 2013 14:34 #5310 by FDR
FDR replied the topic: Devo7e work
My guess (with my faded electric knowlage) is that they bypass the power amplifier, and use the T212 only for amplifiying the telemetry data.
Last Edit: 21 Jan 2013 14:34 by FDR.

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21 Jan 2013 14:37 - 21 Jan 2013 14:41 #5312 by PhracturedBlue
PhracturedBlue replied the topic: Devo7e work
I had already thought of that.
PA_BYPASS is enabled with SW_PA low and SW_TX high. but SW_PA and SW_TX are tied to the same pin. It may be that 2.5V isn't enough to trigger SW_PA but is enough fro SW_TX (they have different thresholds) which would give the behavior you describe without needing to assume SWTX somehow affects gain.
also, the SW_LNA an SW_RX are also tied together and do receive a full 3.3V

I didn't guess at this originally because if you are going to do that, why not just tie SW_PA low and directly drive SW_TX?
Last Edit: 21 Jan 2013 14:41 by PhracturedBlue.

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21 Jan 2013 14:56 #5313 by RandMental
RandMental replied the topic: Devo7e work
Hi Guys

See below for the RF power perfomance of each Devo TX, this is obviously with the Devo software, limited to the requirements of the USA for this band/usage. (I don't know what that is). I post the links here, not the docs due to potential copyright violations outside the USA)

Interestingly the Dev08s has max 34mw output from the T212, and uses the antenna to "boost" the power to 80mW.

This might give you an idea of the designers' goal in limiting the 7e's power.

FCC RF Test reports for Devo TX range

Devo 7e
apps.fcc.gov/eas/GetApplicationAttachment.html?id=1759447

Devo8s
apps.fcc.gov/eas/GetApplicationAttachment.html?id=1630785

Devo10
apps.fcc.gov/eas/GetApplicationAttachment.html?id=1672921

Devo12
apps.fcc.gov/eas/GetApplicationAttachment.html?id=1502543

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21 Jan 2013 14:57 #5314 by FDR
FDR replied the topic: Devo7e work
Probably the PCB was designed for the 100mW, so both SWPA and SWTX should be operated together, but they decided to limit the tx to 10mw.
They didn't want to change the PCB layout, so replaced the R1 with a diode to drop the voltage and so bypass the PA.
It's clearly a bad design, since there should be a pull up (or down) resistor after the diode...

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21 Jan 2013 14:59 - 21 Jan 2013 15:02 #5316 by FDR
FDR replied the topic: Devo7e work
...may be it is because of deviation, which unlocks the tx power limitation of the 10mW versions... ;)
This way it is a HW 10mW version...
Last Edit: 21 Jan 2013 15:02 by FDR.

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21 Jan 2013 15:02 - 21 Jan 2013 15:05 #5317 by RandMental
RandMental replied the topic: Devo7e work
From the FCC Test results:

Devo 7e: MAX E Power 7.55dbm
Devo 10: MAX E Power 19.3dBm

Seems they purposely limited the power of the 7e.

Edit: Look at the Section 3.2 power measurement over frequency, with columns including the antenna gain. Clearly the Devo7e is aimed at the sub 10mW entry level market, thus the diode.
Last Edit: 21 Jan 2013 15:05 by RandMental.

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21 Jan 2013 15:04 #5318 by FDR
FDR replied the topic: Devo7e work
Yep, according to the T212's datasheet, the power loss in PA_BYPASS mode is 3.6dB...

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