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Devo7e work
- PhracturedBlue
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20 Jan 2013 23:42 #5288
by PhracturedBlue
Replied by PhracturedBlue on 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
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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- Xermalk
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21 Jan 2013 07:40 - 21 Jan 2013 07:42 #5296
by Xermalk
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.
Replied by Xermalk on 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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- SadSack
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21 Jan 2013 07:46 #5297
by SadSack
Replied by SadSack on topic Devo7e work
Would it be doable to swap module out for one used in 8s ?
Maybe easier to change than mod module...
Maybe easier to change than mod module...
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- Xermalk
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21 Jan 2013 07:51 #5298
by Xermalk
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.
Replied by Xermalk on 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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- PhracturedBlue
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21 Jan 2013 13:23 #5304
by PhracturedBlue
Replied by PhracturedBlue on 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.
I'll ask over at RCGroups, maybe someone there has experience with the RDAT212.
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- PhracturedBlue
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21 Jan 2013 13:59 #5306
by PhracturedBlue
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.
Replied by PhracturedBlue on topic Devo7e work
Yes it probably would be easier.SadSack wrote: Would it be doable to swap module out for one used in 8s ?
Maybe easier to change than mod module...
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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- Xermalk
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21 Jan 2013 14:09 - 21 Jan 2013 14:10 #5307
by Xermalk
Replied by Xermalk on 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?
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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- vlad_vy
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21 Jan 2013 14:16 #5308
by vlad_vy
Replied by vlad_vy on 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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- PhracturedBlue
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21 Jan 2013 14:27 #5309
by PhracturedBlue
Replied by PhracturedBlue on 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.
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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- FDR
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21 Jan 2013 14:32 - 21 Jan 2013 14:34 #5310
by FDR
Replied by FDR on 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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- PhracturedBlue
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21 Jan 2013 14:37 - 21 Jan 2013 14:41 #5312
by PhracturedBlue
Replied by PhracturedBlue on 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?
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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- RandMental
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21 Jan 2013 14:56 #5313
by RandMental
Replied by RandMental on 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
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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- FDR
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21 Jan 2013 14:57 #5314
by FDR
Replied by FDR on 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...
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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- FDR
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21 Jan 2013 14:59 - 21 Jan 2013 15:02 #5316
by FDR
Replied by FDR on 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...
This way it is a HW 10mW version...
Last edit: 21 Jan 2013 15:02 by FDR.
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- RandMental
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21 Jan 2013 15:02 - 21 Jan 2013 15:05 #5317
by RandMental
Replied by RandMental on 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.
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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- FDR
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21 Jan 2013 15:04 #5318
by FDR
Replied by FDR on topic Devo7e work
Yep, according to the T212's datasheet, the power loss in PA_BYPASS mode is 3.6dB...
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- vlad_vy
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21 Jan 2013 15:05 - 21 Jan 2013 15:06 #5319
by vlad_vy
Replied by vlad_vy on topic Devo7e work
At any case it's not very simple task to modify Devo 7E module. Possible will be easier replace module with Devo 8s module and use any Wi-Fi antenna with U.FL connector or Hitec Optima replacement antenna (inside original Devo 7E plactic antenna).
Last edit: 21 Jan 2013 15:06 by vlad_vy.
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- RandMental
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21 Jan 2013 15:55 #5323
by RandMental
Replied by RandMental on topic Devo7e work
Noticed how the price of a Devo7e has dropped since we discovered this HW limitation 
Walkera DEVO 7E 7-Ch 2.4Ghz Telemetry Function Radio System
User Id: skyes_rocFeedback: 257 | 99.5%
Returns: Not accepted
Buy It Now $39.00 +$25.00 shipping
Walkera DEVO 7E 7-Ch 2.4Ghz Telemetry Function Radio System
User Id: skyes_rocFeedback: 257 | 99.5%
Returns: Not accepted
Buy It Now $39.00 +$25.00 shipping
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- PhracturedBlue
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21 Jan 2013 16:13 #5324
by PhracturedBlue
Replied by PhracturedBlue on topic Devo7e work
Well, the layout of the Devo7e module is completely different from that of the Devo8/10/12 module. But they could easily replace the diode with a shunt for >10mW Txs I guess for future designs.
The CYRF6936 has a max output of 4dbM which Seems to correspond to the pre-antenna info listed on the FCC page for the 7e
The Devo10 docs show that value to be about 12dBm higher which sounds right given that they don't run the CYRF chip at full power in the Walkera firmware.
The CYRF6936 has a max output of 4dbM which Seems to correspond to the pre-antenna info listed on the FCC page for the 7e
The Devo10 docs show that value to be about 12dBm higher which sounds right given that they don't run the CYRF chip at full power in the Walkera firmware.
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- PhracturedBlue
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21 Jan 2013 16:20 #5325
by PhracturedBlue
Replied by PhracturedBlue on topic Devo7e work
FYI, here is an image of the module with the shield removed. the diode in question is just below the xtal
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