Schematics for hobby grade A7105 or CC2500 RXs?

Are there any on-line sources for schematics of commercially sold hobby grade RXs based upon the A7105 and/or CC2500 transceiver chipsets? I'm curious about what causes such large receive range differences between most micro RXs and the full size RXs using a given chipset since the front end sensitivity for all of them should be the same if they're using the same chipset.

Some of RXs are equipped by LNA - Low Noise Amplifier - which enhances range a lot. It is usually PA/LNA, so it affects telemetry range as well. These PA/LNA chips have some 20dB gain, which means they can expand range ten times or so.

Thanks. Any LNA IC numbers for me to get datasheets for?

RFaxis RFX2401C

Example of schematics: www.rfmw.com/data/rfaxis_nordic_nrf24le1...rfx2401_app_note.pdf

TI's CC2590

Search for "2.4ghz rf front end" is amazingly productive.

If your curiosity has been satisfied then very good victhz however if you're interested in more research check any of the open source receiver projects in the DIY electronics sub-forum @ RCgroups

One thread in particular has some very good info. After you read this one search for and read any threads stated by FishPepper, that dude is a freaking RF / PCB genius!

www.rcgroups.com/forums/showthread.php?2...rSky-D4R-ii-and-VD5M

Thanks for that link to RC Groups. I can never have too much info. What I'm trying to figure out is why there seem to be many more good performing long range (maybe not "full" range) micro RXs for Spektrum and FrSky than for Turnigy and FlySky TXs.

Winston2016 wrote: What I'm trying to figure out is why there seem to be many more good performing long range (maybe not "full" range) micro RXs for Spektrum and FrSky than for Turnigy and FlySky TXs.

Well then you're looking WAY to far into it...

Money.

There's no market for "higher end" low end stuff (FlySky/Turnigy). High performance micro receivers exist for Spektrum and FrSky cause people pay >$25 (FrSky) and upwards of $50+(spektrum) for them. When the top FlySky receiver costs $15 there's no market for custom hardware.

And it is so strange, because market is full with, say nRF24 boards with PA/LNA and cost difference with ones without it is not that high.

"There's no market for "higher end" low end stuff (FlySky/Turnigy)."

I can agree that the two are different markets, but I don't see why there wouldn't be a demand in the cheaper market and a capability to make reasonably priced long range mini/micro RXs in that cheaper market. Many of the FrSky and Spektrum mini/micro RXs are not very expensive from places like Banggood.

victzh wrote: And it is so strange, because market is full with, say nRF24 boards with PA/LNA and cost difference with ones without it is not that high.

Thanks. That's exactly my point.

victzh wrote: And it is so strange, because market is full with, say nRF24 boards with PA/LNA and cost difference with ones without it is not that high.

The difference is that those boards are originally made as OSHW arduino toys with no supporting firmware / code supplied with them, they're made by folks like adafruit and spark fun and sold as open source break out modules for hacking.

I stand behind my statement there's no money in developing a high quality low end [brand] RC receiver and supporting its FW development...

Look at the FrSky hardware, the options available large scale commercially all use one dudes stolen (as in non-licensed but originally OS) FW cause commercial development of such a FW just us not practical.

Winston2016 wrote: . Many of the FrSky and Spektrum mini/micro RXs are not very expensive from places like Banggood.

Economics of scale. Go to Digikey and pick a random LNA, price it for 1000pcs, now price it for 10,000.

Also retailers like Banggood don't count as they incur zero development costs they have to pass on...

Cereal_Killer wrote: Economics of scale. Go to Digikey and pick a random LNA, price it for 1000pcs, now price it for 10,000.

Are there fewer low cost Turnigy/Flysky TX owners than there are much higher cost Spektrum/FrSky TX owners? I doubt it and if I'm correct, there's no economy of scale excuses for long range mini/micro receivers being available for Spektrum/FrSky TX owners but not for Turnigy/Flysky TX. I suspect it's more to do with Turnigy/Flysky not believing there's a market for those more expensive receivers for their protocol when there actually is one. When I see a guy doing this:

$50 FlySky FS-i6 2.3km range test - no mods!



I really wonder why Flysky can't shrink that largish stock RX down with a layer or two more buried in their PCB.

I'm sorry bro but developing a product is so much more than PCB design costs...

I'm not now (thank God. I love what I do now, couldn't say that at my old job) but I was in the electronics business a bit (back when "oh computers are where it's at") and there's just so much more to large scale product development than we've brought up here.

Actual HW design / development / sourcing and manufacturing is just a small % of a products final sales cost.


I'm just not gonna change your mind no matter how much I try to explain so I invite you, query some manufacturers and ask them direct. Banggood (eachine / flysky) may be a nightmare to work with for small scale developers but they do have the pull to get a product made... They have a forum of their own you know.

Looking at the schematic might not help reveal the difference in performance. Even using the same transceiver chip, the sensitivity could differ if driven by different protocols (e.g. data rate). Smaller board might have worse power decoupling than the bigger counterpart. So one needs to identify the contributing factors one by one in the comparsion.
I recently played with several CC2500 modules with Arduino. When I set the transmit power to 0dBm (typical value stated on datasheet), the actual output was 6dB lower !! I am going to check whether it is related to the chip itself or due to external matching circuit.

Cereal_Killer wrote: I'm just not gonna change your mind no matter how much I try to explain so I invite you, query some manufacturers and ask them direct. Banggood (eachine / flysky) may be a nightmare to work with for small scale developers but they do have the pull to get a product made... They have a forum of their own you know.

Oh, I'm not interested in developing anything, I'm just curious. Some brochures from higher end manufacturers imply the use of an LNA in front of the RX chip in their micro RXs and that would explain longer range. As for getting anything deeply technical from a Chinese manufacturer/retailer forum, call me extremely skeptical. That's why I came here. I figure if anyone should know it might be people who can reverse engineer TX protocols and then write the code to implement them on the same transceiver chips used in TX mode within transmitters that are used in RX mode within receivers.

ajtank wrote: Looking at the schematic might not help reveal the difference in performance.

I would just be looking for anything obvious like an LNA in front of the RX chip.

There was no LNA, just a ceramic balun before the antenna. I replaced it with discrete L, C by calculation and still no joy. I tried to replace the CC2500 chip but it was affixed to a big ground and my heat gun was just not powerful enough to desolder the chip. I ended up replacing the complete module and everything was within specification again. It seemed to me that CC2500 could vary from chip to chip although I found it hard to believe. The rx was 6dB lower and the tx was 10dB worse. Tried 2 modules with consistently bad results and only the 3rd one was good.

ajtank wrote: There was no LNA, just a ceramic balun before the antenna. I replaced it with discrete L, C by calculation and still no joy. I tried to replace the CC2500 chip but it was affixed to a big ground and my heat gun was just not powerful enough to desolder the chip. I ended up replacing the complete module and everything was within specification again. It seemed to me that CC2500 could vary from chip to chip although I found it hard to believe. The rx was 6dB lower and the tx was 10dB worse. Tried 2 modules with consistently bad results and only the 3rd one was good.

I wonder if the TI CC2500 chips were low quality Chinese ripoffs.

I don't know. However these modules are mounted inside the RF Explorer. The customer service told me this was expected behaviour due to large tolerance.

So if there is anyone out there thinking about getting a RF Explorer: ignore the Wifi Combo, only get either the 6G combo or 3G combo.