Frsky compatibility

I'm thinking.I have an idea not sure is good .It maybe that the pa/lna on cc2500 shift on the output,.. the original frequency set on the cc2500 registers.
You now that "Kreature" guy has uploaded on rcgroups forum one frequecy scanner code for cc2500.

Im thinking to use this scanner(or other scanner) and check the frequencies from pa/lna cc2500 chip.In base of that play with the cc2500 frequency register to match the required output.
This an idea maybe working maybe not(we know already with the bare chip is working) ..I want to try.

For the moment I don't have one pa version...to test.
I'll buy one and test myself.Hope it will not take one year.
I don't know if you play with but I think the key is modifying FREQ1,FREQ0,FREQ2 registers.

Like blossoms, hopes live and die...

Answer from the eBay vendor :

hi,the stock item is V8FR-II HV now.

Anyway, as the non-PA modules work, I can still use the skyartec module to bind to the cheap micro receiver VD5M. That's enough for me and indoor planes.

Thx for the reminder, you saved me some headaches. I'll forget Frsky, until and if, it's solved.

I assume SKYARTEC works with non pa modules? If The pa shifts the freq why isnt SKYARTEC affected? whats diffrent? Just wondering.

Ok that sucks. Using trail and error with diffrent cc2500 modes (maybe implenting a custom protocoll) might give us somthing to go on but its alot of work and a sprectum analyzer would be a must. Btw is there a reason skyartec is the only protocoll that dosent implent changing the power output or was it just low priority.

My non pa module is not working with your frequencies....
CC2500_WriteReg(CC2500_0E_FREQ1, 0x76);
CC2500_WriteReg(CC2500_0F_FREQ0, 0x27);
I cannot bind.

but it works with,
cc2500_writeReg(CC2500_0E_FREQ1, 0x75);values
cc2500_writeReg(CC2500_0F_FREQ0, 0x6A);//

So i wonder if non pa modules have different frequencies.
I test also with:
cc2500_writeReg(CC2500_0E_FREQ1, 0x75);values
cc2500_writeReg(CC2500_0F_FREQ0, 0x27);
an working..so the difference

cc2500_writeReg(CC2500_0E_FREQ1, 0x75);//working
versus
cc2500_writeReg(CC2500_0E_FREQ1, 0x76);//not working

Could these differences be due to crystals or caps?

A friend gave me a V8FR so I could test if the module works with deviation and later install it on his devo.

But before destroying a perfectly working receiver, I'll wait for the dust to settle on this, because I have two skyartec modules and if it would work with them, it would be preferable.

My non pa module is different ,I took it from aliexpress ..it has cylindrical x-tal.
Normally should bind on 2404 base freq .....but bind lower with min 15 khz(76/00)...and It dropped also a lot of frames...I can control a servo but delayed.
These are bad news ..i don't think it can be standardized for all modules.Maybe similar module may behave differently.
I think frsky tune hardware(component selection) both tx and rx modules on the same freq....

The freq values to be change are FREQ1 and FREQ0...try sweeping both registers.
FREQ 2/1/0 make 24 bits word...normally on frsky 0x5c7627 equal 2404GHZ.
Fcarrier=Fosc*FREQ[23:0]/65536

Yes that's the one I have.It is not working on base frequency.I left the FREQ registers on original settings 0x5c7627...and i modified the FREQOFF freq offest , FSCTRL0 register(0XD7 working ,instead of 0x00).However ,I have dropped frames..From time to time the RED led is on.Did you test your code with VD5M rx on 2 way mode?
I think the frequency is shifting in time...with this one.I ordered new one from ebay I'm curious to see if working the same.

I fixed the problem with dropped frames ,made some code mistakes..now no more dropped frames.working ok.
But the main problem remains,,I made it work with this module...when I shift the base frequecy....hacking FSCTRL0 register....

I believe with the pa module some aproach must be done change values of FREQOFF[7:0]..in FSCTRL0 ....

No, your code is good as it is .....I tried to write my own(I'm using BB instead of HW spi to free some pins) in arduino,,..tried to avoid copy your interrupt timer routine(not happy to put 2 interrupts routines on same timer...)...and in the process I made some mistakes.Anyway the frequency shift is there..and is very small around 15Khz...
I'm using...
cc2500_writeReg(CC2500_0C_FSCTRL0, 0xd7); otherwise not working.

About the offset...trial and error....not sure but I think over 128 decrease the base freq and till 128 increase the freq...just guessing based on my experience....according with data sheet is ±202 kHz to ±210 kHz,
I think the base freq must be exactly in tune with rx base freq otherwise not binding...I'll do some more tests.