Teensy4 SDR no FM

M

Meerani

Member
Hello can someone help me

i built a tennsy4 sdr but i can't receive fm.
my setup is
PCB of EA5GKV with DD4WH software Teensy4, PCM1808, PCM5102A ,Frontend is from QRP Labs
Reception up to 30MHz is OK.
With FM, the reception frequency is about 24 MHz too high and reception is very poor
Hardware DD4WH_T4 is activated
do I still have to activate filters for FM_WFM.
Sorry for my bad English, I'm 66 years old and I never learned English in my school
 
Maybe try to set sample rate to 192k or even higher. Also be sure that the CPU freq is 600MHz.
Ensure that your hardware has NO RF lowpass filter.
Most important, for QRP labs hardware, you have to change the sampling caps AND the filter components in the Quadrature sampling detector in order to allow for at least 200khz Audio bandwidth.
 
Thank you for your prompt reply,

i have the cpu set aof 600mhz.
I have already read about the conversion of the QRP-Labs receiver on the Internet.
The problem is that our house transmitter (RADIO_PSR) sends on 100MHz but I receive it on 125.520 MHZ.
Furthermore, I forgot to write that there is no spectrum display in WMW operation and only 5Khz steps are possible.
 

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Probably you want to bypass the audio transformers, because they have much too low audio bandwidth.
Did you exchange the sampling caps and OPAmp filter caps?
 
Hello,
I would like to apologize for the late reply, I was on vacation and my daughter bought a weekend property where there was a lot of work.
Now to my problem, the transmission with the QRP Lab Frontend is known to me.
My main problem is that the frequency at WFM 10MHz is received at 124Mhz.
It would have to be the 3rd harmonic, where can I find the filter calculation for this frequency. Thanks
 
Hi!
Did you exchange the sampling caps and OPAmp filter caps, so that the bandwidth of the hardware quadrature sampling detector is around 200kHz ?
Did you bypass the output audio transformer ?
Did you set the sample rate to >= 192ksps ?
Without those changes you will not be able to receive WFM with the QRPLabs receiver hardware.
 
hello I'm probably too old or got completely stuck.
I need an explanation again, that's why I added the pictures.
The recordings are without a front end, only the frequency output of 7 MHz, 28Mhz is ok and works well with my antenna.
The output is the frequency x4 plus the sample width.
At 100MHz, the 3rd harmonic would be used, which is 33.33MHz plus the sample width, or I have a big mistake in reasoning.
Thank you Meerani

1665039198280.jpg
 
hello I'm probably too old or got completely stuck.
I need an explanation again, that's why I added the pictures.
The recordings are without a front end, only the frequency output of 7 MHz, 28Mhz is ok and works well with my antenna.
The output is the frequency x4 plus the sample width.
At 100MHz, the 3rd harmonic would be used, which is 33.33MHz plus the sample width, or I have a big mistake in reasoning.
Thank you Meerani

View attachment 295141665039198280.jpg
 
. . . you are mixing up the standard mode of reception (SSB, CW, AM etc.) and the non-standard way (WFM)

STANDARD: The QSD uses a LO freq that is 4x the Rx freq
NON-STANDARD: the QSD uses a LO freq that is one third of the Rx freq (using the third harmonic of the Rx freq)

For WFM, the NON-standard way is used.

Sorry, but I will ask you a third (and last :) time to answer my questions --> see https://forum.pjrc.com/threads/71057-Teensy4-SDR-no-FM?p=313770&viewfull=1#post313770
If you do not answer my questions, I will not be able to help you in any way . . .
 
Sorry

I'll get back to you one last time and then everything can be deleted.

I took these pictures without a front end to show that the wrong frequency is present with the 3 harmonics on the si5351.
the WMF itself is not that important, I'm concerned with the wrong frequency output, this has nothing to do with the front end

Thanks for the help
 
no, the freqs are correct.
WFM --> LO is one third of the Rx freq
AM, SSB etc. --> LO is 4 times the Rx freq
 
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