Pages: 1 ... 8 9 [10] 
|
 |
|
|
Author
|
Topic: [solved] Receiving strong sigs 12.KHZ (Read 14073 times)
|
|
DD4WH
positron
alter Hase
 Offline
Posts: 462
Ich liebe dieses Forum!
|
 |
Re:[not solved] Receiving strong sigs 12.KHZ
« Reply #135 on: 04. September 2018, 09:50:37 »
|
|
Hi Francois,
really happy that it solved your problem!
There was a bug in the audio chain, formerly it was like this:
* light low pass filter with only 4 taps @48ksps sample rate
* downsampling-by-4
* heavy Hilbert lowpass filter with +45 and -45 degrees phase shift for I & Q respectively @12ksps sample rate, 199 taps
I changed it to:
* Hilbert lowpass filter with +45 and -45 degrees phase shift for I & Q respectively @48ksps sample rate, 121 taps
* light low pass filter with 4 taps
* downsampling-by-4
The Hilbert lowpass filter with 121 taps prevents the aliasing and suppresses the unwanted signals. Thats DSP standard, so its amazing that it remained unnoticed for so long. Probably my fault :-).
I suspect, the implemented change will also lead to a slightly worse sideband suppression, but as long as nobody notices it, . . . ;-).
In the next days I will finetune a few more things around this bugfix.
Please report anything that could be related to this bugfix.
73 Frank
|
| « Last Edit: 04. September 2018, 09:56:11 by DD4WH » |
 Logged
|
-----------------------------------------
Teensy Convolution SDR
https://github.com/DD4WH/Teensy-ConvolutionSDR
|
|
|
DD4WH
positron
alter Hase
Offline
Posts: 462
Ich liebe dieses Forum!
|
|
Re:[not solved] Receiving strong sigs 12.KHZ
« Reply #136 on: 04. September 2018, 09:55:54 »
|
|
Francois: thanks for your measurements!
The only remaining birdy 24kHz below the wanted signal is due to IQ imbalance, so has a totally different cause than the aliases caused by the fixed filter problem.
73 Frank
|
| « Last Edit: 04. September 2018, 09:56:26 by DD4WH » |
Logged
|
-----------------------------------------
Teensy Convolution SDR
https://github.com/DD4WH/Teensy-ConvolutionSDR
|
|
|
F4HTX
schon länger dabei
Offline
Posts: 66
Scotty, energize...
|
|
Re:[not solved] Receiving strong sigs 12.KHZ
« Reply #137 on: 04. September 2018, 10:10:51 »
|
|
Hi Frank,
Anti-aliasing is always a source of unexpected problems...
Thanks for the explanation, for sure aliasing on a downsampled signal was a little rude 
Anyway I wonder why this appears suddenly on some of the mchfs and not others. There still might have some dependency on hardware implementation.
73's
François
@ Andreas : I will carefully check the SDIN & SCLK signals and publish, but a few time later. Pro's awaiting...
|
|
Logged
|
|
|
|
S53DZ
schon länger dabei
Offline
Posts: 58
Ich liebe dieses Forum!
 
|
|
Re:[not solved] Receiving strong sigs 12.KHZ
« Reply #138 on: 04. September 2018, 10:24:05 »
|
|
| Anyway I wonder why this appears suddenly on some of the mchfs and not others. There still might have some dependency on hardware implementation. |
|
I am asking myself the very same question.
No matter if I had no troubles with aliases here (perhaps because I did not use a wide-bandwidth BPFs > 2k7?) I will do some more measurements to check the behavior after implementing FW 2.9.51 in due time.
73 Bojan
|
| « Last Edit: 04. September 2018, 10:25:15 by S53DZ » |
Logged
|
|
|
|
WD8BXS
alter Hase
Offline
Posts: 286
|
|
Re:[not solved] Receiving strong sigs 12.KHZ
« Reply #139 on: 04. September 2018, 13:30:02 »
|
|
Well Done, Well Done,Well Done,Well Done,Well Done,Well Done,!!!
That fixed it here as well.
Congratulations to all who helped!!
73, de Chuck WD8BXS
|
| « Last Edit: 04. September 2018, 13:30:32 by WD8BXS » |
Logged
|
Thanks,
De WD8BXS vy 73
|
|
|
Pages: 1 ... 8 9 [10] 
|
|
|
|
|
|
|
