big carrier in the middle of my modulation
big carrier in the middle of my modulation
Hello,
I have started for the first time my Digithin this morning.
- Pidatv image 1.2.1
- raspberry model B
it seems to modulate well, but I have a big carrier remaining.
input is 437MHz . I try between -10 and -20 dBm, it changes nothing.
Have you an idea to fix this?
thanks
Jean-Pierre F6DZP
I have started for the first time my Digithin this morning.
- Pidatv image 1.2.1
- raspberry model B
it seems to modulate well, but I have a big carrier remaining.
input is 437MHz . I try between -10 and -20 dBm, it changes nothing.
Have you an idea to fix this?
thanks
Jean-Pierre F6DZP
Re: big carrier in the middle of my modulation
Hi jean Pierre
Looks like the digithin isn't actually getting the right data stream from the Rpi. With an LO of -20 DBm the output when correctly modulated should be 0dBm.
What's the LED doing? It should be flashing every second - if it's not that's the problem and you need to check you're running 333Ks and if you are playing a TS file it is recorded at right bit rate...
Noel
Looks like the digithin isn't actually getting the right data stream from the Rpi. With an LO of -20 DBm the output when correctly modulated should be 0dBm.
What's the LED doing? It should be flashing every second - if it's not that's the problem and you need to check you're running 333Ks and if you are playing a TS file it is recorded at right bit rate...
Noel
Re: big carrier in the middle of my modulation
I have a 20dB attenuator before my spectrum analyzer.
led flash every second.
All seems to work, but there is that high LO signal that remain..
I suppose I must check the level of IQ that go in the modulator, perhaps they are too low?
Jean-Pierre F6DZP
led flash every second.
All seems to work, but there is that high LO signal that remain..
I suppose I must check the level of IQ that go in the modulator, perhaps they are too low?
Jean-Pierre F6DZP
Re: big carrier in the middle of my modulation
Check the level of I and Q just after the analogue filters: junction of C17-R16 and junction of C20-R17.
The levels should be about 120mv pk-pk.
Hopefully it's something simple. I have also seen that pattern if the modulator is faulty. If it's the one I gave you in Portsmouth, I think that came from the Ebay batch from Israel.
Brian
The levels should be about 120mv pk-pk.
Hopefully it's something simple. I have also seen that pattern if the modulator is faulty. If it's the one I gave you in Portsmouth, I think that came from the Ebay batch from Israel.
Brian
Re: big carrier in the middle of my modulation
I have only 40 mv pk pk at C17-R16 junction.
Jean-Pierre
Jean-Pierre
Re: big carrier in the middle of my modulation
What values do you have for R21 and R25? They are 'select by test' to give about 120mv pk-pk. 1k seems to be about the required value.
Even that would not explain the very low level of the modulation, so it must be something else causing it.
Brian
Even that would not explain the very low level of the modulation, so it must be something else causing it.
Brian
Re: big carrier in the middle of my modulation
I have changed the modulator by a new one sent by Brian (thanks).
Now this problem is fixed. when I receive on 437Mhz, max MER is 27dB. using R21=390 ohms, 120mV I have now 29dB MER
Jean-Pierre F6DZP
Now this problem is fixed. when I receive on 437Mhz, max MER is 27dB. using R21=390 ohms, 120mV I have now 29dB MER
Jean-Pierre F6DZP