MattiaM
Active Member
I have a Technics SA5400X receiver that I got for parts and just completed its restoration.
The tuner seems to be working, although reception is quite weak, it only picks very few stations and it is pretty noisy.
I therefore decided to use it to try my first ever alignment.
I currently do not have a distortion meter, but I figured I would use an oscilloscope and reduce distortion by eye/ear for now, my main goal at this stage is to try and grasp a bit better the workflow/procedures and, mostly, to learn something new.
I got a service manual with the alignment procedures, I have a scope and I have access to an HP 8644A RF signal generator.
- First, the FM alignment procedure appears to want me to set the RF SG for different levels of FM percentage modulation. This is quite confusing to me: am I correct to assume that if the modulation frequency bandwith is +/- 75kHz, then 100% modulation is the entire 150kHz bandwith around the carrier frequency and a 30% modulation is 30% of that, i.e. the carrier frequency +/-22.5kHz?
- Second, the alignment procedure defines output levels in (positive) dB, e.g. SG 98MHz (100% modulation with 400Hz), Output 72dB. Am I correct to assume that I should set the SG for an output of -72dBm? Am I also correct to assume that whenever no output is specifiefd, then I should set the SG at 0dBm?
I tried setting the SG with a 90 MHz and 106MHz with a 400Hz modulation signal, I connected the SG to the 300 Ohm antenna inputs with a dummy antenna as specified in the service manual, and I can easily pick the 400 signal both on the oscilloscope and through my speakers. There seems to be quite a lot of interference though, and I need to crank up the volume quite a bit to see a clean sinewave.
I checked the specs of the SG, and it seems to have a quite high FM distortion (I have the Option 04, so I get a 1% distortion), double or example the amount of distortion of an HP8656B. Given that I don't have a distortion meter and the spects of the tuner are around 0.7%THD in stereo mode, I don't think that is too much of an issue for now. However, if I want to play more with tuner alignment, should I get a lower distortion SG?
As always, thanks for the help.
The tuner seems to be working, although reception is quite weak, it only picks very few stations and it is pretty noisy.
I therefore decided to use it to try my first ever alignment.
I currently do not have a distortion meter, but I figured I would use an oscilloscope and reduce distortion by eye/ear for now, my main goal at this stage is to try and grasp a bit better the workflow/procedures and, mostly, to learn something new.
I got a service manual with the alignment procedures, I have a scope and I have access to an HP 8644A RF signal generator.
- First, the FM alignment procedure appears to want me to set the RF SG for different levels of FM percentage modulation. This is quite confusing to me: am I correct to assume that if the modulation frequency bandwith is +/- 75kHz, then 100% modulation is the entire 150kHz bandwith around the carrier frequency and a 30% modulation is 30% of that, i.e. the carrier frequency +/-22.5kHz?
- Second, the alignment procedure defines output levels in (positive) dB, e.g. SG 98MHz (100% modulation with 400Hz), Output 72dB. Am I correct to assume that I should set the SG for an output of -72dBm? Am I also correct to assume that whenever no output is specifiefd, then I should set the SG at 0dBm?
I tried setting the SG with a 90 MHz and 106MHz with a 400Hz modulation signal, I connected the SG to the 300 Ohm antenna inputs with a dummy antenna as specified in the service manual, and I can easily pick the 400 signal both on the oscilloscope and through my speakers. There seems to be quite a lot of interference though, and I need to crank up the volume quite a bit to see a clean sinewave.
I checked the specs of the SG, and it seems to have a quite high FM distortion (I have the Option 04, so I get a 1% distortion), double or example the amount of distortion of an HP8656B. Given that I don't have a distortion meter and the spects of the tuner are around 0.7%THD in stereo mode, I don't think that is too much of an issue for now. However, if I want to play more with tuner alignment, should I get a lower distortion SG?
As always, thanks for the help.
Last edited: