PLL unlocking-exciter common problem!

[radium98]

@Radio Garfield thank will pm you soon

[nrgkits.nz]

I thought I would post an update to this as encountered the same problem recently with a 100w PA in the same box as the exciter which was using a TSA5511. The problem is the PLL reference is not strong enough - try putting a scope on pins 2 and 3 of the TSA5511 and you'll barely be able to detect anything, its about 100mV peak to peak. In the presence of high RF it just gets saturated and hence the thing goes out of lock. If its very well screened, there are no problems. Removing the ribbon cable to the LCD and or earthing the crystal will somewhat reduce the RF interfering with the reference, however the underlying cause of this issue is the reference is too weak.

I've has no problems with other exciters I've built using the MC145170 as a PLL, if you put a scope on the reference of this chip you'll get something like 2v peak to peak which is significantly stronger than the reference on the TSA5511. I have an exciter with the MC145170 installed in the same box as a 300w PA with no shielding at all, there were no problems and it never went out of lock - although there was considerable RF feedback.

[radium98]

thanks nrgkits.nz

[Radio Garfield]

Hi everyone. I was absent for long time, so thank you very much for this update.
It is very important info. Good luck.