Guru
Joined: 09/08/2007
Location: AustraliaPosts: 4406
| Posted: 08:33pm 02 Sep 2017 |
A much better way for mains locking would be to remove the 4Mhz crystal and feed a VCO into there. The grid does not vary much from 50Hz maybe +/- half a hertz at the most.
That would require 4Mhz +/- 40 Khz which is not a large variation.
The phase detector part of the 4046 only has to work at 50Hz so that would be fine, in fact it would be an excellent choice for a phase detector.
But the VCO part of the 4046 is not going to work as high as 4Mhz.
You will need something else for the VCO and there are quite a few different ways to go about that.
A standard crystal just a bit higher, say 4.032 Mhz pulled down in frequency with a varicap diode might be worth a try.
http://www.ebay.com.au/itm/20-pcs-4-032-MHz-4-032MHz-Crystal-HC-49-S-Low-Profile-/263039066997?hash=item3d3e59a375:g:ZMs AAOSwy5ZXDLjp
Some of these low cost Chinese crystals can be a bit off frequency. I you buy a bunch, chances are you can find one that will be ideal that you can vary an even amount either side of 4.000 Mhz
See how you go.
4.096Mhz is another very common and readily available crystal frequency. But there may be difficulties in pulling one of those far enough below 4.00Mhz to be useful, but it may be possible !
Another possibility would be a two terminal 4.00 Mhz ceramic resonator. These are all over the place for frequency, but if you can select one out of a bunch that works just above 4.00 Mhz, then it will be even easier to pull down lower with a varicap diode.
http://www.ebay.com.au/itm/20-pcs-4-032-MHz-4-032MHz-Crystal-HC-49-S-Low-Profile-/263039066997?hash=item3d3e59a375:g:ZMs AAOSwy5ZXDLjp
I have no doubt this can all be done fairly easily, but its going to take a bit of experimentation and testing.
Cheers, Tony.