1/2 frequency oscillator doubler without toko coils?
- Bton-FM
- tower block dreamin
- Posts: 463
- Joined: Sun Jun 16, 2019 2:55 pm
- Location: Beside the seaside
1/2 frequency oscillator doubler without toko coils?
Please could someone suggest a way of doubling a 1/2f vco without using toko coils?
-
- proppa neck!
- Posts: 537
- Joined: Mon Sep 02, 2019 11:06 am
Re: 1/2 frequency oscillator doubler without toko coils?
Regular air coils but will be an add ache to tune.
- Bton-FM
- tower block dreamin
- Posts: 463
- Joined: Sun Jun 16, 2019 2:55 pm
- Location: Beside the seaside
Re: 1/2 frequency oscillator doubler without toko coils?
Have you made a doubler like that?
-
- proppa neck!
- Posts: 2776
- Joined: Tue Apr 05, 2016 1:23 am
Re: 1/2 frequency oscillator doubler without toko coils?
That was the way we always made them! Typically 4 turns at 6mm diameter with a 22p trimmer across it, stretched a bit. The base of the transistor needs to be biased just below conduction, so that the incoming RF nudges it into action. Some folks would couple inductively to the coil, with a couple of turns pushed into the 4 turn coil. The other ways were either to tap the coil for a take-off point, or connect to the collector of the transistor with a few pF into the next stage.
I also used this kind of coil for a tripler to Band II, using a FET instead of the usual BSX20 / 2N2369A.
I'll have a look in the junk pile and see if I can find an old exciter to photograph.
Incidently, if you can't get trimmers any more, you can use a fixed cap of 15pF, 18pF or 22pF, and stretch the coil to tune! It's fiddly, but it works.
Another option - one we're using - is to 3D-print coil formers. We then use aluminium grub screws to tune them.
I also used this kind of coil for a tripler to Band II, using a FET instead of the usual BSX20 / 2N2369A.
I'll have a look in the junk pile and see if I can find an old exciter to photograph.
Incidently, if you can't get trimmers any more, you can use a fixed cap of 15pF, 18pF or 22pF, and stretch the coil to tune! It's fiddly, but it works.
Another option - one we're using - is to 3D-print coil formers. We then use aluminium grub screws to tune them.
"Why is my rig humming?"
"Because it doesn't know the words!"
"Because it doesn't know the words!"