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Unshielded Toko as Oscillator?
Posted: Mon Dec 12, 2022 1:19 am
by XXL
Is there any benefit from using a shielded inductor over a standard toko when using pll ?
I’m wondering if shielded was used back when it was all VFO and it just got carried over to pll designs.
Re: Unshielded Toko as Oscillator?
Posted: Mon Dec 12, 2022 2:17 am
by sinus trouble
XXL wrote: ↑Mon Dec 12, 2022 1:19 am
Is there any benefit from using a shielded inductor over a standard toko when using pll ?
I’m wondering if shielded was used back when it was all VFO and it just got carried over to pll designs.
From what i have observed? If you add shielding to an inductor, the inductance will fall dramatically!
For example? A 10uH free air coil fitted with a shield would end up likely to be 4uH in reality!
Personally, I would shield the whole oscillator if it is that sensitive?
If the inductor is rigid enough and the circuitry surrounding it is unlikely to interfere? There is no need for shielding!
Re: Unshielded Toko as Oscillator?
Posted: Mon Dec 12, 2022 6:01 pm
by jvok
Using a shielded coil can help in at-frequency designs to prevent rf pickup back into the oscillator. Especially in well designed smd boards where there's not much loop area elsewhere to pick up rf, the coil can be the main way for interference to get in. This isn't so much of a problem in doubler rigs.
A shielded coil will have less inductance for the same number of turns than an unshielded one, but you can easily get around that by using more turns. The spec sheet will tell you the inductance for each coil, so you can easily pick a part that gives you roughly the same range as the non-shielded version.
The other thing is that a shielded coil will give you less Q, which means slightly more carrier noise. But this is far less of a problem than interference from rf pickup.
Re: Unshielded Toko as Oscillator?
Posted: Mon Dec 12, 2022 6:57 pm
by XXL
What about half frequency designs ? I don’t use on frequency designs because they hum without a shielding case. Is it really needed for half frequency?
Re: Unshielded Toko as Oscillator?
Posted: Mon Dec 12, 2022 11:06 pm
by sinus trouble
All of my projects are based on 1/2 frequency and shielding has never been required! Even alongside large power amplifiers!
However, i would not say they are completely immune to noise! Mostly caused by PSUs or external audio sources!
Shielding of stages as a whole rather than just focusing on the "Tank coil" can have it benefits? But i would not say it is mandatory!
Re: Unshielded Toko as Oscillator?
Posted: Tue Dec 13, 2022 9:42 am
by Krakatoa
There is another option, which is to use a toroid for the oscillator coil. It provides some sort of shielding by having the magnetic field "encircled" in it. A material 17 toroid should work fine.
Also, for 1/2f you may wind the 6 coils in it and be a compact solution.
Re: Unshielded Toko as Oscillator?
Posted: Tue Dec 13, 2022 9:47 am
by rigmo
jvok wrote: ↑Mon Dec 12, 2022 6:01 pm
Using a shielded coil can help in at-frequency designs to prevent rf pickup back into the oscillator. Especially in well designed smd boards where there's not much loop area elsewhere to pick up rf, the coil can be the main way for interference to get in. This isn't so much of a problem in doubler rigs.
A shielded coil will have less inductance for the same number of turns than an unshielded one, but you can easily get around that by using more turns. The spec sheet will tell you the inductance for each coil, so you can easily pick a part that gives you roughly the same range as the non-shielded version.
The other thing is that a shielded coil will give you less Q, which means slightly more carrier noise. But this is far less of a problem than interference from rf pickup.