Re: Hartley oscillator stability

From: colin (no.spam.for.me_at_ntlworld.com)
Date: 07/13/04 

Date: Tue, 13 Jul 2004 12:54:51 GMT

"Joe McElvenney" <ximac@btinternet.com> wrote in message
news:VA.00000014.009e3f5a@btinternet.com...
> Hi,
>
> About your random frequency jumps, are any of the oscillator
> capacitors silver-mica as they are known to cause this problem?
> This was the subject of a discussion in one of the news-groups
> just recently.
>
> As for the changes in waveform, I would guess you have
> insufficient isolation between the oscillators and the mixer
> circuits - i.e. they are trying to sync-up each other as they
> approach the same frequency.
>
>
> Cheers - Joe
>
>

hmm im having similar problems but with twin crystal osilators as i posted
.., some of the things i found might be usefull ... , are the inductors
screened or beter still toroidal (although u cant tune those without
unwinding a turn )? are the caps polystyrene? rather than ceramic ? is there
any flux anywhere in sight ? is the whole thing in a screened enclosure? are
the coils firmly secured or does knocking it cuase it to jump?

i would of said small heatsinks on the transistors might help with temp
stability although with those 56k emiter resisters i doubt they disipate
anything, but if your using a zener regulated supply i sguest u ditch that
straight away and use a lm78xx, or at least pre regulate the supply to the
zener, do any of the other components gethot and might heat up the
transistors unevenly ? or is there anything that might be cuasing cross
interference ? (signals with high speed edges for example.)

are u using metal film resistors or beter?

interesting about silver mica tho i never knew that, (looks with lower
regard on box of silver mica caps removed from eqpmnt that seldom get used
anyway)

if u want to reduce the tuning sensitivity u can arange it so the ferrite
plug is closer to the center of its travel where it usualy has minimal
efect, by either reducing the capacitance or inducatnce (try spreading the
coils out a bit by or pulling some of the wire off, of course this might
mean u cant tune it to the desired freq anymore, but u can just usualy
unwind a bit without actualy disconecting or breaking it, try a little bit
at a time, but if it has many turns might need to pull quite a bit)

or maybe if you lowered the frequency of both oscilators in the pair then
the diference wld be less afected by change.

Colin =^.^=

Relevant Pages

  • Re: Hartley oscillator stability
    ... About your random frequency jumps, are any of the oscillator ... capacitors silver-mica as they are known to cause this problem? ... Cheers - Joe ...
    (sci.electronics.design)
  • Re: Hartley oscillator stability
    ... > About your random frequency jumps, are any of the oscillator ... > capacitors silver-mica as they are known to cause this problem? ... Picture my desired output at about 50mV, with 200mV of a square wave, ...
    (sci.electronics.design)