Well, I specified the core type as Chris was originally using a
different type, but of course the size is relevant. The diameter is
55mm and I use two cores, one on top of the other, to reduce heat.

Mike, G3XDV
==========

> 3C90 is a type of ferrite material, and doesn't specify a transformer
> type.
>
> What is the Ae (cross sectional area) of that core?
> Or just the diameter to work it out from?
>
> Andy
>
>
> On 2 November 2015 at 13:00, Mike Dennison
> <[email protected]> wrote:
>
> > Chris, my 3C90 transformer has about 16 turns on each winding. (I
> > say approximately as I need to adjust by a turn or two between
> > summer and winter due to absorption/detuning by trees. I would
> > suggest using the thickest wire you have in case you want to run
> > higher power in the furture.
> >
> > As for the variometer, mine covers about 200-500mH and this will
> > tune about twice the width of the 136kHz band (in conjunction with
> > my big coil). Coincidentally it also tunes the 472kHz band when the
> > big coil is removed.
> >
> > Mike, G3XDV
> > ==========
> >
> > > yes, I still have trouble with the workshop alarm going off when I
> > > TX, but seemingly only at night, for whatever reason! Isolation is
> > > something I need to add. I have a 3C90 core spare and will wind a
> > > 1 : 1 transformer for now, just for isolation. How many turns
> > > should I use for best efficiency? I will probably use either 1.5
> > > mm enamelled wire, or maybe some Teflon covered stuff.
> > >
> > > I also need to tame the variometer, it's obviously got far too
> > > many turns on it as just a couple of degrees moves resonance a
> > > long way. I picked up a 2 axis variometer, possibly a goniometer,
> > > that I may ise, with a motor drive. Photos at
> > > http://www.chriswilson.tv/goniometer.zip
> > >
> > > I only gave a fiver for it, so no big deal if it doesn't work out,
> > > but I am about to check what inductances it covers. I think it
> > > should withstand the voltages OK. What do you reckon? It would be
> > > easier to motor drive then the variometer in my loading coil.
> > >
> > > Thanks for the kind words about my progress. Most thanks should go
> > > to G3YXM for helping me get my amp done and reliable, he's been a
> > > Godsend, as have you gentlemen on here.
> > >
> > >
> > > > I agree with Stefan. A transformer (using a suitable core
> > > > material such as 3C90) gives you more flexibility in the future
> > > > It also provides the opportunity to isolate the RF ground from
> > > > the mains supply ground which can improve EMC both on transmit
> > > > and receive.
> > >
> > > > Well done so far. Your signal is very impressive with such low
> > > > RF power.
> > >
> > > > Mike, G3XDV
> > > > ==========
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > --
> > > Best regards,
> > >  Chris                            mailto:[email protected]
> > >
> > >
> > >
> > >
> > > -----
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> > > Version: 2016.0.7163 / Virus Database: 4457/10921 - Release Date:
> > > 10/31/15
> > >
> >
> >
> >
> >
>
>
>
> -----
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> Checked by AVG - www.avg.com
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