Some info you may find of interest on this subject
may be seen on my webpage:
73 & Good morning,
--- Angel Vilaseca <firstname.lastname@example.org> wrote:
> Another situation where excessive wire length can
> lead to unwanted
> resonance effects (overheating) is the plate choke.
> If the plate choke was wound on a ferrite rod, or
> toroid, much less wire
> length would be needed.
> Why is this never seen in classical designs?
> On the other hand, a cathode choke wound on a
> ferrite rod IS a
> classical, but never a plate choke. Why?
> And why is a ferrite rod always used for the cathode
> choke, but never a
> Angel Vilaseca HB9SLV
> Manfred Mornhinweg a écrit :
> > Hi Jim,
> >>> I didn't know they had so much variation with
> >> All of this data has been in Fair-Rite's printed
> catalog for many
> >> years, and that catalog has been on Fair-Rite's
> website as a pdf for
> >> at least 5 years.
> > Could you give me an exact URL for some page that
> gives this information
> > for the 61 material? I couldn't find it, and after
> a few hours searching
> > I gave up. Living in a rural location, my internet
> connection is over
> > the cellphone network, with dismal performance, so
> it's not conducive to
> > efficient web browsing!
> > Also, if you find some place that gives loss
> curves for ferrite
> > materials, that would be very useful too! I could
> find only very sparse
> > single-frequency information.
> > Carl,
> >> Terms such a "should", "could", "most cost
> effective", do not give me
> >> a very warm feeling Manfred.
> > Maybe I misused those words. English is only my
> third language. When I
> > wrote "should be able to work at 1.5kW", I meant
> that when I set out to
> > design this circuit, one of the design goals was
> 1.5kW operation. Later,
> > when the system was ready, I could confirm through
> years of daily use
> > that actually the goal was met.
> > And when I wrote "on a transmission line that
> could have high SWR", what
> > I meant is that this thing had to drive an open
> wire line connected to a
> > random antenna, with completely unknown impedance.
> No design can
> > be guaranteed to work over "any" impedance to be
> found in the real
> > world, so here the goal was to be able to work
> with good performance at
> > SWR levels up to 5:1 or so, and acceptable
> performance at somewhat
> > higher SWR. In practice I have operated into
> antennas that show an SWR
> > so high that the meter reading is
> undistinguishable from infinite. In
> > those cases of course the efficiency must be
> lower, but still the
> > transformer has not blown up despite that use. It
> does get warm though,
> > with some extremely bad loads.
> >> However if you can show 1.8 - 30 MHz performance
> statistics at the
> >> 1500W level they would go a long way to put a
> sense of engineering
> >> reality on the subject.
> > I have neither the instrumentation nor the time to
> do a scientifically
> > valid investigation of the transformer, so I'm
> sorry, I can't provide
> > precise data. I can only say that in practice the
> ferrite material has
> > worked very much better than powdered iron, and
> that theory and data
> > extracted from the relevant sheets beautifully
> explains why. So my
> > assertation is a relative one: Type 61 ferrite
> performs much
> > better than type 2 powdered iron, in this
> broadband high power
> > application, both in terms of loss and in choking
> performance, but I'm
> > not able to provide precise absolute data on
> transformers built with
> > each of the two materials.
> >> His book went thru a few revisions as he was
> faced with reality and
> >> not a lab test at low level RF. At one point
> there were some rather
> >> heated on the air discussions that I partook of
> strictly as a
> >> listener.
> > That must have been interesting! Unfortunately, I
> rarely find anyone to
> > talk about technical things on the air. That's why
> I vent here! :-)
> > In any case, my ferrite balun has been used for
> several years, under
> > many different conditions, at legal limit power
> and all bands, and so
> > far has worked well.
> >> My own experiments with a FT240-61 at 1200W was
> rather dismal with
> >> excessive heating that resulted in tuning drift
> as well as TVI.
> > The three symptoms all sound like you drove the
> ferrite to a much
> > excessive flux density. What flux density did you
> >> At that time I did not own a spectrum analyzer to
> look for non
> >> linearities nor a network analyzer. I now own
> > I'm still at that stage of not owning these
> instruments! And believe me,
> > I would love to get a spectrum analyzer! But it
> should work at least up
> > to UHF, it should have a dynamic range not under
> 90dB, and it should
> > not cost as much as a car. So far this has kept me
> without one.
> >> I then tried T225-2A thru T400-2A powdered iron
> at various power
> >> levels from 500W to "well above" 1500W; the tests
> used from one to
> >> three cores wrapped with Scotch #27 HV tape and
> #14, 12 and 10
> >> stranded Teflon wire. The result was several
> balun 4:1 kits for 500
> >> to 3500W that were sold for about 10 years thru a
> part time business
> >> that I owned.
> > You must have used many turns to get enough
> inductance, and as a result
> > there must have been reduced performance at the
> higher bands.
> >> As expected they were not perfect due to winding
> capacity and trying
> >> for a 1.8 to 30 MHz compromise.
> > Exactly. On powdered iron cores you can make
> baluns that work well over
> > a reduced range of bands, but 160 to 10 meters is
> asking too much from
> > them. There have to be more severe compromises at
> both ends of the
> > range, than if you used ferrite.
=== message truncated ===
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