[Amps] how to wind an HF broadband 10:1 transformer

jeremy-ca km1h at jeremy.mv.com
Thu Feb 28 18:44:20 EST 2008


----- Original Message ----- 
From: "Manfred Mornhinweg" <mmornhin at gmx.net>
To: <amps at contesting.com>
Sent: Thursday, February 28, 2008 2:25 PM
Subject: Re: [Amps] how to wind an HF broadband 10:1 transformer


> Hi Carl,
>
> > Manfred, my reply was assuming use at high power since this is not a
> >  QRP or receiver forum. In that case iron powder is the only accepted
> >  material as has been proven time and time.
>
> A few years ago I needed to make a balun for 160 to 10 meters, that
> should be able to work at 1.5kW on a transmission line that could have
> high SWR. After comparing different powdered iron and ferrite materials,
> I settled for 61-type ferrite for the core. It provided the most
> cost-effective solution, to fulfill the requirements in terms of loss,
> distortion, and bandwidth. I tried to squeeze #2 powdered iron into this
> application, because it's significantly cheaper than #61 ferrite, but I
> found no way to achieve the required performance with this material. So
> I can't agree with iron powder being the only accepted material. At
> least in this particular case, I found ferrite to be much superior.


Terms such a "should", "could", "most cost effective", do not give me a very 
warm feeling Manfred.
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.


>
> > Even Sevik was forced to back down from his ferrite obsession when he
> > was challenged by many and it became obvious that he never tested his
> > designs at power.
>
> The only thing I know about Sevik is his book about baluns, so I don't
> know of his trends over time! Maybe I will come back to iron powder
> someday too, but since having some meltdowns with iron powder, I'm a
> firm fan of ferrite, for most applications including low and high power
> broadband transformers! Which does not mean that I would think it
> impossible to use powdered iron, but just in my experience ferrite
> allows the more effective solution.



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.


My own experiments with a FT240-61 at 1200W was rather dismal with excessive 
heating
that resulted in tuning drift as well as TVI. At that time I did not own a 
spectrum analyzer to
look for non linearities nor a network analyzer. I now own both.

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.

As expected they were not perfect due to winding capacity and trying for a 
1.8 to 30 MHz compromise.
However they worked well, did not overheat when used within their stated 
power ratings and did not cause
any TVI/RFI at home or reports from neighbors. I did not attempt to check 
for feedline radiation as they
were only accessible for a very short part of the total runs.

Antenna tuners that I used were borrowed Dentron, MFJ, Murch and a homebrew 
that was capable
of very serious power. The statute of limitations has expired!

Antennas were a 160M inverted Vee with random length 450 Ohm feeders and a 
80M version
with tuned feeders.

Carl
KM1H










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