The designs in Sevick's book and prior transmission line transformer
design papers and books work well, as long as you pay attention to
details such as winding the turns as tightly coupled transmission
lines. Magnetic flux density in the core can be low, and the core
itself extends the LF range. I built a 1:4 unun for a test setup at
0.3 - 5 MHz at work, using some commonly available Fair Rite
material, where I needed to drive 200 Ohms with a kW of CW power.
Using a calibrated Werlatone directional coupler with Hp/Agilent 437
power meters on the 50 ohm side, and capacitive divider and Pearson
current transformer on the 200 Ohm side, i measured the loss in the
transformer while under full drive. It was similar to what was
measured with a network analyzer at a milliwatt. The transformer runs
cool and does the matching that i built it for.
BTW, Sevick wasn't the first to describe these types of transformers,
as there are papers from the 1950s from Phillips, from Herb Krauss at
Va Tech, in Solid State Radio Engineering by Krauss, Bostian and
Raab, and in many other references. These people didn't just 'dry
lab' data.
73
K5PRO
John
>From: 2 <2@vc.net>
>To: "Dan" <dhearn@ix.netcom.com>, "Yury VE3XB" <ve3xb@sympatico.ca>,
> "AMPS" <Amps@contesting.com>
>Subject: Re: [Amps] 2:1 Transformer
>
>>Yury: You need a copy of Jerry Sevicks book "Transmission Line
>>Transformers". He shows many designs of transformers which have ratios near
>>2:1 as well as dozens of others. These amazing xfmrs have bandwidths of
>>160-10m or more and losses as low as 0.1 db.
>
>? However, as I understand it, Sevick measures the performance of
>his designs at low power.
>Rich, AG6K, 805-386-3734, www.vcnet.com/measures
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