unusuall transformer for common mode isolation

[Bob]

A thread in rec.radio.amateur.homebrew about the Peter Dahl
transformer
company possibly closing down lead me to this unusall transformer
design.

http://www.pwdahl.com/images/tlt.JPG

It's a 2KW AC mains transformer designed for radio towers to stop the
RF
getting into the mains supply.

What is the name for this kind of transformer?

Dahl calls it an "austin ring type" but that just refer to the Austin
insulator
company who also make tower lighting transformers. I'm searching for
the name for this paticular topology.

It looks like it should not work so I'd like to learn a bit more about
it. I'd like to know if it could be used for audio signal isolation.

Bob

 

[default]

On Wed, 26 Dec 2007 21:42:11 -0800 (PST), Bob <bob9@mailinator.com>
wrote:

A thread in rec.radio.amateur.homebrew about the Peter Dahl
transformer
company possibly closing down lead me to this unusall transformer
design.

http://www.pwdahl.com/images/tlt.JPG

It's a 2KW AC mains transformer designed for radio towers to stop the
RF
getting into the mains supply.

What is the name for this kind of transformer?

Dahl calls it an "austin ring type" but that just refer to the Austin
insulator
company who also make tower lighting transformers. I'm searching for
the name for this paticular topology.

It looks like it should not work so I'd like to learn a bit more about
it. I'd like to know if it could be used for audio signal isolation.

Bob

It appears as if it is a toroid mains transformer with the ribbon core
and primary on the on the bottom right, and secondary on the upper
left.

That general type is not for RF but lightening. It provides a
physical gap between primary and secondary to lower capacitance (so
you aren't losing RF to the power mains) while still providing high
dielectric isolation for voltage spikes and getting mains power up the
mast for an aircraft beacon.

It is more common to use chokes for that purpose.

I'd guess that he also has an electrostatic shield (with a gap to
avoid a shorted turn) around the primary for a ground. That shield
technique (completely surrounding the primary - not just the layer
closest to the secondary) is call a "box shield." It is often used to
keep RFI out of power supplies. It is also labor intensive and adds
to the cost of the transformer.


--