(apologies if this article has already appeared here before - I could
not locate it)

Excerpt from
http://www.popular-communications.com/PC%20Highlights%20May08.html

The Ultralight DX Phenomenon

by Bruce A. Conti

First there were crystal radios, then one-tube sets, and now there
are "ultralights." Sparked by the popularity of the Sony SRF-59 AM/FM
Walkman, a very capable retrograde pocket radio, ultralight DXing has
ignited an explosion of experimentation and interest in radio
electronics. In this digital age of endless entertainment options,
including cable TV, the Internet, and wireless phones, the rapid
growth of ultralighting is quite remarkable.

Ultralight Defined

"The sudden boom in ultralight radio interest took everybody by
surprise, and the AM DX community is only now trying to sort out the
definitions, and create some guidelines about this new phenomena,"
said Gary DeBock, a Washington State DXer and ultralight enthusiast,
in response to my inquiries about the subject. "We are still
attempting to create an administrative framework that will give
support and direction to the enthusiasts in this new niche of the AM
DX hobby, and not every decision will be without controversy." DeBock
continued:

DXpedition enthusiasts in particular are already creating a lively
forum of discussion about how these tiny receivers should be used,
and what should be allowed. This is healthy, in my humble opinion. We
have very serious experimentation currently with antenna transplants
into ultralight radios, and one of my own projects transplanted a
6.25-inch loopstick from a Sony ICF-S5 into an SRF-39FP ultralight,
resulting in a huge boost in sensitivity. It certainly isn't a stock
ultralight, but is it on a different DXing level than the Sony ICF-
2010, for example? What if we transplant an even bigger antenna into
an ultralight radio, along with filter mods and other refinements,
making it a DXpedition superstar...would it still be an ultralight?
Whether we agree on this or not, that is the direction that Guy
Atkins, John Bryant, and myself are inclined to go.

World-renowned mediumwave DXers Atkins and Bryant are two co-
conspirators at the forefront of the ultralight movement. Though not
an ultralight, the Sony ICF-2010 is a classic portable communications
receiver best known for its unparalleled AM synchronous detection
circuitry. The 2010 was discontinued in 2003, yet it's still the
reference for comparison of portables to date.
Regarding ultralight experiments, DeBock said:

The "hot-rodded" SRF-39FP already has sensitivity at least up to the
ICF-2010 level, but it is analog and obviously will not be the first
choice of DXpeditioners. We plan to modify a Sangean DT-200VX to make
it a super-sensitive, super-selective digital wonder, but if we
succeed in this, some will obviously question what kind of animal we
have created, and whether it is really an ultralight. Since there is
no judge that can satisfy everybody, the current scramble seems to be
in the direction of making these tiny radios as competitive as
possible for DXpeditions, and letting the AM DX community sort out
the definition concepts later.

The Sangean DT-200VX, like the SRF-39, SRF-59L and others in the Sony
Walkman lineup, has quickly gained superstar status among ultralight
DXers. The "P" version of the SRF-39 was manufactured with a clear
plastic chassis for prisoner use. The clear chassis allowed easy
inspection for contraband by prison security.

Ultralight Classifications

What is ultralight DXing? In its most basic form, ultralighting is
done with a pocket radio reminiscent of the classic transistor radios
from years gone by. Consider it an upgrade from the good old days of
DXing with oatmeal-box crystal radios, a back-to-nature minimalist
movement for radio hobbyists, and for some simply a rekindled youth.