Ultralight Modifications for DXpeditions
Some DXers have inquired about the recent success in modifying the Eton E100 and other Ultralights for DXpedition use, so here is a brief summary of the current progress.
SRF-39FP: This analog model has had various modifications for improved tuning dials, digital readout, monster loopsticks and other changes, but the basic limitation of all these efforts is that without the availability of a commercial upgraded IF filter to improve selectivity, this model cannot receive the 9 kHz splits without the lucky combination of a strong DX signal and little (or no) domestic QRM. The bizarre 50 kHz IF has been a real roadblock for selectivity mods, and without such a mod, the DXpedition potential of all the SRF-39FP (and SRF-59) models is greatly limited. The recent Amidon 7.5" loopstick model, however, shows great promise for domestic DX use because of its extreme sensitivity, and for general TP chasing during which its superior nulling ability can be used, it may prove effective in chasing Asian TP's in the northwest, during the upcoming fall season. One of these models recently received 5AN-891 in Australia, but this was only because of the total lack of domestic QRM on the frequency.
DT-200VX: This digital model has had both transplanted loopsticks and 450 kHz selectivity mods, but not yet in combination. Some efforts were made to replace the stock loopstick with 6.25" vintage ferrite-bar models, but the lack of broadband sensitivity in the digital design hampered the efforts (this was also an initial problem in the E100 modification efforts, until the development of the "sliding coil" loopstick). To my knowledge, all modification efforts were suspended in the spring, in favor of the SRF-39FP and E100 models. Since there has been great modification success with the E100 digital model since then, the DT-200VX, another digital design with similar performance, could also presumably be greatly transformed by the application of upgraded IF filters and a large sliding-coil loopstick.
E100: This model has undoubtedly become the major DXpedition breakthrough we were hoping for. With its 1 kHz tuning ability, 200 memories and 455 kHz IF, its circuitry seems almost perfectly designed for modification into a DXpedition superstar. John Bryant had great DX success in modifying his unit to receive signals from external antennas, such as his superb Wellbrook 4-element Array at Grayland. But even as a stand-alone portable, recent developments have combined to make the E100 an extremely effective DX chaser. The first big breakthrough was the development of the "sliding coil" loopstick, which overcomes the E100's lack of broadband (530-1700 kHz) sensitivity. An offshoot of the alignment process, the "slider" loopstick simply allows the user to peak the loopstick coil on each received signal, instead of securing it at the 600 kHz peak position. Although this concept can be used with any E100 (even stock models), when the mediocre E100 stock loopstick is replaced with a huge Amidon or Stormwise ferrite bar-based loopstick, the application of the "slider" concept provides an incredible increase in sensitivity, boosting the E100 well past the level of any stock portable on the planet.
Another huge improvement was Guy Atkins' suggestion of a Murata CFJ455K5 premium IF ceramic filter, to replace the stock filter. The CFJ455K5 is the same premium IF filer as used in the Eton E1, and it has similar performance in the E100. It cuts through domestic QRM very effectively, and in combination with the larger "slider" loopsticks, the narrow IF filter makes split-frequency DX chasing a breeze. Prior to development of the modified E100's, nobody on the west coast had been able to receive any type of DU signal with any type of modified Ultralight. Now, with three hard-core Washington state DXers using modified E00's, all three of us have logged multiple DU's with ease.. and we can't wait for more :>)
73, Gary DeBock
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