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The SRF-39FP Slider loopstick-- Optimism Slides Away
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Hello Guys,
Because of the success of the Eton E100
Slider loopstick in providing an incredible sensitivity boost to the stock
unit, John Bryant and others have wondered how the newly-developed slider
loopstick would benefit other Ultralight radio designs, like the SRF-39FP.
Having two identical "Amidon SRF-39FP' units with 7.5" loopsticks wound
with 40/44 Litz wire (the same material as the E100 slider loopsticks), I
decided to run a few tests to find out.
The SRF-39FP "prison radios" were the primary
focus of Ultralight radio experimentation early this year, with many
transplanted loopsticks providing huge boosts in sensitivity. The most
sensitive of these were the "Amidon SRF-39FP" units, with sensitivity far
superior to that of the ICF-2010, and roughly equal to the current E100 slider
units. Unfortunately, there is no easy way to upgrade selectivity in these
units, primarily due to the unusual IF of around 50 kHz.
Consequently, as TP-DXing receivers, they fall far short of the E100
sliders, and their great sensitivity is useful only on relatively clear
frequencies, or when the loopstick's superior nulling ability can be used
to advantage. During DU DXing in the summer, for example, the E100 slider
model could receive 11 DU's from Australia, New Zealand, Fiji and Tonga, while
the Amidon SRF-39FP could receive only 1 (5AN-891, on a completely clear
frequency).
The SRF-59/39FP analog series has a smaller
loopstick coil which is used for aligning the 600 kHz peak position, and
theoretically this coil can be also used as a "slider," to peak frequencies
other than 600 kHz (like in the E100 slider design). Unfortunately,
the SRF-39FP smaller loopstick coil behaves far differently than the E100 coil
when it is shifted, making an SRF-39FP "slider" system marginal at
best.
In the E100 slider system, shifting the coil a
very slight amount will provide a huge difference in sensitivity, making
the bar-graph signal strength meter rise from nothing to maximum level
within a tiny fraction of an inch. On the SRF-39FP, the peak is nowhere
near as sharp, but sounds more like a change in audio, as the coil is shifted as
much as half an inch. The shifting of the coil on the SRF-39FP away from
the 600 kHz peak also seems to induce spurious reception of whistles and
shortwave signals, apparently upsetting the alignment of the analog
radio. The marginal improvement in sensitivity on higher frequencies
is more than outweighed by the negative side effects, no doubt due to the unique
design of the RF front end inside the CXA1129N IC chip.
Certain other digital ultralights like the
DT-200VX and the DT-400W have a loopstick quite similar to that of the E100, in
which the coil(s) are peaked (at 600 kHz) very close to the end of the ferrite
bar on the stock unit, and which have extremely sharp peaks over a very narrow
range. These designs can be expected to behave like that of the E100
slider, when an Amidon ferrite bar having a movable coil of 40/44 Litz wire
is transplanted into the circuitry (a nice winter project!).
73, Gary DeBock
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Hi John,
Thanks for your comments. The SRF-39FP
Slider project was probably irrelevant anyway, since until we can find a way to
upgrade selectivity in the Sony analog units, these highly sensitive Amidon
SRF-39FP's will be useful only on relatively clear frequencies-- a
poor choice, compared to the fully-modified E100's.
A DT-400W Slider project is definitely planned
here for the winter, in which piggybacked 40/44 Litz wire coils are shifted
along a Type 61 Amidon 7.5" ferrite bar. My guess is that it will equal
the E100 Sliders in sensitivity, although it's doubtful that we can find
any 450 kHz IF filter that will provide a selectivity upgrade to
compare with the phenomenal 455 kHz Murata filters in the fully-modified
E100's. There are some modest 450 kHz filters that Guy has tried in the
DT-200VX (and a 450 kHz DT-400W filter project posted on dxer.ca) that
might at least provide a moderate selectivity boost, in addition to
the presumed massive sensitivity boost provided by slider
loopstick. Without 1 kHz tuning resolution, the fully-modified
DT-400W's will probably not compete seriously with the Monster E100's, but
they should at least be interesting enough to keep fanatical tinkerers from
complaining about the bad TP conditions during the winter doldrums :>)
John, I still have a "Slider-only" E100 here, and
really enjoy using it during domestic DX, and on daytime band scans in
unfamiliar locations. The Slider-only E100 would be a
real blast for domestic DXers, combining great sensitivity with
outstanding audio fidelity. Unless the user is a hard-core transoceanic DX
chaser (or an urban dweller with many troublesome locals), it may well be the
ideal hot-rodded Ultralight.
73, Gary
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John H. Bryant <bjohnorcas@...>
Excellent report, Gary!
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I was just going to write to you suggesting that, after you complete the 2009 Winter Shootout, you try the Slider mod on a DT-400VX. Although the lack of the e100s 1 kHz resolution tuning might inhibit the DT-400 as a transoceanic DX machine, a "Slider 400" might be a superb domestic DX machine, with or maybe even without an IF Filter mod. I've been spending a lot of time domestic DXing in the last three weeks and I'm beginning to conclude that I like the Slider e100 with a stock filter about as well as one with the Murata filter upgrade for domestic DXing. With the Murata filter, it is a must to off-tune one kHz to get the higher audio frequencies so necessary when trying to sort out a domestic furball... the standard filter seems to operate quite well in those circumstances. Of course, when trying for DX between the 9 and 10 kHz. spacing worlds, the Murata remains the ONLY way to go, IMHO. In either case, I look forward to The Maestro trying a "Slider 400" It could be wonderful! John B. At 10:21 PM 12/16/2008 -0500, you wrote: Hello Guys, |
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