Re: The SRF-39FP Slider loopstick-- Optimism Slides Away

John H. Bryant <bjohnorcas@...>

Excellent report, Gary!

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,
     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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