Re: Matching transformer for PL-380

Gary DeBock

Hi Michael, Hans, John, N3IKQ and all,
It's true that the Si4734 DSP chip in the PL-380 can adjust to a fairly wide range of loopstick coil impedances (nominally 150-450 uH), but the stock PL-380 loopstick (usually around 300 uH) is designed only for acceptable MW band coverage, and is nowhere near the optimal inductance for the Longwave frequencies (experimentally proven to be around 1700 uH, in the exhaustive experimentation described in the attached file). A DXer who wants excellent performance on both bands with a 7.5" loopstick faces a tough choice... either build two hot-rodded PL-380 models (one with a Medium Wave loopstick and one with a Longwave loopstick), or mount a plug-in socket on the PL-380 to switch between the two 7.5" loopsticks. The second approach would probably be a mechanical nightmare for many experimenters, but such a PL-380 model was built here in 2010 to accept the PL-360 7.5" plug-in loopsticks (photo attached).
73, Gary DeBock (in Puyallup, WA, USA)

-----Original Message-----
From: Michael
To: ultralightdx
Sent: Fri, Nov 8, 2013 1:07 pm
Subject: Re: [ultralightdx] RE: RE: Matching transformer for PL-380


----- Original Message ----- From: n3ikq

There is no external antenna input on the PL-380. The DSP chip needs
an inductor for AM/LW and a whip/wire for SW. The details are in
the documentation at Silicone Labs website.


I carefully (!) soldered a LW coil on a longer ferrite rod with
parallel tuning capacitor in lieu of the internal ferrite antenna.

The internal and external tuning capacity co-existed, with
the internal self-adjusting to optimise the total capacitance.
Without the additional external variable capacitor, the
internal capacitance auto-range was not sufficient for
the whole LW band as the inductance did not match
the automatic tuning facility as well as the internal
ferrite winding designed for the purpose, but which
is optimised for 540-1600kHz and less effective on LW.

I used the same external L/C adjacent to the
internal L/C with comparable results. This is doubtless
the safer approach. The hard-wired version produced
better S/N, so would be warranted for optimal performance,
as in Gary's latest posting (We avidly await part 2!)


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