Re: Building a MW Model D 554 uh 7.5" Loopstick with 100/44 Litz Wire Questions

Gary DeBock

Hi Jerry,

Thanks for your question about 7.5" loopstick coil inductances.

The 554 uh loopstick coil inductance called for in the "Supercharging"
article is a value which will give excellent performance on MW, and
also a healthy boost on LW frequencies when used with a 7.5" Type 61
ferrite bar from Amidon. Before Rob Ross received his 7.5" Longwave
loopstick PL-380 he used one of these 554 uh coil 7.5" MW loopstick
PL-380 models to log about 80 NDB beacons on Longwave, even though the
model was designed for the MW frequencies. In response to various
"discussions" on the Ultralightdx list about 18 months ago concerning
loopstick coil inductances and coil orientations for Si4734 DSP chip
models I constructed four different 7.5" loopstick PL-380 models with
varying coil inductances and coil orientations, and tested them
extensively with both signal generator and live signal inputs. The
results are posted at , and
provide detailed answers to a couple of your questions (regarding any
difference between center-wound and offset coils, and acceptable coil
inductances for the Si4734 DSP chip's tracking across the MW frequency

Since I've never designed a Type 33 ferrite bar-based loopstick to work
on the MW frequencies (they are usually preferred for Longwave
frequencies), it's kind of tough to recommend how many turns of 100/44
Litz wire should be placed on the bar for best MW operation. One time
Amidon shipped me several Type 33 ferrite bars by mistake after I
placed an order for Type 61 bars, and a bizarre loopstick using a 7.5"
Type 33 bar was accidentally constructed here with a 40/44 Litz wire
coil designed for the MW frequencies (about 500 uh). In testing, the
loopstick worked fine up to about 1000 kHz, but was a real dud on the
X-band (1600-1700 kHz), which let me know that something was seriously
wrong. The Type 33 ferrite bars are highly anemic on X band
frequencies, an issue that you probably won't be able to solve by
simply adjusting the loopstick coil inductance.

73, Gary DeBock

-----Original Message-----
From: jerry_popiel <jerry_popiel@...>
To: ultralightdx <ultralightdx@...>
Sent: Wed, Sep 7, 2011 10:53 pm
Subject: [ultralightdx] Building a MW Model D 554 uh 7.5" Loopstick
with 100/44 Litz Wire Questions

This is a question likely for Gary DeBock.

Gary, in your Dec 2009 writeup: "Supercharging the Tecsun PL-380
Portable", you stated that for best MW Reception on a 7.5" type 61
Ferrite Rod you wound 81 Turns of 40/44 Litz Wire to get an Inductance
Value of 554 uh, for optimized MW results.

In a recent memo you mentioned that with a type 33 Amidon 7.5" Ferrite
Rod you estimated that approx 50 turns of 100/44 wire would work for
good MW reception. Would the same 50 Turns of 100/44 Litz Wire also
apply for a type 61 Ferrite Rod? If more than 50 Turns were wound ie
say 60 - 70 turns of 100/44 Litz, would this also add some LW
capability to that Loopstick? Lastly should the wire be wound as an
Offset Coil rather than a Center - Wound Loopstick?


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