Sony ICF-SW100 External Antenna?
Brian
I was wondering if anyone has been able to add a longwire antenna
using the active antenna jack? My AN-100 is broke (whip pulled
totally out) and I see in the manual there is 3Vdc at that jack. Is it
at the tip or sleeve?
Thanks for any help!
Brian
John Doty
<tony...@hotmail.com> wrote:
From: j...@space.mit.edu (John Doty)
Subject: Passive antenna for ICF-SW100
Date: 1998/01/17
Message-ID: <69r8j1$s...@senator-bedfellow.MIT.EDU>#1/1
Organization: MIT Center for Space Research
Reply-To: j...@space.mit.edu
Newsgroups: rec.radio.shortwave
Originator: jpd@benz
Design and initial testing of an improved antenna for the ICF-SW100
I've occasionally posted plans for a passive dipole antenna for
the Sony ICF-SW100. I originally built it as a "comparison standard"
to see how well the AN-100 active antenna performed. However,
repeated field comparisons between the AN-100 and my passive dipole
demonstrated that the passive antenna always yielded signal quality
at least as good as, and often significantly better than, the
AN-100. I therefore quit carrying the AN-100 on my travels.
Last year, my SW100 suffered the infamous flexible PC board failure,
so I bought the service manual to find out how to repair it (and
successfully performed the repair). The service manual has a
schematic in it, and from reading that I learned more about the
antenna input, allowing me to improve (I think) the passive antenna
design.
The AN-100 active antenna has a two conductor ("mono") phone plug
as its signal output, but the ICF-SW100 with which it is supplied
has a three conductor ("stereo") jack! Very strange. Looking at
the schematic, the extra connection goes to a 220 ohm
resistor (R47), which is connected to the input of the high impedance
RF amplifier. Plugging the AN-100 into the SW100 connects this
resistor to ground. This apparently functions as termination for
the long AN-100 cable. Here's a bit of the schematic from the
service manual:
C35 C1
Tip >-----||-------||----> to RF amp
| | | |
) D1 V - \
( - ^ /
L10 ) | | \ R47
( GROUND /
| \
B+ |
Mid >------------------
In theory, for a short dipole antenna, the termination resistance
causes a significant loss of signal. I therefore built a new version
of the dipole antenna with the termination open circuited:
10' (3 m) "antenna" 1500 pF (Mini stereo phone plug)
Alligator clip >-------------------------||------> Center conductor
No Connection --> Middle conductor
10' (3 m) "ground"
Alligator clip >---------------------------------> Outer conductor
My previous version had protection diodes built in, but I've left
them out now that I know the SW100 has them internally. The capacitor
is needed to block the power that the SW-100 sends out to operate
the AN-100. The capacitor value isn't critical: anything more than
100 pF should work fine. The alligator clips are there so you can
try available conductors as antenna or ground (sometimes this
helps).
Tests:
In tests in my house, the new passive antenna definitely picked up
more signal than the old version, as judged by the ability of faint
signals to turn on the tuning indicator. Signal to noise improvement
was slight, but my house is relatively noisy, and I often find
quieter listening environments when I travel. I have not yet had
a chance to take the new version on the road. The main hazard of
improving the signal transfer like this is overload, but if that
turns out to be a problem, I expect I can just reduce the signal
by keeping part of the antenna rolled up. In a quiet location
without strong signals, the improved signal transfer should help.
--
John Doty "You can't confuse me, that's my job."
j...@space.mit.edu
--
| John Doty "You can't confuse me, that's my job."
| Home: j...@w-d.org
| Work: j...@space.mit.edu
snow
the SW-100s. I use it and get good results.
Universal Radio sells the reel antenna for about 13 bucks. I love the
SW-100s , a mighty fine radio that outperforms many bigger ones Im have had
plus it is sensitive enough to pull in my favorite FM station while
walking...other small radios have not pulled in far away FM as well for me.
Brian <tony...@hotmail.com> wrote in message
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