Using external antenna with Sony ICF-SW7600G

[sb196...@yahoo.com]

Few days ago I posted several messages asking questions about using an
external antenna with the SOny ICF-SW7600G receiver. I received many
answers, most of them helpfull, some confusing - specially the ones I
received from Sony Service department (thanks to all the people who took
their time to read and answer my notes).

I am posting this message to all the SWL friends who might be interested
in using their 7600G with an external antenna and might have similar
doubts as mine.

I finally got my service manual for the 7600G. I looked up the
schematics and things are as follows:

1.- The ext. antenna socket is "hot", i.e. powered through a 470 ohm
resistence + 100 uH coil. This means that it will deliver approx. 10 mA
DC current to the external antenna circuit. The coil is to prevent
"polluting" the power circuit of the radio with radio frequency signal.
Evidently, the purpose of this arrangement is to "inform" the accessory
antenna when the radio is turned on. In case of the Sony AN-LP1 it
turns on the antenna without need to use the antenna power switch.
However, the 7600G will NOT power the antenna, the 10 mA are not enough
to power the amplifier circuit. The power for the AN-LP1 comes from its
own batteries. You can use this feature with any active antenna by
including a proper power-up circuit - a nice feature if your active
antenna is located far away from the radio and you want it to turn on
and off automatically when you use your radio.

2.- You can connect any other antenna (provided it is correctly designed
and installed) to the EXT ANT socket without risking to damage the
radio. However, if the external antenna circuit has low DC resistence,
it will drain some current from the radio. Therefore, you will
experiment slightly higher power consumption from your batteries (up to
10% at normal listening volume). You can avoid this current drain by
including a small ceramic capacitor (1000 pF) in series with the antenna
circuit, however I don't think it is really necessary.

3.- The 7600G has some basic protection build into the EXT ANT input
circuit. Any static buid-up will be drained off via the power circuit
mentioned in point 1. It also includes a diode pair (1SS123) to protect
the input RF amplifier FET from damage due to too strong signals or an
accidental connection of the antenna to a low voltage AC source. IT IS
NOT A SUBSTITUTE FOR A PROPER ANTENNA GROUNDING AND LIGHTNING PROTECTION
IF YOU USE AN EXTERNAL ANTENNA - YOU STILL NEED TO PROPERLY GROUND YOUR
EXTERNAL ANTENNA AND PROTECT YOUR RADIO, but it builds some margin of
safety to protect the front-end FET - a common problem with the Sony
2001D (2010).

Finally, I tried my 7600G with my brand new RF Systems EMF antenna and
AA-1 adapter. I replaced the aligator clip and the "special" ground
connector with a 1/8" minijack to directly connect the AA-1 to the EXT
ANT socket of the 7600G. The results are rather positive - I have been
able to pick-up some stations that were too weak to be understandable
with the whip or the standard accessory reel antenna. The noise level
(my main problem at my house) was still high - higher than with the
whip, but I only tried the antenna indoors, so I still hope this problem
will decrease when I hang the antenna outside. The build in attenuator
that comes with the AA-1 is a nice feature. I used it quite effectively
to attenuate the signal to a level that still produced understandable
reception, but cutting most of the noise. The EMF did not seem to
create any overloading problems for the 7600G even with some very strong
stations, and the signal-to-noise ratio was definitely much better than
with the whip or the reel antenna. Combined with the synchronous
detection of the 7600G, it was very effective to improve reception of
weak stations that are only 5 kHz apart from a powerfull transmitter.
To note, although the EMF is claimed to be effective from 100 kHz to 30
Mhz, with the 7600G it only works well for SW, the LW and MW reception
was very poor, much worse than with the build in ferrite bar antenna.
Net, I am quite please with the performance of my combination of the RF
Systems EMF antenna + AA-1 adaptor + Sony ICF-SW7600G. I replaced the
aligator clip and the "special" ground connector with a 1/8" minijack to
directly connect the AA-1 to the EXT ANT socket of the 7600G.

I hope other Sony ICF-SW7600G will find this info helpfull and
interesting. Please, don't hesitate to contact me if you have any
questions or comments.