[Hallicrafters] SX-122

[Bill Smith]

Dan, it sounds like A1 is grounded inside the set somewhere.  Possibly, a
short jumper was installed by a former owner between one of the antenna
terminals and ground inside the radio.

Receivers with balanced inputs work much better if the antenna fed with coax
is connected to the receiver through a balun.  We can get into a long story
about this (have on other mail lists), but I have used a TV 75-300 ohm
converter.  The two 300-ohm twin-lead lines are connected to the A1, A2
antenna terminals.  The antenna coax is connected to the S-connector (or
whatever the TV coax plug is called) and the shield of the coax is connected
to the receiver ground using a very short wire.

I am making a lot of assumptions here, such as that you have a dipole
antenna on the roof and are feeding the receiver with coaxial cable, and
that the receiver is well grounded (see below).  If you have a random-length
wire, a balun is unnecessary.

Such TV adapters are lossy below about 3.5 MHz, but the receiver is able to
overcome the loss except at the bottom of the AM broadcast band (700 KHz and
lower).  Winding your own balun is easy and better, but as a quick
experiment, you may be interested in the reduction of local noise, broadcast
interference and other noise that even a TV balun has shown.

The test of whether it is connected correctly is to hook it up, connect a
section of coax to the balun, and short the other end (or switch it away
using an antenna switch).  The receiver should fall almost completely
silent, though it may still pick up some local AM broadcast.

This of course presumes all the equipment is well grounded.  Another source
of "antenna" is the power cord.  It may be helpful to install a line filter,
available from Radio Shack (part no. 273-104).   The line cord is just
wrapped around inside the core.  If you are using a random-length wire, the
power cord may in fact be acting as the station ground, and the the line
filter will actually worsen reception.

Of course if you try this, Dan, you'll have to find out where A1 is grounded
in your receiver and remove the connection.

73 de Bill, AB6MT
billsmith at ispwest.com

----- Original Message -----
From: "DAN COTSIRILOS"
Sent: Saturday, September 14, 2002 12:14 PM
Subject: [Hallicrafters] SX-122


I'VE GOT A SX-122 THAT I THOUGHT WAS LOW IN SENSITIVITY BUT IT TURNED OUT
THAT THE A1 AND A2 SEEM TO BE BACKWARDS.  IF THE A2 AND GROUND ARE LOOPED AS
NORMAL THE RADIO HAS VERY LOW SENSITIVITY.  UN-LOOP A2 AND CONNECT THE ANT
TO IT THE SENSITIVITY GOES UP.  HAS ANYONE EVER RUN ACROSS THIS?  IS IT
WIRED BACKWARDS OR IS A COMPONENT CONNECTED TO A1 BAD?  ANY CLUES? DAN
.