-- A High Performance Indoor SW Antenna
by David Moisan, N1KGH
many shortwave listeners who can't, because of location, infirmity
or a unyielding landlord, put up an outside antenna. Such people
are given two choices--random wire or active antenna. Yet, for
the serious listener, neither choice is completely adequate.
are expensive, apt to generate as much noise as signal, and are
prone to overload. Random wires are cheap (cheapest, in fact)
and easy to put up, but are unpredictable performers. Both subject
the receiver to intermod, spurious signals and other trash.
Loop II is an ideal step upward for the listener who wants something
better than a random wire but doesn't want the expensive dice
roll of an active antenna.
Loop is made up of two components: A tuner, and the antenna cable
itself; the cable can be either 5-conductor rotator cable or 4-conductor
flat phone cable, both readily available from Radio Shack and
elsewhere. The tuner couples the antenna to the radio, forming
a (giant!) L-network. To tune the antenna, you turn a switch for
antenna can give a cheap receiver the sensitivity, selectivity,
or dynamic range it never had, the Carpet Loop will help you get
the last ounce of performance out of your radio.
ago, I was using a random wire. I had severe problems with a local
AM station (2 miles away) on 1230 Khz. I was hearing intermod
from it all over the 9 to 12 Mhz range.
Carpet Loop (which was then just the cable), the interference
was almost completely gone. Also, the signals I was receiving
seemed to be just a little bit stronger. A year later, I built
the tuner, with much better results. I'm convinced I have the
best possible antenna for my location.
stuck in an apartment, if you have a portable like the Sony 2010,
the Sangean 803A or the Radio Shack DX400 or 440, if you have
a tabletop receiver, the Carpet Loop may be for you. It's cheap--around
$25 in parts from Radio Shack, *much* less if you shop around,
and an excellent first project for the technically minded.
Schematics and Parts List
S1 1 pole 6 position ! !
rotary switch ! D1 !
(RS# 275-1386) !---->I----!
C1 365 pf variable ! ! D2 !
capacitor (see ! ! !
text) ! o o !
S2 SPST switch ! \ !
(RS#275-406) --- S2 \ --- C1
D1, D2 1N914 silicon ||| o ---
switching diodes (Earth ! !
(RS# 276-1122) Gnd.) ! !
J1, J2 6-position terminal ! !
strip (RS#274-659 or +G-o<----o----+
Antenna cable: ! o S1 o
! !E !A
5-conductor rotator J1 ! ! o o ! J2
cable (RS#15-1201) ! ! !D o !B !
(see text) 1 |o|----* ! ! !C ! !
2 |o|-------*--!--!--!--!-----|o| 6
Miscellaneous: 3 |o|----------*--!--!--!-----|o| 7
4 |o|-------------*--!--!-----|o| 8
Aluminum enclosure, 5 |o|----------------*--!-----|o| 9
spade lugs, connector |o| (not used) *-----|o| 10
and cable to radio (not used)|o|
(see text), knobs
-*- means: Intersecting wires are connected
-!- means: Intersecting wires NOT connected
Carpet Loop Works
S1, C1, and
the antenna cable connected to J1 and J2 form an L-network; when
S1 is switched between positions A through F, and C1's capacitance
is varied, the impedance of the antenna system changes. When S1
and C1 are adjusted for best signal, the impedance between antenna
and receiver is matched. D1 and D2 provide protection against
static discharges. The G position of S1 grounds the antenna when
not in use. S2 disconnects the ground from the antenna, making
the antenna into a random wire.
exception of C1, all parts for the tuner are readily available
from Radio Shack. C1, the 365 pf variable capacitor, can be gotten
out of an old radio.
no critical parts in the tuner; as long as S1 has at least six
positions, it will do. D1 and D2 can be any silicon diode. Use
any enclosure that's big enough to comfortably install components
for J3, the jack to the receiver, depends on what connector your
radio uses for an external antenna. I used an SO-239 (RS #278-201);
you could also use a TV antenna terminal strip (RS#274-663).
the components on the enclosure you'll be using--all wiring
is point to point. I suggest mounting J1 and J2 on opposite
sides, S1 and C1 on top, and J3 on the other end of the enclosure.
- Wire S1
to J1 and J2. If you use the Radio Shack DP6T rotary switch,
you'll be using just one of the poles. The diagram of the switch
S1 DP6T rotary E o o B
switch G o o A
| o o |
Viewing from P |o o|
bottom of switch | o o |
If you're using the Radio Shack terminal strip, you will need
to drill a hole in the cabinet to pass the wires through from
inside. Use a rubber grommet to keep the wires from chafing
S1 Term. --to--> J1 term. J1 term. --to--> J2 term.
A #1 #2 #6
B #2 #3 #7
C #3 #4 #8
D #4 #5 #9
a wire from J2 terminal #10 to the G terminal on S1, and this
step is done.
and wire C1. Connect one terminal of C1 to the P terminal on
S1. Connect the other end to J3. If using the SO239 or phono
jack, connect to the center conductor. If using screw terminals,
connect to terminal #1 on J3. Skip ahead to step 5.
the P terminal of S1 to J3. If you're using the SO239 or phono
jack, connect to the center conductor. If you're using screw
terminals, connect to terminal #1 on J3.
the G terminal on S1 to J3. Connect it to the ground shield
if it's an SO239 or phono jack, or to terminal #2 if it's screw
D1 and D2 across J3's terminals; remember that D2 is connected
opposite of D1.
construction of the tuner.
of cable you use depends on where you're putting it and how much
you want to pay for the cable.
If you plan
on running it under carpet, then use the 5-conductor rotator cable
mentioned in the parts list. This cable can easily withstand being
stepped on; more importantly, there are no exposed wires to trip
over. It's also easier to wire than phone cable.
not running it underfoot, or if you're cheap, you can use 4-conductor
flat phone cable, available just about everywhere. It's a good
choice for running around baseboards, around windows or in attics.
the cable around, start at your receiver and go around the room--or
the house--and back to the radio. If you're using the rotator
cable, you can make corners by folding the cable at a 45 degree
angle, like folding paper.
cable to the tuner
have two ends of the cable next to the tuner. Strip the ends and
put spade lugs on all the wires. With the rotator cable, mark
the *silver* conductor.
the wire to the tuner using the following diagrams:
FOR 5-CONDUCTOR ROTATOR CABLE FOR 4-CONDUCTOR PHONE CABLE
J1 J2 J1 J2
1 2 3 4 5 6 7 8 9 0 1 2 3 4_5 6 7 8 9_0
^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
Wire S C C C C S C C C C B Y R G B Y R G
(4&5 jumpered) (9&10 jumpered)
((S)ilver, (C)opper, (B)lack, (Y)ellow, (R)ed, (G)reen)
Run a wire--preferably
a large one--from the ground terminal on the tuner (or a mounting
screw on the SO239 connector if you're using one) to a suitable
ground such as a cold water pipe; I grounded my tuner with a short
length of RG58 coax connected to a baseboard heater via an alligator
tuner to your receiver; you're now ready to use it.
to use than to talk about: Tune your receiver to the desired frequency.
Adjust S1 and C1 (or the antenna trimmer on the radio) for strongest
signal. For most situations, S2 (Loop/Longwire) can be left closed
in the Loop position; you may find that setting S2 to Longwire
may work better for mediumwave listening.
Loop II is an inexpensive, easily built, high performance antenna
that can work in almost all apartments.
I can be
reached at the following addresses:Mail:
86 Essex St. Apt. #204
Salem, MA 01970-5225
Let me know
how the Carpet Loop works for you!
© 1996, David Moisan
Last Updated on April 20th, 1996