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Pages from 02 February 1993 .pdf


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Number 5 on your Feedback eerd

The 23-Foot Indoor Antenna
Make an effective 20 and 80 meter apartment-dweller antenna.
by Richard Q. Marris G2BZQ

R

elocating into an apartment for the first
time can have a very traumat ic effect .
This. o f course. al so applies to any othe r
habitation where an HF outdoor ant enna is
no t permitted or is physically imposs ible to
erect.
This first happen ed to me (licensed for
too many years to remem ber how many)
when, ov er 30 years ago, new employment
mea nt moving the QTI{ at regular intervals,
and turned me in to an apartment d weller.
S ince then I've tried and evolved man y
apartment anten na type s, including loops
and hclicals.
~I)·

Solution

With j ust 23 feet o f wire across a room, it
is possible to quick ly gel onto 20 and 80 meters in a minim um of time and at m inim um
cost.
In each successive Q11I move . the good
old 23 feet of wire has al wa ys been used
fir st, to get G 2BZQ back o n the air again
within a few hours of taking up the new residence.
Figure 1 shows the 20 meter version, and
Figure 2 that for 80 meters. Note that the
same 23 feet of wire (A-B) is used for both
bands. Assuming that your transceiver can
be placed in the comer of a room, A-B will
consist o f a drop down of about fou r feet to
you r rig, and the remaining 19 feet will be
h ung ho ri zon ta ll y d iagonally ac ross the
room, at leas t 9" be low the cei ling. Wh ite
PVC covered stra nded hookup w ire (#22
gauge-Radio Shack #278-1218) should be
used as it is incons picuous ag ainst a white
ceiling. It should be supported by nylon fishing line which is also inconspicuous.
This antenna sho uld be kept away from
electrical wiring, water pipes. etc. Terminate
with a small plastic ring at point B, leaving
about 2" of bare wire han ging down. Support the plastic rin g to the room comer with
10 lbs. breaking strai n ny lon fishing line. At
the other comer of the room , support the
wire to that comer with fishing line. leaving
a drop down at A (about four feet), which is
near the transceiver. This is the 23-foot antenna!

For 20 Meters
Sec Fig ure I . As an antenna wire is incre as ed in length above 1/4 wavelength
long. the term inal impedance increases to a
16 73 Amateur Radio Today . February. 1993

·- ;;;;;,;,-,;,; 9------------~T• · -------A 10 B

lenirItl •

,.....

23 ,...

Wi,. End

A

e . eOp F

,K( ~jJ SICT 1a so 23.

............

To TXl ATU ~".

-

L

(See Ted)

Figure J. A 23{001 indoor amennafor 20 meters: Ja ) 20 meter alltellllQ; Ib ) 20 meter helical
ground.
point where the impedance reaches 50 ohms.
Unfo rtuna tely, at the same time the reactance has also increased, but can be tuned
out with a series capacitor (C in Figure la).
This variable capacitor s ho uld be a good
quality ceramic type. of equivalent size to
that in your transmitter's PA. II should be
mounted in a plastic box with a large diameter plastic ins trument knob. Coaxial socket
SKTl can be connec ted to a 50-ohm out put having a pi network output, using a short
leng th o f RG58 feedl ine. Better still . an
exi st in g 20 meter ante nna tu ne r ( AT U)
can be inserted between SKT I and the rig.
This will help elim inate TVI.

For 80 Mei ers
Figure 2 shows that the same 23 feet of
wire is used for 80 meters. with the add ition
of a vertical end hel ical coil L2 which, in
fact , is a combined loading coil and radiating
element added to the end of the 23-fool wire
(A · B).
Using 22' 6" of the same PVC covered
wire, wind 21 feet helically on a 112" diameter wood dowel or plastic tube. spacing the
turns over a width o f 3' 8". A tail of IS" will
be left at the top end and, filled with a strong
cli p, it can be attached to the m ain an tenna
wire at point B. It will be necessary to fit a
suitable wood base to hold L2 ve rtically.

. . . _ ... _FiIIl'Iing

u..

,.+

·• -. -. --. . . ---- _. -.._- -.,•
, I ' " ..


c._
,:(
L1

T... >-~
"
! I:

A

' L1.1._"'1'~

~1C1 so

•-- - - . .. - -- .. . --- .. . --.•

, ........_

I •

t(L'.

....... -.and 011

".11Z· ............

:r.J9

-J:.

L2 .'l_oln_lPO
inau"--al"'- hook... p
wi .., \OOu.... on. lIZ' 00_.
.... nly .pooc:ed owe, "."

Aru
C. SKT)
'" - . . Bo_

.

FIgure 2. The I ndoor 80 m eter

p_. ~u;,;

'
",
+

AI0 8~ . Z3_

,



QlIlelUlQ.

The 23·Foot Indoor Antenna

FEEDBACK
In our continuing effort to present the
best in amateur radio features and
columns, we recognize the need to go direeuy to the source-you, the reader. Arti·
c1e s and columns are assigned fee dback
numbers , which appear on each arti clel
column and are also listed here. Th ese
numbers correspond to those on the feed-

back card opposide this page . On the
card, please check the box which horIestty represents your opinion of each article
or column.
Do we really rea d the feedback cards?
You betl The results are tabulated each
month, and the editors take a good . hard
look at what you do and don't like . To
show our appreciation, we draw one feedback ca rd each mo nth and award the
lucky winner a free one-year su bscription
(or extension) to 73.
To save on postage, why nollill out the
Product Report card an d the Fee dback

card and put them in an envelope? Toss
in a damning or praising letter to the etli·
lor whi le you're at it. You can eios enter
your aSL in our aSL of the Month contest All for the low, low price of 29 cents!

1 Never Say Die
2 Letters
3 QRX
4 Fun a t 10.000 MHz
5 The 23-Foot Indoor Antenna
6 Accurate Low Cost VSWR Meter
7 An Effective 160 Mete r Antenna
8 The "Simplest Transverter"
9 Build the Tone Processor
10 Review: The Dow n
East Microwave WSSK
11 Updates
12 Ha msats
13 Review: The GAP Voyager
DX· IV Vertical
14 Carr's Comer
15 Homing In
16 ATV
17 Hams with C las s
18 QRP
19 RTTY Loop
20 Ne w P rod ucts
21 P a c ke t & Computers
22 Ask Kaboom
23 Special Events
25 73 Inte rna tio na l
26 Deale r Directo ry
27 Above and Be yo nd
28 Ba rte r 'n' Buy
29 Random O utput
30 Propagation
31 Ham He lp

OLL ELECTROniCS CORP.

Continued f rom page 16

Mall Ordel" Electr onic: Perte A nd Suppll••

P.O.
At the transm itter end of the antenna wire.
a simp le LC ATU m atche s the antenna to
your rig. The ATU sho uld be built into a
metal box. L1 consist s o f 14 close-wound
turns o f l 8 -g auge e n am e l coppe r wi re ,
wound on a 1.2" diameter pvC form . L1
should be m our ned in the metal box with at
least a coil di ameter of clearance away from
meta l work. C I should be a good quality
vari able capaci to r of 300 pF c apaci ty, o r
even 500 pF.
The simple ATU consists of L1 + C +
SKTI. in a metal box. However. an existing
good LC. 'T' or other ATU, could be used
in place of the one shown.
Wire length A-B. plus the vertical helical
section L2. fonn the radiating anten na. L2
should be mounted vertically and fitted with
a wood base to support it-it sho uld be at
least 15" clear of walls. etc.
Ground Syste ms tor 20 and 80 Meiers
Ground connections are an ongoing problem with the indoor antenna. If there is a
metal water p ipe cl o se to the T X , then a
short wire stout flex can be cl ipped to it to
form a grou nd. Do not connect to a pl astic
water p ipe . g as p ip e s or e lectric wiring
co ndu it. On 20 m eters. the co n nec ting
lead sho uld not e xceed about six feet, an d
on 80 me ters up to 15/20 feet sho uld be
satisfactory.
Figure lb shows an artific ial ground for
20 meters. It cons ists of 36 fee t of PVC covered stranded wire (Radio Shack #278- 12 18)
helically wound around a six-foot length o f
5/ 8" d iameter do we l of p la st ic p ipe. The
turns should be spaced to fill a length of 5'5"
on the dowel. The en ds o f the winding can
be secured with tape. The connecting lead
sho uld be fo ur fee t lo ng . Th c a rti fic ia l
ground should not be laid on the floor, but
provided with supports at least 24" high and
mounted horizontally. Vari ou s positions relative 10 the anten na should be tried for the
best results.
I developed an excellent artificial ground
for 20/80 meters when living in M inneapolis
in the 19705. The operating positio n wa s
nc ar a very large metal-framed d oubleglazed win dow. A short ground lead was
clipped to the m etal wi ndow fra me and
proved to be most effective on both 20 and
80 meters. I have since tried this idea at other locations. No do ub t it fa nned a ve rtical
ground piane.
Concl usion
Thi s s im p le 23-foot antenna g ives an
apartment dweller a quick and effective way
of working on the 20 and 80 me ter ban ds. Of
course, the high er the antenna the better the
results. I have worked OX on 20 meters using both 10 and I()() watts CWo and up to
about 3,(X)() mil es on 80 meters. However. in
the in tere st s of d omestic safety and TVI
e1imimation, a low power TX is suggested.
no more than 20 watts.

iii

Box 567· Van Nuys. CA 91408
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CIRCLE 194 ON READER SERVICE CARD

73 Amateur Radio Today· Fe brua ry, 1993 17


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