QUICK CONSTRUCTION PROJECT

Build An IndoorFM Ante nrra

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, The antenna,ilselt rs of the same n,n6 Iof rod as lh.e le.gs I used co aps,oterepracement anlenna 'O0S whtch areavarlable from most raaro/Tv sJp;tyshops In .act any .neta rod thal canOe wOrKeO InIO Ine COnlgUrat io,rshown wil l serve the same function.The mini.num ength feqJrred how-ever. s 28 inches

The base of the antenna is a sma boroject bo-x-a plastic case.wrlh a nel_ tal COVeL lnese are avarlaole '.orn Ra- ddro Shack Also.equred

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"o"",it f

chassrs connector, type F-61 ano a 6solder lug. :

Yo,r wrll reed a dfl l l to corrptele lnrs HconstrJction Oroject F rst. rrake a role iIn the center of the plast,c p,oied ;box s bo om Screw the antenra rod in Sl

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PARTS LIST i i4 Replacement antenna masls (ea I I

Radro Shack #15-232, t strl avdrt. I Iable, or #270-1405). !

1 Plastic project box with metal cover I(e.g , Radio Shack #270-230 or {#270-231) j

ne of the biggest barriers togood FNy' reception is the lackol a proper antenna. The wire

dipole that comes with most receiversand tuners seldom does the lob, sohere is how to build something with alitt le more gain and greater versati l i ty.Tethered to the tuner by coaxial cable,this antenna can be moved about theroom to l ind the spot for ideal recep-tion, and it can be put neatly out ol theway when not in use.

I have Jound this antenna to bemuch more sensitive than the usualwlre dipole. Perhaps this is due to thefact that it is lree-standing. A wire dl-pole must be fastened to a wall, whichis sure to degrade its performance.The same antenna posltion doesn't al-ways work for different slalions, how-ever, even when they share the sametransmitting antenna. l/oving the an-tenna just a few feet can make a big

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di l terence. Since the antenna de-q.r iha.r hara is c^ Facv'o rrnve

around, you can usually trnd a positronwhere recepl on is good and noise{ree.

Yea's ago all Fl\.4 stalons LSed horr-zontal po arization, which made il nec-essary to use a horizontal antenna forreceptiol in order to avoid a loss insignal strength of 10 to 20 dB Nowrnosl statrons use circular polarzation,which works with both horizontal andverl cal antennas.

The antenna shown here is a vafla-tron on the vertrcal quarter-wave typeUsLal'y lhe ground plane ,s hor,zon-tal, but here the rods that lorrn lheground plane have been polnteddownward This increases theimpedance frorn 50 lo 70 ohms,which is betler suited to FNy'tuners and alows the rods toserve as a trlpod to supportthe antenna s base

AUD O/JULY 1989

1 Chassis-mount F-61 coax connector(e 9., Radio Shack #278-212).

1 75-ohm coaxial cabl€ with F connec-tors, length to suit (e.9., Radio Shack#15-1531. 16 teet: or #15-15.34, 25teet).

1 75/300-ohm balun translormer (e.9.,Radio Shack #15-1253); needed onlyfor tuners without 75-ohm inputs

1 Solder lug; il unavailable use solde.less ring tongue (e.9., Radio Shack#64'3030, #64'3070, or #&-406).

Miscellaneous: Short wlre, 4 washeG(optional)

A cornplete kit of pa(s is available lorapproximately $12 (plus sales tax lorNew York residents) from: Rivera, 184552nd St., Brooklyn, N Y 11204 Suppliesol kits at this price are lirn ted, however,so send a self-addressed stamped en-velope and Rvera wil l advise you ofupdated prices and delivery dales,where neces5ary.

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i

RICHARD J. KAUFMAN

re kind,psible)h ateruPPlYat canra t ion.rction.

small Pa met- g,m Ra- $joaxial

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ance, both lnside and outside lhecase, when selectrng where to dri l lthese holes. Use a punch to "dlmple"the metal betore dri l l ing. This keepsthe dril l bil from walking away lrom thespot you selected and choosing itsown place lor a hole. lf you don't havea punch, you can use a hammer and anail-just be sure to tap l ightly

Now pass the coaxial connectorlhrough lhe 7s-inch hole and secure itwith the nut that came with it. (The nutshouid be on the inside ot the box.)Attach the egs securely. Solder thesho(est possible piece of wrre to thesolder lug on the anlenna rod and tothe solder tab of the coax connector.(Solder assures a secure connectionand prevents corroston from degrad-ing the electrical contact.) Secure thecover with the four screws providedwith the project box.

Exlend each leg to a length of 28lnches and the antenna rod to 27 Inch-

es, as shown In Fig 1 Genfly lorce thelegs apart, bending the melal cover

:llir l^"]"^9: j?ril^o^ut just enoush toP'uvrus d udurv uc5v.

The coax cable should come downto the surlace on whrch lhe anlennarests belore beginning its horizontalrun; thrs prevents interference with theantenna. l l your tuner or receiver has75-ohm rnpuls, use lhem. Otherwrse,you wil l need a balun translormer eventhough rt slightly decfeases srgnalstrength. You may also l ind that minoradjustments to the rods length wtll im-prove perlormance. In general, rl yourrods a low such telescoping, lengthen-ng the rods wil l yield good results onlower numbered stal ons, while shorterrods wril perform belter on the hrghernumbered ones. In my location, onelength-2g inches for the legs, 28 inch-es lor the antenna-works well fof allthe stations I l isten lo A

;te this $a hole !lroject Er rod in =-

(e s.,aval-

covet

Fig. 1 -Canstructrcn diagam.

place, wilh its retaining screw and lhesolder lug inside lhe box. lt helps tobend the solder 1ug before passing thescrew through it, to allow clearance forthe wire that wil l have to be attached.It 's also not a bad rdea to use washerson the screw.

Next, dri l l a hole for the coax con-neclor in the center of the metal cover.You wrll have to make a 7a-inchhole. lt is suggested that youstart wrth a 7s-inch bit, orthereabouts then eniarge ,.the hole to % inch. Nowuse a ys-rnch brt. l1 youdon't have one, rt maybe possrble to enlargethe hole with a rallail i i leWhen lhe hole rs com-pleted, smooth theedges with a l i le.

Next, make threeholes lor lhe legs-one In the centerof a short side, theother two in lhe cor-ners oJ the oppositeside Be sure to al-low sullcrent clear-

rector

nnec-ihack.4.25

(e.s.,J Onry

ie soloeFlio Shack4-406).washers

rilable foru for1845

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7*AUDIO/ JULY 1989