valentine

VOLUME 17 NO. 2 FEBRUARY 1987

MAIL STOP

Je t Propulsion Laboratory W6VXO Calling MJS 264-419 Eileen McKinney - Editor 4 8 0 0 Oak Grove Drive Pasadena, California 91109

PRESIDENT: Carl de S i l v e i r a KGGM: VICE PRES: Walt Mushagian KGDNS SECRETARY: S i d Johnson WB6VWH TREASURER: Richard McKinney KA6DAN TRUSTEE: Jay HolXaday W6EJJ EDITOR: E i l e e n McKinney KAGDGV

m PROWSB -1OEJ OF 220-222 MHz m AMATEVR SERVICE !

The £ 0 1 1 ~ mssage was received frcen mR,L Wdquarters on February 1 2 . I wanted d u b meYnbers to h o w a h u t it WAF. We need to formdate a Club llespnse, and I s w n-0.n~ of you will want to fi le individml oomnaerrts as well. I w i l l mke mpies of the full NPRM available as s m n as I receive a copy. DE JAY, WGEJJ

Club Meetinqs: Second Wednesday of the month at 12 Noon in 238-543. Everyone is - - - - - - - - welcome - Bring your lunch!

Board Meetinas: Fourth Wednesdav o f t h e month a t (m Dave Smmer, n Z Z , at ARRL Headquarters)

12 Noon in 2 38-54 3. Everyone is FCC has a N~~~ D.oposed me Making welcome - Bring your lunch! proposing to delete the & M ~ U T Sezvioe allmation

a t 220-222 MHz and to make the mhjng allocation Repeater Mtgs: First Thursday of the month at of 222-225 MHz exclusively amteur. The 220-222 MHz

1 2 Noon i n 301-271 . Everyone is hw wwld be -ll-ted to the Land mile welcome - Bring your Lunch? Service under the FCC elm. FCC says it klieves

Newsletter Articles Deadline:

The 7th. day o f each month. If t h e 7 t h . falls on a weekend, the fo l lowing Monday w i l l be the d e a d l i n e . Your articles, ads, photos, diagrams, i n s t r u c t i o n s , o r a r t i c l e s you'd l i k e t o see reprinted from other sources (with the name of the publication, date, etc.) should be submitted t o the above address.

the reallmation ilwould have minim1 impact on mmwt amatew operators and would pmvide much-n& spckm for land mobile operati-. M e r , i n view of +.he current light loadirag of the 220-225 MHz band, and the availability of other amateur bands, it appears that the future needs of the amateur service will continue to be satisfied. We anticipate that this proposed action w i l l have little eoormdc hp~& on amateur operators since mtwx equipmerrt operating in the 220-222 MEIz band could b Mified a t minim1 m e to operate in the 222- 225 MHz portion of the -m."

Permission is granted to copy enclosed a r t i c l e s providing credit is given to i1W6VI0 Callingi'. C a m s i t deadline is April 6 , w i t h replias due April

PAGE 2 W6VIO CF

This ar t ic le s h d d have been written a m n t h ago, but due to termirsal laziness I just got ~ny act together.

Farticiptim Sn the Raze m d e thls yaar was a first for me. In fact, havirrg lived in the L.A. area s h 1955 it was the first t h e I. have ever been to the Parade. This year, llmever, Ffifi Smith, WB6LQP, si5,ned me up as an ATV p x t i c i p n t befare I realized what I was getting inta. A mtomycle mobile omera mii t yet!

'Wha.t do I have to do"? I aslted Phil. "Oh it's shpleil he said. "You just cruise up arad dmn Colorado Blvd on the bike, turn the camera cn an3 off when tiim. ~ou'll love itnt! More a k u t my loving it later.

In add2tim to my novim trial by fire, 21 exper- ienced AW- prticipa- this p. Qmera 1, located at Celorado and Orange G m , was manned by Don brkm N 6 D P and Bob m n e N6AZV. Cu;dra 2, was h the grarad stands on Colorado Blvd Courtesy of Dick H m l h W 6 A W and Fd Mqer n6lX-G. Caxm?ra 4 (trhere was no camera 3) at Colorado ard Fasadens. consisted of Hank Majid K 6 W T and Dennis Smi1-h K46GSE. Camera 5 at Colorado an3 Fair Oaks was run

AlA l l F&tetti$one KAGWMS aHd John W a l k e r Camera 6, at Colorado an3 W i d m s staffed by Mqo Amas KG46Q;D xd Ernie W i l l i a m WBAP. Mike Collis W A W took care of 7 by hj~rrself, on the rwf of the TUCO bldg. Camr.a 8 , was run by Terry Flach W6W, and M Jones N6KCB who w e r e lcateci at Colorado a rd M o l h . Cmnera 9, was a family affair a t Sip- Madre ad. Colorado. Participting m e Jerry 1- KMAQil, W e n e Layton WFE, and G a y layton WBGWV. Carera 10 was operated by qrm maim rnm~ arad J O ~

Shackley M6WS locate3 at Sierra Madre and the 210 frwy. Mobile 1, and 2 were left to the mcytorcycle crazies, Sid Johnsrrn WSWTI, and Mark Fisher WB7PJC. Besides the cmwa ~ l e , Pave Steinfeld m6ZVE held d m the M i a room at mummmt H o u s e , and Fhil Smith W L Q P acted as net conh-01 from the ocrrmMlad center at Orage G m v e and Arkor.

link-ups were h l v e d . Voioe was easy, on 2 meter FM thmt@ the Pacific Telephorte - t e r , w m located on top of the TELCO bldg in Pasadena. Videa, on the a e r hard, is mllsiderably more demanding for a quality picture. The freguen- cies used don't leap tall building a t a single b o d , and ref lect of f of all kjnds of things. 7% overoorne these pwblems, a 434 MHz input- 1265 MHz mtput repeater was set up on the TELCU bldg as a video receiver/&tter for the camera positions. It put out 2 wat ts into an d antenna w h i c h was monitored from as far away as orange Courrty. MRRA cammand Cen*,& CXWRT (&hd law enforcemat), wz-e located behind buildings and such Mich neaessitated two remotes to beam the siqmls around solid objects. Both rebmdcast the 1265 MHz s i w on 10.25 Wz. One to KURT a t he Pasadena civic center, arad one to Tournament House on 0- Grove. A t Tournmmt Kouse the video signal was distributed via coax cable to the media room, FM audio communicatim cater, and the carcrmard trailer. The ccaraMnd center, and CCsllRT were also t ied tmjether by packet radio. Wt of the A W e q u i p m t was hilt and installed by m i e W ~ l l w , WW. It was an -sive set up and worked flawlessly.

Holding d m a camera position i sn ' t as easy as it sourads. Wcblems dwelop, most of which are either crowd or p1ic.e r e l a t d . The base stations fare well usually, but this year camerrl I0 had a problem with a police hdioopter which decided camera 10's r m p r a n d a r r t e r v r a s e t u p w a s m t ~ t o b e there. He hovered overhead issuing, orders through his bullhorn for caiwra 10 to leave innr~liately. After some frantic 2 meter cammications camera 10 was spared ban-t. 7% creepy p2DJ camerzl guys, have a RR problem. People who have been s l e e p k ~ on trhe sidewalk a11 night get upset when camra crews slim up at 6:00 AM, and set up their stat im right h front of every one. It takes some fast talkinq to get pxple to a* you, and a little pushing and shoving got mixed in w i t h the tdl- at one lmation this year. The mobiles have different problems. N e g o t i a t i n g the parade mte is tricky. Getting past the bands is the worst as thew is little cleararm bstween band ad cm&. If your timing isn't perfect you get whacked in the head by a baton twirler or a flag pole swbger. Floats are not always s f e either. Iast year an ann waiving clown float caught M k Fisher by surprise, and tore me m t m off of h i s motorcycle. T h m are rmmds too! Shaking harads w i t h Emwt Borgnjne dur- a parade jam up, going the wrong way on a one way s m t ( G m ) w i t h the oops blessing, talking w i t h f e l l o w Ham along the mute, and sending l i ve video of problems, as they develop, to the parade officials.

It was a I q h u s t h q day. X got home in tb to wat& the last: 5 minutes of the Rose -1 game. Being mrn in Arizona, I loved all 5 minutes- tmgh luck fichigan fans.

Anybody own a mtorcyde who w d d like to j o k ~ IIE ~ y e a r ? ~ k m a ~ m t h e $ a c k a n d I s u r e m ~ l d

Jim tongthori~e WAbKPlJ sent th is T-5a-r a l o n g Prom "Tech

Talk". Thanks f A brisk wunterclockwise rotation

Bill Detwiler, President aJHelpr Imtrunenls, has sent B c W k the follnwirrg helpful hint

Have you ever been f a d with a repeatex that made all the mobiles sound as if they were calling in from a verl; fringe m a ? Except for those almost under the tower, all the re- peated mobile signals had a noisy background? Yet, the total reception range of the repeater receiver seemed to be normal. Distant rnw biles came through OK, but noisy. Why the noise on the mobiles at ranges that should have been heard wthout any noise?

Tn this case, the audio lwel had been set too high at same point ahead of the transmitter modulation limikr. Although the limiter kept the repeater's peak mdulation from exceeding the pmper values, there was no limiting between the sylla- bles d speech. The small amount of noise on normal incornlng signals came right through-way out of pro. portion to the speech signal and, therefore, terribly obvious to the ear.

of the audio level cmtml preceding the modulation limiter should clear things up. 'Ebo much countercIock- wise rotation, hmwer, and the p m per amount of speech clipping will not occur: the effective loudness of the speech will then suffcr.

If the techn~cian who set up the repeater had used a modulation den- sity meter to adjust the levels into the limiters, the problem would never have occurred. Modulation density, in effect, is a measwe of the degree of clipping a m n g in the

limiters If you set for the c m t density reading, you get the proper amount af clipping

PAGE 3 CALLING FEBRUARY 1987

m m (de W6W)

O n January 28 the FCC 51-4 a Report alnd in PR Docket 86-161, N o v i e Enhancement. Fa r t 97 of the FCC m a t i o m was d 8 d to wpand W k c e license privileges to Sndlude Cw, KITY, and SSB on a subband of lQ meters, a d dl d s s i m modes for s u b M in the 220 MHz aid 1270 MHz bands. Follming new p- in effect a t the Connnis- sion, the fill text of the Rep& a d order tns not r e l d immediately.

On February 10 the cwnplete R e p & ard Order was f h l l y released. The paragraphs belm pravide a s m m q of the specific rules chaqes adopted. T?E r e d rules becare effective on KWCH 21, 1987 at 0003. W. In 1-1 t h e , elat's 4:01 p.m. on F&mh 20. Pl~ase help p ~ s the word to your Novice friends m k to use the new privileges Isefore that tb. Tnen let's all get on t5e air on &irh 20 a r a d w e l c c e n e t h e ~ ~ tothesebands.

In summy, the new rules provide the follmkng:

1. N o v i c e s and M i c h m y opmte 28 .I-28. 5 MFIZ, us- A1A arrd F1B emission at 28.1-28.3 and A M and J3E emission a t 28.3- 28.5 MHz. N o v i c e and Technician cmtm1 +%fators are limit& to 200 w a t t s a-t in this band, h t other licensees are not similarly limited.

2 . N o v i c e s may use up tm 25 watts in the 222.10-223.91 MHz band, w i t h a l l authorized emissions.

3. N w i - m y use up to 5 wa t t s in the 1270-1295 MHz band, w i t h a l l authorized emissims.

4 . No amateur station at w h i c h the cwltrrol operator or station licensee holds a Novice class -tor license shall t~ in repater, auxiliary, or -con aperation.

5. nm ex;mciners w i l l be required tm administer fuimm Mwice exams.

6. FIES?XI~ ~ovicie and Technician li- are 'grandfatheredrWo the new p r i v i l q .

7. Element 3 is divided into two m, 3 (A) and 3 (B) , w i t h each W t i o n tm consist. of 25 questions, Resent Tedmician liomsms w i l l t~ given credit for having passed both elements: the future, u m d e s to Technician will only have to pass element J(A) aid future Techn icb -ding tm General w i l l have to pass element 1 ( B ) ( 1 3 words per minute) and el& 3(13).

Tne abve summary was w i v e d via electronic mail ARRL Headquarters on February 10. I will

to provide a copy of the actual Repo& and O W , or significant m t s therefran, for M morrthl s w m o calling.

The FW's -t on Novice ahmemnt caps Lwo y e x s of effort by the ARRL and many m m e d amaY~XE3 to provide an alternative to the m e license as a means to st indate grclwtrh of the Anmteur Radio Service. For mre on the badqround of this effort and what it mans to the AFS, see the upocanirag editorhial in March m.

Don't overlook the fact that the new rules provide additional p r i v i l q f o r Technician licensees: Cd a d HITY at 22.1 to 28.3 MHz, and ard SSB at 28.3 to 28.5 MHz. These privileges w i l l &=aw increasingly useful as the suns@ cycle starts to head upward.

b%ny questions have been raised a t the strange sub- m 220 MHz. The Gonrmissionl s intention in adoptinq the fllbband of 222.10 to 223.91 Wz was to p e d t N o v i c e s all shplex and repter input frequencies, but no output fequm=ies.

Are Novices all& to be -tted on to the y t e r outputs? The FCC's view is that re-- nussion is permitted w i t h i n the terms of the license of the station doing the r d x m m i t ~ . Therefore, N w i - w i l l be perfectly legal to use repaatem rhose inputs are in the Novice subband. Wlt , they can't: "go reversem and transmit in the repeater output.

To carry the discussion a bit further, a T&hnician controlling a crossband mter d d even pmht a Vovice to be r e t d t t e d on two meters, What about retransmitting a Novicei s signal on 20 meters? Well, then i t ' s m longer a rep*, and the rule for third-party traffic would apply. See the ARWs FCCe W k f p , 6th a t i o n , page 7-4 f;ar more discussion on this type of situation.

If you are still ,with me a t this pint, you're R E W X in- in the new nil-! You'll k h ~ i ? q m u c h m o r e a b o u t t h e m i n t h e o c r m i r a g m t h s .

M ( 3 R E N m E F a O M m S r n D ARFX ISSUE SPECIAL CALL SIGNS?

News from the front was fairly quiet in 1986, but they are more than making up f o r it in 1987. A f t e r adoptw the new M e s discussed above, the Ccmrmission on Febmaq 3 issued a @lit mice styled "PRB-3". In it they sol icit cmnmnts and praposdls on the idea of explying an organization in the private sector to handle the assignment of llspecial call signs1' in the hmateur Radio Servie. By special cal l signs they mean any call. but a 2x3 call sign issued by m t e r ta new licensees. All current d l sigm would be frozen - i.e. no current holder of a call would Ice it. Tne new systemD if adopted, wwld apply d y ?.a r w licenses or curwrrt liensees s e k h g a charqe of call sign.

This inquiry has stimlated more spirited debate anmng tP.e officers a-d directors of ARX than any recmt FCC proposal that I can recall. ( m e discussions are aided considerably by the fact that a l l of our officers and directors can rw wrrrmuni- cake by M C I electmnic m a i l . ) S o r e feel that there are too mmy dangers and potential liabilitie and that the hq-oe shouLd not take on this respcplsi- bility. Others say that we would be M o n i n g our m m i b i l i t y as the mtional ~~ciety i f we declind and allowed same other p r i v a t e o r organization to take m the job.

The deadline for cammts to FCC on this proposdl i s April 23, 1987, and reply ccrmmerrts are due by M.rf 22. Y m Southestern Division Director, Fried Heyn, WA6WZ0, and 3 very mch desire same f-ck on this issue. Should ART& take on this challenge or not? Please make your thoughts hmm to one or berth o f us. To be most helpful, your mmwks should reach us well before the Lsaguels m t i v e ccmmit* meeting on Fvrch 21.

PAGE 4 IJSVfO CALLING

Tne followhg are significant emqks frm -3:

"There is a large demand in the Amateur service for c a l l sig-m of choie. Because of limited -, ~e F W cam& honor rques t s for s p c i f i c ca l l s igm. The FCC assignmat system is totally automated: callsigrs are assigned on the station license fmm alphabetized lists arranged accardhq to railing address arrd operator l i m e class.

"It appears that a practical a m & wmld k for the actual station licensing fundim - incldw ?21e actual assignerrt of a callsign - to be performed by the MX: hfore the private sector becomes imrolvd. Then, upwr the l i m i s request, a Special Call Sign Coordinator (SCSC) in the private sector would assign one or more supplemental special call signs. Tne selection system for determining which l i c e n s e e wculd be eligible for which call signs wmld be the prerogative of the SCSC. A apecial. call sign oceild k used in l i eu of the FCC- assigned call sign during the station ickntifimtion required by Sec. 97-84. The assigrrment of a special call sign a d b~ a m i c e for the lioensee, not a mrdition of licensing nor a service replacjng the FCC. The B C would maintain a data base of a s s i w special call signs Tor use in monitmxjng and .ocanpLiance work. Special call sign assi.grrmerrts would mt be hrpwated into the FCC's license data base.

The FCK: would discorrtinue processing requests for call sign m. (The MC ncx~ sysmtically assiqns a different call sign urpon request when a licensee change5 m i l i n g address to a different region or m d e s to a higher operator class.) All ca l l signs cummtly assigned to amatem stations wwild be frozen. XI. new stations, regardss of the lioenseets opmtor class, would be assigneuj. a 2 X 3 f m t call sign from the prefix block NA-NZ. A l l other call signs d d be made available ta the SCSC for assiq-me.W as special call sigrr;. F'wAhermOre, a s call signs which are e l y h in are dmppd f m the FCC data base due to failure to renm the license, they would be available to the SCSC for assi- as s p z i a l call signs."

"The special call siqm assi.gmnent spm that we envision kwuld be o p m t e d on a not-for-pmfit basis !out the S E C d d recover reasonable a t - o f - w a-tive -ts. ii

Please let US heax f m you w i t h ywr reaction to this praposal.

A call from ole N6AW rmirded me that: a full nmW~ had gone by since my l a s t article on DX was preprd. It's been a most eventful mwsth with Peter 1 Islarad being activated to bwxane the l a m addition to the DXCC m t x y list. 1 hope all of you were forhmate enosagh to get at least one a60 with this m p . It was a very w e l l done -tion by two "pros*i. N m for this. month s news.

aKns ImrxmG E L A N D - VK9YS and m w w i l l put this rare s p t on the air between 10 ard 24 February on all bands both phone and cw. I in- to listen for them as soon a s I g e t this article into

D m - laok for NP4TP mtirq from this garden Spot from 5 ta 9 March. No 0th- inform- tion available at t h i s time on this one.

FEBRUARY 1 961

Minutes of Board mting 28, January 1987

FRESm: Carl de Silveria, Harry m k , Sid SO*, m mmsdm, Walt M"skJi.an, Rick " m y , Mark Schaf fer, Dick Wetzel.

1. Mark Schaffer stat& that six of the fall novice class sucoessffilly passed the course (see Jan i m e of wmo calling).

2. A discussion was held xqarding how the radio club could participate in the JPL open house. which will be held the 1st a 21ad weekends in June. No decision was m&d, the Wed to k brought up again at the Feb bard meeting.

3. John Repar r e p o m the new ERC storage drmt2iner has keen installed and that most of the club spare gear has been l d e d into it. John is also in the process of repairing the antenna rotator f m the MesEl while Sam Weaver is working on the bent a n m reflector elmmt.

4. Walt Mushagian reported on f ie ld day plamirrg and pepmtions. Walt is actively pursuing information and ampisition of a balloon suitable to hoist and fly a l q , long wire antmum. A omnittee has been fmmed to design a rd build lone or t w ~ w h beam antemas for field day.

5 . Rick HcKimey m p r t d that 611 of the Voyagerflranus @L cards have been l a l e d and mailed. (Rick desewes a mrqmtulatirms from everyone as he sorted, labeled, etc the hm3r&s of cards virtually unassisted.

6. It was reported that Bn~w mudq has volm- bemd to be the Hot Dog chairman at this years JPL picnic.

Sid Johnson Secretary

GmluC60 I s m - FR/C/m4M: plans op3mtim f m this islard in the miwe of the Indian Oceafi

s'carting abut 15 February. 1 fllsped your k t shot at this one will t3e amund h t h 15002 and 20002 on 20 meters.

MMAWI - 7Q7W i s active frequently on 3792, 7002, 14285, and 21285 lcHz at the a m r i a b t h of the day. Heis a gm3 SLer.

M U I - TZ6AA ( W 4 U Z in -is) should be active as you read this. Also, lc& for lz6FIC fnan 14020-14025 kHz from 18002 mast days.

ST. PETER & PAUL ROCIrS - ZYOSA on cw and ZYOSB on ssb should satisfy yaur neds for this one f m 21 to 22 February. Operation w i l l be on all

SOUIH N!3!WME ISLAND - The a O x V operation fmm this near Antarctic DXCC mmky is scheduled to start tiny time nw. I w k e d an w operating very close to this island just the other even- on the law end of 40 cw at 02002. Keep alert!

ZAIRE - If anyone hears 9Q5NW on 3790, a call an 3788 k ~ z m y d t in a Qso. Look for him at 04302.

mough for m, I've sirrpsly got to get the jmp on the rest of you by turning on the filmmts (its an old rig) ard working all these guys first. Have fun in the pileups. Good Dxirag, W, N6E;T

PAGE 5 'nl6VLO CALLiirG FEBRUARY 1987

Thanks--220 SMA v i a Walt WA6PEA

NW M R G - 7 9 MI SS1 OJ DESI -TORS

h W o ~ l d Adn4nirtratiwr Radio Confermnee of I979 prwid+d for n w miss fan designators. I t is expected that t h ~ s ~ n e ~ e l ~ s ~ ~ f f e a t i o n s w i l l w e n t u a l l y f ind their way Snto part 97. Here is an rdv&nem look at somu of t h m !

Old Type fmirrf on Deri~nrtar N w Type AB L~MODULATEP PURE CC~RRYER N ~ N A1 MORSE T ELEGFZAPMY A I A A! TEL-PE f ELEGWPHY A 1B fi2 MORSE SOLMD MODUlATED A% A 2 TELETYPE SOWP MODUlATED A28 A 3 Wl TELEPHONY, DOUBLE SIDEBAND A3E F13J TELEPHMJY* SINGLE Sl DEBAND 532 A 4 An FFlCSLMILE a 3 C A4 J FACSIMILE, SINGLE SIDEBAND J 3 C A 5 AH T E L N I S 1 ON, DOUBLE S I D E M D A3F AS J TELFJ I S1 ON I SINGLE S I P E W P J 3 F F0 U . M O D 1 I W E D PURE CARRIER N0N F 1 MORSE TELEGRAPW F 1& FE TELETYPE TELEGRAPHY F 18 F2 HORSE S O W D MODULhTED F2A F2 TELETYPE SDWKJ HODULFlTEO F28 F3 F REQUMCY MODULATED TELEPHONY F 3E F4 FREQUENCY HODUUTEP FACSIMILE F3C FS FREQUENCY MOPUtATED f E L W I SI F 3F P PULSE MI SSI OJ W l THOUT MOOULATf ON PBN

C f or ezmpl e, Radar) There r r r o t h e ~ s , but the abwe new miss ion designators are the an** that we are most concerned w i t h in the knataur Radio S.trvirr.

Here's an explanat ion of t h o nrw rymbolo~y First Character:

N = Emission of an unmodulatad tar r ier A mF double sideband J = SSB, ruppsessed carr ier F n: Frequency modulation P - Sequence of un'modutrted pufsrr C - Vestigal s i d e b a n d s

Second C h r ~ a c t e r r 0 r No modulatinlp s igna l i = A r i n g l a chsnnel conta in ing d i g i t a l information, without Zkr usm

of modulating E U ~ C ~ F F ~ E F

2 u A s i n 9 1 ~ channe l c o n t r f n f ng dip4 ta t Informationl w i t h the us* of r modulati .ng cubcarrier

3 r S i n g l e channel w l th a n a t o ~ information t h i r d Characterz

M = No in+orrnation transmitted A r Telegraphy (aural recoption? B * T ~ l r g r a p h y I(autm&tic F W C Q ~ ~ ~ O ~ )

C - facrirni I e D - Data transmission, tetcrmetry, t c t e - c m a n d E Telephony F - T e l w i r i m n

W6VLO CALLING PAGE 6 FEBRUARY 1 9 8 7

T>anks t o J i m Longthorne WAGKPW f o r submitting t h i s a r t i c l e by Motorola C&E v i a "TechTalk

Mobile Radio Receiver Interference in Duplex Operation

C onsider that an automobile consists of a large number of mating metallic parts held

together by various means When the vehicle is in motion, many of these metallic parts move w vibrate independently of each other. This movement creates a number of inter- mittent contacts within the vehicle. If the metallic parts are illuminated with radio fequeng energy from a nearby transmitter, these intermit- tent wntacts become non-linear in- terference generators These natural (environmental) non-linear sources have a voltage-current characteristic curve similar to a pair of parallel front-to-back diodes

The non-linear interference gen- eratars re-radiate energy, received from the transmitting source, as a lew-level broadband energy field. Any receiving antenna, Iocated in dose proximity to these interference generators will pick-up this broad- band energy and apply it to the re- ceiver. The selectivity of the receiver wiEI attenuate most of the interfer- ing energy; however, no protection in the receiver is possible for that par- tion of the energy spectrum which falls directly on channel. This in- terfering energy competes with the desired signal for capture of the re- ceiver. It should be noted that the in. terference mechanism is not radio generated but is a direct function of the environment in which the radio i s operating.

Test Description

radios were used and antennas were locaw at varying positions on the vehicles The Bsts were conducted in fringe reception areas. The results of these tests showed that, in all cases interference was generakd which significantly degraded the desired signal. This was true whether the re- ceiver was operated from the same antenna as the transmitter or a separate monitor receiver and anten- na were used. The following are some examples of environmental non-linear interference sources found in the test vehicles:

I. J h w chrome strips 2. Seat springs 3. Hood and trunk lids and locks 4. Exhaust systems and mounts 5. Bumper mounts 6. Leaf or mil springs 7. Tailgates en pickup trucks 8. Tool boxes mounted on the bed

of pickup trucks Additional-tests were conducted us-

ing a signal generator to drive an antenna and a spectrum analyzer, tuned to the generator output fre- quency, as the receiver. Under these conditions, the frequency spectrum of

nsts were performed on various vehicles in an attempt to identify gome of the non-linear sources of in- terference Sweral types of duplex

JULY 1988

PAGE 7 W6YIO CALLING FEBRUARY 1987

the interference generator (a section of copperclad printed circuit board rubbed with a piece of ground braid) was observed to be a broadband noise field, 40 MHz wide, centered on the source frequency. The test was performed at frequencies in both the 150 MHz and 450 M H z bands with similar results

This test was repeated using a 20 watt W transmitter and a receiver tuned 5 MHz below the transmitter frequency, The interference level so generated was such that the receiver was quieted at the 20 db level when the non-linear source was within ten feet of the antennas This distance will vary depending on the following factors: transmitter power output, ef- ficien~y of the non-linear source, sen- sitiviw pf the receiver and strength of the desired signal.

Having di$ned the source of the interference, a set of conditions can be prehcted which must be present for the phenomenon to m. First,

the receiver must be operating in the presence of high level radio frequen- cy energy within approximately 20 MHz of the receive frequency. The re- ceiver, illuminating transmitter, and non-linear source must be located in close proximity to or on the same vehicle. The vehicle must be op- erated in a marginal signal area (approximately 25 db quieting or less) since the interference is usually at low levels Finally, there must be motion or vibration to create the in- terference Any type of duplex radio will be more susceptible to this phe- nomenon since the fust two wndi- tions exist in normal operation.

The following series of tests should be performed to establish the ex- istence of this problem on specific vehicles:

1. The vehicle should be operated in the area where the problem is occurring or in an area where the problem can be reproduced reliably.

2. The base station transmitter should be turned on to provide a

signal to quiet the receiver. The modulation lines to the base transrnitkr should b AC shorted to prevent any feedback paths in the system between the mobile and basz

3. The suspected mobile trans- mitter should be keyed and un- keyed repeatedly while the vehi- cle is standing motionless In some extreme cases, it may also be necessary to turn the vehicle motor OK. If receiver interference occurs under these conditions, some other probIem exists, such as normal duplex desense (re- ceiver interference caused by ex. cessive on-channel transmitter sideband noise).

4. Step number thee should be repeated with the vehicle in mo- tion. If receiver interference w- curs only when the transmitter is keyed, environmental inter- ference is the cause.)

The solution to this problem is to eliminate the source of the non- linear interference within the vehicles The antenna mounts and general installation should be ex- amined for intermittents This should include all cable connections The antenna should be located in such a manner as to minimize the energy radiated into the vehicle Chis is usually the vehicle roof). Grounding straps should be position- ed across suspected chassis members 1t is important to note that the in- terference can be generated by a radio frequency intermittent as well as a DC intermittent. 'Jbo metallic surfaces sliding across one another make effective non-linear sources Chrome strips and other metal parts which approximate ?4 wave length are very eficient interference generators There is no specific area which can definitely be predicted as a source. Each vehicle may be dif- ferent and most vehicles will pro- bably contain a number of sources If these sources can be located and eIiminated, the problem can be resolved.