February 2001 FOX HUNTING WITH 4-WHEEL DRIVE The last snow of the January 21 st storm ended at 11:30 am and the fox hunt started on time at 12:30 pm Mark, KE1IU, was the fox and he hid at the commuter parking lot on Route 117 that is located just north of the I95/117 Industrial complex There were two hunt teams Randy, N1PTB, Paul, N1ZYB, and Linda, N1ZYC, teamed up in the 4-wheel drive Explorer They had a TDOA, a ZL Special and a new Digital Doppler direction finder New toys are always lots of fun so it turned out that only the Doppler was used by that team Matt, KB1FKL, teamed up with Chris, KB1FUO, and they also had some new equipment Matt had just finished building a Time Difference of Arrival (TDOA) kit and was eager to put it to work finding the fox They also had a Quad which didn't get used When the hunt started the fox's signal was very weak at the Route 12/2A starting location so both teams headed south looking for higher ground Matt went directly to the Route 184/117 intersection to pick up his partner Chris and at the time was not aware that this put them very close to the fox When the fox transmitted, the new TDOA gave them a strong bearing that pointed south down Route 117 The problem is that the TDOA doesn't provide range data, so they drove right past the fox and went to Bluff Point Park Determining range while fox hunting is a science in itself The next bearing they obtained at Bluff Point lead them a little astray and that delay provided time for Team 2 to close in on the fox Linda, Randy and Paul went to Overlook Road near Route 214 and obtained the first Doppler bearing to the fox who was about 32 miles away as the crow flies Randy was favorably impressed with the 4-wheel drive and the Doppler, both of which were used Next then went to the Stop & Shop parking lot at the intersection of Route 184 and Route 12 where they got a solid (one LED) bearing almost due east They drove east on Route 184 and then south down Route 117 to the Industrial Park where I95 crosses Route 117 (Another team going right past the fox!) At the park the Doppler pointed north up along Route 117 Suspecting that this bearing might have been influenced by some signal reflections, a second bearing was obtained near the Pequot Medical Center and it also pointed north along the Route 117 line Linda plotted these last two bearing on the map and the team headed north again on Route 117 After driving only about 1/2 mile, team 2 heard the fox start a short QSO with a non-hunter Linda reported from the plotting room (the back seat) that the Doppler now said the fox was directly behind us to the south (Drove past him again!) One of the advantages of the Doppler is that it works while the hunter is moving They reversed direction and about 200 feet down the road sharp-eyed Randy spotted the fox in the commuter parking lot 73 s Paul and Linda ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ TIPS Net News Effective February 1 st, Bruce, WB1FMP, and Ken, KB1EPU will be the co-net managers of the ever growing TIPS Net Congratulations to you both! H IGHLIGHTS INSIDE THIS ISSUE 1 Fox Hunt Report 2 Upcoming Events 3 What is a Repeater (Part 4) 4 What is a Repeater (Part 4) continued 5 Classifieds, Contacts and Important News 6 Advertisements The RASON Monitor 1
MS Walk-a-thon The 2001 Multiple Sclerosis Walkathons statewide will be held on Sunday, April 22nd with the exception of Woodstock which will hold their event on the 29th Ed, K1UQE is coordinating the ham communications for that one If you would like to come out and help provide health and safety communications on the 22nd for the walk in Groton please contact Kevin, KA6PDG at 860-886-0762 or e-mail kharkins1@junocom The event will kick off at the same location as last year (UCONN Avery Point Campus) We gather at about 7:30 AM and disperse to respective locations Everything concludes around 1 PM There will also be a need for ham operators on a couple of sag vehicles and we will be looking for one or two net controls This is always a fun event and is perfect for those who may be newly licensed and have never done a public service communications event The MS folks always treat us well with coffee and doughnuts in the morning and plenty to eat at lunchtime and of course volunteers get an MS WALK T-shirt Please let us know if you have questions or would like to sign up to work The weather is usually very spring like but this is New England after all Last year it snowed ECARA AMATEUR RADIO FLEA MARKET SATURDAY MARCH 17, 2001 8 AM to 12 PM RAIN OR SHINE ADMISSION: $200 DONATION TO BENEFIT Eastern Connecticut Amateur Radio Association VE test session, Limited spaces available, Must Pre-register Place: Pomfret Community School Corner of Route 169 & 101 Pomfret, CT Tables are $1000 each For more information and reservations contact us at the numbers below Directions: North & South: Rt 395 to exit 93 Go west on 101 to school, 4-5 miles West: Rt 84 East to Rt74 East, To Rt 44 East to Rt 101 East 1/2 mile past 44 & 101 Intersection East: Rt 101 West 4-5 miles after Intersection of Rt 395 Talk in on 147225 Mhz PL 1567, 146520 simplex Info: Contact KE1LI, Paul at 860-928-2456 or KE1LI@ARRLNET The RASON Monitor 2
What Is A Repeater? Part 4 Repeater Duplexers By Mike Martell N1HFX In my last article, we discussed repeater controllers in detail In this article, we will take a look at repeater duplexers The duplexer is really part of the antenna system and allows a repeater to use the same feed line and antenna for both transmit and receive A duplexer is a series of large resonant cavities with special properties It is usually the most expensive part of a repeater system A duplexer has 2 or 3 cavities for the transmit frequency and a matching set of 2 or 3 for the receive frequency Each cavity has both a pass band filter as well as a corresponding notch or reject filter A resonant cavity is normally made of hollow copper pipe usually about 6 to 8 inches in diameter The physical length is normally slightly longer than ¼ wavelength of the desired operating frequency Inside the cavity is a threaded rod which is designed to be rotated to allow its internal length to be adjusted It is this rod attached to a plunger which determines the resonant frequency of the cavity Proper adjustment of this rod determines the pass through frequency of the cavity A similar adjustment of a variable capacitor or inductor determines the notch frequency It is this notch filter that can give us up to 30db of attenuation at a desired frequency The pass band filter allows a particular frequency to pass through with no more than 1db of attenuation At repeater power levels, 30db is not enough attenuation so a second or third cavity is connected in series to increase the attenuation at the desired frequency The RASON Monitor 3
Because all transmitters generate white noise or hiss on a wide band of frequencies, the notch tuning is particularly important on the transmit side of the duplexers For a 100 watt transmitter, all white noise must be suppressed to an absolute minimum of 87db down for a receiver of 15 micro volt sensitivity Most transmitters suppress noise at least 40db down from the transmit frequency This means that we need at least 47db down or a total of 2 or 3 duplexer cavities for the transmit side A repeater that has inadequate suppression of transmitter white noise is often characterized by the consistent snap, crackle and pop sounds in the receiver This condition is easily detected by momentarily turning off the repeater transmitter while monitoring the repeater receiver speaker If the noise is substantially reduced or eliminated with the transmitter off, this may indica te a need to retune the duplexers With modern receivers with wide dynamic range, the need to suppress the transmitted signal on the receiver side of the duplexers is not as great as the transmit side but is still necessary A matching set of cavities on the receive side is provided to suppress the transmitted signal enough to prevent overload and desense in the receiver Without a duplexer, the high level of RF energy from the transmitter would most likely destroy the receiver front end Tuning of a duplexer is best accomplished using a spectrum analyzer but it is possible to do a fair job using less expensive alternatives Use of an HT with a watt meter and a dummy load can be used to tune the pass band of each cavity The notch filter can be tuned using a low power signal generator or HT with an attenuater in conjunction with another HT used to measure received signal strength Normally each cavity is first tuned separately Then each cavity is connected one at a time and then re-tuned together Due to the high cost of duplexers, it is sometimes desirable to home brew a set Unfortunately, construction of a duplexer is beyond the ability of most amateurs Construction requires considerable machining skills and equipment Most of the components must be fabricated The silver lining used on the inner walls of the copper pipes is extremely hazardous Commercial duplexers are designed to be temperature compensated and this feature is especially difficult to home brew Fortunately, most manufacturers offer price discounts to non-profit amateur radio clubs Despite the high cost, duplexers are an essential part of a repeater system Using the same antenna for both transmit and receive insures that users who can hear the repeater well should be able to access it with a reasonable amount of RF power That s it for now Next time, we will discuss repeater antennas and feed lines 73, N1HFX The RASON Monitor 4
C ALE NDAR OF E VENTS?? THE NEXT RASON MEETING WILL BE HELD ON FEBRUARY 21 ST AT 7:30 PM AT THE NORWICHTOWN MALL COMMUNITY ROOM ALL MEMBERS AND FUTURE MEMBERS ARE ENCOURAGED TO ATTEND SHARE THE HOBBY WITH A FRIEND AND BRING THEM ALONG TO SEE WHAT WE RE ABOUT TALK-INS WILL BE PROVIDED BEFORE THE MEETING ON THE 146730 AND 449725 REPEATER THE PROGRAM WILL BE ON TRAFFIC HANDLING THIS WILL BE PRESENTED BY N1PTB Area NETS?? HORIZONTAL ENGINEERS Nightly at 7:00 pm on 146970?? AREA 4 ARES NET Every Monday Night at 8:00 pm on 146670?? AREA 4 Weather NET Every Wednesday Night at 8:00 on 146730 (PL 1567)?? ECTN Nightly at 9:00 pm on 146730 and 449725?? RASON Phone NET Every Thursday Night at 8:00 pm on 28440 (+ -)?? CONNECTICUT Phone NET Mon- Sat at 6:00 pm on 3965 (+ -) and Sunday at 10:00 am?? THE WEATHER NET will meet on 146970 on the First Wednesday of each Month, at 8:00 pm?? TIPS NET Every Tuesday at 7:30 on 146730 (PL 1567) ***********************************?? Check out World 1 Radio on WBCQ 7415 MHz Monday nights at 5:45pm *********************************** RASON CONTACTS President: Mark Noe, KE1IU 860-536-9633 Vice President: Bruce Adams, KA1ZMZ 860-886-1837 RASON Monitor Editor: Randy C Gudeahn, N1PTB 860-886-0345 PO Box 161 Taftville, CT 06380 n1ptb@arrlnet RASON Monitor Publisher: Mike Martell, N1HFX 860-546-9498 Classifieds There are no items reported for sale this month * * *IMPORTANT NOTICE * * * VEOSEC CONNECTICUT CO-CHAIRMEN Michael J Martell, N1HFX Roy Hilt, K1JNR 74 Lillibridge Road 41 Jerome Road Plainfield, CT 06374 Uncasville, CT 06382 1-860-546-9498 1-860-848-3021 2001 VEOSEC AMATEUR RADIO LICENSE EXAMINATIONS MARCH 3, 2001 MAY 19, 2001 AUGUST 18, 2001 NOVEMBER 17, 2001 See January 2001 RASON Monitor for details The RASON Monitor 5
Call Lentini s at 1-800-666-0908 or 860-666-6227 wwwlentinicommcom The RASON Monitor 6