Number 19 on your Feedback card
BiU Brown WB8ELK c/o 73 Magazine 70 Route 202 North Peterborough NH 03458
The W9TE Crossband ATV Repeater ive been asked many times about the pitfalls and obstacles that need to be surmounted in order to successfully build an ATV repeater. This month I'd like to offer you the story of how members of the Fort Wayne Radio Club solved both the technical and political problems involved In Installing a very effective ATV repeater, as described by Jim Pliett K9QMA. The following is his account.
Finding a Site f (K9QMA) am an active ATVer with a few years experience operating simplex. 1 became intrigued with the idea of building an ATV repeater in the Fort Wayne area after seeing the Indianapolis ATV repeater in operation while attending meetings of the Indiana UHF club.
One day, whiEe driving to work, I saw an empty tower at the Indiana/Purdue campus and wondered if there was any possibility of installing our ATV antennas on it. It was located right in the mid-die of the Fort Wayne amateur radio community and was nearly 170 feet talk
Now, how does one deal with the politics of a state-funded community college to obtain permission for a repeater site? Lucky for us> one of our club members worked at the college
Ham Television and helped us gain a favorable position with the college board. Meanwhile, we set out writing letters to the National Weather Service and the Director of Emergency Preparedness describing how an ATV repeater could aid the community in the event of a disaster or emergency. We obtained letters of support from these organizations and presented them to the college board. After a few months of anxious waiting we not only obtained permission to use the tower but they provided us with an equipment room to boot!
We presented the idea of the ATV repeater to the members of the Fort Wayne Radio Club, We weren't sure we could sell the concept to a club that already supported two VHF repeaters and one UHF repeater as well as sponsoring a large Field Day effort. However, since the club was recently solvent thanks to their last two successful ham-fests (and probably thanks also to a few members who just wanted to end the meeting), the motion to fund the project was passed. Our first ATV repeater was getting closer to a reality!
Fortunately for us, Bruce WB8UGV had moved to the area from Dayton, Ohio. Bruce had a lot of experience with ATV repeater design since he built most of the original Dayton ATV repeater We formed the repeater technical committee and started kicking around ideas. We have plenty of UHF voice repeaters in the area and a number of accomplished EME operators (K9KFR and AF9Y)T Keeping In mind that we were the unew kids on the block'' (along with Bruce's blood-curdling tales oi in-band repeater problems on 440 MHz), we decided to go cross-band with a 439,25 MHz input (lower vestigial sideband).
Now, did we want to go with an output on 1,2 GHz or 900 MHz? The t2 GHz band always seemed to be a good band, equipment was available, and the band was rot threatened with extinction, However, could enough interest be generated to inspire lots oi hams to go out and buy downconverters for that frequency to watch ATV? Probably not too many. A few visits to the locaf KMart and Wal-Mart stores provided us with an economical solution. The Gemini "Rabbit" wireless video system operated on the 900 MHz band and was avaifabfe for under $50 (some stores se!t just the receiver for substantially less). Not only do you get a high quality downconverter, but a transmitter is included as weil. With the wide availability of these inexpensive units we decided to go with a repeater output on 910,25 MHz [Ed. Note: Next month's coiumn wit! describe how to instati external antenna connectors on these units and tweak them up for best results,}
Number 19 on your Feedback card
The Antenna System
Although vertical antennas are easy to obtain or build, we opted for horizontal polarization on both bands for added isolation from ail of the nearby UHF repeaters that use vertical polarization and the services in the 900 MHz band that are also vertical,
Ado I pit WA9WTJ was given the task of designing and building a pair of horizontal omni-directional antennas (one for each band), Adolph decided to go with an Alford slot design, which allowed the antennas to sit on top of each other Two- and four-inch diameter thin-wall tubing was obtained from local manufacturing companies and we found some scrap aluminum stock for the support collars, The radomes were built out of drainage pipe we bought at a farm store. To maintain the necessary accuracy for the slots, we had to hire a machinist. Since we had pretty much blown the budget by now, one of our members volunteered to machine the aluminum support collars.
All of the hardware was tested and installed in the equipment rack. After some final tweaking and two revisions of the repeater controller's software, we were finally up and running with a working repeater (at least on the testbench). See Figure 1 for a block diagram of the final configuration of the W9TE ATV re peater, The 5-10 watt driver amplifier was built by Bob Johnson K9KFR Although Sob used discrete components in this design, he recommends an easier approach using a new 10 watt linear brick amplifier that is now available from Down East Microwave, Box 2310, RR1, Troy ME 04987; Tel,; (207) 948-3741 (ask for the Hitachi PF0011 module).
The 100 watt amplifier is a Varian Eimac CV2810* These amplifiers are somewhat rare, but they turn up occasionally at hamfests or In surplus stores.
At last the big day arrived. The club had amassed a 500-foot roll of 7/6-inch hardline for the installation. It was amusing to watch us try to wrestle with this giant coll of coax as we unrolled it and snaked it up two floors to the tower base. School regulations required us to dig into the club treasury to pay for a bonded tower climber, however. The antenna and coax was installed without a hitch. We opted to side-mount the antenna just below the top of the tower, hoping to be a lesser lightning attractor A few days later we carried the repeater rack up three flights of stairs, hooked up the coax and fired up the transmitter. We were rewarded with a perfect 1:1 SWR (another perfect antenna design by WA9WTJ), Bruce WB8UGV headed home and sent the first picture through the repealer. After overcoming a sfight interference problem, we were fulfy operational!
After seven months ot operation, we have experienced very few problems and have been off the air for only one clay when an HV diode shorted out. ATV activity has been picking up in the region, wrth daily contacts being made through the repeater During a band opening on May 9th. the repeater received a P4 picture from Andy W8AHY in WiNiamston. Michigan (150 miles away). Ttial same night Jim W8AC and others in the Cleveland, Ohio, area worked through the repeater and saw the 910.25 MHz output at a distance of nearly 200 miles.
if you're in the area and would Tike to look for the repeater, you can bring up the video ID for one minute on 910,25 MHz by hitting a *88 touch-tone command on 144,34 MHz. Hitting *77 will hold open the repeater tor continuous repeat mode (littfe or no input signal for weak signal reception J for one minute-
To recap, the repeater input is 439.25 MHz and the output is 910.25 MHz. Audio from the input video signal and anything received on 144.34 MHz will mix together into the repeater output audio 5ubearher
Next month we'll take a look at modifying the Gemini Rabbit for use on ATV in the 900 MH2 band. Thanks to Jim Phett K90MA for the above information.
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