ATV Repeater Adventure

I had not been active in ATV for a few years, primarily because of frustration resulting from antenna limitations. In the Spring of 2007 I started to think in terms of a mobile/portable ATV station that I could operate from the local high spots, as well as from our cottage overlooking Lake Michigan. As I started to gather bits and pieces, I was talking with Bryan, KC8LMI, who told me about a new ATV repeater he had installed in Dansville, MI, a little over 8 miles from my QTH. In all of my years in ATV I have never had the chance to operate through a repeater. There are basically two possible configurations for an ATV repeater:

• In-Band. Here both the input and output are in the same band. Since almost all ATV operators have equipment for the 70 cm band (the lowest band for which we have TV privileges), most in-band systems operate on the 70 cm band. Unfortunately, those of us above the "A-Line" cannot use the lower portion of the 70 cm band, so a 70 cm in-band system is out of the question in central Michigan.

• Cross-Band. In this type of repeater, the input is on one band (often the common 439.25 MHz ATV frequency) with the output on another, typically higher frequency, band - often 33 cm (900 MHz), 23 cm (1200 MHz), or 13 cm (2300 MHz). The limiting factor is a cross-band system is the ability of more distant stations to copy the repeater output, as signal losses are much higher as you move up the bands (higher in frequency). A big advantage of a cross-band system (aside from the fact that we can operate above the "A-Line") is that you can monitor your own signal coming back - something which is not practical with an in-band repeater.

The N8OBU ATV repeater in Dansville is a cross-band system, receiving on 439.25 and transmitting at 910.25 MHz. With the input on 70 cm, I had plenty of pieces of gear I could play with, including my old Tridon exciter and a few "brick" amplifiers. However, I wanted an uncomplicated installation for the repeater (or the van if this repeater business didn't work out!). The end result was an order to PC Electronics for one of their 20-watt ATV exciters:

This transceiver is the ultimate for a complete plug-and-play ATV system on 70 cm, but it looks like the last one has been sold (I think it's mine!) and the 20-watt amplifier modules are no longer available. Fortunately there are other combinations of modules that could be made to work - they just aren't as convenient! I would also need a modest 70 cm antenna to get the transceiver's signal to the repeater. I had an old 6-element end-mounted KLM that I felt would probably be adequate, given the relatively short distance.

Receiving was another matter, for 900 MHz was a band I had never operated. The heavy use of 900 MHz for Part 15 devices in built-up areas creates a significant interference problem. This problem is at its worst in the metro areas where you find most ATV repeaters, so cross-band systems typically use the 23 cm band for output. In contrast, the Dansville repeater is quite rural and while there is some interference, it is not insurmountable. Fortunately, Bryan (KC8LMI) had a spare converter (see more on this at the bottom of the page) I could use, so I picked up a 9-element yagi from M2 Antenna Systems:

This model (914-ISP) is from their commercial line and covers 900-930 MHz with 14 dbi gain. It is intended for Internet wireless service and is well-build but modestly priced ($63). While waiting for a break in the weather for a proper installation of the 900 MHz system, I decided to see if I could copy the system at all from the inside of the shack. I propped the antenna up on the laundry basket and found an old piece (very old) of solid RG-58 coax equipped with UHF connectors. With the antenna connected to the downconverter, and the downconverter driving my WinTV adapter, I asked Bryan to fire up the repeater in the beacon mode. Much to my amazement, I saw sync immediately! With a little tuning of the converter and juggling of the yagi, I actually got snowy but useable pictures:

The center and left-hand picture are from the system in the beacon mode while the right-hand image is Bryan accessing the system in the normal repeater mode! The nice thing about ATV is that if you can see anything, relatively modest improvements can yield big dividends.I figured I could easily score a 10 to 20 db improvement with an outdoor installation with decent cable and N-connectors, so I was quite pleased with the results. Now it was a matter of waiting for the weather to break! When it did, the antenna was mounted out on the back roof and fed with a minimal length (35 ft.) of high-quality coax (LMR-400) with properly installed N-connectors. That made a slight(!) difference:

Now that I was set up to receive the repeater, I wanted to see if, with the same short piece of crummy feedline used in the earlier experiment, if I could hit the repeater with my old Tridon exciter - about half a watt output. Here is the result with 0.5W into a small yagi from inside the house:

I honestly did not think I could bring up the repeater, but there it was! Not much to write home about, but then, a few more watts could make a big difference, even from inside!

Here is what 5 watts can accomplish (+10 db), using the same feedline and small yagi! Next step is to move the little 70 cm yagi outside with another piece of coax just like the one I used on 900 MHz. With luck, the PC Electronics exciter will arrive about the same time, saving me the trouble of running the small excited and a separate amplifier!

Here are the two antennas, 900 MHz at the top of the stack and the 6-element 70 cm KLM below. This arrangement is fixed on the repeater in Dansville and will do nicely until I get a new rotator and upgrade the 70 cm antenna for simplex operation.

The same evening the antennas were finally up, I worked KA8ZXX, Bruce, (Bryan's Dad) through the system. To put things into perspective, even though we are separated by only about 14 miles, there is a significant ridge (+50 ft.) that blocks the signal going both ways. Here is what Bruce and Bryan's signal looked like a few years ago. They were running high power and I had a 25 element yagi aimed right at them:

That's Bryan up front with Bruce in the background. The added signal quality provided by the repeater is very significant!

Andy, W8AHY, has been continuously involved in ATV for decades. It was great fun to work him with his first venture with the N8OHU repeater:

Bryan, KC8LMI, has a complete ATV installation in his truck. One Saturday he took off toward Saginaw to install a 70 cm/23 cm cross-band ATV repeater up there. The lower two pictures (below) show some intermittant ATV mobile as he headed up Route 52:

The next morning, with some modest band enhancement, he received this signal from the new repeater:

Not bad DX for a 71-mile path on 23 cm!

Roger, N9UV, has been active on ATV in the Lansing area for many years. Here is his first attempt to access the Dansville Repeater using 10 watts from South Lansing:

900 Mhz/33 cm ATV Converters

About the time I went to get geared up for using the repeater, PC Electronics had discontinued their tunable 33 cm converter and finding one of my own became a real problem. Now, as of November 2007, they have a new converter available - the Model TVC-9S for $159.00. The new model is synthesized with five possible receive frequencies and is very convenient to use. The older tunable model that Bryan lent me to get started worked just fine, but it had to be tuned  very carefully for optimum picture. I was always worried I would knock it off frequency or that it would drift off (never did!). The new synthesized model is just as hot, but now you simply switch to the channel you want and it will always be on frequency!