8/10/09 - SEDRO Digipeater Getting a Facelift.

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kg7hq Sun, 08/09/2009 - 15:44

When something is sickly, we attend to it. When things break... We linger on it.

The SEDRO Digipeater isn't an exception. Last month, the system seemed to disappear off the APRS screens. While the core of the system was just fine, the transmitter lost it's finals reducing it to milliwatts.

As I watched this event unfold while I was in St Louis, MO on business, this gave me a chance to think through the future state for the system. As of 7/31/09, the digipeater consisted of the following...

Toshiba Libretto 60ct Mini-Laptop running Windows 95 in DOS mode. The APRS software was DigiNed. The transmitter was a Yaesu FT-1500 at 10 Watts into a 4-element yagi at 30 feet. This was all ran off a Astron 12 Amp power supply on a UPS.

The above configuration allowed for 1 hour and 53 minutes of sustained operation without commercial power. This was measured earlier this year when Skagit County and the surrounding areas suffered a sustained power outage start from a vehicle accident.

So with things slowly falling apart, what can be done to better server the community? And, how can this be done on a limited budget? Well, for one, an Internet gateway would be a big plus. This will keep East Central Skagit County on the map during all the VHF seasonal propagation changes. Another item is to be able to increase the service life off the commercial grid. This would provide increased stability in support of ARES/RACES missions. After asking around, I was asked about increased range. This is one thing that I won't be able to achieve. Mother Nature has a say in this matter. The topology of Skagit County prevents any clear "digital" path beyond the city of Rockport. Now this doesn't mean the Sedro digipeater can't be heard, it just can't be reliably decoded beyond that area. I have experienced the same results at 10 watts up to 100 watts. So, I might as well leave the power turned down as not to interfere with other operations and receive the benifit of conserving power during emergent situations.

After chatting with individuals from the NWAPRS and WETNET groups, I decided to go with an "open-sourced software" solution to the digipeaters operations. By using an off the shelf wireless router and the Linux operating system, I can not only have a "zero" cost (legally) approach, but also be able to save on power consumption by not running a full sized computer. Wow!!!!! What a bonus! A single item to address two of the above items!

The router of choice in this case is the Linksys WRTL54GS with the OpenWRT Software packages. I will maintain using DigiNed as the APRS Solution due to it is absolutely the most flexible and stable package available. In addition, I will be running APRSD to allow for the gateway functions to my APRS Server of choice.

For a temporary fix, I placed my Taesu FT-1500 from my APRS Tracker in place as the transmitter which is fed into a Kamtronics KAM in Kiss mode. The neat thing about this is that just about any TNC2 has kiss mode which makes this a flexible system to assemble.

The system is up and operating as of the this write up. The coverages are the same but with the addition of the Internet gateway functions. This is being handled through my hope wireless router using WPA2 securities. By focusing in on traffic that is 100Km in distance from the Digipeater location allows for a very small band width footprint on my ISP connection.

My future plans are to do additional refinements to the system where you may see it off line for 5 - 10 minute periods as I slowly adjust the system. I also plan on replacing the transmitter and TNC with new units. Again, I'm looking at reducing the power consumption which should result in a sustaining system that last 3 plus hours without power. I'm also looking at breaking off the transmitter onto it's own UPS in the future.

So here we are, a face lifted system for all to use. Lets go out and have some fun with it! I'll post updates to this article as I accomplish the rest of the upgrades. For additional information on the OpenWRT software packages, visit http://www.wetnet.net . many thanks to Ken (N7IPB) for working with me on the system debugging.