Background: This page attempts to collect ideas and provide inspiration for creating an East Coast backbone 9600 baud Amateur Packet Radio data system for emergency response and backup communications. The route chosen is the same 2000 mile path from Georgia to Maine along the Appalachian Mountain chain shown at right. This path has been proved every year since 2009 during our annual Appalachain Golden Packet Event where dozens of us climb the mountains and set up APRS digipeaters to relay the golden packets the entire 2000 miles. But, now in 2016, to add some challenge to the event, we ahifted from the nominal 1200 baud to 9600 baud for the second half of the event. All the links continued to work as before at 1200 giving us excitement about this potential network. It seems the path is viable for this long hauld backup communications network.
Network Map: The map at right was captured by AL0I to document our LIVE event in 2014, but here we added red circles on all the sites where Hams have permanent access and could possibly install a permanet node in this East Coast 9600 baud backbone. Are there others? Lets pull out the stops and start looking!
The other figure at right show some of the radios that have built in 9600 baud APRS modems and are fully capable to pass traffic on this network. The links below give an idea of the distance of each link:
- - Operating Station. . . . . . Report . Distance . . . . Other End
Permanent Node Hardware: The image at right suggests a possible design for a 5 watt node using a 5W VHF digital radio, a KPC-9612 TNC, a 7 AHr battery and 20 watt solar panel. Packaging for permanent installation in an unattended remote site is the biggest chaallenge to this network.
NODE-to-NODE FREQUENCY - Packet and coordination: Initially we thought about using 6 meters or 900 MHz so that emeregency traffic would not have to create congestion and interference when operating with other VHF/UHF radios at emergency sites. But then we realized the end-user-terminal equipment is almost always going to be an integrated APRS dual band radio, so user operations should be restricted to VHF or UHF, but backbone can be any band. Low band 6m 150W radios are readily availble but BIG and someone has to do the mods. Then at Dayton 2016, we got a batch of data radios, but they turned out to be 800 MHz commercial (see below)...
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END USER FREQUENCY: Bryan and Bill pointed out that end users should not be on the same frequency as the backbone and so that suggests user ports should be on VHF or UHF to work with their existing 9600 baud packet radios. But on the other hand, the KPC-9612 is dual port, with one port operating at 9600 baud and the other at 1200 baud. So naturally, the backbone has to be 9600 baud to handle the bulk of the traffic and so the end user is at 1200 baud on the local frequency. But then there goes the whole idea of taking advantage of the 9600 baud built into all these end user radios! What a conundrum! Maybe eventually we can find some dual port 9600 baud TNCs?
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NODE BATTERY POWER: Presumably, many of these sites will need solar power, so here is a rough estimate of battery capacity. For example, a VHF 5 watt radio and Kantronics KPC-9612 TNC each draw about 40 mA but peaks at 1 Amp during transmit. If we assume a 24 hour dutycycle of about 2%, then the TX average current is another 20 mA for a total of about 100 mA average current drain. A rule of thumb for the east coast is that you get about 4 hours average solar power and that needs to power the system for the full 24 hours. So the solar capacity has to be SIX times the average current to break even on sunny days. Multiply this by at least 3 times to make up for cloudy days and we end up needing about 2 Amps solar charging (24 Watt panel) and about 7 to 9 Ahrs of battery capacity as shown here.
NODE SETTINGS: To make the network as consistent and reroducible as possible we are assuming Kantronics KPC-9612 TNCs at each location set up for KA node operation. Although digipeating for mobiles will not be disabled, that is not the intended purpose of this network. Digipeating is extremely inefficient over long networks compared to the link-by-link acknowledgemnt of the KAnode system.
900 MHz Possibility? Here is a batch of radios I picked up at Dayton 2016. They are clean and support 14.4 kPBs on three serial ports and have separate antennas for TX and RX. But the bad news is that they are 800 MHz and of course we have no access to their firmware and coding. The guy who sold them to me said they were "UHF" so I guesss he was technically correct. Anyway, there are 25 of them and if we can figure out a way to get them to 900 MHz or use them at 420 MHz, then these might also make a nice backbone.
Operating at UHF 420 MHz? Looking at the 800 MHz band plan, these radios appear to be transmitting in the 824 MHz ESMR band and reeciving in the 860 MHz range. A possible way to use some of this hardware is to simply bypass the 45W PA doubler final transistor (824 MHz) and use the output in the lower end of the 420-450 MHz amateur band from the 15 Watt Driver transistor which already works at 412 MHz or so. Then scrap the 850 MHz receiver and stick in our own receiver for 420 MHz?
UHF Exciter Transceiver: The very rugged die-cast box has plenty of room for a UHF transceiver of our choice. The D2294UK 15W driver transistor (datasheet) needs about 1 Watt for full power, so all we need to find is a small 1W XCVR? OOPS... and then add a T/R circuit. Maybe we can do that with 1/4 wave lines and diodes? Or does that just generate products..
Full power on UHF? And since the 45W PA transistor (datasheet) will work fine (See S parameters) down at UHF, maybe we can cut the output strip lines and add inductance and retune it for UHF and get the advantage of the full 45W power? How does one re-bias the PA to encourage it to operate as an AMP and not as a doubler? Higher or lower bias?
See my other GENERAL page on APRS applications and Ideas on The AT
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