Spring 2008 Issue

APRS Tactical Tropo Finder

Two new products this year are Kenwood’s DM-710A and AvMap’s G5 GPS receiver. WB6NOA writes about a unique use for these products in determining where tropospheric duct propagation might be occurring.

By Gordon West, WB6NOA



The AvMap G5 has a 5-inch (diagonal) color screen and a series of five pushbuttons down the right edge of the device. the screen is clearly visible in all lighting conditions and responds well to presses on the “virtual” touch screen buttons. (Photos courtesy of the author)

When it’s summertime, West Coast hams point their arrays to Hawaii. Like clockwork, July will be the “hot month” for the legendary tropospheric duct to open between Hawaii’s Big Island and the west coast of the USA, a distance spanning 2500 miles.

“I am ready for the trip up the mountain, and the beacons are pounding out CW to the West Coast,” comments Paul Lieb, KH6HME, the voice behind the big band openings on VHF and UHF in Hawaii. “Maybe this will be the year we complete on 10 GHz,” says a smiling Lieb, hoping he and Chip Angle, N6CA, will be the first to span the California/ Hawaii duct on X band. Lieb maintains beacons on the following frequencies: 144.170, 432.074.8, and 1296.340 MHz.

The importance of local weather conditions, at each end of the circuit, helps establish the correct altitude of the mainland duct termination. The duct may be at sea level or up as high as 700 feet, yet only be 100 feet thick. Many microwavers have become fascinated with all that APRS can do to spot fellow microwave positions when attempting to work the duct. For more information on APRS and the unattended Pete Brothers weather stations showing temperature and humidity please see: <http://www.aprs.net/vm/ kpc3/remoteu2.htm>.

Kenwood’s dual-band radios, tied into AvMap G5 bidirectional (and portable) GPS 5-inch color-screen mapping equipment, may offer the ultimate in “tracking the tropo,” as well as others squawking APRS who may have found a tropo “hot spot.” The AvMap G5 is a touch-screen, portable GPS receiver with a built-in (external available) 1.5-GHz receive antenna. The AvMap G5 offers cartography all the way down to dirt roads, covering all of the continental United States, Canada, Alaska, Hawaii, and Puerto Rico. It will speak driving directions, show you where the local Starbucks may be, and will go 100% portable in case you want to get out of the “rover” and scout out a walking-only high site.

As a bidirectional GPS, tied into the Kenwood D-7 handheld, or D-700 and D-710 mobiles, it will not only send out your GPS location to other operators, but also receive APRS position reports, including unattended station weather reports, and magically place them as “targets” on the GPS screen. If W6GPS calls you on the liaison frequency, indicating enormous signal strengths coming in from Hawaii, 2500 miles away, you will be able to see his position on your AvMap GPS mapping device and check out detailed weather information that also shows up on the face of the Kenwood!

Furthermore, if you have an internet connection, you can also check <http:// www.aprs.fi> for detailed weather information—along with a whole lot of other information on APRS beacon stations.

“The new Kenwood D-710A has a much improved buffer for packet operations than the earlier D-700,” comments Don Arnold, W6GPS, who is “Mr. Ham Tactical Navigator.”

“The terminal node controller on the new 710A is now in the control head, not in the chassis, allowing for a shorter interface cable between the AvMap and the Kenwood head,” adds Arnold. “I switched out my Kenwood D-700 for the new Kenwood 710A and quickly saw the benefit of the new larger head and the twin radio capabilities of this larger readout,” comments Julian Frost, N3JF. Frost points out there are actually two independent radios in the unit with two independent any-band readouts, where one can be dedicated to APRS 144.390 MHz, and the other to scanning and talking on the local 2-meter tropo liaison simplex frequency, including the capability for weather alert, for you storm chasers.

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