[Alexandria Radio Club Reflector] May 14, 2011 Alexandria Amateur Radio Club Foxhunt Report

[Tim]

May 14, 2011 Alexandria Amateur Radio Club Foxhunt Report

With short notice and little time to prepare, we held a mobile radio direction foxhunt on Saturday morning at 10 AM. Hal KC4ZYP volunteered to be the fox and picked his own hiding location in the City of Alexandria. He repeated a pattern of transmitting for one minute and then going silent for four minutes on 146.490 MHz simplex. The Alexandria ARC 147.315 repeater was used for coordination and several stations provided signal strength reports and beam headings.

I used this foxhunt as a method to test a Doppler Systems mobile direction finding unit and despite bench testing of the unit, I still needed to make a few last minute adjustments and modifications to get everything working properly before the event started.

I took my first bearing from the hill on Van Dorn St. just outside the beltway. This point provides a clear view into the West end of Alexandria and the signal was coming from the North, along Van Dorn St. I drove North on Van Dorn and the next transmission occurred while I was at Van Dorn St. and Edsall Rd. This area is a low spot and the bearing was plagued by multipath and varied wildly. I continued on Van Dorn to Seminary Rd and the next transmission was weaker in strength and the bearing was showing that I had passed the signal.

Turning back South on Jordan St, I heard Ian, N8IK, reporting a strong signal in the West end of Alexandria along Duke St. I searched along Duke St. Westbound and turned South onto Pickett St near the Home Depot and got a stronger signal but still lots of multipath reflections. I climbed the hill and sat on Reynolds St. since it is high ground and waited for the next transmission. A good bearing into Cameron Station was obtained, so I drove to Ben Brenham Park (the site of our planned 2011 Field Day) and waited for the next transmission. This one showed a good solid Westerly bearing, which means I had passed the signal, but this narrowed the search area greatly.

Around this time, Craig, K4GOR, provided a beam heading of 240 degrees from his home in Arlington which he believed to be in the vicinity of Landmark Mall. He was reporting a very strong signal too.

While heading out of the Cameron Station area, I passed the Armistead L. Boothe Park (the site of our 2010 Field Day), and decided to check this area and use the restroom. Much to my surprise, Hal was walking out of the restroom at the same time.

Whether it was a coincidence, or just luck, the fox was found in only 5 transmissions and in 28 minutes at Armistead L. Boothe Park.  This park lies on the extended bearing line from Craig's home station to Landmark Mall.

It was pure luck that my starting point was within 1 mile of the fox, given that the search area of the entire City of Alexandria is 18 square miles. 


Lessons learned:

1) The Doppler direction finder makes fast work of a foxhunt, but multipath will always give a bad bearing. The bearing will swing wildly when moving. Unless you are on a hilltop or in a clear area, the bearing will not be accurate. If the DF vehicle is moving, you really need to average out the general bearing to determine the true signal direction.

2) A method of plotting bearing on a laptop during the hunt will be developed for the next foxhunt.

3)  If you have a Doppler DF unit, a scanner, and a GPS unit operating, you run out of cigarette lighters and power outlets quickly.  Get one of those 3-way splitter adapters to make more outlets available. 

4) Traffic should be lighter if we start the foxhunt a bit earlier.

The next Alexandria ARC mobile foxhunt will be held on Saturday, June 18, 2011 at 9:00 AM. Frequency will be 146.490 MHz and coordination on the W4HFH 147.315+ repeater 107.2 PL.   The search area will be the City of Alexandria limits.  Please pass the word to others that be interested.

Special thanks to Hal for his work as the fox and all of the stations that participated.

Tim

KT4MV