Amateur Radio Fox Hunting – No Animals Were Harmed in the Making of This Blog Post!

The hunt is on! I got wind that the Bristol County Repeater Association was doing another fox hunt thanks to Skip KB1CNB. A few months earlier AA1F and I unsuccessfully attempted to find the transmitter on their inaugural amateur radio direction finding (ARDF) event. We were up for the rematch! Rules were pretty simple: A specific intersection (President Avenue and North Main Street in Fall River) was chosen. And the “fox”, a beeping blooping 5-watt radiofrequency (RF) transmitter, would give a 1 minute signal on 146.565 MHz every five minutes from 10am to 2pm from somewhere within a 10-mile radius from the chosen intersection. Hunters then had to drive around and locate it using whatever RF finding tools they had.

The key factor is ARDF is to figure out the directionality of an RF signal from multiple locations, and then find the intersection point of the various directional trajectories you identified. “Triangulation” of the signal, if you will. The predominant tools to accomplish this are directional antennas (such as both the VHF loop antenna seen in the picture above as well as the handheld yagi, both by Arrow Antennas. As always, I am sponsored by absolutely no one — this is all just my equipment! That said, every ham should have some type of handheld yagi in my opinion).

Attenuators are also available to decrease the signal strength so that your directional antenna does not become omnidirectional in the presence of an overwhelming signal. In the above picture you can see my various active attenuators…none of which I ended up needing this fox hunt.

A standard roof magmount omnidirectional 2M antenna is also a good idea for generally identifying the signal. We also used a handheld gps to mark when the signal was heard (which I found very useful) and a laptop with photo editing software to draw RF signal vectors. A pair of Yaesu FT-4X handi-talkies, one connected to the magmount, and one for the directional antennas with appropriate connectors and coax completed our ARDF kit.

So, a ten mile radius may seem pretty easy…BUT! That translates to an area of 314 square miles! Prior to the trip, I used a screen shot of google maps with the red pin dropped on the intersection of President Avenue and North Main. I established the 10 mile radius shown in pink. I would use this map to mark important landmarks, including the detected RF trajectory. AA1F and I would check in on the BCRA repeater in the morning of the hunt, check in with Fox Control, i.e. Skip KB1CNB, and then drive around until we could hear the transmitter. Once we heard the transmitter, we would find a reasonable clearing to determine the first directionality vector.

Driving around, we heard the transmitter several times before we found a good location to assess its directionality. Our first successful vector analysis (marked with a purple lightning bolt on pictures and maps) was on New Street, the entrance to the abandoned Weaver’s Cove Energy Site on the Taunton River. We were able to assess that the signal was most likely coming from the north of us. I added the first triangulation (blue) line to the map.

We decided to cross the Taunton River and head up its northern/western bank to find another location to take a heading. This led us to the Pierce Beach & Playground in Somerset MA. I identify myself as a hyperlocal traveler, meaning I like to know every sidewalk crack in my backyard. Ham radio and its various activites (SOTA, POTA, ARDF, etc) have given me plenty of excuses to go places I never would have known about. Pierce Beach (marked with a black arrow on the map and pictures) is definitely one of those…who knew there was such a pretty swimming hole on the Taunton River?

Unfortunately, we ran in to a bit of trouble with our yagi at this point. Despite the omnidirectional magmount picking up a strong signal, we could not hear the transmitter with our handheld. Take note of the fact that this location is exactly on the original blue directionality line we had drawn from Weaver’s Cove.

I changed out the coax, and at our next stop, the Somerset Reservoir, I was able to regain the signal. The magenta arrow marks the spot! Interesting tidbit about the Somerset Reservoir? It is fed by the Labor in Vain Brook…foreshadowing??? Again, this location, chosen rather randomly due to simply being able to hear the transmitter, was located directly on our initial transmission vector. Quite frankly, this was disappointing, because rather than finding a second directionality line, we kept receiving the signal on the same trajectory, thus eliminating the potential for signal triangulation. By now, we had less than 20 minute before the end of the hunt.

Regardless, the signal kept getting stronger and clearer on the magmount antenna as we drove up Route 138 into Dighton MA. We knew we were close by, but were running out of time. With 10 minutes to spare, Skip announced that he was going to increase the frequency of the transmitter to 1 minute out of every 2 1/2 minutes. He also told us hunters that he was parked on Route 138. That was all we needed to know…

Within just 2 minutes, and at exactly 1:59pm, we found Skip sitting in his jeep tagged “BCRA” in the parking lot of the Dighton Old Town Hall (happy face on the chart and pictures). It turns out that we were only the second set of hunters to find the transmitter.

But very shortly after a few more persistent participants tracked down the location.

We hung out, chatted, swapped stories, and advice, and went on our merry way looking forward to the next fox hunt! Thank you so much Skip KC1CNB and the rest of the Bristol County Repeater Association for this wonderful event!

And as just a final commentary, what a delightful way these foxhunts are to hone your skills as a radio operator! Our first foxhunt (the prior one the BCRA arranged) was a total failure for us. We ended up 5 miles away from the transmitter by the end of the hunt. Having jumped head first into the HF world of radio in the beginning of 2019 without so much as a thought on the higher bands, I am now circling back around to learn more about UHF/VHF FM transmissions. This foxhunt combined use of the BCRA repeater, simplex phone communication, and simplex tone transmission, all while assessing geographical locations over 300 square miles. It forces you to learn how to get the most out of your radios and antennas, while deepening the understanding of their capabilities and limitations. It is a dizzying experience…and I am a measurably improved radio operator because of it!

Always,
KM1NDY