WEARC Fox Hunt April 2023

The fox:

Bionics MicroFox 15 (@146.565 MHz)

https://www.byonics.com/mf

The "hunting weapons":

MWRF Source SMA Male to SMA Female 6GHz Attenuator 2W (30 dB)

The greatest transceiver of all times: Baofeng UV5R  

SDR: Nooelec RTL-SDR v5 SDR - NESDR Smart HF/VHF/UHF (100kHz-1.75GHz)

USB C Male to USB female adaptor

Compass: BIJIA Orienteering Map Compass

Yagi:

Metal broom handle from the Dollar Tree

Measure tape from the Dollar Tree

RG8X Coax + BNC connector

3D printed support for the measuring tape 

Loop Antenna:

Just a piece of coax and a BNC connector. At the top there is only a coax's shield gap of 1 inch. Pencil is just giving support to the cable. 

https://www.youtube.com/watch?v=zJbBWm6KyOM

Software:

App to calculate antenna dimensions:

https://play.google.com/store/apps/details?id=com.daveyhollenberg.amateurradiotoolkit

SDR for the Android (also available for iPhone):

https://play.google.com/store/apps/details?id=marto.androsdr2

Premium key ($10,99):

https://play.google.com/store/apps/details?id=marto.androsdr.key

Driver (to connect to any SRD USB rig):

https://play.google.com/store/apps/details?id=marto.rtl_tcp_andro

App to mark the bearings:

SigTrax ($3.99)

https://play.google.com/store/apps/details?id=com.amcept.sigtrax

We started at 10AM at the Red Cross parking lot (Point 1 on the map below). Jerry initiated transmission from his HT with 5W in 10-minute intervals, we got 2 bearings (both off) and Yagi was pointing Northwest, Loop was pointing West but also reading Northwest when elevated a couple feet. We decided to go Northeast to a park at Point 2 on the map, at which point we both got a good reading. We were agreeing 100%, and the bearing was PRECISILY pointing to the fox. This was impressive.

However, we were not very confident at that point because it was a parallel line to the fist bearing, but both were pointing West, so we decided to go all the way North to Point 3 where we got the first intersection with bearing from Point 2.

Driving to Point 4 was our best option because we were almost getting out of the 5 mile range, and the signal was strong. We used the attenuator and Jerry called to say that he was going to use just the low power (15mW). Pressure was on. Interesting enough, driving around the car's mobile radio started to receive even in low power. We knew we were close. At Point 4 the Yagi was not very precise, but the loop antenna got a PERFECT bearing Southwest so we narrowed down to the nearest park/public area.

We were close but we got a lot of signals bouncing around in multiple directions. We used the HTs with the rubber ducky antennas. Key factor here was to use our bodies as a barrier to confirm the direction that was not receiving. Holding the HT close we were able to determinate the rough direction and walked 1 block to Point 5 where we saw Jerry! 

From that point we just removed the antenna completely, walked around using the "body shield technique", and voila! Fox was found. 

1:43hs in total (coming back to Red Cross only took 12 minutes). Total distance traveled was 7.99 miles. We used Komoot app to track and made a nice video using the Relive app:

https://www.relive.cc/view/vWqB3jLMmQv

Tips and improvement opportunities: 

1. Clearly it's is a team effort, one driver and one navigator with an Yagi would speed up the process a lot. It might be better to use aluminum wire and a PVC pipe to get a more stable structure and put the antenna outside of the car while driving. A good bearing could be taken in open areas with no buildings around and small corrections could be done while moving.

2. It's extremely important to plan, check the topography to understand where the signal could bounce and try not to go straight to the initial direction but at least 30 degrees off the last bearing to triangulate.

3. Without a signal strength meter it would be impossible. The SDR provides precise readings. Attenuators are very important from close range but it would be nice to have more options, maybe 10 db, 20 db and 30 db and not only one 30 db. Best option is to build a decent one. 

4. Instead of using our body as shields, a better solution could be to use a can and a mini antenna tuned in the 3^rd harmonic (fox frequency X 3 => 146.565 * 3 = 469.695 MHz).

Some ideas to be tested: 

Overall, it was a great experience. From building directional antennas to training navigation skills, this simple and fun experience will test your abilities. We are ready for the next one! 

Best reference to learn more about Fox Hunts: http://www.homingin.com/

Special thanks to Jerry, WB2GZL. He idealized, gave us all the guidance, hid the fox and helped us every step of way!  

73s

KD2WWU