Denver Fox Hunt

July 20, 2003

This is really more of a tribute to the Ramsey Doppler Direction Finder, but here goes:

Since the beginning of time, or at least since 1989, I've been a fairly regular fox hunter here in the Denver area. During that entire time I have never owned a car which I felt comfortable drilling holes into or mounting all types of miscellaneous hardware in order to sport a directional antenna.

So, how did I manage to hunt? Well, I've simply been using an HT and the body block method. I'd get as reliable a reading as possible at the start of the hunt, often relying on spying on the other hunter's yagis as they obtained their first bearing from the starting point. Then I would set my GPS to "drive to" the starting point. In this way, I always knew if I was close to the vector of that initial bearing. For instance, if the starting bearing was due north then I'd expect to see the bearing back to the starting point be 180 degrees. If it was less than that, I knew I was left of the vector and more than that I was right of the vector. Once I had driven near enough to get a good clear signal I would start looking for an ideal high spot from which to take a new bearing. I would proceed in this manner until I found the fox. More often than not I would in fact find the hidden transmitter and much more often than not I would be one of the last individuals to make the discovery. That was just fine with me though as I wasn't really into the competitive aspects with this limited setup. I was just out there to have a good time and find someone to have dinner with! :-)

Over the years Doppler DFers would come and go. One thing that I always liked about their setup was that they didn't have to drill holes or mount massive support structures to carry their DF equipment. But, they were also not usually in the winners circle. Why this was the case I have no idea.

Recently the fox hunters acquired a new DFer, Jim Zimmerman [K0JLZ]. Jim was using a Ramsey Doppler setup. And ... he was always very competitive often winning the hunt. So, I decided it was time to finally get competitive.

I visited the Ramsey Web Site and ordered the Doppler system pre built. Please don't scold me for not buying the kit. I'm just not inclined to building. By the way, the manual is available for download as a PDF file.

Doppler Console

The system arrived and I figured all I'd have to do was yank it out of the box and drop the antennae on the car and I'd be off. It wasn't that simple.

I discovered I needed three additional items.

1.) A power cord

2.) An audio cable to link the audio from the earphone jack of an HT (or radio) to the DF console.

3.) Some real magnets to secure the antennae to the roof of my vehicle.

The power cord was no big deal. A trip to Radio Shack and I was set.

The audio cable proved a bit more surprising. I just glanced at it (the jack on the console) and assumed it was a 1/8th inch phono plug. After all doesn't everything use that jack? But in this case the answer is NO! The Ramsey uses a 3/32nds phono plug. Again no big deal, just a surprise and another quick trip to Radio Shack for a converter.

The magnets...

The antennae were mounted to printed circuit boards and it was up to the purchaser to mount these antennae to the car. The kit included some magnets that frankly wouldn't have held a piece of paper to the refrigerator. Hey that's a bit strong. The truth, the antennas detached from the roof of the car when I reached 40 MPH. And to carry my fairness a bit further, the manual does specifically state that they will only work at low speeds. So, I went to Home Depot. In the hardware section in the fastener subsection there were pretty strong magnets. They were approximately 1.5 inch long by 3/4 inch wide by 1/4 inch tall. I purchased 10 of them (2 in a pack for $1.98). I then meandered over to the paint department and found some double sided sticky mounting strips. I purchased the heavy duty type. If you read the packages the standard type practically screams "I will fail if I get too cold, too hot or too something else", whereas the heavy duty type proclaims they will remain strongly bonded regardless of heat, cold or moisture.

Two magnets affixed to the base of each antenna

I had already used some of these heavy duty stickies to mount the weak magnets. I found out just how robust these things were when I tried to remove the original magnets to replace them with the new ones. It was beyond me. I was sure I'd crack the PC boards. So, I just mounted the new magnets right on top of the old weak ones. In a bizarre way this may actually be beneficial as it adds some additional shock protection with two layers of incredibly sticky bonding tape sandwiched by the old and new magnets and the PC board.

So, just when did I do all this? Why at the proverbial last minute of course. Our hunts begin the second Sunday of the month at 5 pm in the summer (3 pm in the winter). I was out of Home Depot at around 2 pm. I then proceeded to park under the shade of a bank drive thru where I mounted all 10 magnets. This probably took 1/2 hour to 45 minutes. Then it was a snap to throw the whole shebang up on the roof.

Photo in Garage after hunt

Of course, I'd never done more than apply power to the Doppler console before so, now that I had a stable antenna system, it was time to try it out.

Ramsey suggests you tune to the NOAA Weather Radio station as a first step. You can easily determine where it is located and then you can "tune" the Doppler. So, I did just that. Basically you have to do three things.

1.) Get the audio levels correct.

That was easy. There are LEDs that indicate LOW and HIGH audio. The objective, get both lights to extinguish.

2.) Calibrate.

What this means is you have to KNOW where a signal is coming from then adjust the Doppler calibration so that the LED direction indicator is pointing in that direction. This was pretty easy. I drove into an empty parking lot (Sunday), pointed the car directly at the NOAA WX radio station (about 10 miles distant), and adjusted the calibration until the azimuth of the Doppler indicator was zero degrees or straight ahead.

3.) Phase Check

The next step is to ensure that the phase is correct. This is easy to check. You drive in a circle. Essentially if you turn left the RDF direction indication should rotate right so that when you have turned far enough so that the target transmitter is outside your right window the RDF indication should read 90 degrees. I was set to normal phase and everything was working just fine.

I kind of know where the NOAA radio station is but I know EXACTLY where several repeaters are located. So, to really fine tune this thing I fired up my Garmin Etrex GPS unit, marked a waypoint for one of the repeaters in the Denver area (the RMRL 146.940 repeater on Squaw Mountain). Then I drove the car slowly about the parking lot until I was apparently moving directly towards the repeater. I then checked the bearing to the repeater, got out of the car and used a magnetic compass and verified that in fact I was "headed" directly for the repeater. Back inside the car I kerchunked the repeater and calibrated the Ramsey unit.

I figured I was all set. So, leaving the Doppler on I proceeded to drive to the starting point for the fox hunt. That location was across town and offered me the opportunity to jump up on a highway and test the new magnets. I entered E-470 (a highway south of Denver with a speed limit of 70 MPH), accelerated to 75 MPH and everything held rock steady. There were some very light wind gusts that perhaps offered as much as 80 MPH of wind loading. I was a happy camper. I rarely move much faster than 70 during any DF activity (chasing balloons down for example) so I knew I had the wind loading problem solved. I'm an old fuddy duddy so I backed down to 70 to preserve my insurance rates and proceeded to drive to the hunt location. Each time the repeater became active I'd peek at the RDF display and see it pointing just where I'd expect it too. Cool!

I arrived at the starting point early. AMAZING! I'm always late! I was also first on the scene. When ever folks see me at the hunt they all breath a sigh of relief, "At least we won't be last today!" But this time they were and angry mob. "What's this stuff stuck to the roof of your car?", they all wanted to know. Actually they all knew perfectly well what it was as we had Jim as an example over several previous hunts. They all OOOed and AAHed a bit then we awaited the fox. Hey guess who it was. None other than Jim Zimmerman.

He fired up the fox and we all jumped down his throat. It was TOTALLY unreadable at the starting point. DRAT. But, no problem. Jim had previously scoped his hide with Richard Beggs, K0AEM parked at the starting point to ensure it would be readable so he just had to find that hot spot. He did, sort of. All anyone really heard was a slight change in the noise level on the fox frequency (147.555). But it was enough to be sure we were hearing the fox.

There were three hunters on this day. Chris Krengel [KB0YRZ], Benjie Campbell [W0CBH] and myself. Benjie and Chris had very similar beam headings (more or less, due north). However, a Doppler unit, at least this one, hasn't any gain to speak of so I could hear absolutely NOTHING. I couldn't hear anything with the mobile radio and its vertical either. But, being an old hand at that type of obstacle, I just stole Chris and Benjie's heading and we all proceeded to hunt.

The rules for the day were mileage times two plus the number of minutes. Lowest score was the winner. The previous week we had another hunt and I had been on track for a pretty low mileage when I took a wrong turn (mental error with that GPS vector thingie). This time I decided I wanted to attempt to get a very low mileage by driving STRAIGHT to the fox even if I had to go slow and avoid highways that could have perhaps reduced my elapsed time. I knew only one thing. The signal was somewhere north of me. So, I headed up Federal (the closest road to the starting point that proceeds ad infinitum North and South without any detours. At first I heard no signal. Then an occasional audible variation on the fox frequency (no S units, no tone) that seemed to be a carrier. Approximately 7 miles north of the starting point I crested a ridge and the signal finally became something really readable. I glanced at the Ramsey and still nothing. I continued north. A Doppler adds a 500 Hz tone to the audio signal. When you hear that, you know it's mixing with some audio being received on the fox frequency. I heard about a second or two of this tone. I was in traffic so I waited until it was safe then glanced over at the RDF console and voila the last received signal was pointing towards 350 or so degrees or just slightly to the left/west of due north. I felt confident. But, I was descending into another "valley". I passed through that low spot and when I next crested a ridge I finally got a good strong tone. A glance told me the signal was coming from approximately 340 to 350 degrees so I started tacking to the west and north.

The full track, 1 is the starting point and 7 the fox

I am TOTALLY amazed. This worked like a charm. Now I have a slight unfair advantage over some folks. I drive a car with one of those GPS moving map navigation systems in it. So, I can always "look ahead" into developments and be sure I'm not about to drive into some cul de sac type neighborhood where a lot of back tracking will be necessary to resume my march to the fox. So, I always knew when to move north or west without encountering any of these "obstacles".

Each turn was based on a quick glance at the Doppler console

Here's where it gets REALLY COOL!!

I was on a north south road heading north. The DF gear was saying, "Go north young man!" And I did. Now, being a body blocker from way back I have a whole suite of tricks of the trade I rely on. I keep the mobile radio tuned to the fox. I keep an HT down on a seat with the antenna horizontal. When everything starts showing S9+ I know I'm in the neighborhood. I then sometimes tune the HT off frequency 5 or 10 KHz to see what kind of signal strength I'm getting to let me know just how close I am.

This time out I didn't really need to do much. When the HT was S9 and the Mobile was S9+ I just started watching the Doppler more closely. Luckily the traffic was light and I'll also mention here that all you have to do is glance at the Doppler and then return your vision to the road. You can easily discern the direction to the fox with a fraction of a second glance (as long as the signal being received by the Doppler isn't multipathing about and causing lots of skewing.

In this hunt everything was rock steady. I was driving up Sheridan Blvd. As I watched the Doppler it started rotating towards the west (to my left). Then it was pointing straight west. Since this rotation was occurring somewhat fast I was confident that I was close to the target. And since it wasn't too fast I had plenty of time to get into the left lane and ... just when the indicator was pointing due west I found a park entrance which I could turn into. I did. As I entered the park the indication said it was just a little off to the left. So, I followed the road that way (it forked and took off to the north and south). Then the road straightened and headed directly west. As I was poking along at perhaps 10 MPH I noted that the Doppler quickly swung directly to the north (out my right door) then swung behind me. So, I parked!! Got out of the car and grabbed my HT and started out to find the transmitter.

Step one, remove the HT's antenna and see if you can hear the signal. With my Yaesu FT-530 that usually means I'm within 100 feet (possibly a bit more). Of course, I can be fooled by an exceptionally strong transmitter but there are always lots of clues about the base transmitter power by how it sounds as you approach from a distance. This time out I immediately heard the fox at about S3 and I was 90% sure I was dealing with a pretty vanilla 5 watts ... perhaps 3 but certainly not more than 5. And this meant I was very close. I body blocked and the indication was right at the side of the road where the Doppler did a 180. I walked over there, did a spin and found it was indicating a direction away from the road. I started to walk that way and watched the S meter. It was now S9+ so I detuned 10 KHz and still it was S9. With no antenna this usually means you're VERY close. I did a quick 360 body block, had a very good direction indication and so I looked carefully in that direction and voila there was an ammo box about 10 feet away partially hidden behind a trash receptacle with the infamous note stuck to the top. I had found the fox. And I KNEW I'd driven a very respectable straight line to it.

Jim has you read a note. It says, "Call me on xxx.xxx frequency and give me your mileage". I did and to my delight discovered that I was first to the fox. As I was walking back to the car Benjie and Carla (his driver and cohort) entered the parking lot. He found the transmitter with no trouble and soon Chris arrived to our derisive comments on his being last. Turns out he entered the park on the North side and couldn't find an obvious way to the south side. It was necessary for him to exit and re-enter the park. Thus causing a slight delay.

Left to right - Benjie [W0CBH], Chris [KB0YRZ] and Jim [K0JLZ]

Well, it was a great day for me. I've won fox hunts before using the body block method alone but those wins come very few and extremely far between and there is usually a strong luck component involved. This day there was no luck involved. I'd just watched the Doppler and it had led me straight to the fox. My mileage was 16.9 I believe. On mapping programs they all say it's 17 miles when you drive the course I followed. And asking those programs to find the shortest route usually ends up with a 17.5 to 18 mile track. Their AIs don't take as many twists and turns as I did and so adds a few extra tenths of a mile. So, I probably drove very nearly the absolute shortest route to the fox. I consider this mostly luck as I couldn't hear the fox for the first 7 miles. If it had been significantly further to the west I would have had to start zigzagging much further south to get a SHORTEST route.

So, to recap.

I'm very happy with the Ramsey Doppler unit. It was relatively easy to get up and running the first time. And it was absolute simplicity to use during the hunt. Next time I'll probably be able to install it on the car and be off and running in 5 to 10 minutes.

Perhaps this competitive thing isn't so bad after all! :-) But, to tell the truth, I will always be happy just to attend our hunts. After this one we all went to the Armadillo and enjoyed a Mexican repast while chatting about the Hunt, Doppler, the next EOSS balloon launch and various other topics. That's always the real payoff.

So, thanks Ramsey for a nifty DF tool. Thanks to Jim for hiding for us (no one wants to be the fox, we all want to hunt it). Thanks to Benjie and Chris for letting me win and thanks to Ann Foster [K0ANN] who couldn't make the hunt but did make the dinner. Why thank Ann. Well, I groused that I didn't want to hide next month as I had this new toy I wanted to play with and Ann graciously offered to be the fox. Not a terribly difficult task for a YL! :-)

Ann [K0ANN] and Carla [nocall]