Foxhunt Sniffer MK4

[O-Rex]

A bozo in my unit lost our little L-Per  and we are hurting for a DF

Someone recently turned me onto an Austrailian-made DF, a Foxhunt sniffer MK4

We just had a unit finance committee meeting, and I just got the okay to buy one: at about $250, they are relatively inexpensive.

Anyone out there using one?

[BigMojo]

Yup.... Sure am. I have mine matched with a tuned beam from www.arrowantenna.com . I've said it on here before, but the unit is unbelievably intuitive, simple to set-up, and when used with a beam antenna, darn near idiot proof. Depending on the situation, I use either of the first two modes. The first mode when you turn it on takes the sweep tone and raises the pitch as you get closer to the beacon this is a great mode for rookies, as it will get them walking in the right direction, right away. The second mode is the straight sweep tone, but has an audible alert (two raising or lowering beeps) if you are getting getting closer or further from the source. I use this to really pinpoint my bearing. I'm not sure how or why, but the Sniffer seems to be less subject to reflections that the L-per, it's always been really easy to pick out the true signal. I also carry a rubber duck for close in work on a crowded flight line.

What really comes in handy is that is has a display showing "signal strength". I've found that most practice beacons max it out at "7" and real ones at "8" I know when I get to a 5 or 6, that I'm within 100 feet. Range is comparable to L-per, but may be a little less. I also have a generic "scanner" antenna on my truck, that the Sniffer will plug into for driving through neighborhoods. One benefit most people don't look at is that the Sniffer is VERY light, makes for easier long term missions. Also, besides the onboard speaker, it also has a jack for headphones.

I think the biggest negative to the unit is getting in contact with Bryan (the MFG) and placing an order...

[Ricochet13]

Do you have a website address or contact information.  May order one if the price mentioned here holds up.

[O-Rex]

Do you have a website address or contact information.  May order one if the price mentioned here holds up.

http://users.bigpond.net.au/vk3yng/foxhunt/foxhunt.html

BigMojo: So it doesn't come with an antenna?

[O-Rex]

Yup.... Sure am. I have mine matched with a tuned beam from www.arrowantenna.com . I've said it on here before, but the unit is unbelievably intuitive, simple to set-up, and when used with a beam antenna, darn near idiot proof. Depending on the situation, I use either of the first two modes. The first mode when you turn it on takes the sweep tone and raises the pitch as you get closer to the beacon this is a great mode for rookies, as it will get them walking in the right direction, right away. The second mode is the straight sweep tone, but has an audible alert (two raising or lowering beeps) if you are getting getting closer or further from the source. I use this to really pinpoint my bearing. I'm not sure how or why, but the Sniffer seems to be less subject to reflections that the L-per, it's always been really easy to pick out the true signal. I also carry a rubber duck for close in work on a crowded flight line.

What really comes in handy is that is has a display showing "signal strength". I've found that most practice beacons max it out at "7" and real ones at "8" I know when I get to a 5 or 6, that I'm within 100 feet. Range is comparable to L-per, but may be a little less. I also have a generic "scanner" antenna on my truck, that the Sniffer will plug into for driving through neighborhoods. One benefit most people don't look at is that the Sniffer is VERY light, makes for easier long term missions. Also, besides the onboard speaker, it also has a jack for headphones.

I think the biggest negative to the unit is getting in contact with Bryan (the MFG) and placing an order...

You're in Lauderdale??

PM me: your Group CC was the one who turned me onto it.....

[BigMojo]

O-Rex, You have PM.

But for the good of the group here...the Sniffer ships from Australia as is, just "the box" you have to source your own antenna, hence the link I posted to Arrow. He is working on a solution for 243MHz as well, but it isn't ready just yet (I'll be one of the first to know when it is...)

[JoeTomasone]

Mine should be arriving this week.   I plan to try it with several different antennas and will make a full report!

Part of the reason that the sniffer/beam seems more immune to reflections is that, well, it is.     The L-Per receives from all directions at once and uses the strength of the signal at each antenna to determine which antenna is closer to the signal (hence the "turn left/turn right").  Of course, once you've turned and gotten the signal at equal strength to both antennas, you don't know if it's in front of you or behind you.

A beam antenna will see the strongest signal in the direction of the signal, period.   A reflection cannot be stronger than the original signal, and the beam receives best off the front of the beam, so inherently when the beam is pointed at the signal source you get the strongest reading.

Now, this isn't black and white -- the source may be obstructed and you may be seeing only a reflection - but you'll figure that out quick enough once you get to the source of the reflection.  Plus, you won't be wondering if the reflection is in front of you or behind you.

One easier way to think of this is to imagine trying to find a flashlight amongst buildings made of tinfoil.   Your eyes are like beam antennas - they receive best only in one direction, and will lead you towards the source.   If the flashlight is behind something so that you can't see it, but you see a reflection, once you walk to it and look around, you'll see a much stronger "signal" somewhere and head for it.   

This also applies to body nulling (if you do it right - and here's where those of us who can't wear the AF uniform have an advantage!) or to using any other receiver (even the L-Per in receive mode) with a beam antenna.   


So the real advantages of the MK4 Sniffer vs. the L-Per, even when both use beam antennas:

1. The MK4 auto-attenuates the signal as you get too close to it.   No need to change frequencies further away or engage a manual attenuator.   It has several steps for this as well.

2. It can present the signal as a rising/falling tone based on signal strength, which is much easier for your ears to distinguish than a strong/weaker sweep tone.   Think "metal detector" here.


Hopefully it works as well in my hands as it is doing in my head.   


I'll definitely cosign BigMojo's comment on getting in touch with Bryan - he's not big on returning phone calls/emails in a timely fashion.

[BigMojo]

Thanks for the Tech-Geek explanation Joe, much better than I could have done...not bad for a Canon guy.... 

[JoeTomasone]

Gee, thanks, Nikon-man. 

I should point out that a beam antenna WILL receive on the sides and the back, but not nearly as well -- and the degree to which it is biased towards the front (the "gain") depends on how many elements it has (mostly).

Here's a top-down look at the antenna pattern of a beam:



As you can see, the main lobe is off the front, with smaller lobes off the side and back.   As you add more elements (increasing the gain), the pattern would get stretched towards the front (and the lobe would be thinner/more pointy -- reducing it's beamwidth - the angle in degrees in which the antenna will receive a signal from a given source/point) and the side and rear lobes would shrink - something like this:




So a longer beam with more elements is better for our purposes - allows us to get a more precise bearing and from a greater distance - but is more cumbersome to carry/store.

[_]

http://cap-es.net/ES%20Electric%20Technology/Build%20A%20DF%202.htm

In MD we all use the tape measure antenna.  Not as good as a professionally made antenna but still works very well and is a lot cheaper.

[JoeTomasone]

Here's a few notes on my MK4 experience thus far:

When outdoors, it's stupid-easy to find the signal source.   We placed the unit in a plane, gave an L-Per-trained member 60 seconds worth of training and turned him loose, and told him to go as fast as he could.   He walked through the aircraft scattered on the tarmac and walked right to the signal in about 2 minutes - and all but a few seconds of that was walking time.   Literally.

We also tried it in a hangar that had about 6 aircraft in it.   While it was a lot trickier, it was certainly faster and easier than using the L-Per or body nulling with a scanner.     In a worst-case scenario, we placed a training beacon in the U-shaped area between the hangar wall and the open doors, and behind a 55 gallon drum:


      ---------
      !         !!
      !    *   !!
      !    []   !!  <-- Stacked hanger doors
      !         !!--
      !
      !


(Where the "*" is the beacon and the [] is the 55 gallon drum.  Top-down look.) 


I located it in about 10 minutes after chasing some reflections.


The antenna I am using the majority of the time thus far is the 2-element Diamond MAY-1000 portable beam.   It's around $100.00, but is very compact, tunable from 120-500 MHz, and light.   An older 3-element beam I had laying around (2m) performed "OK" (somewhat as expected) and was a beast to deal with.   Carrying the MK4/MAY-1000 combo versus the L-Per and wooden monster is like night and day.   Probably 1/3 the weight and 1/3 the size.   It can all fit in a briefcase or small shoulder bag.

What did NOT work so well was the Radio Shack mobile scanner antenna.   At 2.5 miles from a practice beacon I lost the signal.   The very small 2m/70cm Comet antenna that I use (16" high or so) for 2m/70cm/CAP VHF work was much better at 121.775.   (Thus the thread I started looking for a replacement)

However, in my tests with the Radio Shack antenna, the MK4 was more sensitive than the L-Per.   The training beacon was detected in one test by the MK4 at 3 miles out - and by the L-Per at 2.5 miles out.   All three (beacon, MK4, L-Per) had new batteries. 

One thing I was particularly impressed with -- the directionality and sensitivity of the MK4 with NO antenna.  When in the street and trying to determine which house on which side of the street had the beacon, I merely held the unit out the driver's window (antenna jack pointed at the house) and then did the same out the passenger window and nailed it cold.   The same technique can be used to determine which aircraft in a hanger has the unit (reflections notwithstanding, but as soon as you get next to the plane that has it -- you'll know it - big time).     In a row of closely-parked cars and CAP vans, an untrained member was able to determine not only which vehicle had the beacon, but which PART of the vehicle.    We were able to locate a beacon in a plane down to the seat it was on.   All of the people I've had try it so far that have been DF'ing with the L-Per said they were very impressed; that it cut down the time they would have taken to find the beacon using their favorite methods, and when they heard the price, they were sold. 

So the only thing I really have yet to do is to identify a better mobile mag-mount antenna for 121.5.  Once I do that, I expect to have a killer UDF system in place.

 

[BigMojo]

Told you so.


When you get the best solution for the car mount let me know, that's my struggle as well.

[JoeTomasone]

OK, some more details...


I have two 121.5 mag-mount mobile antennas on order - one is an Icom from some random vendor, and one is (ironically) from L-Tronics.  I have high hopes that the L-Tronics one will be the better of the two since it's the cheapest by far.   I was also surprised to discover that they sell a 121.5/243 beam - that's on it's way as well.   I think the combination of the beam and the MK4 could change the way we find ELTs..  But I'm getting slightly ahead of myself since I have yet to prove in real life what I think will happen. 

Tonight my Wing/DC and I hunted a practice beacon planted by my Grp/CC so that we could compare the old L-Per, new L-Per, and the MK4.    To make a long story short, they performed roughly the same until we got close-in, and then the MK4 took over.   The Grp/CC was nasty, and hid the beacon behind an auto body shop -- he was friends with the owner and had permission -- and the reflections in the front of the building (which was essentially a metal U) were incredible.   As we got out on foot a block or so away, we agreed to split up and try to find the ELT as quickly as possible - myself with the MK4, and the DC with the L-Per.   I found the ELT in about 3 minutes.   He spent 10 or so, then gave up on the L-Per, concluding that it would take too long to locate.   I gave him the sniffer, and 3 minutes later he found it.

Now, before this, he'd been told by one of our Wing Comm Staff that the MK4 was just a receiver, was overpriced at $230.00, etc.   He was also pretty convinced that he could replicate the MK4's performance with the L-Per, his airband handheld, etc. 

Well, let's just say that now he's ordering an MK4. 

My intention, after I go through a few more tests, is to get the Wing/DOS to come check it out, and if he concurs that it's as good as we're saying, I plan to make a formal proposal that we consider going with the MK4 from now on as a standard for Florida Wing.    After all, the combination of the MK4 and the MAY-1000 portable beam is HALF the price of an L-Per - and well within the reach of most Squadrons at $300 or so.   If the L-Tronics antennas work out well, a Squadron could have a world-class DF setup for $400 or so, including the misc. parts needed to mount the MK4 to the antenna and the like.

Now to see if reality will meet my expectations.


OH - and one other thing in the MK4's favor over the L-Per -- it covers our VHF frequencies, meaning that we can use it to DF jammers or perhaps even locate a lost member who has a VHF radio. 

[JoeTomasone]

I made a quickie video to demonstrate the MK4...

http://www.youtube.com/watch?v=s5JSXrffyj0

[BigMojo]

You over-achiever!     j/k Nice work Joe. I've found with my 3 element Arrow Beam, that I get better results with a horizontally oriented beam, I noticed yours is vertical, did you notice much difference?

[RiverAux]

Man, that thing sounds like R2D2 on crack!

[JoeTomasone]

You should match the polarization of the beam (or any antenna, for that matter) to the polarization of the transmitter.    I was out on a ND mission a few months ago and we had a hard time finding an area where the signal strength was such that going on foot was practical.   Just out of curiosity I flipped my beam horizontal and the signal perked right up.   I was pretty convinced at that point that the beacon was horizontal as well, especially since the L-Per that the other team member was using wasn't doing so hot on RX.   When we located it, it turned out to be an EPIRB that was laying on it's side on the kitchen table. 

You can't really see it on the video, but I made a mount plate for the MAY-1000 that allows me to rotate it 90 degrees if needed, and that's why.   You lose a significant amount of signal if you are not in the same plane as the transmitter - and the effect intensifies with distance (less signal and less chance for reflections, which can be in phase with your antenna). 

That being said, you should NOT be getting better results with your beam horizontally polarized when working with a vertically polarized beacon at any reasonable distance unless you have some serious reflections that are coming at you horizontally.   

[JoeTomasone]

Man, that thing sounds like R2D2 on crack!

True, but therein lies the beauty - the human ear responds to changes in pitch much better than changes in volume, so it's much easier to get a good bearing with the MK4 - and you don't have to look at it and watch a needle. 

[BigMojo]

...and that's why I'm still and always learning. I'll have to do some more practice and listen a little closer. Glad it's all working well for you too Joe, you know how much I like my system, you have easier access to the Wing Staff decision makers over there now, so hopefully we can get more of these deployed across the state.

[JoeTomasone]

...and that's why I'm still and always learning. I'll have to do some more practice and listen a little closer. Glad it's all working well for you too Joe, you know how much I like my system, you have easier access to the Wing Staff decision makers over there now, so hopefully we can get more of these deployed across the state.

We're ALL always learning.  That's one of the great things about CAPTALK - sharing the knowledge.

If you want to check the phenomenon out without waiting for a mission, just use your VHF radio or a portable broadcast FM radio - tune it to a station that's a few towns away, then turn the unit/antenna 90 degrees and watch the effect on the signal.   Generally speaking, the closer you are (or the higher the TX power), the less pronounced the effect - but even if you are pretty close, you should still get some hash.   So combine a low powered ELT, some obstructions like buildings, trees, airframes, etc, and some decent distance and the signal is low enough where polarization is important or even critical.

Now, of course, where this becomes a real problem is when you have a horizontally polarized beacon and a vertically polarized antenna on your vehicle roof that you're trying to get AOS with...  No terribly good answer there, of course, but there are some ham antennas that have a "fold-over" option for getting in the car, etc.   I have one that I might play with like that.