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Author Topic: Fox Hunting a Jammer on 2 meter repeaters  (Read 9344 times)

Posts: 112

« on: December 30, 2014, 09:38:30 AM »

I have never been on a fox hunt, so I do not know what is needed or how to do a fox hunt.  I would need a receiver and a directional antenna?

There is a jammer causing malicious interference on 2 meter repeaters in Richmond, Virginia.   

The person plays music or sound files sometimes.   Or deliberately causes noise.  Or bring up and down IRLP nodes to foreign nations like Mexico to to disturb hams currently speaking.  Nothing wrong with IRLP or EchoLink, it is just someone kept bringing up and down on our side while a QSO was in progress.  And this happens many nights too.  However, I think many IRLP functions have been locked down now due to the jammer.  This is shame.  Now, I personally never got into bringing up or down IRLP nodes - it was not my thing.  However, there are new hams that get a radio and license, and they like connecting to other repeaters in the world - that is fine with me.   If you go to another repeater or a simplex frequency, the jammer will follow.   If you mention that there is a jammer or malicious interference, the jammer will cause more interference.  Yet, the jammer seems to smart enough to disappear when we intentionally try to figure out where this jammer is located by checking the incoming frequency.

What can we do?

Daniel, KK4MRN

Posts: 13712

« Reply #1 on: December 30, 2014, 04:23:01 PM »

Hi Daniel,

The first thing is to not talk about it on the air. There may be groups
already searching for the source, but they won't talk about in public
or on the air.  The best thing to do is to contact the repeater trustee
and ask if you can help.  Don't be offended if they say "no", as there
may be efforts already underway.  For example, they might have a
suspect and be waiting for the FCC to come confirm it, and not want
some other hunter to show up and scare the jammer off.

As far as tracking it down yourself, you need a directional antenna
and a receiver with an s-meter:  I use my mobile rig with a 2-element
quad on a mast sticking out the window. One other useful accessory
is an attenuator to reduce the signal strength when you get close.
The best type is an "offset" or "active" attenuator rather than one
using resistors, because it is less susceptible to strong signals sneaking
in through the case of the radio.

All of this can be built inexpensively at home. There are other options
as well, especially when one is trying to be discrete, or where you need
maximum bearing accuracy for triangulating from a distance.

For further info on transmitter hunting, visit K0OV's web site at

Posts: 265


« Reply #2 on: December 30, 2014, 09:32:44 PM »

Hi OM Daniel,

Local hams using beam antennas with rotators and able to receive 'S' meter readings of the jammer's uplink signal could share their bearings to get his approximate location by triangulation.

The next job would be to home in using portable beam antennas and active attenuators such as these.

Good luck!




Posts: 869

« Reply #3 on: December 31, 2014, 11:57:15 AM »

This requires a highly coordinated effort, something which presents somewhat of a difficulty when the interference is sporadic. If the disruptions are regular in nature, then there is no great hurry to catch the offender the first time out. Gather information over a period of time to establish the case.

Rough triangulation by stations with directional antennas is optimum, but not always possible. Make note of who can hear the jammer direct to get an idea of rough location, and whether the station might be static or mobile. Plot it on Google Maps.

If the jammer is mobile, it can be nearly impossible to track and verify.

If the jammer has a 'history' of disrupting a particular net on a particular day or night, then it becomes easier to create a tracking crew 'on call'.

Of course, talking about this on the repeater or even on the same band the disruption is occurring is self-defeating. Use HF, 6m, 220 or even cellphones (with handsfree, of course) for communication between monitoring stations. An iPhone can merge up to 5 callers to create a continuous conference.

All starting location assignments should be predetermined to expedite the deployment of monitoring stations to appropriate locations at a moment's notice. If you are 'hunting', don't use the repeater for coordination. If you are 'in the field' troubleshooting interference to a net, check-in if you like, but don't mention you are mobile. For these situations, it's important the net sound 'normal'. Ideally, the net control need not even know there is a hunt in progress.

It is helpful to have one monitoring station go to the repeater site with a handheld directional antenna to get a baseline direction when the transmissions occur. This will quickly determine if the jammer is nearby, mobile or parked/fixed station.

Some jammers will park very close to the repeater site and use low power settings to prevent their signal from being received directly by most outlying stations. A good indicator this is happening is if few or no stations seem to be able to actually hear the jammer direct, but can't override the jammer and capture the input frequency using normal power required for full quieting.

A weak, scratchy or variable signal can be a sign the jammer is operating at low power, but not close to the repeater, or is indoors on a handheld. Listen carefully to the signal. Picket fencing is self explanatory.

« Last Edit: December 31, 2014, 11:59:16 AM by K5TED » Logged

Posts: 568

« Reply #4 on: January 03, 2015, 12:58:56 PM »

A handheld with a rubber duck held at about 35 to 40 degrees from parallel to your waist will be directive in the direction you face.  Just try it on a known signal by turning in a circle while standing in place.  You'll hear the noise change as the signal increases and decreases.  A hand held with a meter is even better.   If you get close enough to the low life you can remove the antenna and use the radio without it to get a more accurate fix.  The less you talk about  it the better.  220 was used here for tracking 2 meter jammers.   Many lowlife were using "hot" radios and the 220 gang was small enough that we knew no 220  radios were missing.  Jammers everywhere love recognition of any kind.  There are also computer programs which will look at the key up signature of a radio signal on a discriminator.   Haven't seen a radio yet which didn't start a bit low and end  a bit high or vice versa.   Low life are often caught because they use the repeater in the "normal" way when not jamming it and the jamming signal cam be matched with a call sign.  The nice thing about catching a low life with a hot radio is said creature can be busted for possession of stolen property. 

Posts: 418

« Reply #5 on: January 04, 2015, 08:52:11 AM »

Note:  WB6BYU's Link posted earlier is incorrect.....probably due to a typo.

Should be:

Ed,  K7AAT

Posts: 59

« Reply #6 on: January 04, 2015, 02:25:51 PM »

I hunt interference sources on wireless networks and think it wouldn't be too much trouble to locate if you can get some basic info. If you have a directional antenna, is his signal coming from the same direction evry time? if so, he's probably not mobile. I use some specific equipment designed for direction finding, but if you can get a portable spectrum analyzer and a directional antenna, you can zero in on the general location pretty quickly. If it stops, next time, you go where you last saw it and continue. Let's say you determine the interference is west of your location. Depending on signal strength, guess how far you think it could be and head west with your directional gear. Stop every mile and recheck until you see it move north or south. At that point, assuming he's stationary, you are beginning to pass him. move in that direction if possible. Overshooting is fine as long as you can verify you get on the other side of him. The point is to create a circle of where he is and then move in from there. If may take a week of jumping in the car a few times, but once you get it down to a few square miles, you can pull the addresses of all of the licensed hams in the area. Chances are, it is a ham and I would start there.

It isn't as hard as you might think. I often start driving with an omni antenna and a spectrum analyzer. Once I get fairly close, I break out the directional antenna and drive a block, sweep the area, drive a block, etc until I get really close. At this point, it's sometimes helpful to employ attenuators. I use a 0-50dB adjustable which is usually fine. A band pass filter is helpful when you get close too, but not as practical at 2 meters.

If you find him, unless it's a young teenage punk, I wouldn't confront him, record him, the location, anything you can to identify, then call the FCC, or local sheriff may be helpful. I have found the FCC is very lenient on unintended interferers, but can be very harsh on those intentionally disrupting communications. 

Good luck and keep us posted

Posts: 869

« Reply #7 on: January 04, 2015, 08:22:55 PM »

Sometimes they're NOT hams..

Posts: 224

« Reply #8 on: Today at 09:26:37 AM »

There is also another location to find lots of very good RDF info and many of the So Cal (and K0OV) and other RDF'ers monitor.

It is my YGroups RDF-USA        Grin

You may also try to contact your ARRL SM to get to the area OO team alerted. They maybe already on it, just collecting evidence/data. I was once a WI & Los Angles OO Coordinator (in the worst jamming area of the USA with an estimated 50K HAMs). The only issue we had was the lack of ARRL SM support/integrity and with the Govt priorities placed on the small LA  FCC Office, HAMdom was not even on their priority list just considered a nuisance to them (its all politics & budget vs. manpower).

However, by 1990 THEE ARRL HQ took away any/all direct OOC contacting with area FCC offices - everything must go through ARRL HQ (to be filtered for political gains and PR splash). This is when I forever quit the ARRL understanding their real goal [memberships to secure HQ $alaries], an organization that wants to be everything to every one focusing on memberships but failing on items that can reduce memberships, i.e. OO enforcement - making the OO group a mere paper toothless neutered potential tiger.     

Soon you will locate the problem/LID - then comes another layer of frustrations - how (legally) to get this LID off the air..... Here is where I advise all to start your paper trail.... sequentially begin the required process that the FCC mandates before they will act (if they act):
1st write the ARRL SM, with your evidence/data - you may get a placating response/meeting.  Huh
After 1 month nothing changed then;

2nd write ARRL HQ (cc: SM), w/evidence/data and SM letter/minutes, they will refer you back to the SM.  Lips sealed
After 1 month and nothing changed then;

Here is where I add steps to improve successTongue

3rd write WDC FCC (cc:ARRL & your local Mayor/City Counsel/County Commissioners), w/evidence/data and ARRL letters, they will likely refer you back to the ARRL.
After 1 month and nothing changed then;  Undecided

4th write all your Congress-persons (cc:FCC, Mayor/Counselors/Commissioners), w/evidence/data and all letters. HERE is when, with luck, your Congress types will send a query to the FCC - the FCC HATE Congressional queries - who gives them their salaries - this is the only REAL power we have to get FCC to action but you need to arm the Congress-types with all the info proving you worked the system unsuccessfully. Until you get a Congress reply keep sending sending/resending your package to your Congress-persons - get your whole group to send letters to Congress-persons.  Shocked

This is the only game I found that works and I've been advising HAMdom for decades how to play this game. Even then with your perseverance and overcoming frustrations it takes months to maybe get this LID off the air.  Cool


Posts: 224

« Reply #9 on: Today at 09:37:59 AM »

If you find him, unless it's a young teenage punk, I wouldn't confront him, record him, the location, anything you can to identify, then call the FCC, or local sheriff may be helpful. I have found the FCC is very lenient on unintended interferers, but can be very harsh on those intentionally disrupting communications. 


Typically, the Sheriff will not get involved unless it is on their repeaters and even then their hands are tied as it is a FCC Code violation.

I've only seen the local FCC get involved if it is unintended RFI by some commercial entity as the FINES are high to commercial sloppy engineering/maintenance/self-monitoring.

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