Intentional repeater jamming and how to deal with it

[WRAK968]

Good afternoon/evening everyone. Hoping your Tuesday has gone well.

 

This afternoon I experienced my first intentional jamming incident on the repeater. It started as a few key-ups, however when my father asked if I was calling, this unknown individual chose to hold down the transmit button without speaking. They did this for 30 seconds, than a minute, then 5 minutes, then for 20 (Im sure their transmitter is toast now.) At first I suspected that maybe something was wrong on the RX side of the repeater, so I tuned my portable to the repeaters input frequency, and sure enough there was a signal. So my first action was to jump into my SUV and try to track it. I could clearly receive the signal from inside of my house on a portable, so the transmitter couldn't be too far away.  Using both the truck radio and the portable I tracked it to a house about 4 blocks away where a group of young adults were standing in the driveway laughing. I could see an antenna on the pick-up in the driveway and one of them was holding what looked to be a portable radio. At that location, my portable was receiving a clear signal without an antenna and while laying next to my leg. As I drove by, they saw my vehicle and me looking at them and they panicked. By the time I drove around the block, they had removed the antenna from the roof of the pick-up, and all had gone inside, looking out a window for me, and they stopped transmitting.


Now, I would not recommend confronting anyone about radio jamming. There are too many crazy's in the world and really its not something to get shot over. I slowed in front of the house, and acted like I was taking down information, then drove away just to scare them a bit.

Upon getting home, I removed the access codes from the MyGMRS listing. (Its odd they just tuned directly to the DPL I set for the repeater) and over the next day or two I will begin changing the access tones for the repeater. I may even use a split tone just to reduce the likelihood of this happening again.

 

Then I got curious, I wondered what other repeater owners have done during a jamming situation to protect their equipment and stop the jammers from getting in.

 

So to repeater owners out there, have you ever experienced jamming and how did you handle it?

[kidphc]

You all do realize, if the jammer(s) did get the PL times from MyGMRS, they are probably reading this thread and likely enjoying the attention.

If that is the case, those people deserve to lose their license. Goes against the spirit of the community.

 

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[berkinet]

If that is the case, those people deserve to lose their license. Goes against the spirit of the community.

 

They deserve to lose their license for simply violating the regulations for simply interfering with another communication.

§ 95.333 Prohibited uses.

No person shall use a Personal Radio Service station:

...

(d) To intentionally interfere with the communications of another station;

(e) To transmit obscene, profane or indecent words, language or meaning; or

...

 

§ 95.1733 Prohibited GMRS uses.

(a) In addition to the prohibited uses outlined in § 95.333 of this chapter, GMRS stations must not communicate:

...

(4) Music, whistling, sound effects or material to amuse or entertain;

...

(10) Continuous or uninterrupted transmissions, except for communications involving the immediate safety of life or property; and

...

[GuySagi]

Well, berkinet's post is sobering. I did, however, want to thank jec6613 for the tips. Great stuff and very educational. I'm not relying solely on GMRS for punching out an emergency message, but reminders like yours are always smart. The more systems I have, the better off I am. And if the jammer is indeed reading this, if he or she actually can read, not all gmrs transmissions are routine work or pleasure related. In my case that repeater could be lifesaving. If you're jamming it when (God forbid) I need it, I will indeed invest in that doppler system, locate your home and engage an ambulance-chasing attorney to recover that investment in gear, attorney fees, court costs and damages—and I've never, ever done something like that in my life, but when deliberate stupidity jeopardizes my family...I apologize to the fine regulars here for my terse tone and promise to avoid doing so again, dang it. 

 

[w4thm]

lol jammers! That's a sport down here...

 

1) the FCC aint gonna do squat. You rule quoters are spinning your wheels. Even when a case is handed to them on a silver platter with video it still takes a bit of harassing them to get them to show up. 

2) Marc is on the right track. Ignoring them and talking over them demoralizes them. It's no fun kicking a fence if the dog doesn't bark. This works for most situations.

3) On the flip side of what Marc says, some of us down here have become expert hecklers. The last thing a heckler expects is a full on attack from a group of experienced hecklers. You better bring your humiliation "A" game though.

[WRAK968]

 

Well, berkinet's post is sobering. I did, however, want to thank jec6613 for the tips. Great stuff and very educational. I'm not relying solely on GMRS for punching out an emergency message, but reminders like yours are always smart. The more systems I have, the better off I am. And if the jammer is indeed reading this, if he or she actually can read, not all gmrs transmissions are routine work or pleasure related. In my case that repeater could be lifesaving. If you're jamming it when (God forbid) I need it, I will indeed invest in that doppler system, locate your home and engage an ambulance-chasing attorney to recover that investment in gear, attorney fees, court costs and damages—and I've never, ever done something like that in my life, but when deliberate stupidity jeopardizes my family...I apologize to the fine regulars here for my terse tone and promise to avoid doing so again, dang it. 

 

 

A word of warning. I am a licensed security rep, DON'T EVER CONFRONT SOMEONE IN PERSON to make a legal threat. Too many crazy people who would just pull a trigger to get rid of you. Catching or stopping a jammer is not worth your life.

[jec6613]

Well, berkinet's post is sobering. I did, however, want to thank jec6613 for the tips. Great stuff and very educational. I'm not relying solely on GMRS for punching out an emergency message, but reminders like yours are always smart. The more systems I have, the better off I am.

As a quick follow-up, a Rhombic for GMRS packs stupidly small, as small as those tacticool folding antennas. You just need about 4 yards of wire, an 800 Ohm resistor, 4 one foot long sticks, a bit of feed line, and the hard part: a 16:1 balun, and you have 16+ dBd gain, or over 18 dbi gain.

 

Radiotelegraph and telephone services used to use them on HF for AM voice and CW, they provided a reliable link from LA to Shanghai, and London to Johannesburg, among other pairs.

[GuySagi]

Good advice wrak968. I’m too old to get in a tussle that’s for sure.

 

So where do I find plans to build a rhombic?

[kidphc]

https://www.mapability.com/ei8ic/rhombic/rhombic.php

 

Scale down to desirable frequency.

 

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[GuySagi]

Thank you for the link.....looks like an awesome project for me and my grandson. 

[kidphc]

Thank you for the link.....looks like an awesome project for me and my grandson.

Ever thought about a yagi instead. Yes it is directional. But there are instructions all over the internet on homebrew styles, usually using yard stick tape (from harbor freight) and pvc pipe. You can also make an attenuator for fox hunts. Homebrew jpoles are popular to experiment with. All usually costing less $60.

 

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[berkinet]

Ever thought about a yagi instead. ...

 

Yagis are excellent antennas, very useful for many permanent station locations, and, sturdy and easy to build. However, for DFing (Direction Finding) their reception pattern is broader with less of a null just off the center than a rhombic.  Another antenna design that does quite well for DFing is the Loop Antenna.

[jec6613]

Rhombics also travel more easily than yagis generally. A yagi is limited by needing to have a dipole in the middle and ridgid support, while a rhombic is basically a random wire. The half wavelength above ground for that 5 degree upwards angle is tricky for, say, the 11m CB band, let alone something like 160m or 80m amateur bands where the antennas can be multi-acre in size, but for 1.75m Murs and 63cm GMRS it's no problem.

 

The only tricky part is getting the angle correct, and the 16:1 balun to run a 800-900 Ohm antenna.

 

They're also REALLY wideband, so make perfect TV antennas if you want OTA HDTV.

[kidphc]

Yagis are excellent antennas, very useful for many permanent station locations, and, sturdy and easy to build. However, for DFing (Direction Finding) their reception pattern is broader with less of a null just off the center than a rhombic. Another antenna design that does quite well for DFing is the Loop Antenna.

Oh I get it. There is a reason the AARL has it as part of the logo. Is the there that much difference in sensitivity between a loop and rhombic?

 

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[berkinet]

... Is the there that much difference in sensitivity between a loop and rhombic?

 

Good question.  Hopefully someone will answer. Otherwise I will dig around the Internet this evening.

[jec6613]

Is the there that much difference in sensitivity between a loop and rhombic?

Usually a minimum of 14 dBd better. A loop antenna is basically a dipole with its ends curved around - for df work though the pattern of a loop lends it to be compact and it has slightly more gain directly broadside than a pure dipole and a more even falloff as you move side to side, so you can locate better.

 

About the only thing with more directional gain than a rhombic is a curtain array, where an array of dipoles and reflectors an beam a shortwave signal from Alaska to cover all of the Americas, or a caged dipole array - Duga (the Russian woodpecker) is a caged dipole, for instance.

[UHFJim]

Split tone may be the way to go. Helps stop radios with tone scanning features from picking up the input tone, too.

 

I have used reverse DCS on portable machines during emergencies, too.

 

Best way to go.  Smart repeater owners slam the jammers by using a PL or DPL for input (do not list the input on myGMRS), and use a different PL/DPL for receive.  

[berkinet]

Usually a minimum of 14 dBd better. A loop antenna is basically a dipole with its ends curved around - for df work though the pattern of a loop lends it to be compact and it has slightly more gain directly broadside than a pure dipole and a more even falloff as you move side to side, so you can locate better.

...

Thanks for the information. But, just to be sure I understand. Are you saying the rhombic typically has 14dBd more gain than a loop antenna? But, the loop may still be better suited for DFing because of the nulls on each side?

[JohnE]

Split tone may be the way to go. Helps stop radios with tone scanning features from picking up the input tone, too.

 

I have used reverse DCS on portable machines during emergencies, too.

you would be surprised at how many inverse DPL's correlate to a regular DPL and work, if you have the right equipment.

just sayin'

[berkinet]

Security through obscurity is no security at all. Just sayin'.

[marcspaz]

If I want/need security, I sure as heck won't be on GMRS. LOL. I'm just looking for ways of keeping lazy people from busting chops.

[jec6613]

Thanks for the information. But, just to be sure I understand. Are you saying the rhombic typically has 14dBd more gain than a loop antenna? But, the loop may still be better suited for DFing because of the nulls on each side?

 

A loop is generally better for DF because it has a very even radiation pattern, slowly rolling off from peak in a predictable way, and is deaf only end-on - gain is slightly better than a simple dipole.  A rhombic has insane gain, but is extremely directional and basically deaf outside of its narrow forward lobe, and the secondary lobes off at 90 degrees to either side.  That of course makes it excellent for fixed installations, and its ability to fold up very small for UHF and upper VHF is another large benefit.

 

Rhombics fell out of favor mostly because of how large they need to be when set up - four sides of 1.5-2 wavelengths is pretty beefy even on the 2M band, and ideally half a wavelength above ground.  Not a problem for UHF, but big trouble once you start getting towards lower VHF, such as 6m, where each leg is 30 feet long at minimum, and about 10 feet off the ground, and for 160m HF you need 700 foot long sides and it to be about 270 feet in the air ... not ideal.  Once the transoceanic cables opened to replace the HF radio links, they've mostly been a forgotten technology - Yagis are slightly less gain, but you can turn them on a rotator, even for HF bands, and height above the ground is much less important.  Some amateur operators with enough space and finances still do use them though, since they can get around the world on the 20, 40, and 80 meter bands even when they're closed like they are now.

[n1das]

you would be surprised at how many inverse DPL's correlate to a regular DPL and work, if you have the right equipment.

just sayin'

 

No special or "right equipment" is needed.  If a radio has DPL capability, it already has inverted DPL capability.  With one exception (D172N), every code in the table of 104 standard DCS codes has its inverse somewhere in the table.  For example, codes 125 and 365 are inverses of each other.  D125I is the same as D365N and vice versa.  I've been using 411 (normal) (D411N) and its inverse is 226 (normal).  D411I corresponds to D226N and vice versa.  Normal and Inverted simply refers to the polarity of the DCS waveform. By convention, a logic 1 is represented by a positive carrier shift and a logic 0 is represented by a negative carrier shift.  This is considered Normal polarity for a DCS waveform.

 

A DPL word is a 23-bit cyclic Golay pattern with a 12 bit codeword (23,12).  The 12 bit codeword is formed from the 12 least significant bits of the 23 bit DPL word.  The 12 bit codeword consists of a fixed octal 4 (100 binary) followed by the 3 octal digits that you can program.  Notice that the available DPL codes are octal (base 8) numbers.  The 11 most significant bits are error correcting code bits generated by the Golay algorithm from the 12 codeword bits. The 23 bit DPL word is transmitted repeatedly over the air at 134.4 bits/second.  The least significant bit is transmitted first, resulting in the DPL word being played out backwards over the air.

 

Here is the best technical description of DCS/DPL operation that I've been able to find:

http://www.onfreq.com/syntorx/dcs.html

 

Also check out:

https://wiki.radioreference.com/index.php/DCS

 

In my case of dealing with a repeater jammer who didn't have DPL capability and didn't have a clue and thought he knew all there is to know about radio, DPL also stands for "Definitely Prevents Losers" LOL.

[WRKC935]

I have found if you want to 'scare' them.  Get a government looking vehicle.  Couple antenna's and dark tint. 

Get some cheezy sun glasses and park ACROSS the road from them and sit looking serious.  Take some notes and pictures (don't really need the photos but use a real camera and not a cell phone. 

Don't answer any questions when they come over asking about what you are doing and just claim it's an ongoing investigation.  And for God's sake... wear dress clothes, and maybe a tie.  Try to look the part. 

People typically will revert to what they see on TV as being reality if they don't have first hand experience. 

 

Something as dumb as a notepad and a handheld radio you are "talking" into when you see someone doing dumbsh!t like tossing stuff in a dumpster will get them all worried.

We laughed about that for hours.  The property owner even came over and told us the next business day the guy had permission to use the dumpster.  When we explained it to him, he laughed too. 

But the point is to look the part and seem important.  People get all worried when they feel they are being watched.  But be careful... some folks WILL get violent with any sort of provocation.  So don't push, and always keep the vehicle pointed is a direction for easy egress (get away) from the location.