PL/DPL at same time?

EC-7 · Post by **EC-7** » Thu Jan 10, 2002 8:36 pm

Is it possible to encode and decode PL and DPL at the same time? I need higher security into our repeater's input do to someone scanning our PL and DPL codes and using them to access our system. Could I set a DPL on the radio and install a PL encoder and have them work at the same time? Same with decode on the repeater. I don't need encription or anything expensive like that. I'm tired of changing the PL and DPL due to this "CB" retard.

Jonathan KC8RYW · Post by **Jonathan KC8RYW** » Thu Jan 10, 2002 9:19 pm

A good idea... except it's not much of a secret anymore.

Just joking.

Back to the question: I *suppose* you could use DPL and PL, BUT BUT BUT you will have to pay special attention to the frequencies used by DPL and the PL tone. And, since I know little about DPL's frequncy components, I'm not much help.

But, I bet Motorola's Manual on DPL might come in handy: 6881106E83.
_________________
73
KC8RYW

[ This Message was edited by: KC8RYW on 2002-01-11 00:27 ]

EC-7 · Post by **EC-7** » Thu Jan 10, 2002 9:27 pm

I would think in theroy it should work, but I'm not sure, so I'll just have to try it. I looked up your call sign on QRZ.com and noticed that your from Novi, I live in Brighton, what a small world.

_________________
KC8GRQ Mark Rodgers
[email protected]

[ This Message was edited by: EC-7 on 2002-01-11 00:36 ]

Jonathan KC8RYW · Post by **Jonathan KC8RYW** » Thu Jan 10, 2002 9:31 pm

Yep, I'm from Novi. I used to live in New Hudson, and used to spend a lot of time in Brighton. Pleased to met you.

Just wondering, what type of repeater is it.. a neighborhood ham repeater, or something more vital?

Good luck spoiling their fun. Hopefully the unauthorized user will figure out what MURS is for.

_________________
73
KC8RYW

[ This Message was edited by: KC8RYW on 2002-01-11 00:48 ]

EC-7 · Post by **EC-7** » Thu Jan 10, 2002 9:47 pm

It's a MURS repeater. 154.600 :-{ It's not that big of a deal but they are getting annoying I think it is a cable tv or telephone company using handhelds while burring and running wire. I'm assuming that they are going thru all the dip switch positions on thier SPIRIT radios until they access my simplex repeater. Since it's not licensed and doesn't have to be, I can't do anything about it. I also have 2 meter, 440, and multiple bussiness band repeaters, but they are down now. Freq cooridination at a pain to get in this area.

Jonathan KC8RYW · Post by **Jonathan KC8RYW** » Thu Jan 10, 2002 10:20 pm

It always amazed me how many different ham repeaters there are in the Metro-Detroit area. And each of them is used maybe the most of four hours out of the day. And, they are usually 30 watts or so.

There is little reason to have that many different repeaters working independantly, in my opinion.

I say, set up one repeater on a big tower in Southfield, give it 500 watts ERP and rock and roll. Install remote recievers at the neighborhood repeaters sites. Link them all together.

Imagine talking throughout the Detroit area using only a 2 watt HT without changing frequencies. Wow.

Later on, those reciever sites could gain the addition of a linked transmitter. Great for filling in those areas with poor coverage.

Am I dreaming, or is this possiable? (I'm practically asleep right now in reality...)

_________________
73
KC8RYW

[ This Message was edited by: KC8RYW on 2002-01-11 01:22 ]

EC-7 · Post by **EC-7** » Thu Jan 10, 2002 10:37 pm

I agree with you. I always carry my Yaesu VX-5 handheld with me and I wish I could get into some of the local repeaters in Howell, Ann Arbor, Fenton ect. with it. I guess I should set up my cross-band repeater in my car, but that's another antenna. I am talking to Fred KC8ODY in Fenton to link his 220 and 440 machines to mine so we can have a multi band, multi reciever system. I saw you post in For Sale and I have a shed full of older Motorola crystal and other brand radios. I have too much to list. What do you want them for? We should hook up some time. My phone# 810-706-2123 or E-Mail me. Call after noon.

_________________
KC8GRQ Mark Rodgers
[email protected]

[ This Message was edited by: EC-7 on 2002-01-11 01:41 ]

jim · Post by **jim** » Fri Jan 11, 2002 2:03 pm

If you are using all Motorola radios on your repeater, why don't you just set it up so the repeater only activates upon receiving an MDC-1200 signal?

lobos305 · Post by **lobos305** » Fri Jan 11, 2002 5:04 pm

The problem is how to get a handheld radio to transmit CTCSS and DPL at the same time.

Will · Post by **Will** » Fri Jan 11, 2002 7:18 pm

Sorry guys, PL AND DPL at the same time,this will NOT work.
As for having a repeater on MURS, that is a NO NO.

In Los Angeles, if someone is using a legit repeater without the owners permission it is clasified as grand theft, a felony. If the telephone company, or anyone else, was using one of my repeaters WITHOUT my permission, I would hunt them down and advise them. If they continue, I file with the District Attorny's office.

Most use a DTMF code sequence to turn on the repeaters tone decoder for you to use it and then another DTMF code is sent to the repeater to turn off all access when you are done using it or when the "bootleggers" try to use it. If they (Bootleggers) are just simplexing on your input you might have a problem.

Jonathan KC8RYW · Post by **Jonathan KC8RYW** » Fri Jan 11, 2002 7:38 pm

If you were tring to take a "piggy-backer" to court, wouldn't you need some hard EVIDENCE.

I heard somewhere that each transmitter has it's own "footprint." I honestly thought this idea was totally silly.

I suppose you could hide out with a camcorder, patch a scanner's audio into the camera, and make sure the repeater ID's itself after every transmittion. Get a closeup shot of the telephone employee talking into the radio. If the audio is the same, it will match on the tape. Instant evidance. Be sure to get licence plates on the tape, too. That always helps.

Any other tips?

jim · Post by **jim** » Sat Jan 12, 2002 8:58 pm

...I think you should just beat the living hell out of the "abuser" with the antenna on a lowband MT-1000 !!!!
(this was an initiation at our FD years ago!)

Unfortunately, it's going to be hard to stop this person. Maybe, if a local public safety agency experiences any disruption on their frequencies, you could convince the officials that it's the same person and see how fast something's done about it.

hobbes · Post by **hobbes** » Sun Jan 13, 2002 5:36 am

If they are using Spirit radios, then just set up your radio to use DPL -- as far as I know, the cheapie type radios only have analog PL capability.
KC8RYW, here are two links to transmitter ID products. I've heard that the FCC uses a similar hardware solution to help prosecute illegal transmitters.

http://www.motron.com/TransmitterID.html
http://xmit.penguinman.com/xmit_id.html

Will · Post by **Will** » Sun Jan 13, 2002 12:48 pm

Hobbes has a good idea on using DPL as most cheapie radios do not have DPL capabilities.
But if it is a persistant "bootlegger" then they will be using whatever is needed to be able to talk on your repeater. There have been several cases of this in the past years,
even to the extent of the Bootleggers aka Pirates, running legitamate users off the repeater, usally by jamming them out.
I like the idea of thrashing the pirate with a low band MT antenna, altho I perfer a 44mhz stainless steel mobile whip!
Make sure your repeater is full legal and properly licensed then track the pirates down and notify the FCC and ITC and let them handle the thrasing part.

jim · Post by **jim** » Mon Jan 14, 2002 6:58 am

A 44Mhz stainless whip....OUCH!! Just make sure that the end with the spring hit them.

Post by **/\/\y 2 cents** » Mon Jan 14, 2002 9:45 am

Use inverted DPL or MDC1200.....you could also use RAT tones but your radios probably dont support that. If you have mid to high grade motorola radios, they should support inverted DPL.....look for a thing in the RSS that says Inv. DPL, no yaesu Ham bander can decode or transmit a dpl in this format as far as i know. It would take alot more work for a hacker to get his radio to do Inv. DPL and it will probably never be able to decode it...most bootleggers love pl/dpl decode, i know I used to be one myself.

Mike B · Post by **Mike B** » Mon Jan 14, 2002 10:19 am

Each inverted DPL has a corresponding regular non-inverted DPL. For example, you can transmit an inverted DPL of 244 and decode it as a regular non-inverted DPL of 025. Of course you can also decode it as an inverted DPL of 244. The matching pair of regular and inverted DPL codes do not have any obvious correlation.

For example regular DPL 032 = inverted DPL 051; regular 036 = inverted 172; regular 114 = inverted 712; regular 315 = inverted 423; regular 731 = inverted 155.

The simplest way to invert a DPL signal is simply to invert the polarity of the analog DPL signal.

You could use custom non-standard PL tones for reasonably secure protected access, except I am not aware of any legal approved MURS radios that can generate or decode non-standard PL tones.

If you use a non-standard DPL codes, most of the time all you will get is a DPL that will false on lots of different DPL codes.

Jonathan KC8RYW · Post by **Jonathan KC8RYW** » Wed Jan 16, 2002 12:08 pm

About Inverting/Regular DPL codes: check out http://www.n9jig.com/radio/PL.html. There is a good table there that shows each DPL codes invert.

As for using DPL and PL at once, it is possible in theory. According to the Motorola DPL manual, the input to the DPL decode section is low-passed at 150Hz.

What this means is that as long as you use a PL tone above 150 Hz, you should be okay with DPL. Personally, I would suggest using the highest PL tone avaliable, within reason. If you use 151.4Hz, you are probably asking for problems.

So, at least it is possiable to use DPL and PL in theory. I don't think it's been tried it in real-life, though.

Jonathan KC8RYW · Post by **Jonathan KC8RYW** » Wed Jan 16, 2002 12:12 pm

Also, about PL:

FM Stereo broadcasting uses a technology very similar to PL to tell your radio the signal is in stereo. They send out a tone at 19,000 Hz along with the audio. It's called the Pilot Tone.

Just thought I would share that with you.

Nand · Post by **Nand** » Wed Jan 16, 2002 12:52 pm

Jonathan KC8RYW · Post by **Jonathan KC8RYW** » Wed Jan 16, 2002 12:58 pm

On 2002-01-11 20:04, lobos305 wrote:
The problem is how to get a handheld radio to transmit CTCSS and DPL at the same time.

This really isn't very hard.

Comm-Spec makes some good after-market PL and DPL add-on boards. They are small, and should fit in any decent sized HT.

Let's say an HT has PL. So, I'd buy a Comm-Spec DPL board, and wire it in parallel with the OEM PL board.

Again, I haven't done this, but it should work. I can't find any reason why it wouldn't.

Sounds like another "Ham Project" for me to try.

Jonathan KC8RYW · Post by **Jonathan KC8RYW** » Wed Jan 16, 2002 1:40 pm

On 2002-01-16 15:52, Nand wrote:
If you do this, you loos a bit in the audio deviation department. The sum of all of them have to stay within the maximum deviation limit. What ever that is for these radios.
Nand

This is true.

The loss in deviation is the "price" to pay for annoying repeater-pirates.

Of course, if the pirate try's hard enough, and monitors your signal, they could figure out what you are using for squelch.

SO, to prevent this from happening, you could filter out the DPL code on the repeaters output, and hi-pass the PL and audio.

The pirate will monitor the signal, and will only see the PL tone. They'll lose their minds, and move to another target.

Best yet, if you only have a few radios in the system, encode ANI DTMF on PTT. Give all the radios the same number. This could be a way to activiate the repeater. But, don't use ANI to activiate the repeater in this case.

The pirate will think you use ANI to activate the repeater. More fun to annoy them with.

jim · Post by **jim** » Wed Jan 16, 2002 2:58 pm

....I still think that you get two buddies and triangulate seek them....then do exactly what happened to the guy in the movie "Casino" when he got caught cheating them. It will be a while before they're able to push the PTT button again, at least.

Do I sound violent lately?

Jonathan KC8RYW · Post by **Jonathan KC8RYW** » Fri Jan 18, 2002 10:40 am

On 2002-01-16 17:58, jim wrote:
Do I sound violent lately?

Probably.

Violence most likely won't help convience a court that the pirate needs to be punished legally, if someone has already punished them with a lowband antenna.

Will · Post by **Will** » Fri Jan 18, 2002 4:14 pm

Jonathan KC8RYW,

Trying to transmitt PL tone AND DPL code at the same time can NOT be done. If you had bee in the business way back when DPL came in you would know it can not be done.Not to mention type accp.
As for the original problem, SAVE your money because anything you can do the pirates can do. Make sure, as I said before, you are properly licensed and then go after the pirates or change the PL tone after carefully monitoring the input and output frequencies for a vacant tone.

Post by **xmo** » Fri Jan 18, 2002 5:01 pm

I think Will is right that trying to decode PL and DPL at the same time won't work since DPL is basically low speed data. I think it needs the entire low freq bandwidth to itself. The MPU is attempting to determine zero crossings in order to clock the data and the presence of PL at the same time would confuse things.

How about two different PL tones at the same time??? If you were going to put in an add-on encoder anyway - why not a second PL? There are lots of successful 2-tone systems like DTMF. If you choose freqs that are a ways apart the decoders should each be able to filter the discrete tone they are looking for.

It might not keep intruders out forever, but it would sure up the ante!

raymond345 · Post by **raymond345** » Fri Jan 18, 2002 6:18 pm

To the answer of ham radios with dpl
Yes the yeasu 2600 has TPL/DPL/Inverted DPL
We set up radios with a different input dpl and a pl output. works great.
My two pennies Raymond

Jonathan KC8RYW · Post by **Jonathan KC8RYW** » Fri Jan 18, 2002 7:40 pm

On 2002-01-18 19:14, Will wrote:
Jonathan KC8RYW,

Trying to transmitt(sp) PL tone AND DPL code at the same time can NOT be done. If you had bee[n] in the business way back when DPL came in you would know it can not be done.

I'd really dislike to disagree with this statement.

According to the Motorola DPL Therory and Service Manual (6881106E83-A):

"4.3.1.1 Low Pass Active Filter
The low-pass filter accepts an input signal (binary code word from discriminator) which contains the binary code word and audio signals. The active filter attenuates frequencies above 140 Hz (noise and voice signals) and allows the low-frequency binary signals to pass to the data conditioner."

"4.4.1.3 Code Conditioner Module
In recieve mode, recovered audio is applied to pin 1 of the code conditioner module where an active, low-pass attenuates signals above 150 Hz. "

I'm not trying to be difficult, although it may seem that way.

I just want to know why using a PL tone above 150 Hz along with DPL is impossible, given the above info from the horse's mouth?

Will · Post by **Will** » Sat Jan 19, 2002 3:39 pm

John, this is NOT the place to get into the full engineering on this issue. The PL tone will wipe out any of the "data" for the DPL and the DPL "data" will wipe out the PL decoder, enough said on this. Field tests and lab testing has proven this out. Why do you ask, because with heavy co-channel use most DPL users get knocked off by PL tones, and that is why the tests were done.
AND to qoute Raymond, "We set up radios with a different input dpl and a pl output. works great." This will work very well as a deturant.

[ This Message was edited by: Will on 2002-01-19 18:43 ]

Post by **wavetar** » Sat Jan 19, 2002 5:01 pm

I agree with Will. The DPL theory that was quoted conveniently left out the specs. The DPL distortion has to be next to zero, and the PL is supposed to be within tenths of a Hertz to ensure proper decoding without falsing. Having them both on the same carrier will certainly distort them both well beyond specs. It won't matter if they can be separated in the receiver, as the damage is already done. 167.9Hz might end up looking like 156, or 181. Hard to say what the DPL would look like, maybe not recognizeable (to the decoder) at all.

Todd

[ This Message was edited by: wavetar on 2002-01-19 20:05 ]

N9CZV · Post by **N9CZV** » Mon Jan 21, 2002 4:43 pm

I have run PL and DPL together on a micor with very little problems

Post by **wavetar** » Tue Jan 22, 2002 3:31 pm

On 2002-01-21 19:43, N9CZV wrote:
I have run PL and DPL together on a micor with very little problems

Yes, and many others have too, with multi-tone/DPL panels. BUT, that set-up merely allows decoding of PL or DPL, whatever happens to come in, one conversation at a time, NOT together. Or are you saying you were successful in modifying mobiles/portables to put out a COMBINATION of PL/DPL at the same time? And that it was successfully decoded by the same mobiles/portables receiving? Many people would love to see it, if that's the case.

Todd

N9CZV · Post by **N9CZV** » Tue Jan 22, 2002 4:02 pm

I have run links running pl and dpl at the same time I was using 72 mHz and got tired of band conditions keying system so I ran both and yes I encoded and decoded both at the same time. I never put this into practice with mobiles and portibles.

Post by **wavetar** » Tue Jan 22, 2002 5:02 pm

Well, in that case, it looks like EC-7 has found the man he needs to talk to.

N9CZV · Post by **N9CZV** » Tue Jan 22, 2002 5:15 pm

I think that several better Ideas where posted here. I was just saying you CAN run both.

Dave

Gary · Post by **Gary** » Tue Jan 22, 2002 8:29 pm

--------------------------------------------------------------------------------
It's a MURS repeater. 154.600 :-{ It's not that big of a deal but they are getting annoying I think it is a cable tv or telephone company using handhelds while burring and running wire. I'm assuming that they are going thru all the dip switch positions on thier SPIRIT radios until they access my simplex repeater. Since it's not licensed and doesn't have to be, I can't do anything about it. I also have 2 meter, 440, and multiple bussiness band repeaters, but they are down now. Freq cooridination at a pain to get in this area.
______

This was a great topic but did any body read the original question and application ??

Elroy Jetson · Post by **Elroy Jetson** » Tue Jan 22, 2002 9:56 pm

In response to the original question, no, no radio I know of supports simultaneous PL and DPL operation.

DPL may be your best choice. I believe Spirit radios don't support DPL at all, but since that's low tier stuff I don't play with it enough to be sure.

Try yanking the plug out of the wall. That'll keep them from using it!

Maybe you could install a singletone option, if your radios will support it...

I'd chase them off my repeater by firing up an encrypted signal over theirs whenever I heard them. They'd hear lots of noise and might think their radios were broken.

I'm not exactly sure how the laws regarding MURS channels applies, but for GMRS channels, in order to have access to a repeater, you need permission from its operator in addition to a license. It may be true that only authorized users of your simplex MURS repeater are legal, regardless of the (lack of) licensing requirements.

Elroy

Will · Post by **Will** » Wed Jan 23, 2002 10:23 am

Sorry guys, MURS does not permit repeaters according to the FCC.

wb6fly · Post by **wb6fly** » Sun Mar 31, 2002 10:57 am

If you want to deter hackers from learning your input PL tone, you can always use a diffferent encode tone on the output of the repeater. Most repeaters allow the input PL tone to bleed through and appear in the output, so it is easy to learn the input tone. You should select an encode tone that does not cause a beat note. You can also use DPL on the input, but then you greatly limit the number of users to those who have radios with DPL capability, which means commercial or high-end amateur equipment. The down side of using DPL is that alignment of encoders and decoders is critical, and often calls for equipment that most hams don't have. As for using PL and DPL simultaneously, I don't think it can- or should- be done.

Elroy Jetson · Post by **Elroy Jetson** » Sun Mar 31, 2002 12:20 pm

Jonathan wrote:

I heard somewhere that each transmitter has it's own "footprint." I honestly thought this idea was totally silly.

It's very true. Using a high-resolution spectrum analyzer, such as a Tektronix 494AP with 100 Hz resolution option installed, or any of a number of newer analyzers, you can see and print out signatures for any radio, and you will be able to see that the specific pattern of a given radio's emissions will be slightly different than any other. Different spurious emissions, different harmonics, and different levels of each.

An experienced tech who knows a particular radio and its performance on a spectrum analyzer can often diagnose the problem in the transmitter and know exactly what part is out of spec just by looking at the displayed spectrum.

I've worked with a tech who could do that.

Jim202 · Post by **Jim202** » Mon Apr 01, 2002 6:30 am

Just to add a little spice to the comments here, I hear the trend to keep out others from a repeater. There are commercial products available today that will do just that.

There is a product that will generate multiple CTCSS tones in kind of a multi code change. To restate this, the encoder generates different tones at the start of a transmission. Then it goes to a constant tone basis. The repeater has a decoder to listen for these changes and will only decode on the changing tones. A steady CTCSS tone will not open the system. It is missing the multiple tones at the start. If this is what your trying to do, then check with the venders.

Yes there is a way of looking at the transmitter signature to allow access or limit it. Had this on a repeater to cut down on some problems. Only problem was that you had to obtain the signature of all the transmitters you wanted to keep off the system.

Even found that some people borrowed equipment that were allowed on the system. When the problem children used them, those transmitters were also blocked. Now when the radios went back to the original owner, those transmitters wouldn't work on the system.

Jim

RADIOMAN2002 · Post by **RADIOMAN2002** » Fri Apr 05, 2002 9:13 am

Some years back in the early days of trunking,(Not Motorola ) I belive it was a Jap radio that used two PL's at the same time. One high,one low. It did work. You might try that. Also in theory you should be able to use DPL and A high PL like 250.3. A good DPL filter should reject everything above 150hz.
Jim