Repeaters And CTCSS Tones

[Seven-Delta-FortyOne]

It's my understanding that many repeaters can be programed with a separate input and output tones.

So if a repeater was programmed with, for example, DCS 053 to access the repeater, and a CTCSS tone of 151.4 on the output, and you scanned the repeater while in use with tone capture, which code would show up?

Does the tone stay in the radio signal as long as it is being transmitted? If you only had an input tone, would you see it on the output?

When I travel, I often run the scanner to find active repeaters, read the tone, and then put those into the 2 meter rig. Is that tone that I see on the scanner because those repeaters have an output signal, or is that just the input tone repeated?


Thanks for anyone's willingness to help.


Delta

 

[W8VFD]

Your tone capture would pick up whatever tone is on the transmitter of the repeater that you are monitoring.

 

[wb6uqa]

CTCSS

The only reason for ctcss on receive is to eliminate QRM. It must be on all the time in transmit. Most repeaters don[t use ctcss for transmit and DCS FOR receive, they use one for both.

 

[Seven-Delta-FortyOne]

The only reason for ctcss on receive is to eliminate QRM. It must be on all the time in transmit. Most repeaters don[t use ctcss for transmit and DCS FOR receive, they use one for both.

I understand that. I've never personally come across one with different tones, I was just thinking of a way of partially securing a closed repeater.

If it had different access and output tones, I'm wondering if the output could be scanned, and show the input. Of course, that's all moot as soon as someone scans the input frequency. Then you could do a non-standard offset, and really confuse them.......

I was also just wondering if the tone "comes through" the repeater, i.e., is the input tone "repeated" as well, or just the audio.




Delta

 

[WA0CBW]

It depends on how the repeater is built. Normally the receive tone is filtered out and the transmitter re-generates the tone.
BB

 

[SteveC0625]

In some ways, a repeater is no different than your 2m mobile. When you program it, you set a tone for receive and one for transmit. Many ham repeaters don't use PL on transmit so you may only set a tone for transmit on your end, too. You receive CSQ which is what the repeater transmits. Many hams set their receive to CSQ even if the repeater does transmit a PL.

The repeater is the same from a basic point of view. Usually the receiver has some kind of PL on it, TPL or DPL, or maybe they use DTMF or MDC. If things are busy, the transmit side of the repeater might be programmed to send TPL or DPL so that the mobile units can optionally use it to block out distant stations or whatever.

So generally, repeaters don't pass the tone in much the same way that your mobile or ht strips off the tone before the audio reaches the loudspeaker. (Some do, some don't, but that's another discussion. Instead they're programmed to add the tone on transmit, just like your mobile or ht.

There's all kinds of ways to make repeater access more private, but anyone who is moderately proficient at using a scanner to hunt down these things will quickly find the input frequency and the access tone, whatever it may be.

This is the heart of matter which has prompted so many hams to move to some kind of digital radio system on their repeaters instead of conventional analog. That's much harder to decipher if you're trying to access a repeater for nasty purposes.

 

[Seven-Delta-FortyOne]

It depends on how the repeater is built. Normally the receive tone is filtered out and the transmitter re-generates the tone.
BB

Oh. Didn't know that. Thanks.



Delta

 

[Seven-Delta-FortyOne]

Thank you, Steve.


Delta

 

[ShawnInPaso]

Hey Seven Delta -

" I was just thinking of a way of partially securing a closed repeater."

I'm wondering why even bother with securing a repeater? If the repeater has any decent coverage it would be best to coordinate it, in which case you'd be required to provide the CTCSS tones (or whatever). Usually for closed system they are shown online as closed (e.g. repeater book.com) and most hams will respect that. If not, they can politely be told to use one of the many other repeaters in your area.

That being said, if you have some unique need that we don't know about, there are other ways to effectively manage the repeater use. Most controllers will allow you to function on and off the transmitter via DTMF codes. So lets say you have a half dozen repeater users. Each could be provided with the on/off codes. When someone wants to use the repeater they just function it on and then turn it back off when they're done.

Cheers.

 

[mmckenna]

If it had different access and output tones, I'm wondering if the output could be scanned, and show the input. Of course, that's all moot as soon as someone scans the input frequency. Then you could do a non-standard offset, and really confuse them.......

It depends on how badly you need to keep someone out, and how badly they want in.

Separate PL tone on the input and DPL on the output won't stop someone who really wants in. All they'd need to do is be in a high location (or close by) and listen in on the repeater input for your transmitted signal.

Repeater output tones won't stop anyone since all they'd need to do is listen in carrier squelch mode.

DTMF would be an option, but a DTMF digit grab is pretty easy to do.
MDC repeater control would be a slightly deeper step into this. I haven't seen an "amateur" radio that will do MDC. Nothing stopping someone from buying LMR radio that will do MDC, though. Most of the major manufacturers now support MDC thanks to Motorola's patent expiring.

I knew a guy once that had a heck of a time with people hacking into his GMRS repeater. He solved the issue by setting up a single channel LTR system.

Beyond that, you'd need to either look into a digital system and/or a trunking controller. That will push you into the commercial radio realm, but it's pretty easy to set up subscriber access controls on most systems.

That, or encrypt the output, but that's not OK on amateur....

 

[N4KVE]

I was also just wondering if the tone "comes through" the repeater, i.e., is the input tone "repeated" as well, or just the audio.

Delta

We have a local repeater that requires a PL tone to access the repeater, but the repeater itself does not transmit a PL tone. However, the PL tone of the transmitting radio is passed through, so you can set your radio to decode the same PL tone & it works. If you leave the radio in PL decode on that repeater, you will never hear the repeater ID. You will only hear the repeater when someone is actually talking. Most repeaters do not work this way.

 

[mmckenna]

Oh, and "non-standard" PL tones. Many amateur grade radios will only do the EIA tones. Using a non-standard tone is possible with most higher end commercial gear, or "rolling your own" encoders.

Inverted DPL? Might slow some down a bit.

Use one of the older signaling standards like GE-Star? FleetSync, etc.

 

[mmckenna]

If you leave the radio in PL decode on that repeater, you will never hear the repeater ID. You will only hear the repeater when someone is actually talking. Most repeaters do not work this way.

Many commercial/public safety systems are set up this way. Guys that use radios 40+ hours a week get real tired of hearing CD ID's every 30 minutes. Dispatchers will murder you in cold blood if they have to listen to it.

 

[N4KVE]

Many commercial/public safety systems are set up this way. Guys that use radios 40+ hours a week get real tired of hearing CD ID's every 30 minutes. Dispatchers will murder you in cold blood if they have to listen to it.

What's worse are the amateur repeaters that ID with a computer generated voice every 10 minutes. I don't have to listen to that on this particular repeater.

 

[mmckenna]

What's worse are the amateur repeaters that ID with a computer generated voice every 10 minutes. I don't have to listen to that on this particular repeater.

Yeah, or give battery voltage, weather reports, club meeting times, etc. Luckily where I live/work now, simplex is usually good enough. I haven't been on an amateur repeater in many years.

 

[gewecke]

Yeah, or give battery voltage, weather reports, club meeting times, etc. Luckily where I live/work now, simplex is usually good enough. I haven't been on an amateur repeater in many years.

+1 We have two repeaters like that in my area. They just love it when I refer to their repeaters as "Toys R Us" or Fisher price repeaters.:twisted: 73, n9zas

 

[N4KVE]

Yeah, or give battery voltage, weather reports, club meeting times, etc. Luckily where I live/work now, simplex is usually good enough. I haven't been on an amateur repeater in many years.

Fortunately you don't hear that on DMR repeaters. LOL.

 

[Voyager]

Inverted DPL? Might slow some down a bit.

You DO realize that every "inverted DPL" has an equivalent "Normal DPL" code, right? If they try every DPL code they will get it. It might not be technically correct, but will work just the same.

For example, Inverted 023 is normal DPL 047. you can program a radio with either and there will be no difference.

Of course, scanners have made "hiding codes" moot for all but non-standard codes.

So anyone who thinks the inverted DPL codes are more secure is fooling themselves.

 

[nd5y]

Oh, and "non-standard" PL tones. Many amateur grade radios will only do the EIA tones. Using a non-standard tone is possible with most higher end commercial gear, or "rolling your own" encoders

A $30 Baofeng radio is capable of any CTCSS tone from 60.0 to 259.9 Hz in 0.1 Hz increments.

 

[HudsonScannerGuy]

A $30 Baofeng radio is capable of any CTCSS tone from 60.0 to 259.9 Hz in 0.1 Hz increments.

Most buisnesses also use PL tones for store seperation.. and yes the Baofengs will match PL/DPL tones. I had a Baofeng and that was my first scanning type radio. It was interesting to watch it find the tones.