Batboard

I was talking to a friend earlier today about PL and CTCSS. I was trying to explain that PL and CTCSS are exactly the same thing and that PL was just Motorola's wording for CTCSS (just like QT and CG are for Kenwood and Ericsson). He was trying to tell me that CTCSS is when you encode with a tone and PL is when you decode with a tone.

So just for clarification from the experts incase I'm goobering something up. CTCSS is exactly the same thing as PL, it's just the wording that's different. Right?

Yes, they are the same. Motorola pulled a fast one calling it Private Line.

Motorola didn't pull a fast anything, "Private line" is simply Motorola's name for a sales pitch, same as GE, RCA, and everybody else has/had their own name for the same thing. I guess we can all thank the "big makers" back in the day that they actually were able to agree on a standard, otherwise, you'd have to have all Motorola, all GE, all RCA, etc, systems

I don't recall everybody's name, there was several, all mean the same thing.


"Private Line" is no different than any other sales gimmick, such as "positraction" rear differentials. There's limited slip, posi lock, on and on, all do, mean, the same basic thing.

Correct and correct. Each company has called it a different trademarked name, but it all boils down to the same thing.

GE called it CG - Channel Guard. RCA called it QC - Quiet Channel. Most everyone calls it PL just like they call all hand helds "HTs." Both PL and HT are Motorola trademarks.

Tell your friend he's mistaken.

The generic term CTCSS is used by manufacturers other than Moto, GE, and RCA. It stands for Continuous Tone Coded Squelch System and both encode and decode are part of the system. They all use sub-audible (below 300 Hz) standardized tone frequencies. PL, CG, QC are just the individual manufacturer's trade names.

Many of these systems have the ability to eliminate the noise burst commonly heard when the transmitter shuts off. Motorola calls it "reverse burst" because they change the phase of the tone just before turning the transmitter off. This causes the tone decoder in the receiver to think the tone has disappeared, and it mutes the received audio signal just before the noise burst would be heard. Each manufacturer has their own implementation. Some are compatible, some are not.

You can also just remove the encoding tone and keep the transmitter on the air for about 1/2 second before dropping it out. The effect is the same at the receiver - the audio gets muted when the tone goes away, and the noise burst that would be produced when the transmitter finally drops is never heard.

Bob M.

Yes, CTCSS is the generic term for PL - that's why we (Aeroflex) use the term CTCSS rather than PL:

a) because we don't want to have to pay Motorola for the rights to use PL

and

b) we don't want to piss of the other radio vendors by using a Motorola-ism.

And just in case it comes up - DPL (digital private line) is a Motorola-ism for DCS (digitally coded squelch) - DCS is the generic term.

(edit: CTSSS -> CTCSS)

Wowbagger: I think you mean CTCSS, not CTSSS.

I didn't want to go off-topic by even mentioning DPL/DCS.

Bob M.

kcbooboo wrote:Wowbagger: I think you mean CTCSS, not CTSSS.

I didn't want to go off-topic by even mentioning DPL/DCS.

Bob M.

Quite correct - I'll fix my post

==

Tom in D.C. wrote:You guys forgot Channel Guard (GE), which I mention
just to add to the confusion.

wa2zdy wrote: GE called it CG - Channel Guard.

Chris beat you to it a few posts ago.

Todd

My understanding is the Motorola reverse burst standard is a 120 degree phase shift followed by about 180 ms of tone. The other standard is 180 degree phase shift followed by about 150 ms of tone. Does anyone know of any corrections or any other standards?

I have measured the phase shift on the Syntor X 9000 and its not always 120 degrees, sometimes it gets closer to 160 degrees depending on the tone (I have only looked at a few tones so far). If anyone knows, I would like to know how the other radios do their 180 degree phase shift. I'm thinking it might be different like reversing the polarity after the zero crossing or something that would better explain why the two standards never work together.

I have read some of the newer Motorola radios now let you select the other standard as an option in the CPS.

Just to answer the slightly off topic sub-thread, DPL and DCS reverse burst works the same and are all compatible with each other.

Mike B said: "Just to answer the slightly off topic sub-thread, DPL and DCS reverse burst works the same and are all compatible with each other."

DPL/DCS uses a special hang-up signal that's a 134 Hz square wave for some number of milliseconds. The DPL/DCS decoder recognizes this pattern and squelches the receiver audio. It acts the same as reverse burst does with CTCSS, but it is not a phase shift of any kind.

One way I've seen 180 degree phase shift is by using a center-tapped audio transformer, and getting the signal from one end or the other. This was probably used way back in the 1950s and 1960s. The 120 degree tone phase shift in the Micor is done using a multi-capacitor ladder network or filter. It's not precise, and it is frequency dependent.

These days with microprocessors doing everything, they have better control over the preciseness of the 120 degree phase shift, and could reject anything that's more than 60 degrees away from that.

But we're over-deviating off-topic here !

Bob M.

Oops, when I said DPL and DCS work the same I meant the same as each other. Not the same as PL or CTCSS. I should have been more precise.

Back on PL vs CTCSS differences, the X9k creates the PL signal with a 4 bit digital to analog converter. It creates the phase shift by simply holding the digital 4 bit code at a fixed value for the required phase shift period, then it resumes sending new sequential values. My guess is it is not capable of fine tuning the hold time or it might be purposely emulating the old multi-capacitor ladder network or filter frequency dependent variable phase shift (thanks for that input). I did see that it starts missing/skipping sequential 4 bit digital codes when the PL frequency gets towards the upper end. The most likely cause is the CPU cannot keep up with the higher frequency synthesis steps.

So here's a question.

My motorola radio uses DPL. When I talk to another Motorola, it works great. When I talk to my FT-60 ham rig, it sucks. When I talk to a Kenwood/Icom radio, it sucks. It seems that every manufacturer has their own "flavour" of DPL. What gives - I thought it was supposed to be an "across the board" kind of thing, like PL.

For some reason lots of newer HAM radios have really bad CTCSS and DCS Rx decoding. Yeasu put out a hand held took forever to open the CTCSS Rx squelch. Supposedly the factory would fix it if you sent it back. But, then they came out with next generation replacement model it had the same problem like the factory didn't care. There is an outstanding issue with Syntor X DPL programming and a VX-5R HAM hand held. Programming some undefined bits in the DPL field will make the Syntor X DPL work with the VX-5R, otherwise it does not work. Its not even all the DPL codes, just some of them.

On the X9k radio the DPL bits are ramped up and down like a 90 degree segment of a sine wave at both ends. It reduces audible harmonics above 300 Hz, but the receiving radio might have a hard time with the very soft so called "digital" wave form edges. DPL is a marriage between the generator and receiver. Either one can screw it up. At least make sure you are using one of the standard DPL codes. Try different DPL codes too see if at least some of them work with the HAM radios.
http://www.open.org/~blenderm/dcs.html

I don't think you would have this problem with commercial Kenwood, Icom or Yeasu radios. At least I hope not. The HAM ones just seem to suck.

I don't remember if it was PL or DPL, but with the phase shift it is noticable with muting problems between Moto and Kenwood and like radios (squelech crashes, etc). About a year ago there was a lenghty thread about this, and other aspects of how this all works.

I recall that thread, and it was PL and the different phase shifts that are used for the reverse burst.

I do know that the MSF5000 puts out a very nice sinewave that shifts exactly 120 degrees for the reverse burst. They're using a fairly large (by today's standards) microprocessor, and it has very little else to do during that time slot.

DPL/DCS really is supposed to be done using frequency shifting of the carrier. Unfortunately some radios inject it through the audio chain which turns the nice square wave data into sinewaves. Under quiet conditions, the receiver will detect enough of the DPL/DCS signal to work properly, but when conditions worsen, or the receiver limiter can't extract the DPL/DCS signal out of the noise, things get difficult.

Bob M.