Squelch Tones

[crazy_19]

Anyone have any prefrences as to CTCSS over DCS or vice versa. And if any one knows are their any thecnical pros/cons besides greater number of tones with DCS.

 

[nd5y]

I haven't heard of anybody determining if one is actually better than the other in all cases. DPL codes can get inverted which can be a con if not accounted for. Performance under weak/noisy conditions probably depends more on the particular decoder design quality. You can read all about both at:
http://www.onfreq.com/syntorx/ctcss.html
http://www.onfreq.com/syntorx/dcs.html

 

[rapidcharger]

Some would say the DCS is more prone to falsing. Some would also say DCS sounds a lot better than PLs, which a surprisingly large percentage of people can actually hear and they sound very annoying like a buzzing or so I'm told, especially the higher ones.

When it comes to the ham world, there's also the issue of access and if you want to attract people to a repeater, PLs are generally easier to scan for and set up for a lot of people. Personally, I think DCS should be used more.

 

[nd5y]

Here is another good info source that I forgot earlier:
A historical and technical overview of tone squelch (PL, CG, QC, CTCSS, etc.) systems.

 

[AgentCOPP1]

CTCSS seems more reliable to me. There are hardly any repeaters in my area that use DCS (actually there aren't any), but doing a simplex test between two radios, CTCSS usually seems to do a better job at pulling in weak signals.

 

[zz0468]

Some would say the DCS is more prone to falsing.

I see much more falsing with DPL than I do with PL. Also, there is frequent falsing of some PL codes when the DPL turn-off code is sent. So, the two don't play well together. Given the choice, I prefer PL only.

 

[Alarms50]

I liked this post so much from a couple of years ago that I saved it in my favorites, always good for when this topic comes up http://forums.radioreference.com/general-scanning-discussion/183367-pl-dpl-tones.html.

 

[N9NRA]

Personally i prefer DPL, as it has one one facet that i like, unlike PL, a radio set with a DPL code will, so to speak, "bite off" the anoying burst of static at the end of a transmission, this makes a transmission using DPL very quiet when the user unkeys, whereas PL sometimes dosen`t do that, making the end of a transmission kinda noisy. Just my two cents . N9NRA

 

[AK9R]

...unlike PL, a radio set with a DPL code will, so to speak, "bite off" the anoying burst of static at the end of a transmission...

That was a feature that Motorola, I believe, developed and made work with PL. The way they did it was to have the transmitting radio keep sending the same PL tone as it unkeyed, but it would reverse the phase of the PL tone. The receiving radio would see the phase reversal and immediately close the audio gate. That would keep you from hearing the squelch crash on the receiving radio. See the following web page:

Motorola® Reverse Burst & And Squelch

 

[rfradioconsult]

Back in the days of the Motorola Motrac the reverse burst was 180 degrees and was accomplished by the addition of a mechanical time delay relay as the tx-rx relay, a second relay was added to provide the phase shift via a transistor inverter. When you released the PTT the phase shift relay would change state and reverse the phase by180 degrees then a few milliseconds later the main tx-rx relay would un-key the radio.

During that time there was a preferred PL tone range of about 100-160 Hz, lower frequencies was slower to unlock the receiver because of the mass of the viberating reed to get up to speed, higher frequencies were prone to squelch breaks because of the lower mass of the reed. If I remember the Motrac HHT were the models involved.

 

[ramal121]

I believe Motorola uses a 120 degree phase shift. Other manufacturers use a 180 degree phase shift. This incompatibility causes squelch bursts at the end of transmission that is now much greater due to narrow banding. I have a situation where there are Motorola MTR2000 repeaters and Kenwood TK-790 mobiles and the complaints are constant about the squelch crashes.

This point might me moot because I don't think ham gear can even detect a reverse burst.

On the DCS side, the turn off code is a tone at 134Hz. This is industry wide. Ham gear? I'll have to check.

Lastly the decode time for PL tones is around 40 to 50 mS whereas DPL may take up to 3 times that depending where in the digital word you start decoding on ( if that really makes any difference to anyone).

 

[BirkenVogt]

If you are trying to make it a little harder for unauthorized users, it takes a lot more time to try to kerchunk the repeater with every DPL tone than with every regular PL tone which can be done pretty quickly. Modern scanners can display DPL, I know, but not everybody has one. Just another thought.

 

[evfd1625]

Wirelessly posted (Mozilla/5.0 (Linux; U; Android 4.1.2; en-us; SCH-I535 Build/JZO54K) AppleWebKit/534.30 (KHTML, like Gecko) Version/4.0 Mobile Safari/534.30)

And throw split tones in there with a different type of code on the input, then it's exceptionally challenging.