Experiment: how much PL tone deviation is required to reliably key repeaters?

[wayne burdick]

Hi all,

There seems to be some debate about how much FM deviation is required for PL tones used to activate repeaters. There's a wide range of deviation values in use by transmitters, and various "standard" recommendations. The question is how much is needed for reliable operation in the real world.

Our objective is to set the default PL tone deviation in the K3 and KX3 to the lowest level that works in virtually all cases (let's say 98-99%, since there are always outliers). Setting it too high can result in the tone being audible in receivers.

If you have a K3 or KX3 outfitted with an internal 2-meter module (or an external transverter on any repeater band), you could help us with this experiment: just try reducing the PL DEViation value to the point where you can no longer reliably key up your local repeaters.

NOTES:

1. If you're doing this with a KX3, please use the current production firmware (rev. 2.18) or later. Earlier releases may not have provided an accurate PL DEV setting.

2. To adjust the PL DEViation, locate the FM DEV menu entry, then tap '1' to switch to PL DEV. This applies to both the K3 and KX3.

Thanks for the help--

Wayne
N6KR

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[k6dgw]

On 9/6/2014 9:36 AM, Wayne Burdick wrote:
> Hi all,
>
> There seems to be some debate about how much FM deviation is required
> for PL tones used to activate repeaters. There's a wide range of
> deviation values in use by transmitters, and various "standard"
> recommendations. The question is how much is needed for reliable
> operation in the real world.

The Cactus-Intertie [ask Eric] is 500 Hz deviation on 440 remotes. Audio
deviation is 4-5 KHz, usually around 4. Link audio is flat.  None of the
420 Nor-Cal links use PL, but those that do elsewhere are nominally at
400 Hz PL/4 KHz audio deviation.  Any site with PL on an incoming link
filters it out before going into the audio switch matrix.

Cactus works amazingly well, even with a half-dozen or more link segments.

73,

Fred K6DGW
-- No. Calif. Cactus Radio Assn. [NCCRA]
-- Affiliate of the Cactus Intertie
-- www.nccra.us

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[Jim Brown-10]

On Sat,9/6/2014 9:36 AM, Wayne Burdick wrote:
> There seems to be some debate about how much FM deviation is required for PL tones used to activate repeaters. There's a wide range of deviation values in use by transmitters, and various "standard" recommendations. The question is how much is needed for reliable operation in the real world.
I've always seen/heard 500 Hz deviation. The first link says 15%
deviation. The second quotes a standard that says 12%, and quotes email
from a reader saying that 12-14% provides the most reliable decoding
under marginal conditions. Several references note (correctly) that when
PL is heard it is nearly always the harmonics in a tone with distortion.

http://en.wikipedia.org/wiki/Continuous_Tone-Coded_Squelch_System

http://www.repeater-builder.com/tech-info/ctcss/ctcss-overview.html

http://www.radagast.org/~dplatt/hamradio/FARS_presentation_on_modulation.pdf

http://www.metrocor.net/info/ctcss.htm

73, Jim K9YC
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