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Author Topic: Plain Language Signal Reporting  (Read 4050 times)
KE4SKY
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« on: October 12, 2004, 07:15:11 AM »

The R-S-T system of reporting signal quality dates from the early days of radio. It gives voice operators only a vague idea of what their signal is really like at the receiving end.  RST was originally intended for Morse code use and was later adapted for use with voice signals. (Contrary to popular opinion, the "T" in RST can be used in voice communication, to indicate the tuning condition of the sending station – though not applicable in FM, of course.)

The problem with the RST system is that it is usually inaccurate. This is evident from listening in on any contest, where everyone has a signal report of "5-9", regardless of how they actually sound. The fact is, very few people know what "5-9" means - on either end!

The CM ("Circuit Merit") system was devised by HF radiotelephone professionals to better quantify the average quality of a VOICE signal. In telecomm engineering specifications the letters "CM" (voiced as "Charlie Mike") are followed by a figure from 0 to 5 - to indicate the quality of the VOICE.  

However, in EmCom ICS environments we stress the use of PLAIN LANGUAGE. So in addition providing signal reports we should use the plain language equivalents of Circuit Merit, as used in aeronautical, military and maritime HF practice.

CM   PLAIN LANGUAGE  DESCRIPTION

CM5 "LOUD AND CLEAR" No noise, "full quieting* " on FM. Rare on SSB unless conditions are superb.

CM4 "GOOD READABLE"  Slight noise typical of SSB      
                     under very good conditions.

CM3 "FAIR READABLE"  Marginal voice communications
           Occasional fills needed, noisy.

CM2 "WEAK READABLE"  Unreliable, difficult copy,
                     frequent fills needed.

CM1 "UNREADABLE"     Unintelligible.
                     Signal barely evident.

CM0 "NOTHING HEARD"  No audio signal detectable.

(*) - Used for FM communications only, unless your SSB radio uses a syllabic-derived squelch such as SINAD.

The nice thing about this method is that you don't need to explain to people what you are doing. Just use the plain language and it usually works as intended.  
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N4NQM
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Posts: 36




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« Reply #1 on: October 12, 2004, 10:32:40 AM »

The CM reporting system seems to leave out signal strength.  There are lots of QRP stations that have
52 signals and high power stations that should get a 39 report--you can hear that amp but with mediocre readabiliy.  Unfortunately, many hams confuse readability with loudness.

Accurate reports are very useful with tuning antennas, equipment adjustments, etc.

Do you suggest using CM# reports on qsl cards instead of RST### reports?
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KE4SKY
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« Reply #2 on: October 12, 2004, 12:49:19 PM »

Yes,

I use the plain language equivalents of CM on my QSLs. However, I am not an active DX'er and work mostly North American QRP and mobile stations.
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N3ZKP
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Posts: 2008




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« Reply #3 on: October 15, 2004, 08:48:07 PM »

<< The CM ("Circuit Merit") system was devised by HF radiotelephone professionals to better quantify the average quality of a VOICE signal. In telecomm engineering specifications the letters "CM" (voiced as "Charlie Mike") are followed by a figure from 0 to 5 - to indicate the quality of the VOICE. >>

I think you will find this this was actually developed for describing the quality of a voice WIRELINE circuit, not a radio circuit.

Plain English is the best way and the military still has the best system.

Strength:

LOUD - your signal is very strong
GOOD - your signal strength is good
WEAK - your signal strength is weak
VERY WEAK - your signal strength is very weak
FADING - your signal strength fades to such an extent that continious reception cannot be relied upon

Readability:

CLEAR - excellent quality
READABLE - quality is satisfactory
UNREADABLE - the quality is so bad I cannot understand you

Lon
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KC8VWM
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Posts: 3189




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« Reply #4 on: October 20, 2004, 08:50:54 PM »


I like it!!!

73

Charles - KC8VWM
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