S-Meter Accuracy of FLex and Others - Rob Sherwood

I am not sure that the Flex S-meter adheres to the accepted standard of an S-meter. I believe the accepted standard is that the S-meter should register the highest peak that exists with the bandwidth of the received signal. Roughly to me, it appears the Flex S-meter integrates all frequencies within the passband and provides a reading. I am not sure which method is better.


Jim, K6QE

For me, the accuracy of an S-meter's calibration is useful for testing but is over rated and over used for communications purposes. To me, S-meter accuracy is of little value on any manufacturer's radio. Any relative indication of signal and noise strength is all one needs for letting the other station know if you can copy them. The meter reading is more an indication of the path. The station is a factor but only a small part of the equation at best with propagation being, by far, the dominant factor. It seems to me that absolute S-meter readings are used most often these days to feed the ego of the person on the opposite end of a QSO and does little to help the distant station make adjustments such as turning on the AMP or rotating the beam, Etc. So often I hear "you're rig is doing a great job. 30 over here", when it's the propagation that was contributing the most to the meter reading and QRP would have been entirely adequate. You've probably heard the old adage that I worked that station with a wet noodle. In other words, propagation was great and the main reason for the success of the contact. In reverse, the same "he-man" kilowatt station is received with an S-9 meter reading but a local noise source is also S-9 so the communications is marginal or non-existent. What did the S-meter reading tell the distant station in either of these two cases? In my estimation, nothing of real value. For me, the real indication of signal value is the signal to noise ratio. In other words, the signal strength above the total noise strength in the receiver pass band. Any somewhat linear relative strength meter will give you these values, calibrated or not. This SNR, communicated to the the distant station, versus an S-meter reading, is a much better indication of your ability to copy the intelligence being transmitting. No egos involved!

Accurate or not, if there were no S-meters, what in the world would some of the guys on the night time 80M nets have to talk about?!  Just funnin'... 

I've always been under the impression that an S-unit was somewhere in the 5 or 6 db range, but it would make sense that some manufacturers might want to boost sales (and ego's), and use 2-3 db per S-unit. 

@Burt

What you are asking for is that the S-Meter Read a TOTALLY MEANINGLESS IRRLEVENT NUMBER...which while it gives you great comfort that there is no external signal on the terminals is not related to anything that the radio may actually be hearing.

Thermal noise in the front end of the radio?

All radios have internal noise, the flex is simply reporting the signal in the Receiver bins,  sampling..coverting that noise to RF and sending that to the meter. So yes the radio hears internal noise.
Steve Hicks has writen so much on this explaining all this and yet so many still can't get their heads around the technology.

I think this is true. It could be a Flex feature or someone could write it using the API and make a "traditional s-meter" available as an application that could be run alongside SmartSDR. 

Seems that being wrong is more popular than being right these days!

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I would label the Relative S Meter as the Bu** SH*$ meter

There is always Atmospheric noise and local generated electrical noises  around and flexradio reports it.

Tuff to understand I guess.


I might add have fun and connect your ground to your center pin of the pl-259 and out
to the ground rod.

You will be amazed at the local noise. This being I live in the city. YMMV.

Maybe we could debate "over & out" being a paradoxical phrase that John Wayne would have used in the movies - but is something that would never be used in real ACP-125 tactical procedures.

Sorry Paul - couldn't resist. :-)

Roger out.

Most of the time when I hear a station giving reports like "You are S9+30" when I only hear them at S8, I can be sure that they are using about 30 dB of preamp on a rig that doesn't compensate its S-Meter.  Especially since I only run 100 Watts!

Back in my "CB Days" (1972-74) I used to watch guys turn on their external preamp and exclaim "Look at how much more powerful this makes my radio!  It brought my noise up from S3 to S7!  Now I can hear everything!"  Then they would complain about their darned neighbor down the road who was splattering 15 channels wide.  They never understood that they were their own worst enemy by running a preamp that overpowered their receiver.  But then again, sometimes that neighbor was driving a sweep tube amp well beyond saturation with an AM signal and really WAS 15 channels wide!

I like to just lean back and enjoy these conversations, particularly s-meter ones.  Let's see:
 - The Flex S-Meter accurately measures the voltage at the antenna connection but the various authors don't like the accuracy, they want the old inaccuracy.  It also ignores antenna gain and external pre-amps.
 - The dx/contest station cannot be clearly heard but still 5-9 or 5-9-9.  I'm a contester and guilty as charged.  The log needs a number and convention is fill it with a default, even N1MM pre-fills with 599. 
 - And now: "Connect to a dummy load and there is still noise."

On that last one, consider the radio chassis is the other half of the antenna connection (unbalanced input connection).  That chassis is at the junction of two antennae, one the safety ground out to your power panel and ground, and the other your RF ground wire and/or any coax connected.  The centre wire may be on the dummy load but the ground has many signals; then add in the front end generated noise.
An aside: While we are at it, lets tell those electrons to stop jumping out of orbit due to thermal activity or nearby static charges and also demand they do not create EM waves. This is obviously the fault of the Flex management and programmers not an act of nature and the basis of our hobby.

Tongue-in-cheek but also factual (subject to future posts)
Stan VA7NF

NOT TRUE... Definitely NOT MUMBO JUMBO... Basic Math...

When you short the Antenna, you are seeing the Minimum Discernible Signal that the radio is capable of receiving at that Frequency.

S0 by International Standard Definition is -127dBm

If your radio reads Zero when you short the antenna... then any and all S-Meter Readings on that meter are totally wrong.

BUT if it makes you happy to see a totally wrong and totally irrelevant number suggest you buy any Japanese radio.