Flex 6400M noise floor

Rex K0KP

It appears that the following phenomenon is evident.  The design of the Flex makes for an S Meter that is incapable of displaying, on the meter that is, a signal below S 4 in strength.  This is because the receiver is displaying, on the S meter, noise generated internally within the filter via FFT bins.  Is this correct?

Also, what is the matter with having the option to click in a relative reading S meter?   I think a whole lot of Flex customers would appreciate that ability.  We use all kinds of methodologies to measure things, peak, quasi peak, peak to peak, RMS, weighted average, PEP, bandwidth limited, relative indications and so forth in electronics all the time.  

This is ham radio folks, not the National Institute of Standards Laboratory.

Successful business models value their customers opinions and desires.  I'm sure Flex could conjure up an algorithm or two to simulate a relative analog S meter indication as an OPTION to click in if desired. 

Rex K0KP

Well done Elliott.  Exemplary. 

Martin S. W7RU

I am starting to understand why FT8 might become a way to establish a contact better than CW ;-)

N8SDR

You want to see a signal below S4 or S5 simple, narrow up your receiver bandwidth! 

Bill -VA3WTB

You first comment is almost correct. What you are seeing as you pointed out the FFT bins are being sampled, this is not internal noise as such,,but the sampling we can  see in the pass band.
If you narrow the pass band down to nothing you see the S meter read around 1 or 0.
so what we see is the bins in the pass band sampling.

ua3lm

https://youtu.be/zdNczqv93Eo

Burt Fisher

STEVE_KW5TX

It reminds of Joe Biden explaining how the economy is actually GREAT! and we should be thankful! - lol

S5 here on the dummy load... even with the ATT on. Amazing how sensitive this thing is even without an antenna WOW...  hihi
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Mike-VA3MW

@STEVE_KW5TX

We could fake it as all other HF radios do, but we chose to do it accurately. Our engineers are very particular when it comes to doing math correctly.

https://www.flexradio.com/videos/understanding-flexradios-s-meter-readings/

ua3lm

It would be great if FLEXRADIO instead of a useless ATU would make a preselector to the input of the receiver. Like yaesu ftdx101. Maybe then the ADC will stop overloading at night at 7 MHz and during the day at HF ​​bands!
Our Chinese broadcast stations are overloading flex

Mike-VA3MW

@ua3lm

Don't confuse a Radio Antenna Matching Unit with an external antenna tuner with a much broader tuning range. The AMU in the Radio actually exceeds its published operational range.

The Chinese radios aren't exactly clean. I own one and have had it on the spectrum analyzer. It's IMD is terrible.

STEVE_KW5TX

@Mike-VA3MW

So the standard used on my Yaesu and Icom and Elecraft was done by "fake" engineers? ok! got it!

smh

who knew lol

Mike-VA3MW

No, not at all. (assuming we are talking about S meters)

When SuperHet was created over 100 years ago in 1918, that was the best they could do.

So, next it was assumed that when your antenna was not connected, then that had to be S0. That was wrong, but simple to do and calibrate.

But, if you design and sell a radio, you get to build it the way you wish. There is no law or requirement it has to be what it is.

Maybe instead of an S meter, we use Banana's. You could have 10 Banana signal today! (I like the sound of it).

John KB4DU

Art Collins defined a standard for S-meters long ago. His standard included measuring the signal strength at the antenna terminals, 6 dB change per s unit and the other parameters Flex uses. My Icom radios don’t use any of this. Typically 3dB per s-unit but it’s not consistent, and surely not measured at the antenna terminals.

Ken Wells

You will also notice that the S-Meter on the FlexRadio does not change when the Preamp is turned on, as opposed to the 20+ dB increase in S-Meter readings of most other radios when the 20 dB preamp is turned on.

The Flex S-Meter is calculated to lab standards and reflects the actual signal level at the antenna input. So if you give someone a report of S9 +10 dB you can know that it is an honest, calibrated reading, and that won't need to ask "Is that with your Preamp ON or OFF?"