S Meter Reading after Service

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  • Problem
  • Updated 2 months ago
  • Not a Problem
My Open Response to Flex Service Survey

The service agent was great in communication via email on the updated on my repair and also showed concern on the care and treatment of my transceiver.  I would give that person a 10.  "However, my S meter problem is still NOT fixed."  I have spent the time reading all the back posts dealing with S meter readings, and I join the group in frustration that you seem to want to re-create the whole purpose for the readings, rather than fixing the issue.  So, in the future do to my Flex, with or without an antenna connected or pre-amp on or off, RF/AGCT turned off or full, the S meter readings remain 5-6 plus at ALL times.  I will report back to all my contacts that, SINCE I have a FLEX radio I am UNABLE to give you even a close, approximate, true reading of your signal level. 
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Joseph Rodick

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Posted 2 months ago

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Michael Walker, Employee

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Hi Joseph

When you set your bandwidth to 250 and 50 Hz, what does the S meter read when connected to a Dummy Load?

Is it still S5-S6?

Mike

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Joseph Rodick

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When I go to CW and reduce the bandwidth the S meter drops about one S unit.  When I "short out" the antenna input I still show the same 5-6. 
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Joseph Rodick

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Just did a complete reset, at 50 HZ, the S meter is now reading 2.8-3 with or without the antenna connected or even with the antenna input shorted.  However SSB still at 5-6 and CW at 250 HZ 4-4.5.
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Joseph Rodick

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I have read and re-read all those posts.  However, with or without pre-amp on/off, bias on/off, the antenna connected or not connected or shorted.  I get the same readings that I have previously listed to you.   I also went over to a friends house that has an HP Spectrum Analyzer.  When you short or disconnect the antenna on the HP, the readings drop to zero or close to zero, THEY DON'T STAY THE SAME.  How can a Spectrum Analyzer such as FLex or HP read the given spectrum with a discounted or shorted input?  The answer I would give is that it can't.   So why is my FLex acting like this?
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FISHULA X

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I own a 6300. Get this. with no antenna connected, listening at 4 KHZ wide
 I get an S3. with RF gain off.  And with the RF gain on I get an S1 and a quarter..
 That's a head scratcher??? Anyone else?????? 
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Ray - K6LJ

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Hi Joe - Maybe I don't understand this totally either however I went back to Gerald's post and performed exactly what he recommended.

Maybe  pics demonstrate things better. What Gerald said was 

"For Optimal weak signal performance near the atmospheric (antenna) noise floor you want your receiver noise floor to be (sensitivity/MDS) to be 8 to 10 dB below the noise coming from the antenna"

Gerald explained that there is a difference between the 6700 (my Radio) and the 6400-6600 because of the 3rd vs 7th order filter.


So here is what I found to set the sensitivity correctly. Case 1 set -10 preamp gain with no antenna. Note signal strength is -98 dBm.


Next connect an antenna. Note with -10 you see a 92 dBm. That is a diff of 6dBm. According to Gerald this sensitivity is too low should be 8 to 10. 


Next increase the preamp to 0. The sensitivity with no ant to -110 dBm



Next connect the antenna. The value goes to -100 Dbm. That give a diff of 10 dBm like Gerald says is the correct value.


So 1 more time put the preamp at +10. You go -118 dBm and with the antenna connected to -98 dBm. Too much sensitivity.

So if we assume that the 0 preamp gain was correct I then then went to the phone section where I measured -98 dBm on a clear frequency. where the S meter was reading S4 or -98 dBm.
 
Next I tuned to a strong signal that was reading S9 or -65 dBm. The difference -98 - 67 equal to a diff of +31 dBm. 


 Hopefully I understand this correctly and using the stated 6 dB per S unit I found that 31 dBm was about 5 S units above the noise that was reading S4 or -98 dBm. 

So in our case an S value is a combination of the Noise (S4) plus a signal of (S5) = S9. But I think it is more correct to just give a signal report in the dBm value difference as that how strong the signal is above the noise.

Everyone has a different noise floor so what is the best way to give a signal report? 

But as it has been said if you say one has an S9 signal means you have good copy and an S4 is not so good.

I hope this is correct the way I understand things. I also had a S5 with the antenna disconnected or shorted but when connected it I have come to the above understanding.

Ray
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Burt Fisher

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My S-meter does the same thing. Dummy load, S-7.
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Lawrence Gray

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Burt, seems like you have a lot of local noise?  I live not far from you and my 6500 reads "S0", -124 dBm in CW with bandwidth 250.  It reads "S2", -115dBm in USB, bandwidth 2.1.

This is with no antenna, or transverter, connected.

Seems like a lot of local noise or electrical noise in the house?
(Edited)
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Joseph Rodick

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Even with a Shorted HF input? P.S>  Where do you live?  Love to meet.
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Lawrence Gray

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I live in Falmouth, MA.  
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Burt Fisher

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I put a dummy load on the input, S6. I put an antenna on the same frequency using a KX3, S2, with the dummy load S0 on the KX3.  It isn't noise, Flex uses their own way to set the S-meter no one else uses.
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Pat N6PAT

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My 6700 v2.6.0 S Meter for both SSB and DIGU is < 3 and CW is a very low 0.5 hooked to a Hustler vertical

Nice and quiet. Seems to be working properly


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Joseph Rodick

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I used to have a low S meter reading, then somewhere along the line, I have this.   I sent in my Flex for this issue and spent $79.95 for shipping and insurance and got it back with the same issue.
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Bill -VA3WTB

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You must have a 6400 or 6600? It may be a good idea to contact support again and have them run a few test with you, Just don't leave it this way, contact them if you feel the Smeter is not working.
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Bill -VA3WTB

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Joseph, your s meter is working as it should. it sounds like you read a lot on the subject so you must by now understand why it reads what it does with out an antenna connected?

To revisit the main points: without all the math that follows this topic. I have seen Steve explain all this with all the charts and graffs, with math that tires the mind out, I will skip all that and just make this simple...

1 in a receiver there is no such thing as 0 noise. In the radio receiver noise is always present internaly and there are several types of noise in the receiver.

2 in an SDR receiver there are receiver bins, these bins are being digitally sampled all the time. Each bin has noise in it. As we expand our receive band pass filter we expand the number of bins being sampled, thus the noise increases the same amount. Now if we narrow our receive filter to it's smallest, we then are only sampling a much smaller amount of bins, thus the noise is much less.
As we do this we can see the noise go up and down as we change the filter size with the S meter read out. On my 56500 at the smallest filter size my S meter reading is around S1 or a little lower.

3 The way Flex desined the S meter is to work just like laboratory equipment that reads signal and voltages to signals.
The S meter in your Flex is alway reading the digital samples from the receiver bins, this is what your seeing as the receiver is dead without the antenna. If the meter reads 0 with out the antenna, this would be incorrect because there is always noise. If it read 0, then what happened to the noise in the bins? It's still there. If it's there, then the Flex will detect it.

But when an antenna is connected the S meter will read as low as 0 without a signal at all. That would be impossible due to the band noise floor. But in most cases a low signal we can hear will be around S 3 or higher and the meter will reflect that.
In any case, the S meter on a Flex radio is very very accurate. so when you give someone your reading it will be as close as it can be.

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Joseph Rodick

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Thank you for your input, but I am confused, with the antenna input either shorted or disconnected I get the same S meter reading.  With the bias, or pre-amp turned on/off, i still get the same S meter reading.  So is that a reflection of internal Flex 6400M noise rather than the band conditions?
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Burt Fisher

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Flex thinks their S-meter is a laboratory instrument . Trying to get them to have their S-meter work like Kenwood, Yaesu, Elecraft, Icom, Collins, Heathkit, Hammarlund, Hallicrafters is an exercise in futility. They work in the theoretical world, everyone else is in the real world.  
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Brian Denley KB1VBF

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Burt:
As far as I know, they match Elecraft and the Anan radios (both of whom went through these pains) but Rob Sherwood would be the definitive source here.

In any case, there might Very well be something wrong with his radio but we have suggested some things to try to prove that one way or another.

Brian KB1VBF
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Michael N3LI

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I find the Wikipedia page on S meters to be pretty helpful, explaining the differences between legacy and SDR radio S-Meters 
https://en.wikipedia.org/wiki/S_meter 

There have even been suggestions that Flex purposely add a software switch to approximate the largely uncalibrated S-Meters and even a choice of db per s-unit, because  a lot of the Japanese Radios use 4 db per S-unit, and the differences aren't the same over legacy radios scales anyhow. 
https://www.hamsci.org/s-meter-calibration

Notice in the tested radios on that last page, that an S-0 on a KenWood TS-180 comes out at near  S-3 on the standard S-unit (-108 dbm) vs -109 dbm for the standard. 

Bill's answer is exactly correct. The sampled bins determine the expressed Signal level. I''ve never seen an accurate S-0, but if someone does succeed in building a noiseless receiver, it would be awesome. But I'm not holding my breath. 8^)
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Mark K1LSB

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An S-meter reading of 0 does not mean that there is no voltage detected, it means there is 0.1 microvolt detected.

The Elecraft K3S has a measured sensitivity  (per Rob Sherwood) of .08 microvolt.  That means a detected signal at that level is 10dB above the noise floor.

That detected signal is below an S-meter reading of 0, and the noise floor is below an S-meter reading of -1 (negative 1).

To repeat, an S-meter reading of "0" does not mean there is no voltage detected.

With that said, I'm done here.  I have no intention of getting involved in another S-meter argument.
(Edited)
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Rick WN2C

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Just imagine you were in the old days when receivers didn't have S meters and you gave out RST reports by what you heard.
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Dawg Fan

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Exactly my comment....I use my dummy load brain and my ears...I hardly ever look at an S meter...Don't need it.
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Joseph Rodick

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I am not a professional in the field, even though I taught electronics for Sears and STAC years ago.  However, How can any Flex owner give a signal report with these readings?  Right now I have my Flex on 40 meters with the antenna input shorted and I have an S meter reading of 5.5.  So do I give the short an S5 report?  I apologize if anyone thinks I am being facetious, but if I am looking at my S meter, that would be the report.
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Joseph Rodick

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I just had the Flex in for service and they did indicate that they did a pin update and a complete check.  I am being told by Flex in this post that my readings are Normal.  So a shorted or open RF connector would receive an S5 report.  Makes truly no sense to me.  I understand noise floor.   But to say that a short or open RF input connector that reads an S5 with or without the bias or pre-amp turned on/off or the RF/AGCT turned to min or max is normal then I do have to question that.  Thank you for your input. 
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KY6LA - Howard, Elmer

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Actually it makes perfect sense 

if it’s reading S5 then your radio is only capable of receiving -127dBm +5x6dBm = -97dBm at that frequency. 
Legacy S meters measure the AGC voltage not the signal received.  Basically a Fake News analog for some mythical reading. 
It’s almost the 2nd decade of the 21st century so I only give dBm reports 
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Andy M5ZAP

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Excellent descriptions by Bill and Howard. I think I’ve got my head around it now. But like others I have struggled. Are there any flex articles or other literature that make good holiday reading which cover this and other SDR theory in a way a non expert can understand.
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Burt Fisher

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Joseph your comment, " Makes truly no sense to me"  actually makes perfect sense to me because all the radios I have owned have S0 with a shorted input. I care what's coming in on the antenna not how many electrons are flying about internally. I wonder if those that heal to the Flex S-meter criteria give true reports during a contest or go with the 59 flow? 
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Brian Denley KB1VBF

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How many spectrum analyzer receivers have you owned?  Those older receivers, as was said before, were just looking at the voltage coming of the AGC circuit.  Elecraft went though this same argument with their K3 owners and eventually provided two different outputs to pacify some.  SDR console went through a huge fight even after Rob Sherwood told them why.  Flex has gone through this before.  I’m not saying that there’s nothing wrong with your radio but understand that these receivers also measure whatever noise their own circuits pick up.  One way you might check:  take your radio to another location just to see if you get the same results.
Brian KB1VF
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Joseph Rodick

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Howard and Andy, Thank you for your input.  I just can't understand that a shorted RF input would give me an S5 reading.  I guess the old analogy is correct.  You can't teach an old dog new tricks.  Thank you all again 
and God Bless.
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Bill -VA3WTB

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Joseph, are you still stuck in understanding were the energy is coming from when the antenna port is shorted?
(Edited)
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Brian Denley KB1VBF

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Burt is incorrect in putting Elecraft in that pile.  They fought the same battle.
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Brian Denley KB1VBF

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 http://elecraft.365791.n2.nabble.com/K3-S-meter-td1120138.html

Just a sample from the Elecraft reflector many years ago...
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Michael N3LI

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Well now, that  was interesting reading.

I can check out our K3S to see if it reads similarly. If so, I'm suspecting the new K4 will also have an accurate meter, which will disappoint some folks. 
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Joseph Rodick

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Michael;  Thank you for your post, however, I lost a long term friend just because his Elecraft K3 did not come close to measuring up to my 6400M.  After reading all the posts and doing a little research on my own, I have determined that Flex is correct.  Sometimes passion gets the better of us.  I saw first hand how passion can hurt and ruin a relationship.   I personally did not think his K3 was bad, but in a number of areas, side by side, my 6400M won and his passion then anger got the better of him.    There are a lot of good radio's out there, and everyday hams make a decision based on past experience, features, and budget.  I remember when I thought my HW101 was the best of the best.  Bottom line, I posted my comment based on my past experience and knowledge and I have learned that I was wrong in a number of areas.  Learning is good.  God Bless
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Pat N6PAT

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I wouldn't get so hung up on meter readings. Are you making contacts? That's what really matters.

If someone wants their ego stroked or is trying to justify the fortune they spent on a gawky tower and antenna then make them feel better and tell them they're giving you 20+. What difference does it really make? One man's 20+ is another man's S7.


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Lasse Moell

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Sounds like something is not correct with your radio. Never mind S-units or band noise, but if you terminate your antenna input with a 50 ohm load (this is better than shorting the input giving the input circuits a proper load) you should see less reading on the "S-meter" when you have max gain on your pre-amp vs max attenuation.  Once you are convinced the radio is working, re-read what Gerald wrote on the link posted above to have the optimal setting of the front-end gain. I did a quick test on my 6500, using 2,8 kHz BW, and no antenna. With max Att, the S-meter hovers a S5 and drops to a tad over zero when I change to max pre-amp gain.
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HCampbell WB4IVF

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Below are some comments from the op in a previous thread on the problem:

“I have started to have a 5-7 s noise figure on 80/40 meters and a 3 s on 20 meters "with" or "without" the antenna disconnected.”

“This has just started in the last month or so.  I am now unable to hear weak stations because of it.” 

https://community.flexradio.com/flexradio/topics/noise-isjv7sjtdsm3t

This isn’t a radio or S-meter interpretation issue, since it just started, the op says is now unable to hear weak stations because of the noise, and Flex ruled out any problems with the radio.  So it seems to me the remaining possible culprit is local noise of some sort, which is being introduced into the radio even with antenna disconnected or shorted.  My next step would be to track down the source of a possible local noise source (starting with shutting down the mains breakers and running the radio from a battery to rule out the source being in his QTH).

Howard


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Bill -VA3WTB

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Joseph, 
2 things here: The Icom 7300 and 7610 uses some SDR technology, but the radios are made to behave like conventional raios, not an SDR radio. The S meter on the Icom reflect this.

2nd thing: A Flex is a very different radio as it is 100% SDR so it behaves like one.
What we need to find out is were the high noise level your seeing and hearing is coming from, step bye step. I know that you may feel based on your testing with the 7300 that close bye interferance can be ruled out, but we have seen this before and the owner found the sourse of his noise and all was fine.

Because the Icom 7300 uses a much different filter system a lot of this noise may be filtered out already. so lets just focus on your Flex and find out what is going on...
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Michael N3LI

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Could be a few things Joseph. Could be the radios are not hearing very well. Could be you actually have an S-0 noise level. More likely, you like the Japanese method of inaccurate meter readings.

When for some reason I want to read the noise floor, I do it using the restricted bandwidth method, which for a bin sampling radio is the way to go. It gives me readings corresponding to the official dbm levels.

Now keeping in  mind that the S-meter levels for most equipment is simply bogus, the Flex gives us an actual accurate reading. It's right on the side of the SSDR screen. I've taken to giving out dbm, because that actually means something.

I'd be very curious to find out what your noise floor is with an antenna on a quiet band with the radio in CW mode, and 50 Hz bandwidth

I'd be curious to find out what an S-9 Signal looked like on all three of the radios. A lot of Japanese radios are calibrated for S-9, if at all, so there won't be much luck trying to match levels in between 9 and 0. 

In the end, you might need to decide if your desire to see S-0 is a deal breaker or not. Flex made the decision to have the S-Meter reflect actual levels, and the bin sampling method needs small bandwidth. I doubt they will move to purposefull inaccuracy.
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Joseph Rodick

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Michael;  I had a TenTec 599 and a Perseus Receiver.  Both are not Japanese and both gave me the same, normal S meter reading.   Plus,  If I remember right, I never noticed that my Flex 3000 gave me a higher then normal S meter reading.   The only reason why this all started is when I felt that I was losing weak signal reception.  Thank you for your input and God Bless.
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HCampbell WB4IVF

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The Perseus S-meter is accurately calibrated just like the Flex S-meter and should give very close readings to the Flex.  If the accurate Perseus S-meter readings looked normal to you, and since the problem just began AND your Flex was checked out at the factory, I strongly suspect you have a local noise. 

Howard 
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Brian Denley KB1VBF

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Great point!  Joseph: do you still have the Perseus?  It has one of the most accurate s-meters on the planet, if I remember Rob Sherwood’s ratings.  We could get to the bottom of this quick!
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Joseph Rodick

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Joseph Rodick

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This is with the antenna shorted.
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Lasse Moell

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If I see correctly, you do have -8 dB attenuator switched in. I do get the same "numbers" if I use -10 dB attenuator on my 6500. Try set to 0 or even +8 and your S-meter should drop by a few units.
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Rick Ciotti

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With my 6600M set exactly as pictured the S meter reads slightly above S3. With a dummy load, coax shorted or no connection to the antenna port this reading is unchanged. With the 40M monoband antenna the reading is S4. 
(Edited)
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KY6LA - Howard, Elmer

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@Joseph
i am likely an older dog than you are   Hi. Hi. 
To explain the flex meter in simple terms.  Absolute vs Relative   I will explain. 

Flex uses an absolute meter giving exact readings of what it is Hearing 

Legacy S Meters are Relative meters giving some effectively meaningless measure of the AGC voltage.  They are supposed to be calibrated to 50microvolts over 50 ohms equals S9 or -73dBm but due to the non linearity of AGC Circuits, there is no consistency of those readings even between the same models from the same manufacturers.  each S unit is supposed to be 6dB but Almost none are. The Japanese typically range from 3-TO 5 dB per unit.   In othewords a feel good number that is totally meaningless.  if you have a Legacy S meter and you want a useful S number use your ears 

For the unschooled - a politically correct way of describing the Trolls who don’t know what they are talking about but like to argue—. Yes a dummy load connected to the antenna should give you a ZERO reading BUT ONLY IF IT WERE COOLED TO -273K.  BTW S0 is by definition-127dBm and does NOT mean an absence of signal    SO shorting the antenna should not yield -127dBm or S0. 

Think of the Flex S meter like a mercury thermometer. Mercury freezes at -38F   So using it to measure -50F would give you a readings of -38F   The sensitivities of Radios vary greatly by frequency. I posted some graphs several times here  if you search S meters.    If at say14MHz the sensitivities are -121dBm or S1, then there is no way that an absolute meter just like the mercury thermometers can or should  read S0  


By the way I strongly suggest you ignore the Trolls who continually moan about Flex not having a totally useless and meaningless S meter 
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HCampbell WB4IVF

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James, aside from-S meter readings, you said that the noise that just started on the Flex is preventing you from hearing weak signals.  Can you hear those weak signals on the Icom 7300 and Pro 3?


(Edited)
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Michael N3LI

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An actual calibrated and accurate S-Meter is apparently disruptive technology!

This topic is one of the most badly beaten one on this reflector.

One of the first things that comes to my mind is why it is so important that a signal strength meter reads 0 without an antenna. Looking at the display, and with narrow bandwidth, the Signal meter reads as close to the designated value as can be determined when looking at noise floor and eyeballing it. 

Even so, unless one's hobby is reading noise floors, as Shania Twain noted, "That don't impress me much." 

So What on earth should a company making an SDR do? Provide a special inaccurate and uncalibrated setting in order to keep those who insist on a Japanese style inaccurate and uncalibrated Signal strength meter? That sounds so strange, but that is what the demands are.

Then guys like me would howl because I'd look at the right hand side of the panadapter and notice that the dbm of the signal isn't related to the S-Meter. 

This is a technical improvement plain and simple.  I'd no sooner want an old school inaccurate S-Meter than I would want an old school drifting VFO.

I think the major problem is getting people used to S-Meter accuracy. It will take a while, because so many don't know the bogosity of legacy radio S-Meters.
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Michael N3LI

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Also, if a 7300 compares favorably to a Signature series radio in the upcoming tests there is definitely something wrong with the Flex. 7300's are really cute and inexpensive, but after using one during Field Day and during a SET, I compare it to other entery level radios. 
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Burt Fisher

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When I go the supermarket and go to the delicatessen they don;t start the scale at 7 ounces to account for the weight of the container, they zero it so you only pay for the meat. The reason zero is important no one cares what the electrons are doing inside the rig, users care what is coming in from the outside. The value of my Flex is maintained of Flex does well, this idealtic superior attitude does not go over well in the marketplace. When the Elecraft K4 comes out and Flex does well, I was wrong. I don't want Flex to ne a niche transceiver. They set the pace in SDR technology, after what other receiver can capture so much of the high frequency spectrum? The product (currently) is superior but the arrogance on this S-meter issue doesn't help. Are Kenwood, Icom, Elecraft, Yaesu all wrong in the way they present the S-meter?
A simple yes or no will suffice.  
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Michael N3LI

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I want the S-meter to reflect the values as in the image. That is all.

Some people want accuracy, some people, for some reason I cannot fathom, demand inaccuracy. If the best reason is "because that's how it used to be done, even if it's wrong, well - that dog doesn't hunt. Might as well ask for phase distortion to be put back into Flex radios, or demand putting old USB to Serial adapters and Stero cables to run the sound from the radio to the computer because that's how it was done since 1999.

I'm not really certain that my wish for an accurate meter is arrogance. I want my ALC, power levels, S-Meter SWR meter to be accurate.

All of this is because Flex has exposed a dirty secret of Amateur Radios, and some want the inaacuracy to stay secret. The world is changing, and I really suspect that modern Hams prefer accuracy to inaccuracy. 
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Joseph Rodick

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I have always considered a signal report to be just that.  A measurement of their incoming signal.  If on 80/40 If I am getting an S5-S6 on a short input, then do I give that person a S5-S6 plus any increase or do I give them just the increase?  Honesty is giving a true signal report.  Yes every receiver and antenna system will receive differently and time/day conditions play a lot into it, however, at the end of the day, a signal report is just a measurement of how strong they are coming in at that moment in time.   If my noise level is an S whatever then I would give them a signal report of noise level + their signal.  However, If I am getting an S5-S6 with a short input, then what?  
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Doug

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I will try not to sound like a troll but I would like to add this, in all honesty I don't hold much value in receiving or giving an s-meter reading. If a station I am talking to tells me I am 10db over s-9 and I heard him give the last guy a s-7 I assume I am not only stronger than that last guy but have a good signal. I don't expect a calibrated report and when I give a report it is just a subjective reading nothing more and nothing less. I am not being critical of you Joseph but no one or 99% of people don't expect a laboratory s-meter report.   Having said this your Flex IMO is much closer than most radio's on the market and I feel you can give a report and in good faith know it is accurate.
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Michael Walker, Employee

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Hi Joseph

Shorting out the antenna is not the right way to make this measurement since it provides an improper load to the receiver.  Receivers also require matched loads.  

You have to do it with a dummy load.  

I have a pretty quiet HF station, so at local noon on 80M, my noise floor is about S4-5 with +32 dialed in.  And, the same with -8db (attenuation).

It was not until SDRs came into the Mainstream that S unit reporting was done correctly.  Prior to that, it was an approximation since there was no practical way to do the math in analog circuits.  Like Howard mentioned, the meter was driven from a voltage that made an approximation.  Every superhet radio we have used in the past was not worthy of using the S meter as an accurate measurement tool.

To answer your question, all you can do for an SSB station is report on the peak value and based on your comment, that is S7 since that is what you saw/heard. 

I know that is contrary to all the HF radios you have used over the decades.  Welcome to the correct way to measure it and that is the actual energy in the passband.

Mike
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Lawrence Gray

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On my 6500, LSB, 80 meters, bandwidth 2.1, I see -114 dBm ("S2") with no antenna connected, with the antenna input shorted, and with a dummy load connected.  This is with the preamp setting at 0.  With the antenna connected, I see -102 dBm ("S4").
  
In my view, a "no antenna" noise level of S6 is an indication of local noise?
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N5LB - Lionel B

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Checked today 40/20/10 CW  0.4  0dB preamp, into 50 ohm DL with 2 feet LMR400.
S-meter hover S1 +/- and -118 to -119 dBm.
BW at 2.7 -109/110 dBm or S3 +/-
Same as data taken 6 months ago.  I have a good ground system, a lot of copper and many ferrites. 

So, all seems to be as intended by designers.

S6 seems like noise getting into the rig, maybe on ground, outside of coax shield.  
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Joseph Rodick

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Both the Icom 7300 and the 756 pro III showed no S reading hooked up to my same PWR and Antenna System.  Like many, I am just trying to understand.  Thank you for your input.
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Brian Denley KB1VBF

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The Japanese radio smoke little effort for accuracy.  
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Tim W

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Guys I’m learning heaps by reading this thread. I always thought it would be better to give a signal report in dBm. S units seem to be an arbitrary contrived value.
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Burt Fisher

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dBm isn't contrived? It depends on an uncontrolled variable, antenna. 
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Erik EI4KF

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Anyone receiving a report in dBm who is not a SDR user is unlikely understand it and therefore the sender is, in effect, being esoteric. Also try to enter dBm into a logbook program and then perhaps you'll see that you are not really communicating efficiently with your QSO partner. Yes, as Burt says, S units are contrived but they have a communicated meaning.
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Michael Walker, Employee

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Hi Eric

You also can't enter 20 over s9.  :)

The S in RST has nothing to do with an S Meter at all

The S stands for "Strength". Strength is an assessment of how powerful the received signal is at the receiving location. Although an accurate signal strength meter can determine a quantitative value for signal strength, in practice this portion of the RST code is a qualitative assessment.

  1. Faint—signals barely perceptible
  2. Very weak signals
  3. Weak signals
  4. Fair signals
  5. Fairly good signals
  6. Good signals
  7. Moderately strong signals
  8. Strong signals
  9. Extremely strong signals
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Joseph Rodick

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Thank you Michael, you are right on the RST.   However, I use RST only for my CW use.  On phone, I usually give an S meter report unless they are distorted or over driving.
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Michael N3LI

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dbm is not contrived. It is a very specific level as measured at some point in the receiver.  A calibrated and accurate S-Meter reads a specific level at a specific place in the radio.

We'll assume that the sensing point on the radio is appropriate.

The antenna is then a variable, but if we compare a "good" antenna to a "poor" antenna, the good one simply provides a larger signal to the place that is measuring the dbm.

The poorer antenna is simply providing less signal to be measured.

This in fact is how we determine some of the characteristics of an antenna. And to do this, you need a calibrated and accurate meter system.

I first learned of the terrible innacuracies of the legacy meters when I was  making a test of vertical versus dipole antennas on my venerable IC-761. Using a calibrated pad to knock a signal down while I was setting up, the amount of attenuation needed to put the needle on the expected S level had nothing to do with the proper padding. 

Near S-9 it was fairly close to the proper 6 db per S unit, but Below S-5, it was closer to 2 db per S-Unit,  And above S-9 was around 8 db. 

So the verdict was a really nice radio with a not so accurate S-meter. After doing some research, I concluded that this was actually pretty normal for Amateur equepment at the time. 
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John - K3MA

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@Joseph Rodick now you on the right track.  Put the S meter argument aside and compare the rx sensitivity on the Flex side by side with the 7300 on the same antenna listening to the same weak signals at the same time.  After a short period over several samples you will know if the Flex receiver is more, less or the same in sensitivity as the 7300.  If you do not find it to be more sensitive or the same sensitivity as the 7300 then something is indeed wrong.

I have compared several Flex radios this way between at least a dozen different receivers and have never found a signal I could not hear on another radio and not the Flex.  Although I have found some low priced radios that people do not give credit too for their excellent receivers that on the bands receive as well as the Flex.  Maybe they do not get as good results on the test instruments but they sure do when listening for weak DX signals.

(Edited)
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Joseph Rodick

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Later this week I am going to do a weak signal test using my 6400M and an Icom 7300.  However, I do feel confident Flex service did a good job and that my 6400M will be shown to be the better of the two.
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FISHULA X

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So riddle me this.  On my 6300,  lets say on 40 meters  LSB , why when I have an antenna connected and have a noise floor of S 4 or so and then I engage the RF gain, the noise floor stays  pretty much the same but,  when somebody is talking it does not change the signal either other then peaks however, when I engage the RF gain, It makes the person talking more clearer,  less space between us, or as if I instantly got closer, a better arm chair copy. Or as if I had a beam and locked on the signal. All of this done with no significant increase in signal . Perhaps this is the same issue and the topic is related.   I feel that the S meter is just  a point of reference.  Everyone's station and situation is different . I focus on the important things like  ((((((ONE OF THE BEST RX ON THE PLANET)))))))  I have owned many radios and live in a noisy area. The 6300 is thee best RX I have had to date. So when It comes to a perfect S meter reading as I said, It's a reference point. An approximation at best.
(Edited)
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Bill -VA3WTB

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FISHULA, Your radio is taking the signal from the antenna port and converting that into v. And that = S meter information. In almost all conventional radios the signal is through several circuits, the main one is the AGC.

On your Flex the S meter reading peaks are bang on with the signal that is picked up at the antenna connection. It is not an  approximation.
(Edited)
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FISHULA X

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 Thank you Bill for your reply.
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Burch - K4QXX

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I have never understood why I would care if my S meter read 0 when I don't have an antenna connected.  I can't use the radio without an antenna so why would I care what the S meter reads? 
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Stan - VA7NF

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I have stayed out of this until now - Same players, same ignoring facts.

Joseph, I will take your request and questions as not understanding what is happening, so this "Season 2 - Episode 4" of S-Meter Chronicles follows:

The Theory:  1) The front end component of a Direct Connect (directly connected to the antenna and PreAmp) SDR radio is a analogue to digital converter that captures the exact voltage as over 2,000,000  binary numbers per second (avoiding the conversion details and math involved)
2) Every A2D has both maximum (overload) and, significantly in this case, MINIMUM sensitivity levels (binary 0 numbers produced)
3) On all bands, more so as the received frequency is reduced (some at 40M and more so at lower frequencies - check this out on the BC band).

Your Case:  1) Your Maestro is set at -8db attenuation which is delivering signal to the A2D converter SIGNIFICANTLY below the MINIMUM THRESHOLD (more to follow).
2) While this is great for normal signals, you are complaining about the noise floor or very low level signals and the S-Meter reading.
3) Raise the amplifier gain and watch your "noise floor" SEEM to drop

Repeating this on my 6700:
Table of Readings at 7.000 Mhz, CW 500Hz bandpass (standard filter), No Antenna:
Preamp  dbm  S-Meter  Delta            Notes:  
 -8           -106    S3         N/A             Noise < A2D minimum threshold
0              -119    S1      (-13)              Noise level still < A2D minimum
+10         -126     S0.5   (-20 / -7)        Noise level still < A2D minimum
+20         -133    <S0     (-27/-14/-7)   Noise level NEAR or ABOVE A2D minimum
+30         -133    <S0     Same as above  Gain now OVER minimum

This demonstrates that the REAL NOISE level is around -133dbm, <S0.  The -106 level shown at 8db attenuation is STRICTLY because you have chosen to extend the A2D dynamic range in favour of sensitivity to very low strength signals.

So, if you want extreme sensitivity then raise the PreAmp until those signals are within the A2D passband.  If you want more tolerance for very near stations then reduce the gain.  If you want a quieter background then modify the AGC-T, likewise adjust the AGC-T to the sweet point (see other online postings) where the A2D actually expands the gain of the near noise signals. 
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Michael Walker, Employee

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Stan

Thanks for posting that.  I had just got off the phone with Eric in engineering who explained the same thing to me, in a slightly different way.  And, that the PreAmps lower the noise floor resulting in a lower S meter reading.

Nice work,

Mike va3mw
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N2WQ

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The purpose of the S-meter is to measure the voltage applied to the antenna input. The purpose of the S-meter is NOT to measure the internal noise of the AD converter. All that talk about decimation and bins ignores the fact that when the input is shorted the S-meter is showing the internal AD noise, not the input voltage, that we all know is ZERO.


So, yes, the S-meter is dead wrong if it shows anything but ZERO with shorted input.
(Edited)
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Bill -VA3WTB

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Oh no Stan, don't start that!!!!
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Michael Walker, Employee

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What Stan wrote! :)
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KY6LA - Howard, Elmer

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@N2WQ.   You are stuck on the Frozen Thermometer Paradox.   You want to read a temperature below the point where the mercury is frozen solid 

You are also misunderstanding the value of S0 which is BY DEFINITION-127dBm and NOT the total absence of RF. 
So unless you Were able to short the antenna with a Perfect Ground with the entire system at -273K you will still have some signal.  So it definitely follows Ohms law. 
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Burt Fisher

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N2WQ, you are right, that is the way it SHOULD work.
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Stan - VA7NF

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Here we go again - Same old, same old.
It occurred to me that vintage radios (Japanese circa last year) inject a DC voltage into their AGC (they call the knob RF Gain).
As you turn down the RF Gain the S-Meter rises, well into the S-9+20db range; if I ground the antenna when the RF Gain is turned down the meter still reads S-9+20, not zero. 
Instead of the RF Gain, Flex uses the PreAmp, only they maintain +/- 0.5 dbm accuracy at all levels but only when the source signal exceeds the minimum A2D threshold.
We have many English words that cover many posts on this thread including "Dumb" and it's many synonyms or in modern lingo "Troll" 
G'Night all.
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N2WQ

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The OP states that his S-meter reads S5 when the input is shorted. I seriously doubt it that a short at room temperature yields S5. If memory serves me well, S5 is about -95 dbm, I.e. a pretty strong input signal.
(Edited)
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KY6LA - Howard, Elmer

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Depends on the Ground Quality  and FREQUENCY and Ambient noise he picks up from his power supply and common mode currents. 
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Rick WN2C

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S-reading    HF        Signal Generator emf
μV (50Ω)    dBm    dB above 1uV
S9+10dB    160.0    -63    44
S9    50.2    -73    34
S8    25.1    -79    28
S7    12.6    -85    22
S6    6.3    -91    16
S5    3.2    -97    10
S4    1.6    -103    4
S3    0.8    -109    -2
S2    0.4    -115    -8
S1    0.2    -121    -14


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Brian Denley KB1VBF

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Mode and bandwidth?
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DJ1WT

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We all know noisy receiver (e.g. JRC some years ago) masking weak signals, perhaps this Flex is one of those?
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Michael N3LI

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It's quite possible. Unfortunately some of the troubleshooting might have been askew, leading to the never-ending Flex S-Meter versus legacy meter discussions.