S Meter Reading after Service

Burt Fisher

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.  

Burt Fisher

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? 

Burt Fisher

The following companies can't understand that a shorted RF input would give you an S5 reading with a shorted input, Yaesu, Kenwood, Elecraft, Icom, Drake, Johnson, Collins. At an ARRL hamfest in Boxboro, Ma a Flex employee in a presentation said Elecraft was 5 years behind Flex. When an Elecraft owner was told that, he said Flex is a great company. Flex is a great company, are they always right?

Pat N6PAT

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.

Lasse Moell

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.

Ray - K6LJ

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

HCampbell WB4IVF

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

Joseph Rodick

Your right,  I have been with Flex since the beginning.  However, I just can't understand how a shorted RF input can give you an S5 reading.  I guess it is true, you can't teach an old dog new tricks.  Thanks for your input.  God Bless

Bill -VA3WTB

Joseph, are you still stuck in understanding were the energy is coming from when the antenna port is shorted?

Bill -VA3WTB

I got sidetract offering understanding on how the S meter works on the Flex. I beleive your correct. Because the radio tested well at the factory it seem clear that the noise he is having is created at the radio location. Time to track it down.

Michael N3LI

The quick tip is to go to a frequency and place the radio in CW mode, and a bandwidth of 50 Hz. Then read the meter. 

On my radio, if I'm at say 3K Bandwidth, I'm reading somewhere near S-5.
If I'm at 50 Hz, I'm a little less than 1, which corresponds to around -123 dbm. This reading agrees with the official settings. <P>

This is using an antenna. On a Dummy load, it's much lower yet.

Now I am agreeing with Howard. Something  that started a month ago is pretty likely to be a local problem with local noise. Could be a power supply, could be somoene locally raising a little devil's lettuce with a grow light. A lot of different things, but at this point, I'm not suspecting the radio.

As I can duplicate the S-5 condition on my 6600, and I must say - it hears. It hears to the point where I'm switching to WSPR mode because some of the stations I'm trying to contact on FT8 aren't responding. WSPR indicates I'm being heard on some pretty low power - I'm trying to QSO with some deaf stations in some cases.

And are we all up on how SDR radios use a bin sampling method to get signal strength? Purposely displaying incorrect, uncalibrated and inconsistent signal levels as per the Japanese companies seems so wrong. Because it is wrong. 

So Joseph, any chance of you posting some screencaps? We might be able to troubleshoot this. 

Joseph Rodick

I just connected an Icom 7300 to the same antenna and the S meter reading is at zero or just above and the panadapter noise is on the floor when tuned to no signal.   When I short out or disconnect the RF input to the Icom 7300 the S meter goes to zero.  I just had another friend leave and his Icom 765 pro III did the same thing as the Icom 7300.  I do believe that Flex did a good job in checking and doing the pin update however these two radios indicate no local noise or they both are not able to properly detect it.

Joseph Rodick

Joseph Rodick

This is with the antenna shorted.

KY6LA_Howard

@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 

HCampbell WB4IVF

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?

Bill -VA3WTB

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...

Michael N3LI

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.

Joseph Rodick

This week I will have the ability to do side by side comparisons with the Icom 7300 on weak signals.  I'll keep you updated.  

Lasse Moell

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.

Doug

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.

Burt Fisher

Joseph there are those that just have to be right when you see the terms unschooled and trolls  tossed about. There are some very smart people here making comments (and they know it).  Invariably the market place will make the decision.
In the era of video tapes Beta was technically superior to VHS, but VHS won out because they appealed to the average Joe, so we will see whether Flex is like Beta , superior technically but with less appeal to Joe Ham. 

Burt Fisher

No way do you sound like a troll.

VK7WH Winston

I was not going to enter this debate Burt, however I must correct your comment above. It is simply wrong.

The reason VHS won the battle was that Panasonic went to the market with VHS much earlier than Sony did with its Beta system. Nothing more, nothing less.

You were correct, however, in that the Sony Beta unit was far superior to the Panasonic Consortium’s VHS

I’m now out of here, and back to enjoying my 6700. I do hope you enjoy your Flex as much as I enjoy mine,

73 Winston

Tim W

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.

Joseph Rodick

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.

HCampbell WB4IVF

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 

Burt Fisher

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

Burt Fisher

While VHS machines' lower retail price was a major factor, the principal battleground proved to be recording time.
See the source:
https://en.wikipedia.org/wiki/Videotape_format_war

VK7WH Winston

I concede Burt, after reading your link, I was wrong on several points. It certainly refreshed my memory.

I was certain that VHS got the jump, but it seems that, at least in the US, Beta was out first. Maybe we had to wait a while in Australia for Sony to release the Pal version of the Beta format.

At the time, I was working as an engineer in Television Broadcasting where there was almost universal agreement that “Beta was Better”. I can say that I did eventually capitulate and buy a VHS VCR in the mid 1980’s, however there is no question - VHS won the battle almost out of the gate.

i apologise in advance for being off topic, but I wonder if the following words mean anything to any other Flex users. If so, then maybe we could setup another forum somewhere else for a chat

VR1000C AVR1 ACR25 AMPEX ADO etc, etc.

73 Winston

wimston.henry@bigpond.com