6400 sensitivity discussion

W9MO

I guess the best solution for A.J. is to vote with his feet and sell his Flex. 

Bill -VA3WTB

I would not blame him, who wants a deaf receiver as he says. First time I ever heard that complaint about the radio.

Ken - NM9P

You will always need a preamp on 10 and Six Meters. And sometimes on 12 and 15. But remember with the FLEX the preamp will have no effect upon S-Meter readings like many legacy/analog rigs which derive S-meter levels from the AGC loop.

Greg SP7QJF

Namely, 6400 and 6600 are worse than 6700 from before 8 years.
Flex goes backwards instead of growing

David Okay Patton

To say the 6400 is deaf is a real overstatement; however, the preamp setting are much different than for any other HF rig that I've used.  As Tim (Flexradio Customer Experience Manager) pointed out, the preamp is needed because of insertion loss in the preselectors.   

If you have a 6400, you will most likely realize the best receiver performance using 16bB preamp gain as your default setting, and adjust as needed due to band conditions.

I won't argue with anyone that this is an unusual way to configure gain stages. Information on correctly setting the preamp level should be emphasized in the 6400 manual, so that owners don't draw the incorrect conclusion that the 6400 has a poor receiver, when in fact it is actually quite good with correct preamp settings.

Robert Lonn

OK, the Yaesu beats out even my IC-R8600 radio, but my 6600M Flex is just better then my IC-R8600 for raw sensitivity and digging out those weak stations.. OK, so a Camaro all specked out is 1 MPH faster then a BMW M6, but we all know that most would prefer the BMW over the Chevy for so many reasons... Think what one would give up, to jump away from FLEX and over to the 101D!!! The list is very long on give up's... Yaesu did some clever engineering building more of a HYBRID radio then a true 100% SDR box... The July release of the 101MD  200 Watt version will have many options as standard features and said to be $6000 !!!  Raw specifications is good to know, and I am glad Bob creates this list... 

As a Vintage Audio File person, I have the TOP 10 Best all Time FM radio tuners.. This is right off the  master FM radio evaluation.. Took me almost 9 years to get all 10, but have about 25 in my collection.... Funny that most of my all time favorites are NOT in the top 10... Not that they dont perform as good as the top 10, but the Looks Of The Tuners and feature set, is what sets them apart...My Favorite is my rare Grundig T-9000 receiver...

Basically I am saying their is So Much More then just the raw specifications of a radio.. But hey,, I am not telling you something you already dont know!!! :-)

Here is a link in case you never visited this site.. These top tuners do sound SO GOOD!!!! Makes digital audio sound DULL!!!

http://www.fmtunerinfo.com/shootouts.html

Robert

Grundig T-9000 ,, Second best for me, Pioneer F-93 with Space Diversity FM reception..

Doug

I think his receiver is a snowflake in that it is unique and 1 of a kind ! What I find amazing is I actually have to throttle my 6400M back with the AQCT on all bands through 20M. But I have found out you can't operate a Flex like a standard ham receiver. I really feel sorry for him because he is so unhappy and I don't see anything that will change short of selling  He needs to sell his 6400 and move on. Too many great radio's anymore and unlike most if not all other brands a used Flex will command most of it's original purchase price.  I mean this in all sincerely I wish him the best.

Lionel

I did some testing.

28.005Mhz   Slice A on 10m; Slice B on 75m. CW mode 400hz BW  Ant 1 either grounded or connected to 40m dipole E-W at 50 ft. WBN, NB, NR off.  SWR seen by Flex ~ 1.7:1 thru tuner.  Front end filters in Wide mode.  No signal within ~25 khz.

Changing Slice A only;  Preamp is common by design to Slice A and B.

Preamp: 0 dbm
Grounded: -107dbm
Connected -108 dbm ~ 107 dbm

Preamp: +8
Grounded: -116dbm
Connected: -116dbm

Preamp: +16
Grounded: -124dbm
Connected: -121dbm

Preamp: +24
Grounded: -132 dbm
Connected: -124 dbm

Preamp: +32
Grounded: -140 dbm
Connected: -124 dbm

In my location external band noise seems to limit at -124 dbm.  This is a similar situation as frequency is lowered.  Above +24 db on 10m on this day and time, additional gain doesn't seem to be useful. 

The 6400 is my only Flex so for 6600, 6700, I don't know what they would show, though the same setup and documented results would be interesting. 

I ran the same test on my prior Flex 5000 and 6300 but, of course the data was misplaced by the IT staff. 

A.J. AJ2I

Thanks for the additional testing lionel. I think I'm going to keep my 6400 and just use +16 all the time. Thanks to all the people who have done additional testing and help in documenting this limitation and workaround confirmation. I'm not unhappy, just disappointed. I'm on the other end of the spectrum. I'm not a contestor, I'd rather have a more sensitive radio then a top of chart dynamic range radio. When the guy in Wallis and Futuna is 4/3 with heavy qsb on 15m, I need that extra sensitivity and lower noise floor. I dont need to worry about someone 2 kcs away. When I bought the radio I expected great performance, not just ok performance. Different tools for different purposes

Lionel

I'd like to see the numbers from a 6600 or 6700 using the same test setup.

Using a 40m dipole on 15, especially with the EW orientation, the band is generally dead at all preamp settings, a situation that I'm correcting with a NS dipole, I hope. 

When I get to 80-40-30 a low noise rx antenna might help; my local suburban/rural noise level is above the ITU curves.

For my use the ability to hear weak stations generally seems adequate but I know it depends on the particular activity and the entire station system.  That said, expectations matter, and I can see how it is letting you down in a quiet environment. When I chase spots I do get frustrated at times when others are working the DX and I cannot hear them at all; more a function of the antenna - my working theory anyway. 

Enjoy 15, I'll have to wait for higher SSN's. I checked 10m this morning and the band noise is -118 here and could be from many sources, more or less uniform across the spectrum.  Solar I guess. 

KF3F

For what it's worth, my 6600 with an RF Gain of 16db receives the same as my Kenwood TS-850.
Signal strength is the same as well as weak signal copy capability.

W9HH - Steve

I always wondered where the 6400 would end up on Sherwood's charts and suspected the results wouldn't be as good as everyone originally thought. So when the tests were finally published on the website a few weeks back, I was a bit disappointed. Still love the radio though, and it does just about everything I need it to do for my style of operating. No plans to sell it because of the test results, It's not going anywhere. Maybe this will put things in perspective:

https://www.youtube.com/watch?v=up6QB3qyc6M

73 -

K0FLY

I have looked at the receiver block diagrams of several of the radios listed in 
Sherwood's table.  Most of the radios have a dedicated "RX RF amplifier" stage in front
of their mixers to help obtain  sensitivity values. 

Flex 6000 radios have a dedicated variable -10 dB to +32 dB amplifier stage in front of their 
16 bit A to D converter, however, Flex calls this amplifier a "PRE-AMP" not a "RX amplifier". 
The Flex PRE-AMP is the same as other manufacturers RX amplifier.  The beauty of Flex radios is that you can set the gain that you need per band.  I think that we may have gotten hung up over naming conventions.

It would be nice to know what the Rx sensitivity of other radios is with out the fixed gain 
RX amplifiers.  I know that the FT-5000 can be set to 0, 10 and 17 dB gain.  The FT is speced at 
.2 uV with 17 dB gain RX amp enabled.  Flex 6400 was measured at .6 uV with 16 dB of gain.  
Yeah that's down from the FT but we got +24 dB or 32 when needed.

I think that Flex is doing very good with ~-111 sensitivity, and  no gain in front of the 
16 bit A to D converter.  Remember Sherwood measured both sensitivity and close in 3rd order IMD 
with  16 dB gain in front of the A to D.  (100 dB IMD isn't to shabby)

I'm happy with the sensitivity of my Flex radios.
  .

Gayle K0FLY   

K5ROX

a general statement like this simply isn't true.
A direct sampling radio receiver will out perform any superhet receiver.

K5ROX

I have many radios, many pretty old and my flex 6600 will not receive a signal that my others wont, my 6600 isn't any better.  I had a 6300 and it was same.

Paul Bradbeer

Good post, Gayle. The important thing is that we're discussing different RX architectures. Flex has enough gain in the RX system to hear very low down (about -140dBm) ; the fact that you may have to use 32dB of gain to get there is irrelevant! I use my 6400M extensively on 6m weak signal, and at my quiet QTH I am using the +32dB preamp. So what? ...Nothing wrong! Paul M0CVX

A.J. AJ2I

My difficulty is running out of AGC-T when you run the preamp that high. I usually run mine about 25 when I'm at +16. But when you get to +24 or +32 you can goto 10 on the AGC-T

KF4HR

"A direct sampling radio receiver will out perform any superhet receiver."

Check the specs on the ICOM IC-7851.

Steve

Terrible title for this thread.. it would make one think that the radio sucks and it does not.  usable sensitivity
is dependent on many variables.  Just my opinion.

James Whiteway

Poor antennas can make a great receiver preform poorly. Good antennas can make an average receiver work well. Even to the point of overloading the radio. The better the antenna the better, to a point, any radio will receive.( and transmit) James WD5GWY

Ken - NM9P

Are you saying that your "sweet spot" where the noise just begins to drop on a quiet frequency is not reached until you move from the right all the way down to 25?  (Or 10, with +24 or +32)  On which band, and with what antenna?   

Ed Stallman

>>>with the FLEX the preamp will have no effect upon S-Meter readings like many legacy/analog rigs 
That's not true , on 6m all I do is raise the preamp gain and the s-meter lowers 'At a -8 S=Meter =1.5 , each step up in gain the S-Meter lowers until I get to a +16 @ S zero 

mikeatthebeach .

Yes, the IC-7851 is great but check the price !!!!!

Ken - NM9P

Are you talking about the S-Meter level of the SIGNAL or of the background noise?  or both?

Bill -VA3WTB

Ken, 6m is the only band were the ant gain effects both the noise floor and the S meter 

Ed Stallman

50.092 CW , filter 100Hz 
Gain @ -8 
S meter = 1.5
DBM-115

50.092 CW , filter 100Hz 
Gain @ 0 
S meter = 1/2 to 3/4
DBM-123

50.092 CW , filter 100Hz 
Gain @ +8
S meter = 1/4
DBM-130

50.092 CW , filter 100Hz 
Gain @ +16
S meter = 0
DBM-135

50.092 CW , filter 100Hz 
Gain @ +24
S meter = 0
DBM-137

Going to +32 , maybe DBM went to --138 , so with preamp at +24 on 6m you scratch 2 coat hangers together and I'll hear you 
Ed N5DG

Manuel Maseda

Great post Gayle. For those that don’t know him Gayle is a highly respected retired Rockwell Collins employee.

Ken - NM9P

On my 6500, I always use the max preamp (+20 dB) for best noise factor on 6 meters.  It is standard operating procedure for any of these rigs.  

As I understand it, the standard test for whether you need the preamp (and how much you need) is to switch between your Dummy load and your antenna.  If the switch to antenna makes the noise floor rise by 8 dB or more, then your receiver noise figure (which is improved by the preamp gain) is low enough so that the signal from the antenna is overcoming the internal noise generated in the receiver.  If not, you need to add preamp.  

On lower bands the preamp is not necessary and their use only reduces the dynamic range by roughly the same amount as the excessive preamp that is being used.  

Needing to use 24 or 32 dB of preamp gain on 6 meters is not a design flaw, it is part of the system gain distribution.

Another crude way I check it, is as I move the preamp from 0 to 10 to 20 dB with the antenna connected, if the noise floor drops appreciably, I needed the gain.  If it doesn't drop more than 5-8 dB, then I may not need the extra notch.

s-meter variations is something I will need to examine.....

Ken - NM9P

Michael Wheatley

What are the recommended preamp settings for 6400 on 160-20? 17-6?  I saw the post in which Tim Ellison recommended +16 but I'm not sure he meant all bands.

Michael -- KM6LHD

George KF2T

One thing to remember, gang. Per ITU-R P.372.7, radio noise vs frequency data indicates that it pretty much doesn't matter outside of a lab environment. Most every modern receiver has an MDS at or below typical noise environments in the real world. A few dB that you could not possibly discern shouldn't be an issue.

As others have said, other factors, including IMD, filtering, dynamic range, etc., will quickly overwhelm the putative noise level differences. Radio manufacturers often "trade off" one value for another for marketing or engineering ease. It's not indicative of a "good" radio vs. a "bad" one.

Most of all, your environment affects your receive capacity. If you are experiencing noise in excess of the ITU table, don't be surprised. Noise levels have been increasing steadily in the developed world as more noise sources (switching supplies, a million kinds of devices, energy-saving lamps, etc.) that the real curves probably ought to be revised upward.

Rob Sherwood is a careful professional who provides excellent information. It is our job to read it in context and understand the very real differences between lab testing and the real world.