6400 Noise Floor

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I have seen lots of questions about why the noise floor is about -110.  How do you lower it and is there a setting to make it better.  Note: My preamp/RFgain is not on.  
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Mike

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Posted 2 months ago

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AH0U

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The best way to lower the noise floor is to move to some remote island where you are the only person and your Flex is the only electrical device within 10,000 miles. The radio hears what is there so go where it ain’t... the internal noise of the Flex is not worth mentioning
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Bill -VA3WTB

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Your noise floor is determind by your radio invirement. Some people live in a high noise floor and others in a lower noise floor. . We use the AGC-T settings, this makes the noise floor sound more tolerable.
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Dave Skinner

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I live out in the country and the noise floor on my 6500 is -110. Nice and quiet.
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Robert Lonn

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Interesting Question!!! Wonder what the noise floor would be on the MOON?????? :-)

Robert
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Craig Williams

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My 6400 is -130 on 40 meters now. Yes, i live in the country.
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Ng Rocky

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a bit out-topic, does anybody use MFJ-1026 with Flex6400?    Does it reduce noise in urban area well?
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K9SO

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Aside from moving to the country or the moon, there are some things you can do. The absolute noise floor, while important, is not the most important thing ... but rather the s/n ratio of the signal you're trying to receive. Also, the "noise floor" displayed on the screen isn't really the same number as the true floor. Look to your S meter on the slice flag and change it to read in dBm. You'll see that the "floor" is a function of the receiver bandwidth. Any noise level comparisons are meaningless unless they're made using the same bandwidth. Most published data are taken at 500Hz. 

I asked a similar question some time ago and received an excellent answer from Gerald on the post linked below. The method he describes for setting front end gains work well to optimize the s/n ratios for any given antenna and location. 

Outside of that, you should not look to the radio itself to improve your noise floor... investigate some low noise receiving antennas or track down the sources of your noise.

Gerald's response is here:

https://community.flexradio.com/flexradio/topics/6600-noise-levels-10db-higher-on-my-new-6600-vs-my-...


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HCampbell WB4IVF

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Variable phasers like the MFJ-1026 probably won’t reduce your noise floor (unless your noise floor is determined by a local noise source), but yes, they can be quite effective in nulling out locally-generated noise from one direction whatever your location.  However they also null out desired signals from that same direction.  Receive antennas as K9SO mentioned are other (and usually better) options.  They include the Pixel loop, Beverages, 4-squares, SALs, etc. (I use Beverages).

Howard


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Bill W2PKY

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What is the noise floor with no antenna connected to the radio?
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K9SO

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Hi Bill,

I'll refer you to the comparative receiver testing data published by Sherwood Engineering to answer your question:

http://www.sherweng.com/table.html

Here's what he says about what the noise floor measurements mean:

"Noise floor measures how weak a signal one can hear.  Practically it is only of significance on the higher HF bands due to the higher level of band noise on the low bands.  This assumes you are listening on your transmit antenna.  If you are using a Beverage or a low gain loop, then it could be an issue on any band.   
 
The noise floor is measured with a 500 Hz CW filter bandwidth, assuming the radio has a CW filter.  There is a note on the measurement if the radio only had an SSB bandwidth. Older radios (Drake, Collins) had no switchable preamp.  Compare them to a modern radio with Preamp ON or Preamp #1 ON. A noise floor of -135 dBm is more than adequate on 15 meters in a quiet rural location.  A lower noise floor (-138 dBm) might be useful on 10 meters in a quiet location.  Serious 6 meter DXers often use an external lownoise preamp to get the noise floor down to -140 dBm or a few dBm lower.  If you are in the city, hardly any of this matters due to all the local noise. (On 15 – 6 meters, hardline would be important to reduce the feedline loss to make the best use of the noise floor.)   
 
Noise floor is quoted in dBm (power).  Consider it a similar measurement to Sensitivity on SSB, which I quote in microvolts (uV).  Noise floor is a 3 dB S+N/N ratio, usually measured at 500 Hz bandwidth.  Sensitivity is a 10 dB S+N/N ratio, usually measured with a 2.4 kHz bandwidth for SSB.  Due to the wider bandwidth on SSB, the signal vs. the noise sounds about the same by ear. " 

73, 
Fred Glenn
K9SO
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Bill W2PKY

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Hello Fred-

I am aware of everything from Sherwood Engineering, I'm interested in your reading with no antenna connected.
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Fred Nassar

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Bill, my signal levels without an antenna connected on 20 meters is:

On USB @2.4 khz BW
-105 dbm with no pre-amp
-120 dbm with 16 db pre-amp
-127 dbm with 32 db pre-amp

On CW @400hz BW
-114 dbm with no pre-amp
-128 dbm with 16 db pre-amp
-135 dbm with 32 db pre-amp

With the antenna (8 ele Log pointed in the direction of propagation) connected:
USB @2.4khz BW
-98 dbm with no pre-amp
--99 dbm with 16 db pre-amp
-100 dbm with 32 db pre-amp

CW @400hz BW
-106 dbm with no pre-amp
--108 dbm with 16 db pre-amp
-108 dbm with 32 db pre-amp

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Bill W2PKY

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Fred-
Thanks for the info, from your first post could not understand if you had a lot of antenna noise or the settings on the preamp was causing the high base line.
8 ele log antenna probably has a lot of gain so sounds like everything is fine.
If you rotate the beam does the noise go down? Maybe you are pointing at a noise source? 
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Fred Nassar

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Bill, yes part of my problem is some powerline noise and when I am 90 degrees to the noise it goes down significantly.  I have the power company tracking it down. I have been providing them with some data to help. They are supposed to dispatch a crew to correct a couple of transformers about a block south of me. I am hopeful that will take care of the issue. Thanks
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K9SO

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Bill, sorry I misunderstood your question... .

Here are my 20m 6600 numbers:

On USB @2.4 khz BW
-102 dbm with no pre-amp
-118 dbm with 16 db pre-amp
-128 dbm with 32 db pre-amp

On CW @400hz BW
-111 dbm with no pre-amp
-126 dbm with 16 db pre-amp
-136 dbm with 32 db pre-amp

With the antenna (3 element SteppIR (band after dusk):
USB @2.4khz BW
-103 dbm with no pre-amp
--113 dbm with 16 db pre-amp
-115 dbm with 32 db pre-amp

CW @400hz BW
-111 dbm with no pre-amp
--122 dbm with 16 db pre-amp
-124dbm with 32 db pre-amp
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Stan - VA7NF

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Mike,
The key phrase in your original question is "My preamp/RFgain is not on." 
With no antenna the signal strength will drop as preamp gain is increased until the frontend A2D converter is no longer below minimum signal level.
As shown in the two comparison sets, the APPARENT signal level will drop with preamp gain until the antenna noise is within the A2D range, then it remains steady as preamp gain is increased.

As the superhet RX raises the S-Meter with RF Gain reduction, the Flex raises the S-Meter as the preamp gain is lowered.  The reading being 0 signal + or - the RF Gain/attenuation equivalent in dbm