MDS ON 80 METERS

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  • Updated 4 years ago
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  • (Edited)
A GUY WAS ON OUR NET WHICH HAS 5 Flexes on it and was bashing the radio because of the ARRL review showing a -119 dbm MDS on 80 meters, saying it does not hear well on that band due to no preamp available. My noise floor on 80 is 115 dbm due to static which makes it a moot point for me. I understand the reason being to avoid broadcast station interference. I would appreciate some discussion on this point from the community and Flex engineering. I would like to have an intelligent answer for this guy. He is very anti SDR so I want to have the a very well informed come back to him. Also what do you see as a noise Floor at your QTH on 80M? meters?
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Alan Nusso, N4BV

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Posted 4 years ago

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Larry Davis

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put up a better antenna or some rx antenna
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Rhett Aultman

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I was just monitoring 80m last night and had a noise floor between -110 and -120, and there was LOTS of activity on it.  I'm in a noisy environment (residential part of Oakland, CA, small backyard), and was using a Buddipole that was set up for 40m.  But, man 80m was clear as a bell.
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George Molnar, KF2T, Elmer

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It's pretty unlikely there is anywhere you could go with less noise than the MDS spec. Unless he is using an inefficient antenna (deliberately or otherwise), the ambient noise level will be well above the MDS, making the case moot.
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Jim, KJ3P

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Out here in the semi-country, the best 80-meter noise level is usually around 113 dBm.  Of course, with the JT modes, I sometimes get a decode below the noise level! Your buddy certainly wouldn't want to chew the rag with signals that low.
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Duane, AC5AA

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And remember, noise levels in the southern US on 80m are higher than they are up further from the equator.  But still . . .   Here in Austin, TX on a quiet afternoon, I see -104 dBm noise level.
(Edited)
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KY6LA - Howard, Elmer

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Official Response
The charts say it all
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George Molnar, KF2T, Elmer

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Yep.
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Robbie - KI4TTZ

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Noise level at Robbie's house: S9+20 :-( (kidding...sorta)
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Ken - NM9P, Elmer

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I have that kind of noise when my seven year old son is in the room...ba da boom!

But seriously. In southern Indiana, I seldom see a noise floor on 80 that is less than about -100 dBm.
(Edited)
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George Molnar, KF2T, Elmer

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Here's a good article: http://g4fkh.co.uk/wp-content/uploads...

In it, you can see that the mean atmospheric noise around 80 meters is around -97 dBm. Please ask your friend how he gets rid of the extra 12 db to even begin needing a preamp. Also, remember to measure on the s-meter (hover over it or use an app like Flexmeter) using 500 Hz bandwidth and no preamps to get a reproducible result.
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Steve N4LQ

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Just watch....He will come back with something like: "Well, that doesn't matter...I need alll the gain I can get to boost those weak signals then I'll reduce the noise with my super noise reduction button!
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Simon Lewis

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I would suggest that in nearly all cases on HF using modern radios that equipment capability is not the limiting factor but natural / man made noise is. On VHF I have such a quiet location that I can detect warm/cold bodies when I rotate the array - even then I am using preamps / transverters in that chain. Figures are one thing - real world is another - I'd ask him to demonstrate how he see's a preamp helping with S9 static crashes. Sadly I think your flogging a dead horse .. if he's anti SDR then you arguing with a brick wall. I see the same lame trolling on Eham - leave them to it :) 73 Simon ZL4PLM
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Jason Whiteaker

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Yes, and if the noise argument goes away, the anti-SDR folks do the tried-and-true, "...real radios have knobs!" schtick. :-)
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Steve - N5AC, VP Engineering / CTO

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The "other guys" create a great MDS by throwing a preamp in front of their receiver signal chain and leaving it on all the time (this is not the preamp control on the radio, but is just "always on" RF gain).  This results in a great MDS figure ... and worse IMD numbers, worse overload, etc.  We could have easily thrown a preamp in front of the receiver and left it on all the time to result in a better MDS ... but why would you want an MDS below the atmospheric noise level?  All you are going to do is amplify the noise.  If the signal is below the level of the atmospheric noise, no amount of gain is going to coax a signal out of the noise, it just increases the noise along with the signal and the signal remains buried.

In fact what you really want in most receivers is attenuation on 80m, not more gain.  This is solely because of the atmospheric noise level around our planet.  This is why some radios provide an attenuator button (although most do not know when to use it).  

It used to be that better MDS was the "holy grail" in the radio business.  That is until the MDS on everything was at or below the atmospheric noise level.  Anything beyond that won't improve your receiver, it makes it worse.  It may not be intuitive, but it's correct.
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Dan -- KC4GO

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Most of the time on 40 all the time on 80 and 160 the attenuator is on. The pre-amp almost never comes into play below 15 meters.
I even find this true in my mobile installation. (not FRS but may take it this year)  Antennas here are not monsters  mostly wire and a all band Comet 250 to listen on. 
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WA2SQQ

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Alan, in my professional life I work with digital cameras. Every day we have people complaining about some obscure artifact that's only visible when you view the image at 400%. We have a name for these folks - "pixel peepers".  For this person who complains about the spec, ask him to explain it to you - bet you he can't! These people are all about finding numbers to use as the basis for an argument.
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Duane, AC5AA

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I'll bet he's one of these guys who takes the rig out of the box when new, turns it on and immediately turns on the highest gain pre-amp that it has and never turns it off no matter what!   (And I love my Nikon D7100!)
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Steve W6SDM

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As to Alan's point, as a hobby photographer I run into people who feel that digital photography isn't real photography.  In order to be a "real" photographer you have to be using film.  My name for these folks is Kodak shareholders.

People like the SDR hater you are talking about can never be convinced.  They don't have an open mind, which is unfortunate because it means they will never learn anything.  All of the technical explaining in the world, and there are a lot of great explanations in this thread, won't make any difference  to them. 

I was around when single sideband was purported to be the death of amateur radio.  It was going to plunge us into a dark abyss of hearing only half of what was said and making all of us sound like digital voice.  My VHF/UHF rig is a Yaesu FTM-100DR and I hear people talking about digital voice communication being the next big step backward for amateur radio.  They said the same thing about FM.

As a novice and starting general, I worked 80 meters using a Hallicrafters S38 and a dipole in suburban Los Angeles.  Talk about noise...