What Causes These Waveform Humps

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I have these "humps" in base noise level on 15 and 17 meters (see the image). On further investigation, I found that as I spread the frequency span, these "humps" occur over a broad range, peaking around 18 MHz, and dropping off in intensity as I scan either direction, disappearing around 12 MHz and  30Mhz. The images here are taken with all cables except power and LAN disconnected . With the antenna coax connected (between the 6700 and the amplifier) these humps increase in amplitude.

Does anyone see similar "humps"? I need to know what might be causing this?


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W5UN_Dave

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Posted 4 years ago

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Paul Christensen, W9AC, Elmer

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Yes, these are switch-mode harmonics. The humps are characteristic of switching supplies that use little or no EMC mitigation techniques. LAN Ethernet birdies also typically repeat every "x" kHz but their spectra is almost always very sharp and not broad.

The noise source may, or may not be in your home. I typically go to an Elecraft K3 on battery (to completely shut down the LAN) in order to systematically find any in-home noise source.

Paul, W9AC
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K1UO - Larry

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Hi Dave,  If the amplifier is your SPE2K with its switched power supply that may be the culprit.  I used a 220V 15A  CorCom line filter to isolate my SPE switch mode harmonics from getting into the f6k.
regards
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W5UN_Dave

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Here is what is so distressing to me: I am running my K3 using NaP3 for the visual spectrum. The K3 is running from the same MFJ switching power supply as the 6700, and is connected to the same 2K-FA amplifier.  I see no such humps, nor hear any noise change as I tune the K3 through the hump frequencies as seen on the 6700.

I am puzzled. Where to go from here? Is this a Flex problem? Is it that the noise floor on the K3 is that much higher? Both the K3 and the 6700 show a -120 db noise floor at 18 Mhz. There is a 20 db noise rise on the 6700 spectrum display from noise floor to hump peak. I am seeing essentially the same noise floor level on the K3's Nap3 spectrum, but NO hump.
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Paul Christensen, W9AC, Elmer

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I see similar results.  I am using my K3 with a SDR-IQ receiver, tapped from the 8 MHz I.F.  The Flex 6700's panadapter is significantly more sensitive.  It's not that the noise floor of the K3 is higher, but the panadpater is not as sensitive as that in the 6700.

On the K3, tune in to where you would see the humps on the 6700.  Put the K3 in wide AM mode and listen for hum as you slowly sweep the VFO through the hump.  You may be able to hear the switch-mode hum but not see it on the K3.   This was happening to me last week on 80m.  Couldn't see the humps on the K3/SDR-IQ but could hear the hum on noise peaks.  The 6700 detected it both with hum in the audio and the panadapter. 

Paul, W9AC

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W5UN_Dave

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Yes, I hear it on the K3 at AM and low level. This is going to be a tough one to crack here. WOW, the 6700 has SOME capability to detect this so plainly. It is aggravating to see this right where I want to hear CW on 17 and 21 mhz. I need to get this mess fixed before the waterfall comes.
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W5UN_Dave

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I am totally stumped on this one. See my picture and someone please tell me if you have seen similar humps and if you were able to cure this problem.

Thanks for the comments and suggestions received thus far.

I have turned off every device in the house but the humps remain. My closest neighbor is 1/2 miles away, so I can't believe it is from them. What about power company, could this be some of their doing?
(Edited)
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Norm S

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Do you have any solar equipment running?  How about electric fence?  I pick up solar controllers 1/4 mile away.     
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W5UN_Dave

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nothing around here that I can tell