Noise / Interference Help

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  • Updated 5 years ago

I am asking for some help with identifying and elimination of a gruesome noise issue I am seeing on lower frequencies below about 25mHz.  

I am posting links to two pictures of the waterfall / panadapter screen on 14mHZ.  One is with a narrow signal and the other shows a wider band width signal that comes form the battery charger on my inverter/charger system..

Noise picture:  https://www.dropbox.com/s/i5ktzv4df05jvs6/Noise%20-%20Charger%20Off.JPG?dl=0https://www.dropbox.com/s/zyxs62o83n8hxbg/Noise%20Charger%20Off.JPG?dl=0

Nosie with Charger On: https://www.dropbox.com/s/0ly5q5fzqz0x7wa/Noise%20Charger%20On.JPG?dl=0

MY BOTTOM LINE QUESTION: To understand what I am seeing and determine if changing to a full sine wave inverter/charger system is the answer.  This will mean spending about $2K on a new system so I am hoping to be able to feel confident that this will be money well spent.

Background:

I operate from my motor home which has a modified sine wave inverter/charger (Xantrex Freedom 458 http://www.xantrex.com/power-products/inverter-chargers/freedom-458.aspx )

There is a new full sine wave inverter/charger available (Xantrex New Generation http://www.xantrex.com/power-products/inverter-chargers/freedom-sw-12v_newgen.aspx )

My radio is powered directly to 12V off of the batteries.  I have four 6 volt batteries wired in series/parallel to provide 12V power. 

The problem is definitely coming from the inverter charger.  With the inverter in "off" running to curbside AC, I still get a high peak signal on what seems to be 40kHz harmonic.  When I have the battery charger "on" there is an added wideband interference that rides on this 40kHz signal. 

If I use an MFJ-852 noise meter I do not see any signal near the inverter/charger electrical bay but I do get a low gain signal near the area that my Flex 6500 is located. 

I checked the DC with a scope and did see a spike on DC when DC coupled and I get massive signal when AC coupled.  I have added an ICT Power Conditioning Module at the DC source to the radio and the scope does show that the AC signal is being filtered.  Unfortunately, this filter has not cured the interference.

Thanks in advance for anyone taking the time to provide information / advice.


Duane

N6DMR



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MH_Flexer

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Posted 5 years ago

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Photo of George Molnar, KF2T

George Molnar, KF2T, Elmer

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Your plan will probably help, but I'd suspect there are other noise sources at work, too. Can you isolate down to just the rig and laptop, both on battery? How is the grounding, cabinet bonding, and lead placement? It may be possible to improve things "enough" without spending a lot. Only "may" - but worth checking.
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MH_Flexer

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Thanks George. Your comment got me thinking, I have a central ground in the radio cabinet, but I just realized I am grounding to the frame of the slide out which may not have a good ground to the chassis or earth ground. I will do a little ground braid work to insure the grounding is optimum.

Good idea to check the basics!

Duane
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K1FR

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Duane:  I have a Freedom inverter/charger on my sailboat and experience much the same issues.  When at the slip I have to turn the charger off if I fire up the HF rig.  Away from the slip and on batteries alone or with the engine charging the batteries all is well.  Have been thinking of a new charger, but my at slip use of HF is pretty minimal.  Good luck. Nice looking motorhome!!  

73, Tom
K1FR
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KY6LA - Howard, Elmer

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1.  Suggest you read my presentation "How to build a quiet station"  https://db.tt/xG8SOiRI
2.  Have you tried putting lots and lots and lots of Toroids onto everything and everywhere.?
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Stan - VA7NF

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From the picture it appears the -ve is floating and it sounds like switching signals are coming out the AC and DC leads.  Also from the panadapter shot it appears you need 30-40dB suppression to bring the RFI below the noise level.

Ensure there is low RF impedance between all 4 leads and chassis ground - Use good ceramic capacitors (.01 ceramic/RF or thereabouts) inside the case, if you feel comfortable opening it up.

That low RF impedance will stop the noise from coming out of the box, especially with the torroids increasing the RF impedance on all leads on the outside.

The presentation by Howard is a good read.

Stan

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MH_Flexer

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Thanks guys.

Howard,

I have read your presentation a few times and I just re-read through it again as you suggested.

I have toroids on all DC and Audio leads in and out of the radio. My antenna connections each have a series of 16 toroids daisy chained with the coax wound thru them. I have no "wall wart" transformers anywhere. Everything that had a transformer is now direct to 12V. I use the 5V Zener style charger for my mobile phones and tablets.

I do need to go over the grounding scheme carefully to be sure I have that working as I noted above. This may be something that I can improve. I also have an ICT PDM filter box right at the radio.; on my scope the DC going to the radio is relatively clean.

****** The MFJ-931 artificial ground is interesting, as I rarely have the ability to have access to ground rods. I do have a common ground point with a pass thru ground connection to the outside. I doubt if
I can put down a counter poise at 1/4 wavelength. Do you think the MFJ would support with outside ground counter poise of 20 to 40 feet?

The MFJ-852 is on 135mHz, it does not "see" the noise I have on 25mHz and below. My issue is also with a known problematic power system, the dreaded Modfied Sine Wave.

Duane
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KY6LA - Howard, Elmer

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1. You can always make a Faraday Cage for your inverter, then ground that cage.. that will stop direct radiation for the Inverter
2.  Even more Toroids on every line in and out of that inverter

3.  I have used the MFJ-931 with all sorts of different ground lengths.. It all works together as a system.. so test it...
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MH_Flexer

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Good ideas Howard.

Since you have used the MFJ-931, is this some thing that can be put in my radio compartment tuned once for a given location?

I have all the radio stuff under the dinette seat in the MH. If I can tune this occasionally or when I travel to a new location it would be pretty good to try it.

Duane
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KY6LA - Howard, Elmer

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Never tried it from a MH but I have lived in Condos where it made the difference between working nobody and working somebody.

The MFJ-931 needs to be optimized for each frequency you us so it is definitely NOT set it and forget it...
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MH_Flexer

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Stan,

I am OK working inside the Freedom 458 box, I have had it apart for cleaning a few times already. 

Your suggestion is to use the .01 capacitors on DC ground and power as well as AC neutral and power? 

I just want to be clear on the AC side. 

I also have a spare UPS that I can try to use as an ancillary filter on the AC line.

Thanks for the suggestions.

Duane

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MH_Flexer

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Tom,

I appreciate you reply as well.  Your issues with the Freedom 458 help to confirm my own opinion of the noise.  It is interesting to actually see this noise on the panadapter.  

My issue revolves around being at "dockside" condition practically all of my radio time.  I stopped using the radio when driving the motor home a few years ago <grin>.


Duane

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MH_Flexer

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George,

I did not reply to your question regarding 12V DC operation,  Yes, I have shut down all AC power and run off only the battery with my laptop on battery power as well.  The interference practically disappears in this mode. 

I am going to try improving the RF grounding and also adding capacitors inside the inverter/charger case.  I know the source of the noise in general but need to find a way of filtering or eliminating it.  I am not yet convinced that it can be filtered completely based on the modified sine wave it generates.

Duane

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MH_Flexer

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Gents,

I have been doing a bit of research on modified sine wave inverters.  An interesting factor is that they sort of perform like an Uninterruptable Power Supply or UPS.  On a high current scale, they convert from 12Vdc to 120VAC, just like a UPS. 

I have a PowerVar Power Probe 115 which shows the noise levels on an AC line between neutral and power as well as common mode noise.  This box removes the AC source sine wave and shows just the noise between the lines.

I found that on the PowerVar website  http://www.powervar.com/education_details.php?id=2   there are some videos that give great insight as to what I am dealing with.  Starting from a modified sine wave (a square wave) THE DIFFICULTY IN POWER CONDITIONING INCREASES AND MAY EVEN BE IMPOSSIBLE.


I have a call into to PowerVar Tech support to get their thoughts on whether a power conditioner will work for me.

Here are links to a series of PowerVar  You Tube videos that discusses the noise issue on AC power lines:

Part 1 https://www.youtube.com/watch?v=vgH-bUmqKfE

Part 2 https://www.youtube.com/watch?v=vgH-bUmqKfE

Part 3 https://www.youtube.com/watch?v=hTEzi_5ZVqY

Again, many thanks to all the great community folks who have responded.