Yet another interference problem

[VK3ERW]

Now that I've finished my HF antenna (Longwire) installation I've discovered that most of my HF band is flooded with interference at S9+ rendering most stations unreadable unless they can push above 9+. I'm expecting my call sign to come through any day now but with this type of interference I'll be restricted to the 2mt/70cm until I can find the source of the problem.
The interference strength decreases above 20MHz but is still present. The lowest level I can see on any band is S3.

I have attached a recording of the noise - according to my analysis it's 100Hz but I'm happy to stand corrected on that.
The second recording is of a station with S9+30 and the interference is still present.

The transceiver is an Icom IC7100 with an AH-4 tuner and a 21mt long wire.
I have the same problem with my SW receiver, a Kenwood R1000).

The AH-4 has a good earth connection (earth stake and water pipe) and the antenna is between 6 and 8mt above ground.

Any ideas on what could be culprit or how I can go about finding the interference source would be greatly appreciated.

Many Thanks

Erwin
(hopefully VK3MEB soon)

[VK4TI]

Now that I've finished my HF antenna (Longwire) installation I've discovered that most of my HF band is flooded with interference at S9+ rendering most stations unreadable unless they can push above 9+. I'm expecting my call sign to come through any day now but with this type of interference I'll be restricted to the 2mt/70cm until I can find the source of the problem.
The interference strength decreases above 20MHz but is still present. The lowest level I can see on any band is S3.

I have attached a recording of the noise - according to my analysis it's 100Hz but I'm happy to stand corrected on that.
The second recording is of a station with S9+30 and the interference is still present.

The transceiver is an Icom IC7100 with an AH-4 tuner and a 21mt long wire.
I have the same problem with my SW receiver, a Kenwood R1000).

The AH-4 has a good earth connection (earth stake and water pipe) and the antenna is between 6 and 8mt above ground.

Any ideas on what could be culprit or how I can go about finding the interference source would be greatly appreciated.

Many Thanks

Erwin
(hopefully VK3MEB soon)

Simplest way to start is power the whole house down at the mains switch , run the radio off a battery , is it fixed ?
if it is then power the house unplugging everything adding items one at a time until you find it . If powering the house down did not fix it I would be looking outside at the power poles and bad insulators , get back to us if this is the case , and good luck
Barry

[VK4FLR]

Hi Erwin , Sounds like typical hash from a unsuppressed grid inverter system - got any neighbors with solar panels on their roof - it should disappear at night though when the sun goes down ???

73
Frank VK4FLR

[VK2OMD]

Now that I've finished my HF antenna (Longwire) installation...
The transceiver is an Icom IC7100 with an AH-4 tuner and a 21mt long wire.
...

The thing that distinguishes a "long wire" is that it has an endfire radiation pattern, and that happens when the wire is longer than about two wavelegnths... so your 21m end fed wire qualifies as a long wire on the 10m band and above.

That kind of antenna system is often installed so that the active part of the antenna is located quite close to house wiring which is a potential source of noise, a lightweight ground system often exacerbates the problem.

The good news is that noise sources in your own house may well dominate the noise you receive, if you don't have solar power it is within your scope to power the radio from a battery and turn the entire house of at the main switch(es). (It is a bit more complicated if you have solar power which also needs to be shut down.) If it is a stand alone residence, that is a most worthwhile test. If it makes a substantial difference, you can turn appliances back on progressively observing the noise and possibly identify some troublesome appliances.

Owen

[VK3ERW]

Frank, Barr & Owen,
thanks for your tips.
You got me thinking along the right track. The 100Hz signal seems to be spot on 100Hz and that pointed me towards rectifiers, and, as you suggested, solar grid inverters.
I don't have solar installed but I do have an ABB Variable Speed Drive (VSD, also called Frequency Inverter) installed on my swampy Aircon.
Aircon Off - Interference gone
The VSD rectifies 240AC (1Ph) and produces 3Ph 240AC (adjustable frequency, hence variable motor speed) connected to a standard asynchronous 3Ph motor, wired in delta. VSD's are well known for causing interference and are normally only used in industrial environments.

A closer look at the installation revealed that the VSD is fitted with a filter (ABB, made for this VSD, required for domestic installations) on the power supply side - this filter is there to prevent rectifier transients getting back onto the grid.

The VSD output is controlled by an IGBT module which generates lots of switching transients and therefore the cable to the motor acts as an antenna. The motor cable should be shielded (according to instructions) but in my case is not! The motor cable runs into the swampy ( a large aluminium box ) which may contribute to the radiation.

Listening to my transceiver has shown the frequency of the noise to change with motor speed. In fact, I can hear exactly how the IGBT firing changes as the motor load changes.

I'll try and get some shielded motor cable tomorrow and see how that improves the situation.

With 3 days of 40 DegC the families demand for the aircon wins over my demand for interference free HF

Any other tips on resolving VSD interference issues are greatly appreciated.

Cheers

Erwin

[VK4TI]

Frank, Barr & Owen,
thanks for your tips.
You got me thinking along the right track. The 100Hz signal seems to be spot on 100Hz and that pointed me towards rectifiers, and, as you suggested, solar grid inverters.
I don't have solar installed but I do have an ABB Variable Speed Drive (VSD, also called Frequency Inverter) installed on my swampy Aircon.
Aircon Off - Interference gone
The VSD rectifies 240AC (1Ph) and produces 3Ph 240AC (adjustable frequency, hence variable motor speed) connected to a standard asynchronous 3Ph motor, wired in delta. VSD's are well known for causing interference and are normally only used in industrial environments.

A closer look at the installation revealed that the VSD is fitted with a filter (ABB, made for this VSD, required for domestic installations) on the power supply side - this filter is there to prevent rectifier transients getting back onto the grid.

The VSD output is controlled by an IGBT module which generates lots of switching transients and therefore the cable to the motor acts as an antenna. The motor cable should be shielded (according to instructions) but in my case is not! The motor cable runs into the swampy ( a large aluminium box ) which may contribute to the radiation.

Listening to my transceiver has shown the frequency of the noise to change with motor speed. In fact, I can hear exactly how the IGBT firing changes as the motor load changes.

I'll try and get some shielded motor cable tomorrow and see how that improves the situation.

With 3 days of 40 DegC the families demand for the aircon wins over my demand for interference free HF

Any other tips on resolving VSD interference issues are greatly appreciated.

Cheers

Erwin

Congratulations on finding the problem , obviously you need a tradie who knows their stuff to stop the problem however is the cable that radiates exposed to access ?
perhaps if you can wrap it temporarily in metal foil to test the theory if safe ?
Take care
Barry

[VK3BY]

Erwin

We have ABB speed drives at work for supply and return air systems. Along with the shielded cable they also use metal cable glands to complete the shielding. Not sure if this is possible in your install, good luck with it.

Regards
David
vk3by

[VK3ERW]

Thanks to everyone for your suggestions.

Progress report:
I managed to get shielded motor cable installed last night. The shield is terminated to an earth terminal on the VSD end and to the motor housing on the other end.
The cable is a 2.5sqmm 3 core + Earth.
Unfortunately I can't get hold of the metal (EMC) cable glands until next year so had to do it without.

The shielded cable has improved the situation by dropping the interference from an S9 to an S7 and even lower on some bands. However, interference is still present and causing a problem.

I also installed an earth connection (6 sqmm) from the [metal] air-condition duct to the swampy aluminium box onto an earth stake right next to the air conditioner (located under the house).
It made no difference whatsoever.

To achieve proper EMC compliance (according to manufacturer) the VSD needs to be installed in a metal enclosure - that's not surprising, considering that the housing of the VSD is plastic and allows the IGBT and other components to radiate freely. So there is still a significant amount of radiation going out uninhibited.

The next step is to install the VSD into a metal enclosure and run the motor cable through EMC cable glands.

Regards

Erwin

[GM3SEK]

Thanks to everyone for your suggestions.
Progress report:
I managed to get shielded motor cable installed last night. The shield is terminated to an earth terminal on the VSD end and to the motor housing on the other end.
The cable is a 2.5sqmm 3 core + Earth.
Unfortunately I can't get hold of the metal (EMC) cable glands until next year so had to do it without.

The shielded cable has improved the situation by dropping the interference from an S9 to an S7 and even lower on some bands. However, interference is still present and causing a problem.

Good - the drop in level shows that you're on the right track. If you are presently using tails of wire to make the shield connections, the proper "360 degree" cable glands could make another big improvement.

Even after you have thoroughly RFI-proofed the VSD-motor pathway, it may not kill the interference completely because there may be other pathways for it to get out, which will then need to be tracked down in their turn.

I also installed an earth connection (6 sqmm) from the [metal] air-condition duct to the swampy aluminium box onto an earth stake right next to the air conditioner (located under the house).
It made no difference whatsoever.

Not surprising. People really do expect magical results from earth stakes, but inside your swampy the powers of the Earth Mother are weak.

To achieve proper EMC compliance (according to manufacturer) the VSD needs to be installed in a metal enclosure - that's not surprising, considering that the housing of the VSD is plastic and allows the IGBT and other components to radiate freely. So there is still a significant amount of radiation going out uninhibited.

Be careful about that word "radiation", because the interference is almost certainly not radiating directly out of the VSD (it's physically too small to be an effective HF antenna). Any electromagnetic coupling is likely to be very local within the VSD itself, and then the interfering signal flows out as RF currents along wires.

Always focus on the currents, and remember that currents flow in loops so the return path is just as important as the outward path. Probably more important, in fact - the return path is most likely where mistakes have been made, so probably that is also where the cures can be found.

The next step is to install the VSD into a metal enclosure and run the motor cable through EMC cable glands.

By doing this you are taking a firm grip on the current return path as well as the outgoing path. When you do install the VSD inside a metal box, leave room to install an extra mains filter inside the box as well. The IEC-connector style is best because it doesn't allow any unfiltered leads inside your shielding perimeter.

73 from Ian GM3SEK

[VK3ERW]

Thanks very much Ian, great pointers in your post, much appreciated.

I have ordered an enclosure with plenty of space so I can add other items.
Didn't mention a couple of control wires which go to a relay (for fast/slow speed selection), they could be acting as an antenna. In any case, the whole installation is going inside the metal enclosure.

Erwin

[VK4JAM]

Just in case you find other issues once you have solved the current one ... you could try a MFJ Noise Canceling Signal Enhancer MFJ-1026 (or similar product)

http://www.dxengineering.com/parts/mfj-1026

You will find several reviews on You Tube. Some times the noise source is something you just can not control

[GM3SEK]

Thanks very much Ian, great pointers in your post, much appreciated.

I have ordered an enclosure with plenty of space so I can add other items.
Didn't mention a couple of control wires which go to a relay (for fast/slow speed selection), they could be acting as an antenna. In any case, the whole installation is going inside the metal enclosure.

Erwin

There are several good articles about current loops, shielding and bonding by Keith Cherry in the The EMC Journal. The diagrams in these three are particularly worth a close study:

http://www.nutwooduk.co.uk/pdf/Issue98.PDF - specifically about VFD/VSDs.
http://www.nutwooduk.co.uk/pdf/Issue101.PDF
http://www.nutwooduk.co.uk/pdf/Issue103.PDF

The monthly 'Banana Skins' column is always a good read too.


73 from Ian GM3SEK

[VK4WDM]

Also remember that "ferrite is your friend." One of the best AR investments I have was made was to buy a box of clip-on ferrite beads and they are on to every lead and line in the shack, and any power leads either in the shack or nearby are wound through a ferrite torroid.

"Wall warts" are another source of interference - nothing that a hammer won 't fix

Good luck!

73

Wayne VK4WDM

[VK3ERW]

Next Chapter:
The drive is now installed in a full metal enclosure. I think the RF earth is solid, but I'm happy to be corrected on that one.
All wires entering the cabinet are fitted with ferrite.
The motor cable is shielded, the shield is terminated in the metal EMC gland at the bottom of the cabinet.

The gland nut is plastic, that's all I had at the time, as the glands come without nuts. However, the metal gland does make contact with the bottom part of the cabinet.

I've stripped back the powder coating wherever I attached a nut/bolt.

I did study the VSD related article in The EMC Journal (thanks Ian) and it did provide me with an appreciation of the difference between RFI earth and Protective earth.

The result of all this was not worth the effort - the interference is still as bad as ever and I feel that I have still not solved the problem .

Any suggestions are most welcome.

Erwin (VK3MEB)

[VK3BY]

Erwin

Try the ABB Tech people they maybe able to offer a solution. See if there is also a filter between the drive and motor.

Also try Westek in Laverton they sell a range of filters and supplied me with some when I was having trouble with solar power inverter.

The Tech people were also helpful.

http://www.westek.com.au

Good Luck

David
VK3BY

[VK5RC]

Hi Erwin
Some silly thoughts from me.
When you powered down the Aircon, was the radio on battery power? Is there a difference in noise between being on a mains driven PS or battery, i.e. is the interference primarily conducted via mains? If you cut the mains to the radio room does it make a difference?
The earth connections have been checked for conductivity?
Could the interference be conducted through to the motor and be radiated from there? ?add ferrites to motor lines.
I can't pretend I am helpful in interference issues, at my old QTH I could never transmit on 7Mhz without flashing my garage sensor lights, NOTHING I tried worked, so I moved to 14Mhz!
All the best
PS while typing this reply my autocorrect kept on suggesting you put ferrets on the cable! I am not sure that would help! Although after a bit of frustration with interference you might feel like it!

[VK3ERW]

That's a new one - I haven't tried ferrets, but I can well imagine by the time they have eaten through the cable the interference issues will be gone !

I have done the necessary tests to check that the interference is coming via RF and not via mains.

I will check the earth connections, but can't imagine the crimped lugs or copper studs to cause a problem.

The motor could certainly be radiating, but how do I prevent that? It has good earth and shielded motor cable.

I have another drive (to replace the ABB ACS140) ready to go but with this heat I can't get downtime on the aircon to change it over!

I have also got a different EMC gland on order, one which does't require the shield to be terminated at the gland, instead, it just makes contact with the shield at the gland but leaves the shield intact. This gland will allow me to run the motor cable shield all the way to the drive.

[GM3SEK]

"Earth connections" are not going to help you here. To minimize interference, you need to focus on the short, direct bonding connections between the different parts of the appliance, and on forcing the heavy pulsed currents to flow in tightly confined loops.

In other words, this isn't about connecting things to the Mother Planet - it's about connecting things together, and doing it in the right way.

Talk about "earthing" is just dragging your focus away from what really needs to be done.


73 from Ian GM3SEK

[VK3ERW]

.. you need to focus on the short, direct bonding connections between the different parts of the appliance....
Talk about "earthing" is just dragging your focus away from what really needs to be done.
73 from Ian GM3SEK

Ian,
that's exactly what I took from the articles you referenced in your earlier post and that's what I've tried to implement. You are right in pointing out that I shouldn't call it "earth" but old habits die hard! In my own mind I now differentiate between "Protective Earth" and "RF Earth", thanks to the EMC journal article.

As you can see in the photos I have used the stud on the enclosure as a central connection point for my RF Earth wires with short pieces of 6 sqmm wire connecting it to the gear tray and the other parts of the cabinet. I'm trying to prove a path back to the metal part of the VSD (the back wall).

The motor cable shield is currently terminated at the EMC gland (due to the type of gland) but I have already got a "Through-Shield" type of EMC gland which will allow me to run the shield all the way to the VSD. Currently the motor cable is unshielded between the gland the the drive.

I'd appreciate your comments on the RF earth wiring shown in the photos to point out where I've gone wrong with putting the theory into practice.

Cheers

Erwin (VK3MEB)

[VK3ERW]

I'm happy to report that I have solved my interference issue by replacing the variable speed drive with a different brand.
As soon as the drive was installed all interference was completely eliminated, not just reduced, but completely gone, from S9+ to S0

The new type of drive is a Vacon 20. Even before I had the screen (on motor cable) properly terminated there was no interference. It appears that this drive is emitting none (or a lot less) EMC when compared to the ABB ACS100.

I compared the specs for both drives:
ABB: "with input filters conducted emission complies with the limits for unrestricted distribution class in First Environment as specified in EN61800-3"
Vacon: "compliant with EMC emissions level C2"

One manufacturer calls it "First Environment" the other "Category 2", both of which (as I understand it) refer to a domestic environment (as opposed to an industrial [second] environment or Category 3).
Looking at the data sheets I can see no difference [in EMC emissions] between the two brands, they are both suited for domestic installation ….. but my HF radio tells a very different story!

I have attached a couple of pictures to illustrate the new installation.

Thanks to everyone for your input and assistance in resolving this problem.

73

Erwin (VK3MEB)