Fridge interference on HF radio - 2 questions..

[Conachair]

I have onboard an Icom ic7000 (no ham license yet so recieve only) . And a fridge! Danfoss with a 101n0210 controller. Apparently a notorious source of RF noise.

Playing around this morning i hooked up the radio to a battery not connected to anything else to check if the noise was coming up the power input but it seems to be airborne.
Well, think google may have already helped with that, if it works. Ordered an aluminium case from here so revamped question 1...
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Has anyone replaced their controller 101n210 with a 101220 and did it help? Seen mentioned elsewhere that the 220 may have ferrites inside as well.
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2nd question- In messing around I noticed that the radio would run with just the positive main batt power connected, turns out that the usb/ci-v adaptor plugged into the laptop is providing an alternative sourcd to neg, and thus to the ground as well. Being a steel boat this makes me nervous - would it be worth putting in an opto isolater here, assuing it would work for 19600 baud data?

Any hints welcome, thanks

 

[lenseman]

Placing a tin box around the offending item will work 'to a greater or lesser degree'. It is like keeping smoke inside a brown paper bag!

1) RFI from the fridge
Paddy, is the fridge 12 volt or 12/250volt and is the RFI there when running mains or 12 volts or both. I am trying to find out the source, either switching in the controller or the compressor itself?

The only sure fire way of finding this type of fault is by using a oscilloscope (and or a spectrum analyser) and checking for spikes and transients on the DC rail and then trying to decouple down to earth instead of boxing it up. Boxing the RFI is the cheap and cheerful way but not the correct way of eliminating RFI.

You will probably find that the RFI is 'airborne' as the spikes that causing the interference are leaving the fridge by way of the external leads connecting it to the yacht supply. These fridge leads in turn then become RF radiators. RF chokes (either ferrite or inductive) depending on the type of spike frequency are the correct way to go.

2) Your question about operating the Tx/Rx with the neg lead disconnected.
The fact that you can run the Icom with the negative lead disconnected is very dangerous (to the computer) because you would only have to key the Tx on the Icom momentarily and by mistake and you will burn out the USB port. There is no question about this as the USB port would not be able to handle about 25 Amps!

If you intend to disconnect the power from the Icom, always disconnect either the positive or preferably both power leads.

 

[Conachair]

Placing a tin box around the offending item will work 'to a greater or lesser degree'. It is like keeping smoke inside a brown paper bag!

1) RFI from the fridge
Paddy, is the fridge 12 volt or 12/250volt and is the RFI there when running mains or 12 volts or both. I am trying to find out the source, either switching in the controller or the compressor itself?
---
Fridge is 12v only, RFI seems to be airbourne (?), from googling they are known for it, that is the controller seems to get the blame rather than the compressor. Thats just from t'interweb though.
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The only sure fire way of finding this type of fault is by using a oscilloscope (and or a spectrum analyser) and checking for spikes and transients on the DC rail and then trying to decouple down to earth instead of boxing it up. Boxing the RFI is the cheap and cheerful way but not the correct way of eliminating RFI.

You will probably find that the RFI is 'airborne' as the spikes that causing the interference are leaving the fridge by way of the external leads connecting it to the yacht supply. These fridge leads in turn then become RF radiators. RF chokes (either ferrite or inductive) depending on the type of spike frequency are the correct way to go.

2) Your question about operating the Tx/Rx with the neg lead disconnected.
The fact that you can run the Icom with the negative lead disconnected is very dangerous (to the computer) because you would only have to key the Tx on the Icom momentarily and by mistake and you will burn out the USB port. There is no question about this as the USB port would not be able to handle about 25 Amps!

If you intend to disconnect the power from the Icom, always disconnect either the positive or preferably both power leads.
--
Yep, think the second path to earth can't exist, but the full power of the radio being able to go through the laptop sounds too scarey, need to do something about that. Can you get an off the shelf data opto islolater??

Thanks for the help

.

 

[Reverend Ludd]

Placing a tin box around the offending item will work 'to a greater or lesser degree'. It is like keeping smoke inside a brown paper bag!

1) RFI from the fridge
Paddy, is the fridge 12 volt or 12/250volt and is the RFI there when running mains or 12 volts or both. I am trying to find out the source, either switching in the controller or the compressor itself?

The only sure fire way of finding this type of fault is by using a oscilloscope (and or a spectrum analyser) and checking for spikes and transients on the DC rail and then trying to decouple down to earth instead of boxing it up. Boxing the RFI is the cheap and cheerful way but not the correct way of eliminating RFI.

You will probably find that the RFI is 'airborne' as the spikes that causing the interference are leaving the fridge by way of the external leads connecting it to the yacht supply. These fridge leads in turn then become RF radiators. RF chokes (either ferrite or inductive) depending on the type of spike frequency are the correct way to go.

2) Your question about operating the Tx/Rx with the neg lead disconnected.
The fact that you can run the Icom with the negative lead disconnected is very dangerous (to the computer) because you would only have to key the Tx on the Icom momentarily and by mistake and you will burn out the USB port. There is no question about this as the USB port would not be able to handle about 25 Amps!

If you intend to disconnect the power from the Icom, always disconnect either the positive or preferably both power leads.

Agreed.
These kind of things might help a lot.
link

 

[lenseman]

Fridge is 12v only, RFI seems to be airbourne (?), from googling they are known for it, that is the controller seems to get the blame rather than the compressor. Thats just from t'interweb though.

The controller gets the blame as it is a component any salesman can sell you to try and cure the problem.

If you wrap cooking foil around the outside of all the compressor leads without shorting them out and then bond the cooking foil down to earth this would be a far cheaper 'test' before spending money on a new tin box (Faraday Cage) or Controller.

Yep, think the second path to earth can't exist, but the full power of the radio being able to go through the laptop sounds too scarey, need to do something about that. Can you get an off the shelf data opto islolater??

The second path to earth is the USB port and I wouldn't need a crystal ball to know that it will start smoking if you transmit with the negative lead disconnected. All you would be left to do is to measure the smoke but boxing it up would not cure the problem but there again . . . . by this time you would not have a RFI problem!

You probably disconnected the negative lead thinking to yourself that if it touches 'ground' anywhere, it would be OK and cause no problems whereas, if you has disconnected the positive lead, you would need to insulate the end to save shorting it to earth?

As a first choice, always disconnect the Line, Live, +ve feed and insulate correctly but disconnecting both leads and you will be fireproof !!

 

[starfire]

Paddy,
Normally an HF rig would have an RF ground rather than
just relying on several feet of black wire.

You have a steel boat, from the earth stud on the radio & if you are using one the tuner, take a copper strap to a good earth on the hull.

This should be copper braid or strip of around 50mm wide, reason being, at hf frequencies most of the current flows in the surface of the conductor due to skin effect.


Have a look at :- http://www.sailcom.co.uk/antennas/index.html#Dynaplates


You do not need the dynaplates (steel boat) but the grounding principles still apply.

 

[lenseman]

Agreed.
These kind of things might help a lot.
link

The trouble with buying these ferrite clamps as a RF choke to the interferer is the fact that you really need to know the PRF (Pulse Repetition Frequency) of the interferer and note the manufacturers specification to see if these are the correct ferrite composition for this particular RFI problem.

There are many hundreds of differing types of ferrite chokes and you could be throwing good money after a bad problem.

You need to try cheap methods before you go out and spend money on something a salesman 'suggests' might work?

Also you might find it useful to check the routing of the wiring to both the fridge and the transceiver. Do the run anywhere near each other and suffer from coupling. Changing the routing of the cables can effect a vast improvement. The same with the antenna routing? Does it run close by the fridge. Are the fridge and radio on the same side of the yacht?

Questions, questions?

 

[Reverend Ludd]

The thing about SSB boat antennas is that they are generally a simple long wire up the backstay. This is really a 1/2 wave antenna with the earth providing the other 1/2 of the signal. Therefore the better the earth the better it will work.

 

[Conachair]

The controller gets the blame as it is a component any salesman can sell you to try and cure the problem.

Thread here about it - http://www.boatkb.com/Uwe/Forum.aspx/electronics/2228/SSB-noise Though sounds like no one has nailed it completely , other than it ain't the termostat.

If you wrap cooking foil around the outside of all the compressor leads without shorting them out and then bond the cooking foil down to earth this would be a far cheaper 'test' before spending money on a new tin box (Faraday Cage) or Controller.

Can't get to them, must be inside the chassis somewhere. Ordered new case already, 25 quid as opposed to some nearer 200 for new invertor and case Disconnected the fan but that didn't help.

The second path to earth is the USB port

I was thinking of doubling up connections to the boat ground which i don't want to do, only at one point which is the engine. But the second path to neg is indeed the usb, might be quite depressingly exciting for a moment if i'd hit transmit


Think i need to sort out a better scope or spectrum analyiser to see log what's going on. Any good software ones for PC?

Ta

 

[Conachair]

The thing about SSB boat antennas is that they are generally a simple long wire up the backstay. This is really a 1/2 wave antenna with the earth providing the other 1/2 of the signal. Therefore the better the earth the better it will work.

I have a dipole up the mast at the moment. But not transmitting. Think I need a balun. Though must ask Mr google what one is first

 

[lenseman]

. . . Think I need a balun. Though must ask Mr google what one is first

A Balun is the shortened word for Balanced to Unbalanced matching RF transformer. This tries to match the 50Ω output from the transmitter to the unmatched antenna (back-stay) in your instance.

You should find a good ATU will be as effective.

 

[lenseman]

. . . . . Think i need to sort out a better scope or spectrum analyiser to see log what's going on. Any good software ones for PC?

Software 'scopes and spectrum analysers are very expensive for what they are and really don't justify the expense if you are only going to use them for a limited time.

I have a Phillips Dual-Trace Scope and also a Spectrum Analysers but getting it up to St Kats would be a problem due to parking and I am certainly not going to try and carry them both on the Underground!!

 

[Reverend Ludd]

I have a dipole up the mast at the moment. But not transmitting. Think I need a balun. Though must ask Mr google what one is first

Mmm A Balun isn't going to help with your RF problems I wouldn't have thought. It's shielding you need

You sure you have a Dipole ? No piccies I suppose?

 

[Billjratt]

I had this problem on the last boat - and will no doubt have it again when I get the rig installed on this one.
I asked Waeco about it and got a slopey shoulder response. The fact that the compressor manufacturer has now brought out a "fix" in the form of a screening box infers they agree that their device is radiating. I will now go and chop up a bit of ally to make a screen...
I wonder if they can sell this product in USA? (FCC regs)
For the grounding issue, it probably wasn't going through the Laptop, rather the antenna RF ground, easily tested by removing the USB and trying again.
As for all the analysers, sledgehammers and nuts come to mind. For a scope, there is freeware that will run through the soundcard on the laptop.

 

[lenseman]

. . . . . For a scope, there is freeware that will run through the soundcard on the laptop.

It probably won't be very fast. You need to see fast rise times and transients which the PC based software probably would not be able to handle. They are great to see DC levels, sine/square waves and switching circuits.

Don't get me wrong, I like "Free" but it might not be suitable for your purpose.

 

[Conachair]

Mmm A Balun isn't going to help with your RF problems I wouldn't have thought. It's shielding you need

You sure you have a Dipole ? No piccies I suppose?

Not too sure of anything apart from what mr google has told me I have a line tied off to the bow and the pushpit in an inverted V to the top of the mast, inside that line there's a wire down each side of the mast with the shield and conductor attached to each wire. If you know what I mean

Works anyway, I can get psk31 from russia etc and voice from all round europe, and can just get some weather sats. So can't be too bad considering i'm moored up between lots of tall buildings.

If i could calm down the noisy fridge a bit it would be christmas come early One shall persevere

 

[Conachair]

For the grounding issue, it probably wasn't going through the Laptop, rather the antenna RF ground, easily tested by removing the USB and trying again.

Tried that, defo the usb

 

[Reverend Ludd]

Not too sure of anything apart from what mr google has told me I have a line tied off to the bow and the pushpit in an inverted V to the top of the mast, inside that line there's a wire down each side of the mast with the shield and conductor attached to each wire. If you know what I mean

Works anyway, I can get psk31 from russia etc and voice from all round europe, and can just get some weather sats. So can't be too bad considering i'm moored up between lots of tall buildings.

If i could calm down the noisy fridge a bit it would be christmas come early One shall persevere

If it works then great, does sound like a dipole so a Balun may help signal reception if you spot a cheap one but obviously is not worth the worry.

 

[Conachair]

Paddy,
Normally an HF rig would have an RF ground rather than
just relying on several feet of black wire.

You have a steel boat, from the earth stud on the radio & if you are using one the tuner, take a copper strap to a good earth on the hull.

This should be copper braid or strip of around 50mm wide, reason being, at hf frequencies most of the current flows in the surface of the conductor due to skin effect.


Have a look at :- http://www.sailcom.co.uk/antennas/index.html#Dynaplates


You do not need the dynaplates (steel boat) but the grounding principles still apply.

Thanks for the link. The ground side of things will become more important when I get round to transmitting. Need to set up the ATU as well, which all needs grounded back to the engine. On the radio the neg, antenna shield and earth lug all seem to have continuity so in a way it's already connected to the hull, but one thing at a time , I'll get there in the end.

 

[pappaecho]

The RF interference could either be via the 12 volt circuit or by transmission in the air.
To find out which, wrap the compressor in aluminium foil, and the earth it. You have a Faraday cage which will stop all air based transmissions. That at least lets you narrow the search for the culprit