fridge interference and navtex

Conachair

Conachair

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Trying to recieve a weatherfax the other day I was getting loads of interference and tracked it down to the fridge. Am I right in thinking this would affect the navtex as well? I tried to recieve a navtex using jvcomm and the ssb and got nothing.. Assuming the fridge is upsetting the navtex (nasa navtex pro) is there way of getting rid of the interference from the fridge short of turning it off?
TIA
 
Navtex is a radio transmission of data. Any interference that upsets the radio signal (thats louder than the signal from the receivers viewpoint) will likely upset the audio that you feed to your PC (or laptop) for JVCOMM to decode. This will end with garbled decoding.

Somehow you need to eliminate the interference.
What you could do is tune your ssb receiver just off the frequency that you use to get your navtex, - to a quiet part of the band, and switch your fridge on and off while you listen to the audio. This will give you an idea what the interference sounds like.
How to eliminate it?
Check antenna: can you get it further away from the fridge? If so the further then better.
Check fridge: is it a 12V DCone (or 24V)? then perhaps a capacitor across the power supply. (If you don't feel competent at this don't do it). This is a similar thing to how cars used to have "suppressors" on the spark system.
Check earthing: Is radio earthed? Is fridge earthed? Earhing might help, try it and listen to the noise.
In these things listen to the noise; you want to get it as low as possible so that when you tune back to the navtex station, its all you hear.
 
Fridge is a 12v danfoss compressor. Any idea what size capacitor I could try? Fridge isn't earthed but it's a steel boat so don't want to have anything electrical connected to the hull.

Thanks
 
If the fridge has a brush type motor, then as close to the motor terminals as possible is best place to put a cap. Try about 10nF. The value isn't critical, and playing with a few values from say 1-100nF might do.
 
The Danfoss is possibly invertor driven. Unless you know the details it's impossible for anyone to advise. Either ask Danfoss, ask a pro firm of ssb installers who might have details of all the common products or try to get a radio ham friend to come over and sort it out for you. Suppression is very difficult.
 
Hi
The interference will arrive via the pc power leads of your radio or PC, electromagnetic interference(EMI) or via the air, radio frequency interference (RFI). you can get filters for both forms of the interference from Maplin or such outlets that may help. Do as Geoff suggests with the antenna. Place as far away from the fridge as possible. Also Lemain is correct, but it can be cured or reduced as other users of similar equipment will confirm.
Good luck with it.
 
My Danfoss invertor-driven is almost totally power supply-borne interference. The Danforth kits are nicely made and don't seem to put out much airborne in the bands that interest me.

I've tried all the obvious and simple fixes in my toolbox and got bored with it. So now I turn off the fridge when I want a clean signal on those bands /forums/images/graemlins/wink.gif The problem is that the waveform changes as the load changes so you get it nice and quiet, then it drifts off again. I'd have to put a fairly advanced filter in the leads but I have more interesting and pressing things to do.
 
Turning off the fidge is fine for weatherfax, it's navtex that I really want to work. I'm assuming that since the nasa ssb is getting loads of interference then the navtex (nasa navtex pro) will be also. I won't get a weatherforecast every day from tarifa, again I'm assuming that this is caused by the fridge, maybe there are too many assumptions here but can't think of any way of checking the navtex. One option I suppose would be to run it off it's own battery for a few days and see if the weather comes in more regularly.
thanks
 
you mention SSB, so you can listen to the interference.(and see what turns it off) I had a Waeco whose electronic control box was very noisy, (not the compressor) on 1010 and 14303 etc. but the lower frequency used for navtex wasn't affected by it. Quite often Navtex is corrupted by marina noise (civilisation!) and as soon as we out at sea it comes through OK. Try listening to 490 or 518 on the SSB to identify any noise.
 
The Danfoss Compressor uses a microprocessor which generates the three phases for the motor. It also uses a pulse width modulation to minimize the power used by the compressor.
It is a very clever device.
Because of the harmonics it’s basically impossible to get rid of the RFI. The cables to the motor are not screened either.
Danfoss sells a different inverter ( Metal box etc.) to overcome this problem, but it cost almost as much as a new compressor.
I find it ridicules that Danfoss can sell the standard compressor for marine use and has an extra device for additional money….
 
That exactly fits my own observations. Thanks for explaining the hardware. As you say, it could be very hard to get rid of the RFI (my experience) - would be do-able but would require some development - quite a few weeks at a well equipped bench with all the hardware variants, not easy.
 
[ QUOTE ]
I won't get a weatherforecast every day from tarifa,

[/ QUOTE ]


fwiw, I receive Coruna navtex from my area, and I have found countless messages stating "Tarifa navtex station will not broadcast due to technical problems, we apologize etc etc"

so maybe Tarifa is not broadcasting after all (?)


also, I personally have found no interference at all between my fridge (danfoss too) and navtex, even when its antenna was less than one metre from the compressor


cheers
 
[ QUOTE ]


fwiw, I receive Coruna navtex from my area, and I have found countless messages stating "Tarifa navtex station will not broadcast due to technical problems, we apologize etc etc"

so maybe Tarifa is not broadcasting after all (?)


also, I personally have found no interference at all between my fridge (danfoss too) and navtex, even when its antenna was less than one metre from the compressor


cheers

[/ QUOTE ]
Now that is exactly what I want to hear /forums/images/graemlins/ooo.gif I can turn fridge off when getting a weatherfax, if the navtex is happy then so am I, just not sure how to double check. Latest cunning plan is to run ssb off separate battery, make sure fridge is running and recieve a navtex using jvcomm, if the navtex gets it as well than all good. One of these weeks I'l get around to it, sounds like getting rid of the rfi from fridge is not easy so I'll try to see if there is a problem before trying to fix it.
Thanks all.
 
The control Unit BD35/50F Part Number 500281-1
price ca. 130 Pound Sterling
Has been developed by Danfoss to cure the RFI problem.
They should deliver all Compressors for the marine market with this control unit.
We should really all complain to Danfoss. It is ridicules to deliver a unit with strong RFI and then to sell as an extra another control unit to cure it. Navtex reception is basically impossible when the compressor turns on.
I am sure the price difference in manufacturing of the two control units is just a few pence, but Yachties are stupid….because we are all rich…..
 
[ QUOTE ]

Danfoss sells a different inverter ( Metal box etc.) to overcome this problem, but it cost almost as much as a new compressor.
I find it ridicules that Danfoss can sell the standard compressor for marine use and has an extra device for additional money….

[/ QUOTE ]

So tell them the standard model is not fit for purpose (unacceptable EMI for marine use) under the sale of goods act...
 
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