View Full Version : Mains filtering problem? Please help RFI...

11-04-2009, 10:26 PM
Hi all

And greetings from London - thanks for any help and advice in advance.

The shack is a seperate building to the house, on a seperate fused ring main about 100foot away from the house.

I am using an FT-897 for HF, an LDG AT-1000 autotuner, and the antenna installed is a 186foot doublet, centre fed with 450ohm feeder - feeder about 100foot long with a balundesigns 4 to 1 current balun with a ten feet piece of good quality coax connecting it to the LDG ATU as this matcher only accepts coax.

The 186 foot doublet is up 40 feet above ground level at its highest point and drops to about 20 feet above ground level on each end, and it is set up as an inverted V in a straight line.

I have quite an extensive earth system - from the ATU to the first 8 foot copper rod which is connected using thick half inch wide tin multi stranded earthing wire which is only 6 foot length from the ATU to the first ground rod. I have 10 x 8 foot earth rods spaced about 4 feet apart all connected by the same half inch multi-stranded tin. Each item on the shack desk is earthed to the ATU, ie Radios, amps etc etc.

When I TX on HF, on 80m as an example, with just 25watts output power on SSB, it kills ADSL - the router is in the house 100foot away from the shack. I It kills DSL both wired DSL and wireless DSL - it all stops until about a minute after I stop TXing then it comes back on again.

Also, a few weeks ago a neighbour told me her television set was turning off and on when I was transmitting operating on 80m SSB with about 400watts.

A local amateur told me as my antenna system is balanced, and a good earthing system he thought it must be being caused by RF being introduced into the mains system. I wasnt sure, but I am no expert so I plugged in a dummy load into the ATU instead of the doublet and transmitted - wired DSL and wireless DSL is fine - it only crashes when the doublet is plugged in.

The local amateur still thinks it is mains born interference and tells me I should invest in some mains filtering.

In the UK our mains is 240v.

So couple of questions.

1) Does this sound like mains born interference, and if so can anyone point me to a filter that I can put in line in the shack. One I have found is listed on Ebay, take a look at:

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=120483658596&ru=http%3A%2F%2Fshop.ebay.co.uk%3A80%2F%3F_from%3D R40%26_trksid%3Dp4712.m38.l1313%26_nkw%3D120483658 596%26_sacat%3DSee-All-Categories%26_fvi%3D1&_rdc=1

Or ebay.co.uk item number: 120483658596

The local amateur tells me I need to get a filter which filters the Neutral, Earth and Live wire in the mains system.

Will it filter it both ways, ie will it kill any mains born interference that I may receive into the radio?

Even if the DSL problem is not mains bound - is it still worth adding a filter just to be sure and to do 'best practise'

Any other filters other than the one listed above?

I saw someone on the net suggesting to use a 'line conditioner' by APC similar to the ones that can be seen here:

http://cgi.ebay.co.uk/APC-UPS-Line-R-Power-Conditioner-Reg-1200VA-LE1200I_W0QQitemZ140357297060QQcmdZViewItemQQptZUK _Computing_PowerSupplies_EH?hash=item20adf263a4

Or go to ebay.co.uk and type in item number: 140357297060

But these APC Line conditioners do not appear to me to have any RFI filtering ?

Anyway, enough words from me

Hope you can help

Thanks, and 73 Simon - UK

11-04-2009, 11:20 PM

If you think that your are introducing RF into the mains system via the mains cabling your PSU runs from one easy step would be to run the shack from a car battery as a test. This would isolate you from the mains and test if not being connected to the mains resolves the problem, if it does cure the problem then mains filtering may work :)

I have used mains filtering in the past but only for reducing inteference being caused to my equipment.

I seem to recall an article in Radcom recently about DSL problems do you get Radcom , if you are loosing wireless and wired network it sounds like your router is dropping the DSL connection.

Do you actually loose ethernet connectivity or just internet access ?

11-04-2009, 11:39 PM
Do you actually loose ethernet connectivity or just internet access ?

I guess the DSL modem/router rebooted due to RFI.

11-06-2009, 01:27 AM
There's a fair chance that the telephone/ADSL wires are acting as a receiving antenna. Even though the received RF will be common mode, it will be at a high enough level to cause the ADSL "receiver" problems.

Try using a dummy load. That should fix the problem, and absolve the mains wiring. ;)

Our club shack computer loses its 56kb connection when we transmit with an antenna 60 feet away. ;)

11-07-2009, 10:47 AM
A ham up the road had a strange RFI problem. Turned out his house electrical earth had gone away. The previous owner of the house had a water pipe leak fixed.
The plumber had used some plastic pipe as the replacement. The result was that the houses electrical earth was removed when some of the original copper water pipe was cut out and the plastic pipe was installed.
This created both an electrical hazard and the RFI.
Regards Trevor VK3PD (ex VK3ADU)

11-07-2009, 01:15 PM
Way back when I was designing microwave ovens, some for Europe, the UK was on 230v and Europe on 240 (or maybe I have that backwards). Over time the standard was going to shift of 235. Just curious, please update me on this situation.

TOM K8ERV Montrose Colo

11-07-2009, 03:48 PM
The question is, are the power lines feeding your house above ground or buried? If the are buried then it is not likely but possible. It is more likely that the noise is coming from another source that may require some detective work.

Give M3HKU's suggestion a try. Use a car battery and see if the noise disappears. If it does then the brute force line filter you mentioned will help. If not then you will have to start looking elsewhere.

Lastly, if the power lines are above ground there are a number of things associated with elevated power lines that can cause serious radio noise.

11-07-2009, 05:27 PM
This is curiosly like brute RF overload from your antenna system to the affected appliances.
Also RFI to your receiver is probably radiated from the power lines to your antenna and not conducted thru power wiring to rig !!
Good luck with that mess.
I had to move out of the city to escape that noise !

11-07-2009, 05:36 PM
Way back when I was designing microwave ovens, some for Europe, the UK was on 230v and Europe on 240 (or maybe I have that backwards). Over time the standard was going to shift of 235. Just curious, please update me on this situation.

TOM K8ERV Montrose Colo

Was 240V in the UK Tom, and largely still is but the tolerance is downgraded to suit Europe.

11-07-2009, 05:45 PM
There are variations in the "brute-force" line filter. It's not recommended to have an RF choke in the earth/ground line unless necessary, for the usual safety reasons, and one thing I only discovered recently relates to the capacitors from line to earth/ground after the chokes, that is on the equipment side of the filter.

If you have any thyristor switching devices, say in a PSU, the presence of capacitors theoretically allows enough stored energy to allow an instant and infinite rise-time for the thyristors and could damage them. I wouldn't worry too much about this though because firstly it's an industrial problem rather than domestic, and secondly your average PSU should have enough inductance on the input to limit rise-time so as not to destroy any semiconductors.

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