[RFI] Noise .....

[EDWARDS, EDDIE J]

Roger P [SMTP:ve3zi@hotmail.com] wrote:
> Gentlemen
> I would much appreciate some help in solving a noise problem which I 
> have. 
> For the past few months I have been plagued by what I thought was 
> power line noise. This is intermittent on 160m (my main operating 
> band), but fairly constant on 14 and 21 MHz. 
> The characteristics of the noise on 160 is that there is a frequency 
> range of between 10kHz and several hundred kHz which has impulse type 
> power line noise. However, at the edges of the this frequency range 
> there is some sort of switching signal which is a few kHz wide. 
> Outside this range the noise level is zero. The noise ranges from S8 
> to S9+ depending on the antenna I use but is loud on all of them. The 
> bandwidth and centre frequency of the noise varies both by drifting 
> and by sudden frequency jumps. Sometimes the noise is wideband so that 
> it extends down into the broadcast band and up to several MHz. On 
> increasingly rare occasions it is inaudible. When it first started 
> I am of the opinion that it was much worse during the day but now it 
> seems to make little difference. 
 
Hi Roger:
Your description above makes me suspect you're dealing with two different
noise sources.  I also suspect the sources are in a neighbors house maybe
even one of the vacant ones.  

The description of noise with a "frequency range of between 10kHz and
several hundred (maybe 70-100?) Khz" with "drifting" and "jumping" center
freqs and with some sort of change in noise and/or level on the edges of the
noise range.  The other key is that "outside the range the noise level is
zero".  Based on that description I'd start looking for a Taiwanese made
Touch-Controlled lamp as the source of this noise.  They are not UL listed
and are made very cheaply.  

If this is your problem, let us know and we'll get you some things to try
out to reduce the noise.  Ferrite Cores can help as well as RF Chokes on the
control line (yellow wire to control box).  There was just a real good
thread on this recently here.

Have you noticed any of these freq jumps occurring when you transmit?  I
discovered I had complete control over one neighbors lamp and it was a 3-way
or 3-level lamp so that I could turn it on to the low setting by keying and
unkeying; then change it to medium again by keying; and then up to high; and
finally off again.  I could follow it by the freq. change of the noise.  I'd
do this for 5-10 minutes on a clear freq on 20 meters before they'd unplug
the lamp.  I even tried sending them messages using the lamp L-M-H-Off
cycle, but they never decoded them to my knowledge.  They had just moved
into the house and probably thought the house was haunted!  ;^D  I latter
saw a touch lamp in their garage sale that summer!!

Then you also said "Sometimes the noise is wideband" up to "several MHz".
Now this could be "sparking" noise from power lines generated by loose
hardware on a pole; or even from a defective doorbell xfmr that is
intermittently acting up; or some other electric device like a fish tank or
water heater that's defective.  

> On the hf bands the noise is much worse on the tribander than on the 
> trap vertical, and peaks when the beam is aimed at the 
> transformer/pole on my property. 

This could just mean you're xfmr is a resonant point for the "conducted"
noise.  You'll get standing waves (Peaks/Nulls with changing polarization)
as you travel along a power line when tracking noise.  It kinda difficult to
ignore these characteristics, but you must in order to follow the overall
noise level increase or decrease.

>  It does not appear to be 
> deterministic at all, but sounds like a typical ragged power line 
> noise. It seems to be there most of the time, and is typically S7 on 
> the beam. Of course, the pole is at a bearing of 45 degrees!

Yes, a touch lamp can generate this type of noise and will be there as long
as the lamp is plugged in.  On or Off doesn't matter, but it can change in
level sometimes from On to Off or if it is a three-way lamp.
 
> The noise is definitely (?) not coming from my house as it is still 
> there with the main breaker out and listening on a battery receiver.

Good work.  Always rule out your stuff first.
 
> My first attempt at tracking was with a small broadcast receiver. I 
> found I could only hear the noise at all if I was right next to a 
> pole. I walked along a lot of the poles and hit them with a 
> sledgehammer. Probably imprudent, but no change in the noise on any of 
> them. 

PLEASE!  I really suggest NOT doing this.  The worst that could happen is
that you could be killed by a falling power line or heavy hardware.  The
least is that you could cause a power outage, and then just try to get your
neighbors to cooperate in searching their house for the noise source, and
they'll certainly have a bad view of "that ham" who caused the outage!

> My second was on 2m. Nothing heard at all anywhere.

On an AM rcvr, not FM. Right?  You won't hear it on FM at all.  If this was
on AM then this tells me that if it is powerlines, the source is not nearby
but far away.

> I then made a large (1.5m sides) 160m loop, and started to listen with 
> the following conclusions:
> 
> 1. The noise is definitely being radiated by the power line. It is 
> inaudible more than about 100m from the line.

It is being conducted by power lines and then re-radiated locally.  If you
were getting direct radiation, you'd start picking it up on VHF AM rcvrs.

> 2. The separate power line to the east (see above) is quite clean and 
> clear.
> 3. I am totally unable to get a proper bearing on the noise. I get 
> nulls, generally to the closest pole. The signal strength is fairly 
> constant along the line. Sense (cardioid) bearings all point at the 
> power line.

Definitely conducted noise!

> 4. I would need to get several wavelengths from the line to take a 
> bearing which may point at the noise source. Unfortunately, I would 
> not be able to hear the noise at that distance no matter how large a 
> loop I was to construct! Also, it is physically difficult to get there 
> as it is virgin bush (or water).
> 
> 5. I cannot imagine that the noise is being transferred along the 
> underwater cable, so it is presumably being either generated within 
> one of the 15 permanent homes or by the power or telephone line 
> equipment. It 'cannot' be the holiday cottages as these were certainly 
> unoccupied when the noise started.

The lamp noise is probably not from the holiday cottages, but the other
intermittent broadband noise very well could be.  So don't rules them out.  

I don't know how long the under-lake cable is but powerline noise can be
conducted for many miles (kilometers) causing RFI the whole way along.

> 6. The telephone line splits from the power line at one point and the 
> noise gets progressively weaker as one moves along the line. There is 
> a telephone switching (?) box where there is no noise, but there is a 
> strong unmodulated carrier on 1925kHz audible. However, this carrier 
> is not audible more than a few feet from the switching box.

This shouldn't be a problem for you if it's that weak.

> I can think of no alternative but going cap in hand to all my 
> neighbours and asking them very nicely if they would mind tripping 
> their main breaker for a minute while I check for noise. I hate the 
> idea of doing this, especially as if it is one of them I then have to 
> ask them very nicely to trip individual circuits...

This is exactly what you'll have to do to find the touch-lamp source.  Time
to put on your Ham Radio PR cap.  I don't know what the regs are in Canada
that equate to FCC Part 15, but here in the states the law says these
devices cannot cause interference and if they do they must be removed from
service.  However, the FCC won't enforce this so you must work with the lamp
owner to come to a mutual resolution.  So be very nice and cooperative.  

Good Luck & 73,
de ed -K0iL



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