Am I hearing things?

Tonight was the first time since we moved into the new house that I spent some serious time tuning around the HF bands and listening. I was kind of amazed at how much I was hearing - for example, right now on 40M I am hearing 13 CW, 2 Olivia, and 2 SSB contacts between 7000 and 7100 kHz, and that's only with a piece of coax running under our house (none of my antennas are up yet).

Unless we've had a resurgence of ham activity lately, my only conclusion is that the noise level at my new QTH is way, way, WAY better than the old one. There, on a typical weeknight, I could only hear a couple of CW and maybe 1 digital QSOs above the S7-S9 noise.

By comparison, I'm hearing AC2K in Redmond, WA, and he's S8 on this underground antenna, while the background noise level is S0 or S1. I'm getting excited!

Blissful silence - Is the noise finally gone?

I don't want to count my chickens before they're hatched, but I haven't experienced the 80/40M noise problem since a few days ago. Maybe it's gone?

Interestingly, the same day that I stopped hearing the noise, I visited my neighbors and checked in with them about any RFI they'd been experiencing (their living room is about 40 feet from my G5RV). I'd operated in the NAQP SSB contest the day before, and they noted that they'd heard some RFI coming out of their subwoofer ("it sort of sounded like Vietnamese").

I explained that I'd been operating using a different transmission mode called single-sideband, and that the sound they'd heard was probably me. I also explained that there were some things they could do to eliminate the problem, especially reducing gthe length of cable going to the subwoofer, using some sort of twisted-pair cabling, and using some special devices (RF chokes) to eliminate the interference. I gave this speech a bit half-heartedly, since they're renting while their house is being renovated, so they'll be moving out in a few weeks anyway.

Now, these are really nice people, and have been great neighbors, so I decided to mention to RFI coming from(I think) their garage - who knows who's going to move in next? And if the noise-generating device is part of the rental, now would be a good time to figure out where it is so I can contact the property owner about fixing the problem.

The reaction was very positive; I was invited to look around, inside and out, and I looked for possible RFI sources. While walking around, I described the problem I was having, the hours I heard the problem (about 1600-2300 local time) and made a point of explaining that I could hardly hear anything on my radio while the noise was happening.

I didn't see anything obvious, so I explained that, if the subwoofer RFI was a problem, I'd solved a similar problem with my son's stereo, and I'd be happy to advise them on a solution, but more likely, it wouldn't be much of a problem before they moved back into their remodeled house.

Now, a week later, I've not heard any significant noise problems on 80 or 40 in the evening hours. Last week, I had a very pleasant experience operating in the CQWW 160 CW contest. And tonight, when I tuned around 160, 80, and 40M, the highest noise level I saw was S4-S5.

It could be a coincidence, but I suspect my talk caused my neighbors to turn off some piece of electronic equipment that was radiating noise. I need to check in again and see if this is the case (and thank them!).

80M Inverted-L

The other night I launched a tennis ball into the same tree my 40M vertical is in, and pulled up a 66-foot wire to use as an inverted-L on 80M:

(can't see it? ha!)

I've "repurposed" the feedpoint of my 40-m droopy radial vertical - the 40m vertical element is still in the tree, just not attached, in case I want to switch back.

So the radial field is the same one I used for the 40 vertical - 6 runs of #18 wire buried in the front yard, asymmetrically (tunneling under the street = not recommended).

My initial observation: this thing is great at receiving the local noise generated from my neighbor's garage. For example, on 3530 kHZ:

Noise floor, noise off, G5RV: S2
Noise floor, noise off, inverted-L: S9

Noise floor, noise on, G5RV: S5
Noise floor, noise on, inverted-L: S9+10dB

My guess is that the inverted-L is just a generally better antenna, so it's just doing a better job of picking up signals, including local noise.

The neighbor garage noise sounds like this. It's pretty regular, in that the time between bursts, the duration of the bursts, and the very loud noise at the end of each burst repeat consistently.

It's odd that the G5RV is much closer to the noise source, yet receives about 30-40 dB less signal. One significant difference between the antennas is their polarization. Could polarization account for that much difference? I doubt it... there must be something else at work here.

Update: 01/15/2009: my first QSO on this antenna was DS1REE in Seoul, South Korea, at about 5am local time.

TiVo RFI update

I found a way to stop the RFI coming from my TiVo on 80 meters: unplug the S-Video cable from it! Our TV is connected to the TiVo via the RCA cables, so the S-Video output wasn't being used. Unplugging it from the TiVo solved the problem.

If I actually were using the S-Video output, I would have needed to try to stop it from radiating, but this fix is a bit simpler!

So, if you're experiencing this kind of noise, it might be coming from the S-Video cabling.

A "go kit" for TVI and RFI?

What sort of things should I have an hand to solve RFI problems? I understand that it's risky installing devices on neighbor's equipment, but I would like to keep some things on hand to solve any problems I might have in my own house, and then can point to them and say "this solved my problem".

So far:

• A FT-240-43 toroidal core, used to make a common-mode choke for feedlines. Wrap about 10 turns around the core: https://www.amidoncorp.com/skus/search?query=FT-240-43.
• Having some snap-on cores might be helpful - although they aren't as effective as toroidal cores, they're really easy to install, so having a few of them might help identify which cable is the problem, and you could use a toroidal core then.
  
• A high pass filter for 75-ohm CATV coax: http://www.mfjenterprises.com/Product.php?productid=MFJ-711B
• A ferrite rod.
  
• A low-pass filter on my station wouldn't hurt.
• What about pickup from speaker lines? In the old days, you'd slap a capacitor across the speaker lines, but my ARRL RFI book suggests that modern audio amps won't like that.

Harris, K9RJ, pointed me to a great article written by Jim Brown, K9YC: A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing

80 meter noise, part 2

I took a look at the audio capture of the 80M noise, and here's when it's happening. Entries are start time (local PST), duration, comments.

• 0900-1400 - quiet, no noise
  
• 1400 (2m 22sec) - first time heard today, stops abruptly
  
• 1522 (3 min 15 sec) - fades out slowly
• 1535 (14 min 5 sec) - stops abruptly
• 1556 (7 hr, 35 min, 7 sec) - longest on period. Very strong, S9. Ends abruptly at 2331 local. Here's the very beginning of this.
  
• 2331 - 0829 - this is a long period where the noise appears at a reduced amplitude (probably S1 to S3) for a period (30 - 90 seconds) and disappears for several minutes. The pattern tends to be regular, e.g. at about 0300 local time, the pulses come about every 18 seconds, with a duty cycle of about 50%. Here's a sample.

For reference, local sunrise is at 0700 and local sunset is at 1652 today. This pattern is rather odd. The long "on" period from about 4pm to 11:30pm local time really sounds like something humans would do when it gets dark, but I'm a bit stumped by the repeating patterns all night, which finally seem to disappear about 8:30am (which is when you might expect people to be out of a house).

80 Meter Noise

I'm tackling the most egregious noise first, and that would be the S8-9 noise across the 80 meter band with 60 Hz hum.

To get a better idea of when this noise happens, I tuned my receiver to a frequency where the noise is loudest, and started recording it in Audacity on my PC. I started it this morning, and will stop it tomorrow morning at the same time. Just looking at the waveform in Audacity, it's pretty easy to pick out when this noise starts and stops, which I hope will prove helpful in locating the source.

Tonight I turned up the volume on the rig to see how loud the noise was, and it was S8-9. I took another walk around the neighborhood with my portable Sony shortwave receiver, like last night, but was a little more thorough on determining the boundaries of where I could hear the noise, and it's definitely coming from my next door neighbor's house. I noticed that the noise is extremely loud right at the south end of our property, across a fence from their garage.

Since the Sony receiver was getting overloaded when I was in that "hot zone" on the south end, I needed something with an attenuator. My little Yaesu VX3R handheld radio is a terrific miniature VHF/UHF handheld, but as an HF receiver, it leaves a lot to be desired. In this case, though, it was a help - sort of like having an HF receiver with an attenuator you can't turn off! It happens to have just the right (lack of) sensitivity for this task, and it doesn't really register the noise until I'm a foot or two from our fence, and locates the noise source laterally along the fence. Whatever it is, it's coming from my neighbor's garage, and there are a couple of boxes mounted on the exterior wall of the garage that might be the source.

Now that I'm pretty certain about this, I'll stop by and ask to poke around a bit (we have a good relationship with our neighbors).

This RFI sleuthing is sort of fun...

The Noise in my Head

Here are some audio clips of the noise I hear at my QTH:

• The typical broadband noise I hear most of the time. This was recorded 0830 local time, Nov 22, 2008 on 7030 kHz, and had a signal level of S9. This noise is present on 1.8, 3.5, and 7 MHz. It is absent on 10MHz and above.
  
• An S9+20 dB noise burst, 1.3 seconds in length. I hear these frequently in the evening. Recorded Nov 19, 2008 on 7022 kHz at 1900 local time. Unknown what bands other than 40M this appears on.
  
• A narrowband signal, several kHz wide, S8, on 3515 kHz. This is pretty obviously some piece of consumer electronic equipment, probably in my house, or in our closest neighbor's house. AHA! It's our new Series 2 TiVo. Interestingly, our older TiVo, which we still have, does not cause this RFI.
• A fairly clean carrier that repeats about every 69 kHz across the 20 meter band. This turns out to be our Xantrex Grid-Tie Inverter for our solar energy system (turn off the inverter - carriers go away). It's S9 on the G5RVjr, which is close to the PV array, but a few S-Units lower on the 40M vertical. It's definitely a problem, but I consider it a lower priority since a notch filter could null it out (note to self: need a radio with a dedicated knob for the notch filter, or an auto-notch DSP).
• An S9 noise across all the 80 meter band with peaks every 60 Hz. Audio spectrum:
  
  
  
  
  
  Walking around with a portable shortwave receiver, I think I've located the house that's the source (one of our neighbors), and at first thought it might be their fluorescent porch light. I just happened to be listening this evening and the noise stopped abruptly at 10:20pm local time. I checked, and the porch light was still on, so that's not it. Coincidentally, our other neighbor's sprinkler system turned on at the same time. Probably unrelated, but I have heard of sprinkler systems being RFI sources.
  
  Around 11:00pm local time, I started to hear the noise again, although its signal strength was much lower. When I walked around with the portable receiver, the signal seemed to be mostly absent where it was before, and was much louder near the neighbor's house with the sprinklers. So I'm really not sure what's going on with this.
  

Well, two sources identified.

I also plan to start keeping a log of when I hear these, so I can try to correlate them to their source.