RFI/TVI Baseline and Solutions

RFI/TVI baseline:

I had a few hours to myself yesterday, and spent some time collecting a set of TVI/RFI baseline data: what devices in my home are receiving signals from my station, on what frequencies, and at what severity. I should add that some of the audio/video devices in my house have had some RFI mitigation applied already - I did not remove those mitigation devices. Those mitigation devices are:

- I replaced the long audio speaker leads (zip cord) on our home entertainment system and my son's stereo system with some custom-made twisted-pair speaker leads (2 different color wires + 5 minutes with an electric drill = twisted pair). These speaker leads have a 1-inch-long ferrite core around which the pairs are wound:



The cores are some things I had in my junkbox, so they're made of unknown material. I think they probably came from Weird Stuff, so who knows what they're made of, but they seem to have helped. Before replacing the speaker leads, transmitted CW on 10 meters was clearly audible in the speakers of both our home entertainment system and the stereo in my son's room. Seems like a success.

- A Bencher low-pass filter just past the transceiver in my station. I had no real reason to suspect any sort of problem with harmonics, but the filter was $85 and that's cheap peace of mind for me.

The next day, I did a survey with the following parameters (values used for this test):

• Input parameters:
• Antenna (G5RVjr - closest antenna to home electronics equipment in our house)
• Transmitter power (100w)
• Mode (CW)
• Devices:
• Home Entertainment System:
• Sony Trinitron 27" CRT-style television
• Pioneer Receiver
• Sony DVD player
• TiVo Series 2 DVR
• JVC CD/Tuner (in my son's room)

The RFI/TVI problems I have are:

• 160M: not measured (I currently have no antenna that will load on 160)
• 80M: no RFI/TVI observed
• 40M:
• FM tuner audio disrupted by sent CW
• When watching DVDs, screen flashes
• 20M: no RFI/TVI observed
• 15M:
• FM tuner audio disrupted by sent CW
• 10M:
• FM tuner audio disrupted by sent CW

After recording the baseline data in a spreadsheet, I tried the following:

• Disconnected the external FM antenna from the receiver, and there was no longer any RFI (nor was there any signal from KQED!). The external FM antenna is a 4-element yagi about 2 feet below the feedpoint of the G5RVjr. Assuming this was some sort of a fundamental overload problem, I dug an old 300-ohm high-pass filter out of my junk box and put that between the 75-ohm transformer (the FM antenna is fed with RG6 coax) and the receiver. Problem solved!
• Set up to duplicate the DVD interference, and discovered:
• Disconnecting the DVD player from the TV only reduced the interference slightly
• Disconnecting the RF input from our cable system made the TVI go away completely.

My best guess is that there's some sort of common-mode coupling coming in on the CATV feedline (it runs very close to the G5RVjr's feedline). So I'll try a common-mode choke once I get some ferrite parts big enough. A small snap-on choke didn't help matters.

So, at this point, unless there are some gremlins I haven't found yet, the only problem I'll have is if someone is watching a DVD and I'm transmitting on 40M with the G5RVjr. That's actually fairly unlikely, given that my droopy radial vertical works better on 40M anyway, and it's never caused any TVI I'm aware of.

So I'm pretty close to being able to declare my own house clean, which is a big confidence-builder for going QRV in contests.

TVI: 80 meters

Operating PSK31 tonight on 80 meters, I noticed that there is a very small amount of interference in the form of horizontal lines. This only happens when I transmit on the G5RVjr with more than 25 watts (at 25 w, the lines are just barely discernible; at 100 watts, they are visible but I wouldn't call them annoying. Should be easy to solve...

(It's nice being able to run the shack - which is in the garage - from my laptop via Remote Desktop while sitting in the living room watching TV.)

TVI - collecting data

We've got some minor TVI and RFI problems in our house that I'll need to tackle at some point.

Our home entertainment system consists of:

• A Sony Trinitron 27-inch color television (CRT-type)
• A Sony DVD player
• A Pioneer stereo receiver
• A TiVo Series 2 DVR
• Conventional (non-digital) cable TV
• The cable enters the house and goes to a "T" connector. One branch goes to the cable input of the TV, the other goes to our TiVo.
  

Symptoms/Observations:

• During operation on almost any HF band, there is some TVI, but only when the TV is connected to the TiVo. If I switch the TV to its cable TV input, there is no TVI.
  
• The interference usually manifests itself by changing the picture to black-and-white, or reducing the color. There may be some crosshatching.
• Interestingly, this is most pronounced when running PSK-31 and no data is being transmitted. When just keying down for a few seconds in CW mode, there is a brief flash of "color dispearance" and the set seems to recover. I'm not sure why, but transients (key-down, or AFSK shift) seem to be involved.
  
• It happens even when I reduce the power output to 5 watts, although it is more pronounced at higher output levels.
• It's worst on 20 meters, but occurs on at least 80, 40, 20, and 15 meters.
• The TVI happens even if I am transmitting on the 40m vertical in the front yard.
• We also saw TVI when I was using a temporary 160M longwire fed from the feedpoint of the 40M vertical.
  
• The amateur antenna feedlines (coaxial cable) for the G5RVjr and temporary 20M vertical run underneath the house through the crawlspace, and exit at the back of the house right where the cable TV lines enter.
• The feedline for the 40M vertical also runs through the crawlspace, but exits on the east side of the house, and comes no closer than 25 feet from the TV/cable lines.

The fact that the TVI is present when using the 40M vertical suggests that the cause isn't feedline radiation, or you'd expect that the TVI would be worse on the antennas at the rear of the property.

I could also swear that the TVI problem got worse when I pulled our old TiVo out of the system (it's been powered off for a while now) and I hooked our new one into the audio/video inputs used by the old one.

My best guesses:

• The signal is being picked up by a cable connected to the TiVo, and the TiVo is the TVI victim,
• The TiVo has poor shielding, and is getting overloaded.
• The signal is being picked up on a cable from the TiVo to the TV

I'll do some experiments with disconnecting cables and see if I can narrow things down. Since the TiVo is also an RFI source, I suspect I'm going to have to expend some effort on it.