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Author Topic: Invisible Fence RFI - Need measurements  (Read 1033 times)

Posts: 38

« on: July 24, 2018, 05:14:20 AM »

I am working on resolving an RFI issue with an Invisible Fence (ICT-801) in the 3-8 MHz range. I don't have access to the equipment until the day to try out various fixes.

I'd like to model/test some of the potential fixes before then.

Anybody have one of these model Invisible Fences that would be willing to make a few measurements for me? I'm looking to get a look at the output waveform, and some measurement of the buried loop inductance.

Posts: 3354


« Reply #1 on: July 24, 2018, 05:33:33 AM »

Compliance US and Canada FCC ID: KZ3-050261IC: 2430A-050261

This device complies with Industry Canada rules. This device complies with part 15 of the FCC Rules.Operation is subject to the following two conditions: (1) This device may not cause harmful interference, and (2)this device must accept any interference received, including interference that may cause undesired operation.CAUTION: Modification or changes to this equipment not expressly approved by Radio Systems®may void the user's authority to operate the equipment.

NOTE: This equipment has been tested and found to comply with the limits for a Class B digital device, pursuant to part 15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful interference in a residential installation. This equipment generates, uses, and can radiate radio frequency energy and, if not installed and used in accordance with the instructions, may cause harmful interference to radio communications. However, there is no guarantee that interference will not occur in a specific installation.

If interference does occur to radio or television reception, which can be determined by turning the equipment off and on, the user is encouraged to try to correct the interference by one or more of the following measures:

• Reorient or relocate the receiving antenna.
• Increase the separation between the equipment and the receiver.
• Connect the equipment to an outlet on a circuit different from that to which the receiver is connected.
• Consult customer care, the dealer, or an experienced radio/TV technician for help

After you have tried the remedies above, the next thing to do is contact the manufacturer.  If you start adding to or changing any part of the device, you may have no leverage with them so aviod that until you have made contact.

Posts: 3552

« Reply #2 on: July 24, 2018, 06:30:04 AM »

The test report for emissions coincidentally omits the below 30 MHz plot and only gives a partial table of values. Interestingly, the test was also conducted without an antenna (the buried loop) attached to the device.

The conducted emissions test shows peaks at ~8.5 MHz and its first and second harmonic. This is a strong indication that its primary frequency of operation is near 8.5 MHz.

The impedance characteristics of the buried loop will be completely installation dependent and is not predicable.

It is nice that you are trying to resolve this but in the end, if it is causing interference, the owner of the device is responsible for correcting it or shutting it down. The manufacturer is not responsible except in the case of a violation of FCC emission limits - which they claim they do not violate.

- Glenn W9IQ

- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.

Posts: 38

« Reply #3 on: July 24, 2018, 03:11:12 PM »

It transmits at VLF - 7 or 10 kHz, the 8 MHz emission shouldn’t be necessary component of its performance. I have talked to the manufacturer, who recommended a number of things - but the only things that would be a quick and easy fix was to either change the AC adapter or put a Corcom 10VK6 filter on the output. The first is a great idea; the other looks like a hack but its good to have as an option. Snap-on chokes were more palatable, so I'd like to identify some options for those.

I've sparing just about all the details but if somebody out there has one of these Invisible Fences I'd be glad for any of the measurements you can take.

Posts: 1045

« Reply #4 on: July 24, 2018, 03:30:11 PM »


Saw this from a post on "All About Circuits" forum:

"I am told that Invisible Fence uses 7.5 or 10.8 KHz with a modulation of 30 Hz."

I'm sure it generates all kinds of harmonics.  One guide for testing the fence said you can listen on an AM radio set to 600kHz or so, but you need to turn the fence field width up high.

I see they make GPS-based "Invisible Fence" type systems now, so no wire is needed.  They should get one of those!

But yeah, maybe it's not the fence transmitter, but a reallly crummy switching AC adapter.


« Last Edit: July 24, 2018, 03:33:30 PM by N7EKU » Logged

Mark -- N7EKU/VE3
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