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Author Topic: Tracking down 3.5795 mhz colorburst interference  (Read 8404 times)
K3VAT
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Posts: 730




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« on: September 30, 2013, 10:34:42 AM »

I recently erected my lowband vertical.  One of the first things that I noticed is that I have a strong S9 +15db modulated signal centered on 3.5785 mhz with repeating signals every 16 khz.  The signal seems to be on 24/7.  I understand that this signal is associated with colorburst technology used in TVs.

The signal definitely originates outside my house, but I can't seem to get a 'fix' on which house may have devices that are the probable source.

Q: would this interference be associated with a certain type or brand of TV?
Q: is it only TVs that use this technology - could something else besides a TV be the source?
Q: how does one isolate the offending equipment?

Any assistance appreciated.

73, Rich, K3VAT
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W1VT
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Posts: 841




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« Reply #1 on: September 30, 2013, 11:07:21 AM »

http://www.riana.com/electronics/docs/MM5369.pdf
The MM5369 chip, together with a colorburst crystal, can generate a 60Hz clock

http://mysite.verizon.net/cpthaines/id73.html
There was also a DTMF chip to use the colorburst crystal as an accurate frequency reference.

Typically, you locate the source by the process of elimination, turning off circuits, or by direction finding.

Direction finding on 80 meters is typically done with a loopstick antenna.  You can get a very sharp null.

http://forums.qrz.com/archive/index.php/t-159976.html
Another popular frequency is four times the colorburst frequency--you could actually have that divided down by a digital device instead of an actual colorburst crystal.

Zack W1VT
« Last Edit: September 30, 2013, 11:36:49 AM by W1VT » Logged
K3VAT
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Posts: 730




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« Reply #2 on: September 30, 2013, 12:11:43 PM »

Thanks Zack for the references.

OK, we used a portable SW radio tuned to 3.58 mhz with short whip and interference seems to emanate from an outdoor Power Company power box several houses away.  Signal is strongest both right at the box and at the home's electric meter.  No other strong sources were detected.

Could these power boxes or meter have the offending chips installed?  Recommended next step?

thanks, Rich
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W2MV
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« Reply #3 on: October 02, 2013, 01:08:52 PM »

The fact that you stated it repeats every 16 KHz leads me to believe that it may be a TV horizontal sweep freq problem. Perhaps it's mixing with the chrominance subcarrier oscillator of 3.579545 MHz. What do you mean by "Power Company Box?"
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K3VAT
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« Reply #4 on: October 02, 2013, 07:38:16 PM »

The fact that you stated it repeats every 16 KHz leads me to believe that it may be a TV horizontal sweep freq problem. Perhaps it's mixing with the chrominance subcarrier oscillator of 3.579545 MHz. What do you mean by "Power Company Box?"

W2MV - Thanks for the response.  The local power utility company has green colored 3'x3'x3' boxes in the front yard of every 4 or 5 homes on my street.  We have all underground utilities and these boxes seem to be the distribution point for our house utility feed.  I don't know what is inside; on occasion, there is an audible hum coming from them.

Regarding the 3.579545 signal: I can view it on my panadapter.  It is not just a single unmodulated carrier - the waveform is rich in complex sidebands that are several dozen hertz wide.
 
73, K3VAT
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WX7G
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« Reply #5 on: October 03, 2013, 09:32:24 AM »

The utility box is not the RFI source, it is an egress point. Find the offending box and one of the houses connected to it is the RFI source.

A simple way to find the RFI house is to shut the AC power off (with the home owner's permission) to each house in turn. This may be faster and less intrusive than entering each house and sniffing with a receiver. When the RFI house is found, the AC power to each room is switched off one at a time to find the RFI room. When the RFI room is found, the AC power to each device is disconnected to find the RFI device.
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K3VAT
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« Reply #6 on: October 03, 2013, 10:13:47 AM »

The utility box is not the RFI source, it is an egress point. Find the offending box and one of the houses connected to it is the RFI source.

A simple way to find the RFI house is to shut the AC power off (with the home owner's permission) to each house in turn. This may be faster and less intrusive than entering each house and sniffing with a receiver. When the RFI house is found, the AC power to each room is switched off one at a time to find the RFI room. When the RFI room is found, the AC power to each device is disconnected to find the RFI device.

OK, we've located the house that is the RFI Source.  It is the one closest to the utility box.  The signal strength of the offending interference is a bit higher at the home's electric meter (as compared to right next to the utility box).

Hopefully, I can follow your excellent above recommendations ... I'll report back on this in a few days.

thanks again! 73, Rich, K3VAT
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K1DA
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« Reply #7 on: October 31, 2013, 09:14:37 AM »

Do the new digital TVs still use the 3.5 MHZ colorburst for anything any longer?  If not, and I don't think so, I'd be looking for an old analog TV, probably a cheap ACDC one. 
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KD0REQ
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« Reply #8 on: October 31, 2013, 10:02:26 AM »

3.58 colorburst is specific to NTSC system color TV sets (and the zillions of cheap (donkey) gizmos that used that 35 cent crystal for their clock, from computers to alarm clocks.)

there is no need for it in the computerized flat screen HD sets.
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