[RFI] RfI in CCTV reader

Dale Svetanoff svetanoff at earthlink.net
Thu Jun 28 10:27:40 PDT 2012


Thank you for the reply comments.  There are many people on this list who
are more expert than I am on some RFI issues, but I'll start things rolling
with a few remarks based upon your reply:

1.  The good news is that you don't have a problem when not using the
amplifier.  I failed to ask what rig your using, but for now, I'll assume
that it delivers 50 to 100 watts in the barefoot mode.  That means your
CCTV system has a threshold of interference somewhere between 100 watts and
600 watts, a range of about 7 dB.  That is not a large window, so more good

2.  While I am not familiar with the Cobra Ultra-Lite antenna, I do see two
problems associated with it: A) It is only 50 feet away from your
equipment.  Depending upon the part of the antenna that radiates most of
the RF field, that is less than one-half wavelength on 75 meters, putting
you and the equipment into a high level field strength.  B) The antenna is
fed with ladder line and a balun.  Where is the balun located?  If it's in
the shack, then you have ladder line with large fields around the
conductors close to the equipment.  Hopefully, the balun is outdoors, with
coax between your tuner and the balun.  Although fields around a balanced
transmission line will cancel if the currents are equal, any imbalance in
the current will result in field radiation from the line.

It is no surprise to me that the "brute force" power filter did not help. 
The problem is not likely due to anything having to do with the AC power
line feeding the CCTV equipment.  More likely, the problem is caused by
coupling of strong 75m RF onto the connecting cable between the camera and
monitor and/or direct radiation into the circuitry of the camera or
monitor.  This now brings up the issue of providing external RF chokes on
the connecting cables, applying absorption beads or toroids to the power
supply (wall wart, perhaps) that runs the camera or monitor, and even
presents the possibility of having to provide some sort of internal
shielding in the equipment.

With a threshold of only 7 dB, the logical choice would be to apply RF
absorbing chokes over all connecting cables between the camera, monitor,
and power supply.  However, these must be made from materials that are
effective at 3.5 MHz - the usual general purpose clamp-on ferrites are made
for much higher frequencies.  

An alternative to modifying the equipment would be to move the antenna
further away.  If that's possible, placing it at least 100 feet away from
the equipment could solve (or reduce) the problem.  Of course, operating
without the amplifier is another choice. Bottom line: you must reduce the
net RF field seen by the CCTV equipment.  You can do that by moving the
antenna further away, placing the balun outside (if it is not now outside),
reducing power, or beefing up the equipment and its cabling to withstand
the field strength you have.

I'll leave it at that for now.  Let us know what you think might be easiest
for you to implement.  I assume that the manufacturer has no plan in place
to help with RFI issues, although they should.

73, Dale

> [Original Message]
> From: Vin Santis <vinsantis at sbcglobal.net>
> To: <svetanoff at earthlink.net>
> Date: 6/28/2012 10:31:13
> Subject: RE: [RFI] RfI in CCTV reader
> -----Original Message-----
> From: Dale Svetanoff [mailto:svetanoff at earthlink.net] 
> Sent: Thursday, June 28, 2012 12:39 AM
> To: Vin Santis; rfi at contesting.com
> Subject: RE: [RFI] RfI in CCTV reader
> Vince,
> We need a little more info so we can be more effective helpers.
> 1.  What band or bands do you operate when the problems occur?
> 75 meters
> 2.  Do you have any problems when running without the amplifier?
> No
> 3.  What type of antennas do you use and where are they located, relative
> the camera and monitor?  What distance is between the antennas and this
> video equipment?
> The antenna I was running  before the oct snow storm  was a Cobra Ultra
> fed with ladder line  through a 4:1 balun.  The distance between the
> and the cctv was about 50'.  
> 4.  What is the make and model of the amplifier?  What modes do you
> when using it?
> Ameritron ALs 600. Usually ssb.
> Thanks - your answers may be of help in working the issues.
> 73, Dale
> Thanks Dale
> Vince, N1VS
> > [Original Message]
> > From: Vin Santis <vinsantis at sbcglobal.net>
> > To: <rfi at contesting.com>
> > Date: 6/27/2012 6:56:10
> > Subject: [RFI] RfI in CCTV reader
> >
> > Hi
> >
> > I'm a legally blind ham and depend on a cctv device made by
> EnhancedVision.
> > I had destroyed two cctv's with rfi.
> > What seems to happen is the flat  screen monitor  permanently shuts 
> > down
> and
> > I'm not sure if the problem is in in the monitor or in the camera.
> > The manufacturer has been of no Help. I've gone so far as to use a 
> > brute force ac line filter with no result.
> > My operating conditions  includes using  a 600 watt amplifier when the 
> > problem has occurred Any help with this problem will be gratefully 
> > appreciated.
> > Vince Santis, N1VS
> > Winsted, CT
> >
> > _______________________________________________
> > RFI mailing list
> > RFI at contesting.com
> > http://lists.contesting.com/mailman/listinfo/rfi

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