[SBE] OTA digital TV interference

Mon Mar 16 13:22:58 EDT 2015

Reflections (multi-path) cause loss of data bits as the bits cancel.
In a diversity system, it would be difficult to 
get the two antenna in phase at the receiver as 
the phasing is dependant on frequency.
If you used quad shield from the antenna to the 
receiver, you will be as immune to EMI on the 
feedline as you can get, short of using something like heliax or rigid line.
Once the data bits are interfered with on the 
antenna, you will not be able to recover the original data train.
You might want to try pointing the antenna at a 
billboard to see if you can get a cleaner signal from there.

My suggestion would be to move the antenna.

73
Glenn
WB4UIV

At 11:49 AM 3/16/2015, you wrote:
>Thanks everyone for your thoughts on this.
>
>FWIW, I believe all Chicago TV channels are now UHF.
>
>I had this idea that a quick and cheap fix for 
>EMI might be to put a ferrite bead or some type 
>of choke on the coax from the antenna to TV, to 
>act as a filter for noise.Â  But this
>probably wouldn't do much good if the noise 
>spectrum was large.Â  Maybe it might only clear 
>up a couple of channels.Â  Not sure if I would 
>be on the right track with that idea.
>
>If reflections, does there exist a diversity or 
>similar type of antenna system that would not be too expensive?
>
>If someone is only interested in local OTA TV in 
>the city, it's too bad that there might not be a solution for this.
>
>On Mon, Mar 16, 2015 at 10:28 AM, John Peterson 
><<mailto:jpeterson at prairiepublic.org>jpeterson at prairiepublic.org> wrote:
>In general VHF channels would be more 
>susceptible to EMI and UHF channels more so to 
>reflections, and from my experience, higher UHF 
>channels are more prone to reflections then lower UHF.
>
>John Peterson
>CSTE
>Fargo, ND
>
>On Mon, Mar 16, 2015 at 10:14 AM, David Baker 
><<mailto:dbaker at addison-il.org>dbaker at addison-il.org> wrote:
>The location is within 10 miles of the station 
>transmitters on Chicago's west side, and signal 
>strength is strong on most channels while the trains are not on the tracks.
>
>Partial or total breakup/loss occurs while 
>trains are moving on the tracks or standing 
>still.Â  Some types of trains have a stronger effect than others,
>for example if a freight train is moving through 
>or stopped, vs a commuter train.Â  Also, some 
>channels are strong during train presence, with minimal breakup,
>while others have total loss at the 
>antenna.Â  This led me to think EMI over 
>reflections.Â  I have to admit I have not yet put a spectrum analyzer in place
>to see what is happening there.
>
>On Mon, Mar 16, 2015 at 9:50 AM, George J Molnar 
><<mailto:George at molnar.com>George at molnar.com> wrote:
>When I was Chief at a station in Chicago, we saw 
>both train (â€œL") reflection and pulse noise 
>from the electrical system as interfering 
>possibilities. Especially where the tracks were 
>reasonably close (say in direct sight, and between the RX and TX).
>
>Filter unlikely to help, sadly. Only better antennas & feedlines,
>
>
>
>George J Molnar
>KF2T | AFA9GM
>Nevada, USA
>Twitter: @GJMolnar
>
>
>
>>On Mar 16, 2015, at 7:46 AM, John Peterson 
>><<mailto:jpeterson at prairiepublic.org>jpeterson at prairiepublic.org> wrote:
>>
>>How far from the tracks/trains is the recieve site?
>>I would think you are dealing with reflections 
>>off the trains, rather then EMI.
>>
>>John Peterson
>>CSTE
>>Fargo, ND
>>
>>On Mon, Mar 16, 2015 at 9:30 AM, David Baker 
>><<mailto:dbaker at addison-il.org>dbaker at addison-il.org> wrote:
>>Good morning!
>>
>>I'm wondering if any TV station engineers are 
>>addressing the problem of OTA digital TV 
>>interference and loss near trains, or if a 
>>solution can be recommended for this 
>>problem.Â  For apartment buildings especially 
>>where antenna height is not an option, if that 
>>would fix the problem at all.Â  Can a filter be 
>>installed between antenna and TV that would 
>>help to remove what I think is EMI coming from the trains?
>>
>>Thanks for any suggestions!
>>
>>--
>>Thank you,
>>
>>David Baker, 
>><http://www.sbe.org/sections/descriptions.php#CBTE_CBRE>CBTE, 
>><http://www.sbe.org/sections/descriptions.php#CBNT>CBNT
>>Media Production Coordinator
>>Community Relations Dept.
>>Village of Addison
>>office: <tel:630-693-7554>630-693-7554
>>cell: <tel:708-935-7829>708-935-7829
>><http://www.addisonadvantage.org/>www.addisonadvantage.org
>>
>>_______________________________________________
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>--
>Thank you,
>
>David Baker, 
><http://www.sbe.org/sections/descriptions.php#CBTE_CBRE>CBTE, 
><http://www.sbe.org/sections/descriptions.php#CBNT>CBNT
>Media Production Coordinator
>Community Relations Dept.
>Village of Addison
>office: <tel:630-693-7554>630-693-7554
>cell: <tel:708-935-7829>708-935-7829
><http://www.addisonadvantage.org>www.addisonadvantage.org
>
>_______________________________________________
>The SBE Roundtable, <mailto:SBE at sbe.org>SBE at sbe.org
>To unsubscribe, go to 
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>
>_______________________________________________
>The SBE Roundtable, <mailto:SBE at sbe.org>SBE at sbe.org
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>
>--
>Thank you,
>
>David Baker, 
><http://www.sbe.org/sections/descriptions.php#CBTE_CBRE>CBTE, 
><http://www.sbe.org/sections/descriptions.php#CBNT>CBNT
>Media Production Coordinator
>Community Relations Dept.
>Village of Addison
>office: 630-693-7554
>cell: 708-935-7829
><http://www.addisonadvantage.org>www.addisonadvantage.org
>_______________________________________________
>The SBE Roundtable, SBE at sbe.org
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