9000SMC and television interference

I have just installed a customer using a 9000SMC and 13dBi yagi antenna. She tells me that there is interference (snow) on TV channels 2 and 5 which disappears if she unplugs the SM’s transformer.

Has anyone experienced this problem? Is there a resolution?

Don’t know if it’s pertinent, but the SM is set for all frequencies, has NAT enabled, uses a color code, is set to update the interface every 2 seconds, is running 7.3.6 and hardware scheduling, otherwise pretty much default values for configuration settings.


I have experienced issues before with 2.4GHz FHSS setups. I had moved the antenna from underneath the TV antenna to the roof and it seemed to have resolved it.

I have not run into issues yet with 900MHz TV interference, although I’m going to find out later today when I do a couple site surveys. I can leave another message with the results.

Ever since I got ‘burned’ once using 2.4GHz, I now check, and double check, to make sure there is no TV antenna interference during any survey I do. This area where I’m is country and backhills, so MANY people have TV antennas since they can’t get cable or don’t want to pay for satellite.


Since Channel 2’s video carrier is at 55.25 MHz, and Channel 5’s is at 77.25, it’s most likely that the interference is either desensitization of the TV due to strong RF (which would be cured by physically separating the SM’s antenna from the TV antenna) or the power supply is putting out noise. I strongly suspect, from the minimal description, the latter.

One thing you could do as just a quick check, is go out and take a suitable battery power supply with you. Power the SM from the battery and check the TV for interference, if it is power supply related, then the interference will go away, if it is desense, then it will still be there.

Of course there a other things which might be wrong, but the first and easiest thing to check is the power supply.

I have had this happen before. The easiest way for me to solve it at the time was to move the radio away from the tv antenna.
When I researched this issue later that evening, I found that the most common reason for this was not having the antenna mast properly grounded. I have not had another chance to actually test this theory… and it may not apply to all situations… but worth a quick look.

I took a battery backup unit to the site and used it to power the 9000SMC in order to isolate it from the house’s electrical system. Same problem.

The over-the-air antenna is located in the attic and the 13dBi yagi and 9000SMC just above it. Both the TV antenna and yagi are in-line with the ridge, pointing in the same direction, if that’s relevant.

Here’s a view of things looking directly down on the roof ridge.

I will visit the site with a TV/satellite installer who is good at what he does and we’ll try the grounding suggestion.

’ /
’ /
’ /
/ ----tv-antenna---- ’ yagi->
/ ’
/ '
/ ’

Hmmm. I see that all of the spaces (spacing) was removed from my beautiful roof design!

The homeowner has cost themselves a lot of dB of tv signal having the antenna inside the attic, and it doesn’t take much nearby signal to swamp the receiver.

Can you accomplish more vertical separation, at least of the yagi?

Another thing that could cause tvi is if the antenna feedline and the data line from the the SM are routed close together. Check the antenna feedline (usually, for a tv antenna, some sort of twinlead) and see if it is physically close to the data cable, if it is, try putting some twists in one or both of them (tv twinlead, unlike the way most homeowners install it, is meant to be twisted to reduce interference) and if the feedline is coax, from a balanced antenna without a balun, then that may explain a lot.

It just occurred to me to wonder if, on a connectorized SM, which I have no experience with, the feedline to the yagi is twinlead or coax, and if it is coax if there is a balun at the antenna.

if that satellite guy is real good he will sell them one and then it will be fixed hehe.

did you change power supplies sometimes one will have more noise than others?

And did you leave the power supply plugged in but leave the cat5 unplugged to make sure it was the power suppy or the radio?

These folks already have a satellite dish. The over-the-air antenna is simply for receiving local TV stations - news and local programming. Local TV reception up here is bad, but not bad enough to get the local broadcasters to approve satellite feeds of the major networks so over-the-air is the only way to get them.

The antenna is in the attic simply because of aesthetics. It’s very common around here.

The cables from the TV antenna and the SM are not close together - probably no less than 15’ apart at any point.

Thanks for the suggestions - we’ll try everything.