Picture freezing on cable system when transmitting

[Riktar]

 My brother is running a Kenwood TK-8180 mobile as his base unit. He is running 75 feet of LMR400 cable to a Browning BR-6140 antenna in the attic of his garage. Every time he keys his mic the picture on his TV (In his living room on the first floor. His radio is in the basement) picture "freezes". He is using Spectrum cable TV. We have not checked to see if this happen for broadcast but I am not having any picture freezing issues and I do use broadcast TV.

 

 Anyone else ever run into this?

[Logan5]

He may have bad cable or a connector. I have had this happen also compact LED bulbs dim and or flicker.

[marcspaz]

That seems to be an excessive amount of RFI.  I run 1500 watts and high-gain antennas on UHF, VHF and HF at home and there is no RF interference with anything in my house.

 

Along with a bad connector on the cable lines, as mentioned above, there could be an improperly installed connector on the radio's antenna transmission line on the radio or antenna side.  I would ground the cable box, cable coax connectors, the radio, antenna transmission line on both ends, and be sure the antenna and mast are properly grounded.

 

May end up being a junk cable, though.

[Riktar]

Thanks for the suggestions!

 

I am heading over to his house on Monday and we will check on connections and ground paths we use.

[Riktar]

This is really weird. The ONLY channel that freezes on his cable box is Fox News. There may be others but out of the 30+ channels we tried the problem did not occur.

 

Aside from checking all the ground connections I had it in the back of my mind that maybe the GMRS frequency might be close enough to the rf frequency of his remote. But he said that he only has IR for his remote. 

 

And even if it was a case of interfering with the pause button command on the remote, why would it only occur on one out of 200+ channels?

 

Just for clarifying, as soon as you key the mic the picture freezes and the sound stops. As soon as you release the mic, the picture jumps forward to the present and the sound restarts.

 

This is a real head scratcher....

[marcspaz]

Wrap the cable box in foil and make sure the foil is wrapped tight, touching the ground leads on the cables.  See if making a local Faraday cage changes anything.

 

If you have a meter to test with, add a wire or alligator clip from the foil to the electrical ground on an outlet (normally the screw to hold the face plate on is grounded for safety).  Don't put anything in the outlet though... bad stuff will happen.

[Jones]

If his Fox News is on Cable channel 64, then you can't do anything about it.  CATV Hyperband channel 64, no matter whether it's NTSC analog or ATSC QAM Digital, covers a 6MHz wide bandwidth between 462 and 468MHz.  If you transmit anywhere in there, (GMRS) it will overload the TV or converter box.

 

Likewise, if you are transmitting in the 70cm ham band, depending on what frequency you are using, you will wipe out Cable channel 59, 60, or 61. the 2-Meter ham band rides on the same band as Cable channel 18, and MURS will wipe out channel 19.

 

NOTE: Cable channels above 14 are NOT the same frequencies as over-the-air TV channels above 14.  Also note that with digital TV, the station can display whatever "virtual channel" they want you to see.  Perhaps your local CBS affiliate still advertises themselves as "News-4", even though they switched to RF channel 27 over 19 years ago.  Cable systems like to call digital channels much higher numbers such as "Hyper-tier 653" because it makes them sound bigger than they actually are - makes you think they have more channels out there that you just don't pay enough to get.

 

Here is a list of actual frequencies vs. channel numbers for Standard, IRC, and HRC type cable systems, along with standard over-the-air broadcast.

 

https://www.jneuhaus.com/fccindex/cablech.html

 

The visual carrier frequency is shown in this chart. TV is transmitted in Vestigial Sideband mode, meaning a full carrier and upper sideband, but the lower sideband is rolled off 1MHz below the carrier. The lower edge of the channel is 1.25 MHz below the visual carrier and the upper edge is 4.75 MHz above the visual carrier.

[Riktar]

 That explains alot. I am going to have my brother try keying his truck radio in the driveway to see if the same thing happens. 

 

 I also believe we can get by on a lower power setting. Currently he is using a TK8180 (30 watt) for his home base and a TK8180H (45watt) for his truck.

 

 He does NOT want to interfere with his neighbors tv's so hopefully if we dial the power back (I think the 8180's are 10 watts on the low setting) it will be enough to still keep the connection between us but eliminate the cable box freezing.

 

 Thanks for the explanation!

[Jones]

You should also check the quality of the cable that is being used, and perhaps call the cable company to upgrade it for you.  Most CATV systems these days use a quad-shielded cable with special type F connectors, which helps cut down or eliminate this type of interference.  If your house is still wired with the old-school RG-6 or even worse, RG-59u, then it is past time to replace your cable, and the CATV company may do it at no cost to you if you ask them, and explain the problem.

 

Also check any cable splitters you have, and be sure they are not the cheap Chinese type with chrome or gold plated plastic cases.

[gortex2]

Also check for splitters in the house. Way back when i worked for Spectrum we would get calls with similar complaints. Alot of times we found splitters with 2 cables and 1 or  empty ports with no terminations on them. As others said check the COAX. Anything less than RG6 shielded can cause the issue. My motor home would block on on multiple channels when my GMRS repeater (in the MH) would transmit. Found alot of connections (rg58) with crimps looking like they used a pair of pliers. I replaced all cable in the MH with RG6 quadshield and all my issues went away.