K
kenglish
Guest
Got a chance to do some playing Wednesday...I tuned in to local KDYL (AM 1060, Salt Lake City) and they sounded a bit noisy.
Turns out, they were running their night power instead of daytime level....(oops).
Since I was also looking for Tropo on the VHF TV bands at the time, I noticed that the noise was most prominent when the TV was seeing snow, but was much less when I tuned to something with video (a DTV channel, or just brought up the EPG), so it must have been the sweeps in the CRT set.
So, I did some experimenting with my box of Ferrites. The TV, as well as most everything else, has always had it's (three-wire) power cord wrapped about ten turns thru an Amidon FT-240-J Ferrite Core...that's from my old shortwave radio days. I put them on the radio, the TV and VCR, and on all the other "noisy" devices. (The 240-size core passes the big, three-pronged plug, with the turns of cable as well. The "J"-series is supposed to be good for absorbing RFI from about 500 KHz to 20 MHz.) But, the TV sweep noise was still coming through now.
The VHF antenna coax was also run through an FM trap and a 50 MHz Low-Pass Filter, so I figured the noise might be on the shield side of the coax. Turning off the DTV converter box didn't make a difference, but turning the TV off did.
I wrapped the RG-6/U antenna cable through an FT-140-J core (I had a slew of them in my kit) about 4 times, making about a 4 to 6 inch diameter loop, and it made a huge improvement in the radiated noise. I suspect, though, that passing the video cable on the TV (which is being used as a monitor) might help, too. It appears that the CRT noise is being conducted via the composite video cable's shield, around the converter box, and right on up the coax shield to the TV antenna, which is near the AM radio/shortwave receive antenna. I'll try the video cable, with and without the antenna cable later.
Maybe others can try this, too. Next, I'll have to work on some neighbors' Plasma TVs.
Turns out, they were running their night power instead of daytime level....(oops).
Since I was also looking for Tropo on the VHF TV bands at the time, I noticed that the noise was most prominent when the TV was seeing snow, but was much less when I tuned to something with video (a DTV channel, or just brought up the EPG), so it must have been the sweeps in the CRT set.
So, I did some experimenting with my box of Ferrites. The TV, as well as most everything else, has always had it's (three-wire) power cord wrapped about ten turns thru an Amidon FT-240-J Ferrite Core...that's from my old shortwave radio days. I put them on the radio, the TV and VCR, and on all the other "noisy" devices. (The 240-size core passes the big, three-pronged plug, with the turns of cable as well. The "J"-series is supposed to be good for absorbing RFI from about 500 KHz to 20 MHz.) But, the TV sweep noise was still coming through now.
The VHF antenna coax was also run through an FM trap and a 50 MHz Low-Pass Filter, so I figured the noise might be on the shield side of the coax. Turning off the DTV converter box didn't make a difference, but turning the TV off did.
I wrapped the RG-6/U antenna cable through an FT-140-J core (I had a slew of them in my kit) about 4 times, making about a 4 to 6 inch diameter loop, and it made a huge improvement in the radiated noise. I suspect, though, that passing the video cable on the TV (which is being used as a monitor) might help, too. It appears that the CRT noise is being conducted via the composite video cable's shield, around the converter box, and right on up the coax shield to the TV antenna, which is near the AM radio/shortwave receive antenna. I'll try the video cable, with and without the antenna cable later.
Maybe others can try this, too. Next, I'll have to work on some neighbors' Plasma TVs.