[CQ-Contest] Power levels and TVI-some additional details
aa5jg at fidmail.com
Mon Jan 10 17:54:12 PST 2011
Thanks for all of the replies and information so far. Here are some answers to questions people have asked me, plus some additional details about my station and TVI.
The neighbor used to be on rabbit ears a few years ago and had TVI quite often from me. Never complained except for one time when the University of Oklahoma was playing in the national championship game-we live 60 miles from OU. I was on 30 meters at that time.
SInce then they have gone on cable. She said the interference didn't occur very often now and wasn't concerned about it. Seems like she could live with it. DIdn't tell me not to operate or to do anything to my station. Almost seemed sorry that my daughter and her daughter brought it up to me. It did happen last night and I was on 6m at the time. I was on HF much of Saturday doing the NAQP. Didn't get any reports of TVI then. I tried to find out when else I was bothering her TV but she really didn't volunteer any information. She didn't say that it occurred on Saturday or was bad then or anything like that.
The neighbors are on the same cable system we are. I have a TV in the shack about 5 feet from the rig, another in the living room about 15 feet from the shack, and a few others in the house. Did some testing today with the in-shack TV and the one in the living room.
On 6 meters this afternoon on 6 meters it was shutting off the TV in the shack, and was causing some interference on the one in the living room. I had the 6 meter antenna going into an antenna switch so I could switch it between 2 different rigs. I bypassed this and ran the antenna's coax straight to the antenna tuner. This eliminated the turning off the shack TV and lessened interference in the living room.
Later tonight I tried out the different HF bands on the TVs. On the living room TV HF caused some lines in the screen or other interference on the lower TV channels. The shack TV wasn't affected much but then it was on a higher TV channel. Just tried it on a lower channel and it was taking a beating. Lowering my power to 25 watts eliminated problems in the living room TV. Also eliminated the interference on the shack TV.
So that is the current situation. I have a Drake Low Pass filter all antennas go thru, and the antenna tuner is grounded using 1/2 or 3/4 inch braid to a ground rod outside the shack. Don't have a connection to the rig, but then it is grounded thru the tuner anyways using the coax jumpers between the rig and the tuner. The antennas are a homebrew G5RV type dipole and a 3 element yagi for 6m.
73s John AA5JG
----- Original Message -----
From: Ron Notarius W3WN
To: aa5jg at fidmail.com
Sent: Monday, January 10, 2011 8:40 PM
Subject: Re: [CQ-Contest] Power levels and TVI
Before doing anything else, you need to find out exactly what's being affected. Otherwise, you may waste time and energy on the wrong solution, that is, "fixin' sumthin' dat ain't broke."
How many TV's are affected?
How old are they?
Are they all on cable?
Is the cable itself, how should I put this, uncompromised? (I can tell you from experience that, shall we say, creative cable splices can compromise the system and let leakage in)
Does it happen on all HF bands, or only one?
Does it happen on CW, SSB, RTTY/Digital, all?
I know of a case of someone who had 4 TV's. one was a cheapie (at the time) portable on rabbit ears. It picked up everything, but of course, it was all the fault of the ham. None of the other sets, no other neighbors, no other electronics had a problem. When that set was put on cable, the problem disappeared.
At my previous QTH, I found out the local cable company was blaming me for QRM to (then) cable channel "14". Turned out the problem was caused by a botched splice (no shielding!) at someone's house, when they tried to add extra rooms "on the cheap". Oh, and this house was located near the 140 ' commercial tower that carried municipal communications, including the local VFD, and guess what they actually were picking up?
If it's cable leakage, or an old cheap set in a plastic case (no shielding), reducing power may not cure the problem, especially considering the proximity. Worse, you may find that reducing power doesn't fix the actual problem, but forces you to compromise (by running lower power) which doesn't fix a bad install or a cheap set.
Also, try a high pass filter on the feed of the set itself. Might not help if it's a shielding problem on the set itself (plastic case) but might help if it's the cable.
And... get ahold of Ed W1RFI up at ARRL Hq and ask him for suggestions. He's forgotten more about RFI/EMI than I'll ever know!
73, ron w3wn
Jan 10, 2011 02:07:45 PM, aa5jg at fidmail.com wrote:
I found out yesterday that I am having some occasional TVI with one of the
neighbors. She is really cool about it but I don't know if it is also an
issue with others in the neighborhood, plus I would like to be courteous
about my operating as well. I am using a low pass filter, so I am assuming
that the TV's front end is getting overloaded at times, as our houses are
only a few feet apart and they have cable for TV instead of picking it up
off the air. I am running 100 watts to a pretty much unity gain antenna.
What power levels do others find works to reduce TV overloading? Would
going to 25 watts make a big difference? Need to drop power further than
73s John AA5JG
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