[Elecraft] K3 Noise Blanker ahead or behind roofing filter?

[Bill W5WVO]

Most RF-spectrum noise generated by TV sets and computers and radiated by the 
power line is common-mode noise, and the typical differential-mode (in-line) 
power filter will do nothing to suppress it. You need to make a common-mode RF 
choke. Get some large ferrite toroid cores (Palomar Engineers as well as 
others sell them) and wind the entire power cord of the TV through a couple of 
these in series. (In less severe cases, just one toroid may do the trick.) The 
toroid needs to go as close to the TV set as possible, as any unshielded 
conductor between the toroid and the power supply will still radiate.

You can also encase the whole power cord in clamshell ferrites if you can find 
them in the correct size, but I've found this to be less effective than 
toroids. The benefit of this method is that you don't have to supply an 
extension cord to replace the length of the power cord you wound through the 
toroids.

Bill / W5WVO


Brett gazdzinski wrote:
> I would ask the people if I could put a filter on the power
> line to the TV.
>
> That might reduce or eliminate the QRN.
>
> Maybe get a surge protector/filter setup and convince them
> it's a protection device for their investment.
>
> I bought phone filters and installed them on the neighbors on both
> sides of my house to eliminate the AM getting in the phones.
> I also had to filter an audio system with extended speaker
> wires as I came through quite loud even with the thing
> turned off. Some caps across the speaker outputs cured it
> totally!
>
> Brett
> N2DTS
>
>> -----Original Message-----
>> From: elecraft-bounces at mailman.qth.net
>> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of
>> Kenneth A. Christiansen
>> Sent: Tuesday, June 12, 2007 7:50 AM
>> To: elecraft at mailman.qth.net
>> Subject: [Elecraft] K3 Noise Blanker ahead or behind roofing filter?
>>
>> I have K2 SN 1031 and an IC-746PRO. Last week my next door neighbor
>> brought home a large screen TV that looks to be the rear projection
>> type. I didn't pay much attention to it as they unloaded it
>> but now find
>> it puts out lots of QRN. It  puts out S9 on the PRO 60 HZ QRN
>> on 20, 15,
>> 10 6 and 2 meters. Those are the bands I have antennas that work. The
>> noise blanker in theK2 and the PRO both eliminate this bad QRN right
>> down to the background noise :-)  when there are now strong
>> signals on
>> the band but when a strong station such as the W1AW code
>> sessions come
>> on 20 meters, (20 over 9 in ND), than the K2 using NB1 has problems 5
>> KHZ or so either side of W1AW. NB2 has problems up to 10 KHZ
>> either side
>> of W1AW and the PRO has problems 15 KHZ either side of W1AW
>> :-( . Is the
>> noise blanker on the K3 ahead of the roofing filter or behind the
>> roofing filter. If it is behind the roofing filter buying a
>> K3 might put
>> me back on the air :-)      but if it is ahead of the roofing filter
>> than would I have the same problem as the K2 :-( ? I have
>> looked at the
>> FAQ part of the Elecraft K3 site and do not find the answer to this
>> question. I just need a short answer so please do not start a long
>> thread on my station or observations etc.
>>
>> 73 and thanks for the help.
>>
>> W0CZ
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