[HCRA] KB6NU's Column for February 2013

[Rick Lindquist]

Thanks for sharing, Larry. 

Another noise source you might consider before you start throwing breakers is your cable box or Internet/phone modem. I had extremely high noise on the low bands, especially on 160, from my Time Warner Internet/phone modem (mfd by Arris). Like many such devices it contained a switching-mode power supply. Once I determined that the box was the source, I was able to ameliorate the noise considerably by coiling the power cord around a toroid, putting ferrite beads on the CAT-5 cables, physically moving the box and wrapping the box partially in heavy aluminum foil that was grounded to the cable shield (I call this "the tinfoil beanie treatment").

Recently I swapped out the noisy box for a very quiet Scientific Atlanta box. Now all I can hear is the noise from the nearby overhead power lines. My next move will be a call to Bangor Hydroelectric.

73, Rick, WW1ME (ex-N1RL, WW3DE)
Harrington, Maine

-----Original Message-----
From: hcra-bounces at mailman.qth.net [mailto:hcra-bounces at mailman.qth.net] On Behalf Of Larry Krainson
Sent: Monday, February 25, 2013 10:29 AM
To: HCRA Email List
Subject: [HCRA] KB6NU's Column for February 2013

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Something for everyone to enjoy reading:


Hi, folks--

Here's my February column.

Dan


Ferreting out noise sources

By Dan Romanchik, KB6NU

About three months ago, I put up a 20m antenna—an end-fed, half-wave antenna (http://www.kb6nu.com/kb6nu-finally-builds-an-end-fed-half-wave-antenna/). 
Right off the bat, I was flummoxed by the high noise level. It was nearly S9, obliterating all but the strongest signals.

The strange thing about this noise was that I was only experiencing it on 20m, and only using this antenna. If I switched to my 40m dipole, the noise dropped back to the S1 - S2 noise level that I usually experience here. 
(Yes, I know. I'm really lucky to have such a low noise level here.)

It didn't really make any sense to me that this antenna would be so susceptible to noise while my other antennas weren't, but I just couldn't come up with any other explanation. I was not experiencing any noise on any of the other bands, after all. Sometimes 40m is so quiet here that I check to make sure that the antenna is connected to the radio.

As luck would have it, I stumbled upon the noise source a couple of days ago. I had taken the laptop I normally use in the shack somewhere one day last week, and when I returned it to the shack that evening, I switched the rig over to 20m before connecting the power supply back to the laptop. No noise! When I plugged the power supply into the laptop, the noise jumped up to S9 again. The problem noise source was found!

I posted about my experience to my blog and to the HamRadioHelpGroup (http://groups.yahoo.com/group/HamRadioHelpGroup/). Mark, K5LXP, one of the gurus on HRHG, advised me to throw the main circuit breaker in order to determine if it was something inside the house generating the noise. Bob, K0NR, commented on my blog post, "I have found that flipping off circuit breakers in my house is a good first step to try and find a noise source. 
Usually ticks off the family, but what the heck :-)" Either of these methods will help you determine if a noise source is inside or outside of your house.

I'm still thinking that the way my antenna is positioned may have something to do with its picking up the noise generated by the power supply. I plan to play around with the positioning of the antenna once the snow melts and see if that makes any difference. Until then, I can work 20m with the power supply disconnected and run the laptop off the battery.

So, the next question you might ask is how does the antenna work? It seems to be putting out a very good signal. One evening last week, I worked several DX stations, including 6W/HA0NAR in Senegal. It's not a beam, but I'm pretty happy with it.

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When he's not worrying about his signal-to-noise ratio, Dan, KB6NU publishes the "No-Nonsense" series of amateur radio license study guides. The latest in this series is the No-Nonsense Extra Class License Study Guide. For more information, go to KB6NU.Com or e-mail cwgeek at kb6nu.com.

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