[HCRA] KB6NU's Column for February 2013

[Larry Krainson]

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.

===================================================

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.

###