Locating sprogs in the shack

[voltz]

Hi all,
I thought i would share something that could be useful to those wanting to locate unwanted noise / spikes / sprogs in the shack.
Its pretty simple and since there's been a few threads asking about it, I thought i would post this.

Its basically using your receiver as a signal meter, tuned to the unwanted spike for max signal. This is the signal you want to locate and hopefully reduce. Connect a length of coax, anything will do, 50 ohm like RG58. Make a loop in the end around 1 to 2 inches wide with the inner exposed and shorted to shield to form a basic pickup loop. Now its simply a case of moving around and 'sniffing' for the source of the spike. Watching the S meter and listening to the audio at the same time.

This method is quite effective and you should get to within an inch or two of the offending item. If the signal gets too high as you close in, simply use the attenuator. Once found, its a matter of fixing the issue. Usually, by better grounding, shielding or filtering.

As an example, i recently had a major problem on 40m. With two big spikes both around S9+10. It sounded like 50hz buzzing so i guessed it was either lighting or computer monitor related. After thinking about it, i came up with the sniffer loop idea. Sniffer loops are not new, but i'd never heard of it being used as a sprog locator before in the shack. Using the receiver as a one point spectrum analyser as it were. Anyway after walking around with the loop, i located the source to a KVM switch which was connected to 3 PCs. All the PCs have ferrite filters in line, so they are good enough but the KVM was going crazy. I located the fault within minutes using the loop and was able to determine the KVM was in fact faulty. I then fixed the KVM by adding a proper ground link internally which connects the earths of the monitors. That fixed it - and the spikes were 100% gone.. Joy, i can hear 40m again.

I hope this comes in handy, its cheap and easy to do.

[ConKbot]

Yep, simple loops are great for sniffing. I had a potted widget fail at work, and with a loop around it going to a spec-an, I was able to see various oscillators working or not working, see which dc-dc converters were operating, and in an hour or so have a pretty confident cause of failure.
The bnc to 5-way binding post adapters are pretty handy for making up a quick loop or dipole as needed for stuff like that.

[voltz]