[RFI] Oscilloscope requirements for power line noise locating

[N1BUG]

Thanks for the thoughtful reply Frank.

I guess my problem is that I still don't know with certainty exactly 
what the "video out" on these CATV FSMs, level meters, or signal 
monitors really is. Is it the output of the AM detector, making it 
essentially baseband from 0 to 300 kHz or so? Or is it an IF output 
of some sort? Sorry if this seems dumb, but I just don't know what 
I'm dealing with. I read in one manual something that suggested the 
video out level tracked with the meter reading. That suggested to me 
that it may be somehow tied to the AGC, but what that means I'm not 
sure. Any type of technical information on those units seems to be a 
closely guarded secret. Maybe I'll have to buy one and reverse 
engineer it to find out.

I had 95% success this last summer using audio only (or audio plus 
signal strength meter) on my tracking tools, but felt like I was 
spending too much time making sure I had the noise(s) that were 
actually causing interference and not just unrelated (localized) 
noises I happened to stumble across during the hunt. Some of them 
sounded a lot like the source I was after but turned out not to be. 
A complicating factor was having so many sources that I could never 
hear just one at a time. I would like to try it with the ability to 
see "signatures" as I hunt. Perhaps it won't help.

Paul Kelley, N1BUG
RFI Committee chair,
Piscataquis Amateur Radio Club



On 12/30/2012 01:19 PM, Util.RFI.pro wrote:
> The capabilities of the scope are determined primarily by the
> frequency of the signal you want to observe. I use a scope only
> to observe the audio output of the built-in AM/FM radio in my
> work van. My ears are not able to distinguish the changes in
> volume that occur as I drive by sources I hear at 1710 kHz. The
> scope is an effective signal strength indicator. Virtually any
> o'scope will work if you are just looking at audio.
>
> If you want to observe the RF envelope, you will need more
> complex stuff to do that. I don't believe that's either necessary
> or worth the effort. The only time I want to observe an RF
> envelope is when I'm transmitting. In that case, I use the
> CleanRF signal tap system (http://www.cleanrf.com) which is fed
> to a basic scope to provide envelope and trapezoid images for
> distortion analysis. But I digress...
>
> I'm a firm believer in keeping things simple...very...very...very
> simple. All of the tools I use to chase RFI are designed for the
> purpose and have no fluff. The o'scope I use spends only a
> fraction of its time in my work van displaying the AM radio
> audio. Most of the time it's on the work bench doing more
> difficult jobs. As much as possible I try to buy and use tools
> that perform multiple tasks.
>
> If I can hear the source on any of my portable receivers that
> already have a signal strength indicator, the scope is
> unnecessary. I rarely have to compare the "signatures" of
> different sources. I can usually tell if I'm chasing the right
> source just by listening. Purists will poo-poo my claim but I
> hold up my 100% success rate as evidence that I'm doing something
> right.
>
> Essentially, you want to equip yourself with tools that give you
> the info you need to pinpoint the source. Simple is always better
> and easier to use. The frequency of the source you are chasing
> will determine the type and capability of the tool(s) you use.
>
> Good luck!
>
> 73,
>
> Frank N. Haas KB4T Utility RFI Investigator Florida
>
> Sent from somewhere in Frank's electronic universe
>