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
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