[RFI] How very interesting...

[Larry Benko]

Probably a little of both Dave.  I could tell you how cool it is to 
drive around watching the spectrum but you wouldn't fully appreciate it 
until you actually did it.  This happens too often in life for most of us.

You gain a lot more if you are the passenger and can focus on the 
display.  If you lived closer to me (Colorado) I would have taken you 
for a drive a long time ago.

73,

Larry W0QE


On 8/25/2016 9:09 AM, Dave Cole wrote:
> On Thu, 2016-08-25 at 08:16 -0600, Larry Benko wrote:
>
>> No Sh-t Sherlock!!  This was a comment a guy I used to work with would
>> say when someone touted something that was blatantly obvious!
> Not sure how to take the above...  As humor or sarcasm...
>
>> I have also felt this way for a few years.  I built an active hi-Z
>> preamp on a magnetic base with a 4' whip and drive around with a
>> Perseus receiver.  Looking at a wide chunk of spectrum was the only
>> way W0IVJ and myself were able to show Century Link how much VDSL2
>> radiates (an SDRPlay ws used for the VDSL2 stuff).  We drove up a
>> street with a Century Link engineer in the back seat of the car and
>> pointed out exactly which houses had DSL service. Without getting out
>> of the car we were correct about 80% of the time and sometimes were
>> off by one house.
> Rather than look at things in real-time I wanted to be able to see them
> over long time periods and frequencies, so I could characterize an area
> for RFI...
>
> A most curious thing has developed, if you look at the graph at around
> 6.900 MHz., at the bottom, you see an interesting haze forming up, that
> is some sort of broadband RFI, (looks to be around 500 KHz wide, and
> getting wider with time.
>
> It is now very wide and very strong, (I will update graph in a bit).  I
> wonder what it is...  It's not in the ham bands, so I really don't
> care about it, but it is most interesting...
>
>> Driving through a commercial or industrial area is especially
>> interesting as the noise floor varies easily 1000x (30dB) within a
>> several hundred feet.
> I have a working GPS connected to the computer, and am going to be
> taking wide-band signal levels and GPS locations, then logging that
> data.  I will then graph the data on a Google map...  I want a detailed
> heatmap of RFI for my area.
>
> I had a prototype working last year, but have not followed up on it, I
> did have success in creating a crude heatmap.  It did make it simple to
> follow which power lines were carrying RFI around the area, they clearly
> stood out from the background.  In fact, it was like having a big huge
> arrow pointing to the RFI source...  I think I could locate RFI to the
> house now, using an omni antenna pretty simply by just looking at the
> resultant map.
>
>> Hope others will realize that this is an extremely good way to track
>> down RFI while being stealthy.  A non-directional antenna will never
>> replace a directional one but is an additional tool.
> That is why I mentioned it here...  Next for me will be to follow what
> you are doing in real-time, using a loop to watch a set of signals drop
> as I rotate it, as opposed to looking at an S meter.  Seeing a
> constellation of signals drop together as a loop is rotated, really does
> sort of connect them...  They look the same, they drop the same, and
> then I should be able to follow them via the heat map.
>
> This may be a very useful tool to gauge overall RFI in an area for the
> FCC study, once calibrated.
>
> I now have a winter project!
>
> -- 
> 73's, and thanks,
> Dave (NK7Z)
> For software/hardware reviews see:
> http://www.nk7z.net