[RFI] False Alarm

Dan Zimmerman N3OX n3ox at n3ox.net
Sat Sep 27 16:59:00 EDT 2008

I was out trying to locate some arcing on my 20/17m relay switched Moxon,
which became noisy on 17m recently.

I built W1TRC's ultrasound listening device about a year ago to try to help
me track down noise around here, and I took it out to the backyard to see if
I could hear some arcs and determine if I had to take the antenna down or if
I just had replace some ground-level wiring or such, and I noticed a
strange, loud noise coming from my shed's rolling door.  I determined it was
a reflection, and followed the path to a spot near where my cables all enter
the house, where I found it VERY, VERY loud.

It was sort of like this:


the "Braaps" had a very square-wave character to them.

So I look around, all I can see are wires... I figure I never remember
hearing anything on the radio with that character, so I go back to walking
around to different points in the yard listening to the Moxon.

I get over near my tomato patch and all of a sudden




I search around and find that yes, in fact, my tomatoes are emitting even
louder ultrasound than my wire entry area was.  Now I'm really stumped, I go
upstairs in the house and point around, thinking maybe the neighbors have
something going and it just *seems* like it's coming from my tomato patch,
but no, I get up there and find I'm pointing at the tomatoes.

I put on a tinfoil hat and told my wife that the tomatoes were emitting
ultrasound; her response was "we've got a backyard full of wires, it's not
the tomatoes"  ... ;-)

I'm pretty sure she's right but I just have to go and check *one more time,*
and that's when I found it.

A grasshopper.

Sitting on a tomato leaf.

A structure on his back vibrating in time with the noise.

I've got GrasshoppeRFI.

- - - - - - -

Anyway, the ultrasound thing works ;-)  Build one, and when you're not using
it you can hand it to your kids and let them have a blast finding ultrasound
bugs in the backyard... and you can have them find other noises too ;-)


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