It can be conducted overwhelming the spectrum analyzer (although unlikely)
It could be large amplitude at an IF frequency (thus the "broadband
everywhere symptom)
Might try a portable tuned receiver and start searching for the origin.
- Robert -
On Thu, 26 Mar 1998, Scott Douglas wrote:
> Hello Group -
>
> Here's a problem for you all to think about and hopefully help solve.
>
> I have a room in the corner of my building where I perform EMI pre-scans.
> Occasionally throughout the day I have a major interference show up on my
> analyzer. It does not come from the EUT. This is broadband, from 30 MHz to
> 1 GHz, at levels up to 70 or 80 dBuv. It is not like a flat carrier but
> rather more like PWM driven motor noise. It lasts from 15 seconds to 1
> minute in duration. Then ambient returns to normal.
>
> We are a typical ITE manufacture. Our Genrad tester, wave solder, air
> compressors, motor generators, air conditioners, plumbing waste pumps do
> not appear to be the cause although none have been absolutely ruled out.
> The frequency and duration would seem to eliminate them however.
>
> We have swamp on one side, the interstate highway on another, fields on
> the third and the town on the last side. The only potential source I can
> find is a medical clinic about 350 meters away from us. They are the
> nearest building (the next being twice that far) and have an X-ray
> machine. Yesterday I went there at lunch and asked was the X-ray in use
> that day and they said yes but could not tell me a specific time that it
> was used.
>
> A software engineer here tells me that he has experienced radio problems
> in the parking lot outside my corner of the building. When he parks in a
> certain spot, his FM radio (the entire band) gets wiped out by a
> zhhzhhzhhh kind of noise. Move the car several feet any direction the
> problem goes away. This closely resembles what I see on the analyzer. Our
> analog guru suggests it is not the x-ray system as x-rays only last a few
> seconds. A one minute x-ray would burn you up he says.
>
> I never noticed this interference in another corner room of my building
> diagonally opposite my present location nor have I noticed the FM radio
> problem myself.
>
> Questions:
> 1. What are the possible sources of such interference?
> 2. Is the problem radiated or conducted? I suspect radiated as the signal
> goes away when you disconnect the antenna from the analyzer.
> 4. Why does this problem show up in only a small specific location on our
> property?
> 4. What are the potential solutions?
>
> I will be happy to answer any other questions you think of (if I can) and
> I look forward to the interesting comments I will receive from you all.
> Thanks in advance.
>
> Scott Douglas
> [email protected]
>
>
