Ed, Good work. Thanks! you have answered a lot of questions, but get this:
The spectrum that you measured is not just a function of the emission from
the baggies, it is also a function of your antenna, which was cut for 300 MHz.
The fact that you still had a 35 dB signal to noise ratio at 1 GHz shows
that the emissions are powerful and broadband.
One of us needs to do it with a broadband antenna. I have been
pretty busy, but we have all the right equipment, a nice anechoic chamber
etc. Maybe this weekend. Plus, I dont have a boss that's going to yell at me
for fooling around in the lab. I OWN the lab. (yes, it IS nice!)
Regards,
Lou
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>From: [email protected]
>Date: Thu, 18 Mar 1999 14:59:33 -0800
>Subject: Spare Change
>To: EMC-PSTC <[email protected]>
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>
>The Coins-in-a-bag thread has been moving from anecdote to anecdote for the
past
>week or so. Let's take this to the next level---sloppy field testing!
>
>This morning, I procured two fresh, new 1 gallon size Baggies brand plastic
food
>storage bags, a single Baggies brand sandwich storage bag, and $3.06 (6
cents, 7
>nickels, 4 dimes and 9 quarters) in clean US currency.
>
>I cut a whip antenna to 25 cm length (banana/BNC adapter included),
yielding a 1/4
>wave antenna for roughly 300 MHz. I then used this whip as a monopole antenna
>connected first to my Tektronix TDS 640A oscilloscope (1 GHz real-time BW)
and then
>to my HP-8562A spectrum analyzer.
>
>I placed the coins into one of the 1 gallon bags, and inflated it with a
swooping
>motion through the air (my breath has high humidity). I held the bag only
by the
>neck, trapping the air and causing the bag walls to bulge, approximating a 10"
>diameter sphere. I then vigorously shook the bag, at about 12" in front of
the whip
>antenna, while observing the displays.
>
>++++++++++++++++++++++++++
>
>TEST RESULTS
>
>Oscilloscope, 5uS/div, 1 V/div
>
>Test 1: 2.46 Vpeak, with an exponential decay lasting over 45 microseconds
and a TC
>of about 25 microseconds. The risetime is about 136 nanoseconds. A view of the
>acquired waveform and an expanded risetime view is attached as Coins.zip.
>
>Test 2: 2.64 Vpeak, similar decays. This has an interesting double
discharge at the
>leading edge. An initial discharge triggers the scope, then another
discharge hits
>about 500 nanoseconds later. A view of the acquired waveform and an expanded
>risetime view is attached as Coins.zip.
>
>Note: It only takes a few shakes to get a decently high discharge.
>
>And now, on to the spectrum analyzer. Similar test distance and conditions.
Using a
>1 MHz resolution bandwidth, a 1 MHz video bandwidth, 0 Hz span width, 0 dB
of RF
>attenuation and peak hold trace.
>
>Test 3: 10 MHz
> 31 dBuV noise floor
> 59 dBuV transient noise peaks
>
>Test 4: 100 MHz
> 31 dBuV noise floor
> 62 dBuV transient noise peaks
>
>Test 5: 500 MHz
> 31 dBuV noise floor
> 70 dBuV transient noise peaks
>
>Test 6: 1 GHz
> 31 dBuV noise floor
> 66 dBuV transient noise peaks
>
>Test 7: 5 GHz
> 31 dBuV noise floor
> 50 dBuV transient noise peaks
>
>Test 8: 10 GHz
> 35 dBuV noise floor
> 40 dBuV transient noise peaks
>
>Test 9: 15 GHz
> 43 dBuV noise floor
> 47 dBuV transient noise peaks
>
>Test 10: 500 MHz
> 31 dBuV noise floor
> 70 dBuV transient noise peaks
> Note: I removed all coins except the 6 cents.
>
>Test 11: 500 MHz
> 31 dBuV noise floor
> 70 dBuV transient noise peaks
> Note: I removed all coins except the 7 nickels.
>
>Test 12: 500 MHz
> 31 dBuV noise floor
> 70 dBuV transient noise peaks
> Note: I removed all coins except the 9 quarters.
>
>Test 13: 500 MHz
> 31 dBuV noise floor
> 70 dBuV transient noise peaks
> Note: All coins back in the bag.
>
>Test 14: 500 MHz
> 31 dBuV noise floor
> 61 dBuV transient noise peaks
> Note: All coins back in the small sandwich size bag. (Maybe less
vigorous
>shaking.)
>
>Test 15: 1 GHz
> 31 dBuV noise floor
> 53 dBuV transient noise peaks
> Note: All coins back into the gallon bag. I exhaled into the bag
several
>times, causing visible condensation on coins and bag walls. The observed
transients
>were far fewer numerically, and of lower magnitude.
>
>
>What this seems to show is:
>
>1. There are measurable emissions present across the spectrum from 10 MHz
to 15 GHz.
>2. The emissions clearly stand out from the ambient noise level of an open
>industrial area.
>3. It is easy to create several volts into a high impedance load.
>4. The generated levels do not depend on having a mix of different coins.
>5. One type of coin works about as well as any other.
>6. High humidity within the bag inhibits noise generation.
>7. It's time for lunch.
>
>
>Regards,
>
>Ed
>
>
>--------------------------
>Ed Price
>[email protected]
>Electromagnetic Compatibility Lab
>Cubic Defense Systems
>San Diego, CA. USA
>619-505-2780
>Date: 03/18/1999
>Time: 14:59:35
>--------------------------
>
>Content-Type: APPLICATION/zip; name="Coins.zip"
>Content-Description: Coins.zip
>
>Attachment Converted: C:\NETEMP\Coins.zip
>
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