Ed, Conclusions:
1. At last! Some real data! 2. You must not have enough to do! Jim Dr. Jim Knighten e-mail: [email protected] <mailto:[email protected]> Senior Consulting Engineer NCR 17095 Via del Campo San Diego, CA 92127 http://www.ncr.com <http://www.ncr.com> Tel: 619-485-2537 Fax: 619-485-3788 -----Original Message----- From: [email protected] [SMTP:[email protected]] Sent: Thursday, March 18, 1999 3:00 PM To: EMC-PSTC Subject: Spare Change 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 -------------------------- << File: Coins.zip >> --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
