Question about FCC part15.247

[katykaty03]

fcc part15.247

Dear all,
I have a product using DSSS. If should fulfill FCC part15.247. However, I can't understand one of statement below. would you pls help?
Part 15.247(2)
---quote--
(2) Systems using digital modulation techniques may operate in the 902 - 928 MHz,
2400 - 2483.5 MHz, and 5725 - 5850 MHz bands. The minimum 6 dB bandwidth shall be at least 500KHz"
kHz.
--quote--


I can't understand "The minimum 6 dB bandwidth shall be at least 500KHz"

According to this statement, the result is always "pass"? because the bandwidth can be infinite whatever the setting of RBW !? is that "the minimum" should be "maximum"?
I think the test should be as figure. am i right?

 

[biff44]

fcc part 15.247 dsss

Well, it is a spreading issue. The FCC wants to make sure that your code is efficient enough to spread the energy out far enough to make your transmission less likely to jam someone. For instance, if you had a lot of unmodulated carrier leakage, your 6 dB bandwidth would be very narrow, and you would fail the test. So you start your transmission, you look at the screen of the spectrum analyzer, you peak the marker on the highest (should be the center) go out to the 6 dB down points and make sure they are at least +/- 250 KHz from the channel center.

I do not know what to set the RBW and VBW to. Maybe you can look up the FCC test reports of some other similar systems on the FCC site. You need to know the FCC ID number on the bottom of the competitor's parts in order to look up the test reports. I bet you will find one of them that details exactly how to do that test.

 

[ricksidd]

6 db bandwidth fcc

The use of spread spectrum technology (FHSS, DSSS and OFDM included) in the License free ISM bands are meant to ensure coexistence of multiple systems. The above one is the FCC specification to get the desired environment.

-Sidd

 

[Azulykit]

500 khz fcc digital modulation

I concur with biff44 in his comments. It looks like the FCC is saying that your bandwidth be no more narrow than the 500 MHz (at -6 dB) points. They are trying to make sure that you spread wider than the 500 MHz.

 

[katykaty03]

6db bandwidth 500khz

I think so. but I am so confused of the word "minimum". I think they should remove this word

 

[arool]

fcc part 15.247

Hi,

You need minimum 500KHz 6dB BW (maximum can be infinite) for given DSSS signal.

Need to measure 6dB BW with Spectrum Analyzer setting of RBW = 100KHz (VBW = Auto).

Also maximum Transmit Power Spectral Density = 8dBm/3KHz (measured using Spectrum Analyzer with RBW = 3KHz & Sweep Time = Span / RBW in sec).

To create DSSS signal you can even use simple clock signal for spreading, provided you meet 6dB BW >=500KHz, PSD = 8dBm/3KHz & the maximum peak output power of the intentional radiator shall not exceed 1 watt (with antenna Gain upto = 6dBi which gives 36dBm EIRP).


Check : https://gullfoss2.fcc.gov/oetcf/eas/reports/ViewExhibitReport.cfm?mode=Exhibits&RequestTimeout=500&calledFromFrame=N&application_id=358082&fcc_id='SP2-RG4-J01'