The FCC disallows amateur spread spectrum communications below 220MHz. At the moment the relatively new digital mode, ROS, is considered, by some, to be spread spectrum. So this mode is getting little to no use in the US.

It doesn't seem much different than other tone digital modes though, and never claims a bandwidth larger than phone.

What is the definition of "spread spectrum" according to the FCC?

In what ways could ROS be considered spread spectrum?

What about ROS suggests that it's not spread spectrum?

The only page on ROS I've been able to find, http://rosmodem.wordpress.com/ , doesn't seem to have an in-depth explanation of what the mode is and does.

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    $\begingroup$ Can you site your source for your assertion that the FCC disallows this mode? When I look for one, I find a bunch of hearsay, and then the conversations end when someone cites a source that says it is allowed. $\endgroup$ Dec 18, 2013 at 18:18
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    $\begingroup$ The FCC does not disallow this mode. Some statements from the FCC could be interpreted as allowing his mode, but they seem to keep their distance from a solid affirmation. He closest I've seen is arrl.org/news/fcc-reaffirms-statement-on-ros where the ARRL appears to neither agree nor disagree with the statement that it is spread spectrum. Still, I've edited the question slightly, and the title and three questions posed are still valid without asking for the FCC or ARRL opinion on the legality of the mode. $\endgroup$
    – Adam Davis
    Dec 18, 2013 at 22:38
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    $\begingroup$ I'm studying for Extra now and the study material states that spread spectrum transmissions are allowed above 222Mhz, with a maximum output of 10W. I don't think he's asserting that the FCC disallows the mode, but they do disallow spread spectrum transmissions below 222Mhz. (my comment came between the OP edit and the OP comment above) $\endgroup$
    – rhaig
    Dec 18, 2013 at 22:40
  • $\begingroup$ Worth noting here that as of 2015, there's very little limitation left in the US on spread spectrum. Mostly just record keeping, and it can't be used to obscure the meaning of a transmission. $\endgroup$ May 19, 2018 at 13:23

5 Answers 5


Some consider ROS Modem Spread Spectrum because of statements on the author's website call it: Frequency Hopping Spread Spectrum. It's worth noting that the author is European and in Europe, spread spectrum is allow on the HF bands. Undoubtedly, part of this is marketing. Describing a new mode as Spread Spectrum gives it a more techy feel and spread spectrum is something that came out of the military, further increasing the cool factor.

The FCC's definition of Spread Spectrum:

Spread spectrum techniques are emissions that use bandwidth-expansion modulation >techniques to intentionally spread the information transmitted over a wide bandwidth. At any frequency in the frequency segment or bandwidth the SS emission occupies, either the spectral power density of the transmitted signal is reduced to a comparatively low level or the duration of the transmitted signal is very brief.

Source: WT Docket No. 10-62 RM-11325 REPORT AND ORDER
Adopted: February 22, 2011 Released: March 4, 2011

The FCC's ruling on the matter simply reaffirms what SS is and where it's allowed. They didn't rule that ROS is SS or not. This probably has more to do with conflicting information and lack of clear guidance. The author calls it SS, but examining the actual protocol reveals that it's not. It's not very popular in the US (largely due to this conflict) and so the FCC didn't have the number of opinions it usually gets when considering a ruling.

To lump the remaining two questions together:

It's not spread spectrum; it doesn’t hop the VFO frequency. It is simply FSKs according to a programmable algorithm, and it meets the infamous 1kHz shift 300 baud rule (FCC §97.307(f)3):

Only a RTTY or data emission using a specified digital code listed in §97.309(a) of this part may be transmitted. The symbol rate must not exceed 300 bauds, or for frequency-shift keying, the frequency shift between mark and space must not exceed 1 kHz.

Digging into it further, ROS uses multiple tones over either a 2kHz or 500Hz bandwidth, (the frequencies for each mode/bandwidth are hard coded in the software). According to the rather thin documentation, ROS has three main speeds, 16 baud, 8 baud and 4 baud. There are some special modes, such as 7bd/100Hz for 136 and 502kHz (and 80m for some reason), plus an ‘EME’ mode for use on 2m and some other bands, for weak signal work as it has, in theory at least, the capability to decode signals that have a Signal to Noise Ratio (SNR) of -35dB, which is even lower than WSPR.


FYI, several years ago I emailed a person at the FCC about this question. I forgot her name but she was the person that replaced Riley Hollinsworth. She replied and said clearly to me that she considered it illegal. She did not say that the FCC considered it SS and officially declared it illegal, she simply said that the author of ROS said it was SS, and therfore she was taking him at his word, and therefor it is illegal. I think she is wrong, but you will really have to convince me this mode is SO GOOD that the benefits of using it outweigh the risks.

  • $\begingroup$ This would be a much more compelling answer if you could provide some references. $\endgroup$ Jan 5, 2015 at 19:51

Following on from the difficult question
When is a door not a door ? ....When its a JAR

All Ham data modes that pass via SSB tx audio channel are grouped under the heading of J2D..

How the audio is generated or decoded is of no interest or than is shares the same generic title 'Spread Spectrum' which , now covers 'all aspects' of data processing of this type , the FCC classed the test modes as J2D , just the same as Olivia , MFSK , JT65 WSPR, pactor or any other audio based system

Nonsense based round secrecy issues are flawed , as the same program's are available to all stations, try decoding Olivia , without the correct software , not possible , it therefore must be a secret code , use any of the available packages and it decodes , therefore its not a secret code...

So when is a mode secret and SS ?

Ans Not when everyone has the same software and it passes via SSB sound channel


So can we all get back to qrp dxing on the same qrg again ?

To quote the part-97

The FCC issued STA to test Spread Spectrum , for Ros and Chip64

If you look up the FCC website you'll see the interesting thing about the STA is the Emission Designator classification that was used - J2D

Modes which that have that designation are by the FCC's own definition NOT "SS emissions". J2D modes are already permitted on HF.

This sounds like people have been doing what we have done, taken SS to mean an abbreviation for Spread Spectrum when in fact the FCC's definitions are clear that the two are not the same. J2D is not SS (SS emissions would be specified as JXX) J2D is covered under the Section 97.3 Federal definition for Data.

As you know the FCC regulates Amateur Radio transmissions by what might be called "Content Type". The definitions for CW, Voice, Image, Data, SS etc are all in Section 97.3 at http://www.gpo.gov/fdsys/pkg/CFR-2011-title47-vol5/xml/CFR-2011-title47-vol5-sec97-3.xml

The Data definition says: (2) Data. Telemetry, telecommand and computer communications emissions having (i) designators with A, C, D, F, G, H, J or R as the first symbol, 1 as the second symbol, and D as the third symbol; (ii) emission J2D; and (iii) emissions A1C, F1C, F2C, J2C, and J3C having an occupied bandwidth of 500 Hz or less when transmitted on an amateur service frequency below 30 MHz. Only a digital code of a type specifically authorized in this part may be transmitted.

  • $\begingroup$ This answer would be much better if you had better, more specific and useful links (like, to this STA that you mention), and edited it to be shorter and to the point. $\endgroup$ Aug 23, 2014 at 20:27

If it fits into SSB bandwidth it is not spread spectrum, and it does fit.


Your lucky anyone is actually posting on the issue , links etc below

J2D is audio via sound channel , the SS the part 97 is directed at is base band [base band = ultra wide band ]and even defines the PN number generators taps to ensure commonality..

1 Spread Spectrum in a modern sense covers now as a group heading all aspects of data processing and bandwidth is a design choice , just as Olivia has various b/w options , still uses DSSS Direct Sequence Spread Spectrum , referring to the Pseudo random number generator used to add redundancy to the data , nothing wrong with that , been in use for 10/15 years now the world over .

2 ROS uses modern techniques , that utilise Spread Spectrum techniques within audio bandwidths, offering the next generation , low s/n high data rate and multi qso access . DSSS and CDMA , CDMA as in mobile phones allows multiple simultaneous access to the same qrg , hence the number of qso's showing on 14.103 , providing the MOST EFFICIENT USE OF BANDWIDTH of and HAm data mode , A topic that is dear to the congested band uses in the US ? the answer is already in use WW

3 The SS trials ran with no problems , however due to external off shore usa , influences , the end game was never played out and the situation remains frozen in time .. if ever the subject is raised , the flow of nonsense reaches levels that even broke the yahoo data group , its owner posting 'Thanks for all the fish' as a last gasp for reality , linked to the number 42



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