Hi Jose,Of course we start that way (using a SSB filter), but then a Pactor station will come on, cover the upper fourth of the ROS signal, and decoding becomes garbage until it leaves. With a more narrow mode, the Pactor station can just be filtered out at IF frequencies and not affect either the AGC or the decoding of something like MFSK16 or Olivia 16-500, as long as those signals are sufficiently away from the Pactor signal (even if they are still within the bandwidth of a ROS signal).
In the case of CW stations, during the contest, they just appeared in the SSB filter bandwidth, and therefore among the ROS tones, and some of those also stopped decoding until they left.
Let's say a MT63-500 signal appears at 2000 Hz tone frequency (i.e. covering from 2000 to 2500 Hz) at the same signal strength as the ROS signal. Will ROS stop decoding? If a MT-63-1000 signal appears at 1500 Hz tone frequency, will ROS stop decoding? If this happens and there is a more narrowband signal like MFSK16, for instance, covering from 500 Hz to 1000 Hz, the MFSK16 signal can coexist with the MT63 signal unless the MT63 signal has captured the AGC and cutting the gain. If it has, then passband tuning can cut out the MT63 signal, leaving only the MFSK16 signal undisturbed and decoding. In other words, there is less chance for an interfering signal to partially or completely cover a more narrow signal that there is a much wider one, unless the wider one can still decode with half or 25% of its tones covered up. The question posed is how well ROS can handle QRM, and that is what I tried to see.
If ROS can withstand half of its bandwidth covered with an interfering signal and still decode properly then I cannot explain what I saw, but decoding definitely stopped or changed to garbage when the Pactor signal came on.
73 - Skip KH6TY jose alberto nieto ros wrote:
Hi, You must not filter anything in the transceiver. You must pass all bandwith in your receiver because filter are doing by the PC better than you transceiver.------------------------------------------------------------------------ *De:* KH6TY <kh...@comcast.net> *Para:* digitalradio@yahoogroups.com *Enviado:* lun,22 febrero, 2010 18:31 *Asunto:* Re: [digitalradio] ROS Advantage?Howard, After monitoring 14.101 continuously for two days, I find the following:1. CW signals (of narrow width, of course) during this past weekend contest often disrupted decoding, and it looks like it was not desensitization due to AGC capture, as the ROS signals on the waterfall did not appear any weaker.2. Pactor signals of 500 Hz width, outside the ROS signal, that capture the AGC, do desensitize the receiver and cause loss of decoding, as expected. Passband tuning takes care of that problem however.3. Pactor signals which have the same degree of darkness as the ROS carriers, and occur within the upper third of the ROS signal, cause loss of decoding, and it is not possible to fix the problem with passband tuning, as trying to do that appears to take away enough of the ROS signal that the degree of frequency hopping used is insufficient to overcome. Receiver is the IC-746Pro.4. If more than one ROS signal is present on the frequency, ROS will decode one of them - apparently the strongest one - and the weaker one is blanked out until the stronger one goes away and the the weaker one is decoded.5. Compared to Olivia 16-500, for example, the width of the ROS signal seems to be a disadvantage as far as handling QRM is concerned. Five Olivia 16-500 signals will fit in the same space as one ROS signal needs, so QRM, covering the top 40% of the ROS signal, for example, would probably not disrupt any of three Olivia signals in the bottom 60% of the ROS signal bandwidth.In other words, the wide bandwidth required for ROS to work is a disadvantage because IF filtering cannot remove narrower band QRM signals that fall within the area of the ROS signal, but IF filtering can remove the same QRM from the passband that has been narrowed to accept only an Olivia signal. A much wider expansion or spectrum spread might reduce the probability of decoding disruption, but that also makes the signal wider still and more susceptible to additional QRM. The advantage of FHSS appears to be more in favor of making it hard to copy a traditional SS signal unless the code is available, than QRM survival, but on crowded ham bands, it looks like a sensitive mode like Olivia or MFSK16, because it is more narrow, and filters can be tighter, stands a better chance of surviving QRM than the ROS signal which is exposed to more possibilities of QRM due to its comparatively greater width.The mode sure is fun to use and it is too bad it does not appear to be as QRM resistant as hoped, at least according to my observations.Another problem is finding a frequency space wide enough to accommodate several ROS signals at once so there is no cross-interference. It is much easier to find space for five Olivia or MFSK16 signals than for even two ROS signals.These are only my personal observations and opinions. Others may find differently.I still plan to find out if ROS can withstand the extreme Doppler shift and flutter on UHF which just tears up even moderately strong SSB phone signals. Olivia appears to be the best alternative mode to SSB phone we have found so far and sometimes provides slightly better copy than SSB phone, but for very weak signals, CW still works the best. Even though the note is very rough sounding, as in Aurora communications, CW can still be copied by ear as it modulates the background noise.73 - Skip KH6TYHoward Brown wrote:Aside from the legal aspect, does anyone have an opinion as to whether the limited hopping (within the 3khz that it hops) helps the robustness of the waveform? If it makes a tremendous difference, maybe we should all work to get it accepted.Howard K5HB ------------------------------------------------------------------------ *From:* J. Moen <j...@jwmoen.com> *To:* digitalradio@ yahoogroups. com *Sent:* Sun, February 21, 2010 9:13:50 PM*Subject:* Re: [digitalradio] FCC Technology Jail: ROS Dead on HF for USA HamsBonnie's note describes the US/FCC regulations issues regarding ROS and SS really well. It's the best description of the US problem I've seen on this reflector. After reading what seems like hundreds of notes, I now agree that if ROS uses FHSS techniques, as its author says it does (and none of us has seen the code), then even though it 1) uses less 3 kHz bandwidth, 2) does not appear to do any more harm than a SSB signal and 3) is similar to other FSK modes, it is not legal in FCC jurisdictions. As Bonnie points out, ROS "doesn't hop the VFO frequency," but within the 2.5 bandwidth, it technically is SS. This would be true if ROS used 300 Hz bandwidth instead of 2.5 kHz, but hopped about using FHSS within the 300 Hz bandwidth. So I have to agree the FCC regs are not well written in this case. Regarding the corollary issue of US/FCC regulations focused on content instead of bandwidth, I'm not competent to comment. Jim - K6JM----- Original Message ----- *From:* expeditionradio <mailto:expeditionra...@yahoo.com> *To:* digitalradio@ yahoogroups. com <mailto:digitalradio@yahoogroups.com> *Sent:* Sunday, February 21, 2010 5:09 PM *Subject:* [digitalradio] FCC Technology Jail: ROS Dead on HF for USA HamsGiven the fact that ROS Modem has been advertised as Frequency Hopping Spread Spectrum (FHSS), it may be quite difficult for USA amateur radio operators to obtain a positive interpretation of rules by FCC to allow use of ROS on HF without some type of experimental license or waiver. Otherwise, hams will need an amendment of FCC rules to use it in USA. Sadly, this may lead to the early death of ROS among USA hams. If ROS Modem had simply provided the technical specifications of the emission, and not called it "Spread Spectrum", there would have been a chance for it to be easily adopted by Ham Radio operators in USA. But, the ROS modem designer is rightfully proud of the design, and he lives in a country that is not bound by FCC rules, and probably had little or no knowledge of how his advertising might prevent thousands of hams from using it in USA. But, as they say, "You cannot un-ring a bell, once it has been rung". ROS signal can be viewed as a type of FSK, similar to various other types of n-ary-FSK presently in widespread use by USA hams. The specific algorithms for signal process and format could simply have been documented without calling it Frequency Hopping Spread Spectrum (FHSS). Since it is a narrowband signal (using the FCC and ITU definitions of narrowband emission = less than 3kHz) within the width of an SSB passband, it does not fit the traditional FHSS description as a conventional wideband technique. It probably would not have been viewed as FHSS under the spirit and intention of the FCC rules. It doesn't hop the VFO frequency. It simply FSKs according to a programmable algorithm, and it meets the infamous 1kHz shift 300 baud rule. http://www.arrl. org/FandES/ field/regulation s/news/part97/ d-305.html# 307f3 <http://www.arrl.org/FandES/field/regulations/news/part97/d-305.html#307f3> This is a typical example of how outdated the present FCC rules are, keeping USA hams in "TECHNOLOGY JAIL" while the rest of the world's hams move forward with digital technology. It should come as no surprise that most of the new ham radio digital modes are not being developed in USA! But, for a moment, let's put aside the issue of current FCC "prohibition" against Spread Spectrum and/or Frequency Hopping Spread Spectrum, and how it relates to ROS mode. Let's look at "bandwidth". There is the other issue of "bandwidth" that some misguided USA hams have brought up here and in other forums related to ROS. Some superstitious hams seem to erroneously think that there is an over-reaching "bandwidth limit" in the FCC rules for data/text modes on HF that might indicate what part of the ham band to operate it or not operate it. FACT: "There is currently no finite bandwidth limit on HF data/text emission in USA ham bands, except for the sub-band and band edges." FACT: "FCC data/text HF rules are still mainly based on "content" of the emission, not bandwidth." New SDR radios have the potential to transmit and receive wider bandwidths than the traditional 3kHz SSB passband. We will see a lot more development in this area of technology in the future, and a lot more gray areas of 20th century FCC rules that inhibit innovation and progress for ham radio HF digital technology in the 21st century. Several years ago, there was a proposal to FCC to provide regulation by bandwidth rather than content. However, it failed to be adopted, and ARRL's petition to limit bandwidth was withdrawn http://www.arrl. org/news/ stories/2007/ 04/27/101/ ?nc=1 <http://www.arrl.org/news/stories/2007/04/27/101/?nc=1> Thus, USA hams will continue to be in Technology Jail without access to many new modes in the foreseeable future :( Best Wishes, Bonnie Crystal KQ6XA
