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 KH6TY
Howard 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 Hams
Bonnie'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 Hams
Given 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
