John
--- In digitalradio@yahoogroups.com
<mailto:digitalradio%40yahoogroups.com>, Tony <d...@...> wrote:
>
> John,
>
> The first thing that comes to mind is whether there were any ground
wave
> signals mixing with sky waves during your field tests? It's been shown
> that NVIS throughput can fail when the sky wave echoes interact with
> ground waves. The sky waves take more time to arrive at the receiver so
> you can imagine what the difference in timing does to copy when the two
> signals interact. This is what the NVIS simulations were based on; two
> channels, one with no delay (simulated ground wave) and the other
with a
> 7 ms delay (simulated NVIS sky wave).
>
> January's path tests showed that PSK-R appeared to be less robust than
> BPSK under NVIS simulation while the white noise tests clearly showed
> PSK-R the winner in terms of sensitivity. Your field tests seem to
> reveal the same results in terms of which modes have the edge in
> sensitivity, but not necessarily the edge in terms of dealing with
> multi-path timing delays. I could be wrong though and there may have
> been strong evidence of ground wave interaction? It can be difficult to
> tell; some paths are more obvious than others. Hellschreiber is the
only
> mode I know of that can visually indicate this sort of thing, but
that's
> not an option with PSKMail.
>
> Hope to hear from you soon John.
>
> Tony -K2MO
>
>
>
>
>
> n 4/1/2010 9:45 AM, vk2eta wrote:
> >
> > To Tony (K2MO) in particular, but not exclusively:
> >
> > Following your simulation results on these modes in January I have
> > done a few tests in the field and I have to say that I don't
> > understand the results.
> >
> > Please note that I am not trying to make a point, but to understand
> > why the theory does not seem to match the practical side.
> >
> > My tests simply revolve around examining the bahaviour of the Pskmail
> > server adapting speed to the conditions.
> >
> > We have in the latest version a table of modes that the server can
use
> > by shifting up and down, one mode at a time. It does so by relying on
> > the s/n report gathered from Fldigi and the number of repeats due to
> > damaged ARQ frames.
> >
> > The list is arranged in an empirical order of speed vs robustness and
> > is the following for regions 2 and 3:
> >
> > THOR8 MFSK16 THOR22 MFSK32 PSK250R PSK500R PSK500
> >
> > The MFSK/IFSK family of modes are normally the modes of choice for
NVIS.
> >
> > This week I did some tests at 95 miles in a strait line from my
server
> > on 40 and 80M between about 1PM to 2PM local time so obviously in
NVIS
> > conditions.
> >
> > What I noticed every time I would connect in MFSK16, the server would
> > progressively shift the TX mode up into the PSKR modes, up to
PSK500R,
> > but never to PSK500.
> >
> > I also noticed that there would be no fallback from PSK250R to MFSK32
> > after a shift up from MFSK32.
> >
> > So my interpretion is the following:
> >
> > If the PSKR modes had a weakness in NVIS conditions, I would see the
> > server moving continuously between MFSK32 and PSK250R: good reception
> > in MFSK32, speed up to PSK250R, poor reception, return to MFSK32,
etc...
> >
> > Also since it did not go up pass PSK500R to PSK500 it indicates that
> > in these particular cases the PSK500R modes was starting to show
signs
> > of limitations and the server calculated that there was not enough
s/n
> > margin to shift the speed up.
> >
> > Selective fading is very visible especially on the PSK500R mode of
course.
> >
> > So my question is: in the simulation you performed, are there
> > parameters that maybe would need to be looked at to explain why these
> > modes seem to behave well in these conditions or are there other
> > variables to consider?
> >
> > Also trying to get a more formal comparison, how would you design
some
> > practical tests that minimize the effects of variation in propagation
> > in the field?
> >
> > On this point I was thinking of sending a set text in different modes
> > and repeating the test several times, interleaving the modes so that
> > in average it would be unlikely to be just propagation. Mode1, Mode2,
> > Mode3, Mode4 then again Mode1, Mode2, Mode3 etc... repeated say 5
> > times. Then taking the average result for comparison.
> >
> > Best regards,
> >
> > John (VK2ETA)
> >
> > --- In digitalradio@yahoogroups.com
<mailto:digitalradio%40yahoogroups.com>
> > <mailto:digitalradio%40yahoogroups.com>, "vk2eta" <vk2eta@> wrote:
> > >
> > > Hi Tony,
> > >
> > > Thank you for the simulation results. I will report any field
> > results for PSKR modes in NVIS conditions.
> > >
> > > Regards,
> > >
> > > John
> > >
> >
> >
> >
> >
> > __________ Information from ESET NOD32 Antivirus, version of virus
> > signature database 4993 (20100401) __________
> >
> > The message was checked by ESET NOD32 Antivirus.
> >
> > http://www.eset.com <http://www.eset.com>
>
__________ Information from ESET NOD32 Antivirus, version of virus
signature database 4994 (20100402) __________
The message was checked by ESET NOD32 Antivirus.
http://www.eset.com
