Thank you for that Jim,
As you well know ,transmitting data modes on 500 is not a simple mater
and takes a great deal of technical input to ensure the system is on
frequency , stable , liner and fit for purpose , and not causing
interference to the other two band users. reports of over modulation and
distortion detectable at range may be appreciated by the few, but are
in fact an allegation of criminal activity as defined in the 1949 post
and telegraph act , a fact that's perhaps not lost on the real pirates
of this world when the custom and excise where given durastriction
over the implementation of the act , transmitting out of band is
defined as operating out side the terms of your licence and are
therefore in breach of the act .
As for trailing data modes and yes , fully aware of the SS nature of
the mode , and very well it works too ...
we should be mindful of the reason 'we' are on 500 in the first place
and to the quite level headed approach of Ofcom ... sure SS is banned
in the usa and now after the second 'Concorde' moment is the Domino
data mode that also used SS .... after the arrl made good use of it
for disaster communication over such a long period ....
Of interest tonight was the low power qso between Gary and myself
using the Ros eme mode , with a power reduction from my station of
3 watts feeding the antenna via a 20 dB attenuator, 30 mW to the
antenna , which roughly requires 50 Watt to radiate 100 mW erp .. a
thither reduction of 500:1 ! This level produced 100 % copy over 30
miles to a similar Ae , the Ros 500/8 mode failed at a signal level
of approximately 10 dB higher ( I will check with Jose, to see if this
measurement is as expected)
73 - G ..
--------------------------------------------------
From: "James Moritz" <[email protected]>
Sent: Friday, April 30, 2010 8:41 PM
To: <[email protected]>
Subject: LF: Re: ROS s/ware
Dear Dave, LF Group,
>Their first suggested working frequency on 20m put it splattering
right over the IARU beacons on 14100, which it seems the developers had
never heard of.
"Splatter" usually refers to distortion products outside the signal
bandwidth of a signal, but these don't really occur with ROS and other
constant-amplitude, FSK, modes since there is only a single tone being
transmitted at any one time, and so nothing else to intermodulate with,
even
if the TX is highly non-linear. So this complaint is technically
nonsensical, although 14.1MHz obviously isn't a good choice of frequency!
What people seem to get excited about is that the transmission has a
bandwidth of 500Hz, or 2.2kHz - somewhat wider than some other modes, with
the objective of trading off increased bandwidth against achieving
increased
robustness. The theory is fine; finding out if this actually works and
offers any practical advantages is why we should be trying it out of
course.
The 500Hz bandwidth easily fits into the "digital" segment even of 500kHz,
so no problem there.
BTW, now getting about 95% copy of G4WGT/ 100% of G0NBD having a QSO in
ROS
500Hz / 16baud mode - the bandwidth and centre frequency is as
advertised -
see attachment. Might try transmitting later, but have some other problems
to sort out first...
Cheers, Jim Moritz
73 de M0BMU
|
