Jose,
I will be using 432.090 MHz because that is definitely legal for US
hams. I will be testing the effect of severe Doppler-induced fading and
flutter. We badly need a mode for 432 MHz that has good sensitivity and
can survive fast Doppler shifts, and I hope a FHSS mode like ROS is
going to do it. Will have a result around the last week of next month.
The hflink published ALE frequencies might be a good alternative for
others around the world, since ALE users should not notice the FHSS ROS
activity (according to the ROS documentation) and their soundings are
infrequent and of short duration, so they should cause minimal
interference to ROS activities. They are also already in the area for
wide bandwidth signals, I think.
On 20m, those frequencies appear to be 14100.5, 14109.0, and 14.112.0.
See http://hflink.com/channels/.
Keep in mind there are NO frequencies completely free of QRM except on
VHF and UHF, but some can be found on HF that have less opportunity for
interference than others, so the ALE frequencies might be a good place
to try. Of course, ALE users MUST, by US law, be sure the frequency is
clear before transmitting, and the same applies to ROS users. We all
have to share frequencies, since no frequencies are "owned" by anyone,
but are used on a first-come, first-served basis.
73 - Skip KH6TY
jose alberto nieto ros wrote:
Please, give a frequency alternative to 14.101
------------------------------------------------------------------------
*De:* KH6TY <kh...@comcast.net>
*Para:* digitalradio@yahoogroups.com
*Enviado:* lun,22 febrero, 2010 22:39
*Asunto:* Re: [digitalradio] ROS Advantage?
That is good, Dave, except for receivers that distort heavily when the
AGC is disabled. If you just use manual gain control, and reduce the
gain for strong signals, the effect is the same, only manual. You will
lose the weak station because you have reduced the gain and the
sensitivity. The only way to still copy your weak station and get rid
of the strong one is to filter at IF frequencies, which is what fixed
filters or passband tuning does. IF DSP will do it also these days,
but it needs to be at IF frequencies and not audio frequencies if you
are going to prevent AGC capture by an unwanted stronger signal.
14.101 is adjacent to Pactor activity and if you monitor it long
enough, you will see the Pactor station stop decoding of ROS. However,
most of the automatic Pactor activity we hear is in the US, so the
problem may not be as big on the other side of the big pond.
73 - Skip KH6TY
Dave Ackrill wrote:
KH6TY wrote:
> 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.
>
As with many other digital modes, I've been using it with AGC
switched off.
Dave (G0DJA)
