[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

RE: Mobile, FM and GEO... why ?



> I'm still wondering why amateurs want to have an FM mobile 
> connection via a 
> GEO satellite.
> From experience with my portable satellite station I can tell 
> you that even 
> the LEO's are not really easy to work, and definatly not in an city.

You obviously never worked SO-35 then...  A Mode B LEO is very easy to work.
I used to work it from trams (streetcars) and trains on a regular basis.
And as for pedestrian mobile, I used to walk around and work SO-35 as easily
as talking on a mobile phone.  For more info, refer
http://vkradio.com/sat.html.  Actually, I had much better results on later
tram/train ops, because I'd worked out the noisy areas of the tram to avoid,
so overcame the downlink issues I referred to in the October 2 1999 entry.
Came close to repeating the same feat with a pair of HTs and UO-14, but the
right opportunity to go all out never presented itself.  Mode B is
definitely WAY better than J for LEO FM accessibility.

> 
> The station is a back-pack station with 20W on 2m and 10W on 
> 70cm and an 
> self-made (arrow alike) 2m/70cm handheld antenna. On my 
> web-page you can see 
> that it has been used through whole Europe :-)

Hmm, with that kind of setup down here, you'd just about blow the bird out
of the sky!  I used to be one of the stronger stations on SO-35 with
probably around 10-20W EIRP.  3.5W into my homebrew antenna (details on the
same site as above).

> Now back to the GEO. The downlink may be compairable with the 
> AO40 or Ao10 
> downlinks. Ao10 has abt 50W PEP and Ao40 on 13cm has 50W too. 

But AO-40 and AO-10 don't have downlinks dedicated to a _single_ station.
They have to be shared among many (hence the "Keep 10 dB below the MB"
instructions), and the more stations you get, the higher the peak to average
ratio on the transponder (regardless of whether the uplinks are using FM or
SSB), which drives the power per station down even more.

As for tests, I did my own interesting tests via FO-20 and FO-29 a long time
ago.  Keyed the 2m HT (1.5W) and got a very good carrier back.  If I dropped
the 2m uplink to 0.25W, the return signal was noisy but readable.  UO-14
like performance from a bird nearly twice as high.  

> So how you want to do this with a mobile station, having less 
> power, less 
> antenna gain and lot of interference and reflections of 
> nearby buildings. On 

We can eliminate the urban problem easily.  Remember, this is more of a
"utility bird" than a "DX bird".  Urban stations have no need to directly
uplink into the bird - there are a number of systems that will allow linking
to it.  Keep the uplink for stations in remote areas (there's not too many
repeaters accessible from the Simpson Desert or most other parts of inland
Australia).  Urban stations can dial it up via IRLP, Echolink, etc on their
VHF/UHF repeater.

> the other hand it is also a huge problem with operation. 
> Local FM repeaters 
> are a good example of it (in my country I notice this often) that 
> none-mobile stations occupy the relais and use it as chat box, while 
> mobile/portable stations have to wait till they finally 
> switch of the ptt 
> switch after hearing a long long story.
> 
> What about some kind of international round, where people all 
> around the 
> world can log in and talk about their experiments. Then the 
> GEO-sat could be 
> switched on at a particulair time and after the round it can 
> be switched of. 
> To avoid time problems, their can be done E.g a round when Europe has 
> evening and later a round when USA has evening (when sat is 
> between EU and 
> USA).
> Only a few round-leaders are needed in the several continents 
> that control 
> the round and keep the topic at a good level.
> 
> Just an idea to make the crowdy FM more interresting, and to let it 
> contribute to the whole world.

I like the idea, and with a bit of work, and some technology, you could make
it accessible to a lot of people.  Where it would really shine is in more
sparsely populated areas of the globe (like over here), including the
oceans.  

Now, (pipe dream mode on), if 3 such launch opportunities came along, it
would be nice to have 3 such birds following each other around the globe,
120 degrees apart, providing another means to keep hams in remote places in
touch with each other.  With the resulting 24x7 access, they would be
potentially useful for emergency communications in remote areas. One can
only dream..

This correspondence is for the named person's use only. It may contain
confidential or legally privileged information or both. No confidentiality
or privilege is waived or lost by any mistransmission. If you receive this
correspondence in error, please immediately delete it from your system and
notify the sender. You must not disclose, copy or rely on any part of this
correspondence if you are not the intended recipient.

Any opinions expressed in this message are those of the individual sender.

----
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
Not an AMSAT member? Join now to support the amateur satellite program!
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home