[serval-project-dev] Serval Mesh and ham radio
W5SVL
w5svl at aol.com
Tue Oct 30 15:03:29 PDT 2012
A quick internet search shows the Australian Advanced and Standard ham
licenses are very similar to the US licenses. There is no longer a
requirement to learn morse code. The US hams are allowed use of
the 902-928 Mhz frequencies, but I did not see these frequencies allocated
to Australian hams. The Australian Standard license allows hams to use
the 2.4-2.45 Ghz frequencies which would cover the first 6 wifi
channels. Ham radio operations within these 6 wifi channels would allow
experimentation with higher power levels. Ham radio is worldwide, so many
of the operating practices are quite similar. My coverage with the 15 db
vertical extends out about 5-6 miles, but it is not reliable at these
distances because of local trees. I really should find a way to put my
antenna up higher or try another location. You are correct with the +42 db
gain, but I must have some unknown losses in the connectors or coax.
Miccrowave frequencies easily lose power in coax transmission. I have
experimented with horizontal polarization and this works better because you
receive much less vertically polarized interference from conventional
wifi. The 36 db commercial internet providers advertise coverage for about
9 miles, so you see what you could do with a taller antenna. And yes, your
handheld phones can operate at long wifi distances because I have done that
during a test of emergency operations.
The US hams seem to be drawn to the HSMM MESH concept. I have tried to
send Serval Mesh messages through HSMM by using 4 routers, but it does not
work. There is very little experimenting being done with smartphones as I
have done. Perhaps this may change if the Serval Mesh becomes known. Good
luck with your program.......
David, W5SVL
On Tuesday, October 30, 2012 2:39:16 PM UTC-5, Paul Gardner-Stephen wrote:
> Hello,
>
> This is really interesting. What range were you able to obtain
> between the phones and your 15db omni?
>
> Also, to clarify my understanding of your link budget versus "normal"
> WiFi, you had +27db from your amplifier, then +15db from your antenna,
> for a total of +42db gain. 42/6.02 ~= 7, so we should expect 2^7 =
> 128x range compared with WiFi, provided that there is no source of
> interference to drown out the phone being heard by your amplifier on
> the way back in (excuse my fairly crude understanding and
> terminology).
>
> If all of that is correct, and you have a low noise floor so that your
> amplifier can be fully effective, it sounds like the typical
> ~100m-150m outdoor range of a wifi phone should become up to 12.8km -
> 19.2km. Naturally I am very intrigued to find out just how far you
> were able to get coverage.
>
> Meanwhile, what are the ham regulations like in the ISM band centred
> around 915MHz?
> Also, do you have any knowledge of how the ham regulations differ
> between the USA and Australia?
>
> Paul.
>
> On Wed, Oct 31, 2012 at 4:20 AM, W5SVL <w5... at aol.com <javascript:>>
> wrote:
> >
> > On Tuesday, October 30, 2012 12:56:12 AM UTC-5, Jeremy Lakeman wrote:
> >>
> >> On Tue, Oct 30, 2012 at 2:50 PM, W5SVL <w5... at aol.com> wrote:
> >> > Greetings from Texas. I am a ham radio operator and I have been
> >> > experimenting with the Serval Mesh by using 2 inexpensive unactivated
> >> > Android smartphones. I am attempting to use the Serval Mesh through
> an
> >> > existing HSMM MESH network. HSMM MESH is an experimental ham radio
> mesh
> >> > network that uses the first 6 wifi channels in the 2.4 Ghz band. The
> >> > radios
> >> > used are older versions of the WRT54G router that have been flashed
> with
> >> > a
> >> > new firmware. There are some awesome communication possibilities
> here,
> >> > but
> >> > I do not have the networking skills to do this. Maybe my idea is not
> >> > possible, but hopefully someone will comment.
> >>
> >> So after a quick bit of research;
> >> - HSMM is a custom radio protocol that exposes a standard IP network
> >> interface
> >> - olsr is being used to mesh these devices together
> >> - other devices may use the network through the LAN interface
> >> So you would have a second access point that the serval phone can
> >> connect to for internet and mesh traffic?
> >> This doesn't sound like a network that serval can transparently
> >> co-exist on. Yet.
> >>
> >> Though we have done some initial work to support serval nodes
> >> discovering each other over an olsr network, we haven't built any
> >> protocol to exchange reach-ability information for other locally
> >> connected serval phones. This is a reasonably large piece of work that
> >> we don't have the time to build right now.
> >>
> >> You could build servald for the mesh routers and run it on every
> >> device in the network. Though our routing protocol is not as mature as
> >> olsr.
> >>
> >> > Also as a ham, I can legally use much more power on the 2.4 Ghz
> band,
> >> > and I
> >> > have found the Serval Mesh to work very well through a bi directional
> RF
> >> > amplifier installed between a router and an external antenna. There
> is
> >> > no
> >> > internet connection here. I am just using the router as a radio
> >> > repeater.
> >> > Has anyone else tried this? This would not be using the HSMM MESH as
> I
> >> > mentioned above, since only one router would be used. This one
> router
> >> > repeater could really be useful in emergencies. Please give me some
> >> > comments on both of these experimental ideas. Perhaps I should
> consult
> >> > with
> >> > a ham operator who has more networking knowledge than I have. Any
> help
> >> > will
> >> > be appreciated.
> >>
> >> So this router is operating as a simple ethernet bridge?
> >>
> > I configured an old Airlink router to broadcast my ham call as the
> SSID.
> > The router was in the access point mode. I used wifi channel 1, which
> is in
> > the ham bands. No encryption was used and I did not connect my DSL
> internet
> > into the WAN port. This router had a removable antenna which I removed.
> I
> > then connected the router to a 27 db gain bi directional amplifier whose
> > output was sent to an external antenna amout 25 feet up. I used 25 feet
> of
> > low loss microwave coax. The external antenna was omnidirectional and
> had a
> > 15 db gain. I connected my 2 Android phones, that were configured to
> the
> > Serval client mode, with the router. Now I was able to make Serval Mesh
> > calls and send SMS messages over a large coverage area. This was all
> > experimental, but it showed me that the Serval Mesh could cover a large
> area
> > with only one wifi router. This trial was just to see how my wifi could
> be
> > used on the ham bands and it had nothing to do with the HSMM MESH
> > configuration.
> >>
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