Serval Mesh and ham radio

[W5SVL]

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. 

 

 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.

[Jeremy Lakeman]

On Tue, Oct 30, 2012 at 2:50 PM, W5SVL <w5...@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?

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[W5SVL]

    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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[Paul Gardner-Stephen]

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.

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[W5SVL]

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

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