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Re: "Soundmodem" relays for amateur internet backbone

Posted: Tue Sep 13, 2011 10:24 pm
by Svartalf
Quote from MoonShadow on September 10, 2011, 00:31
\Ain't the network effect grand? It's why I start to feel stupid if I can't access the Internet for more than a day. The ability to answer a question in near real time is downright addictive.

It is, it is.

Re: "Soundmodem" relays for amateur internet backbone

Posted: Wed Sep 14, 2011 12:30 am
by MoonShadow
Quote from Svartalf on September 13, 2011, 23:23

Sounds like to me we need to contemplate looking into Dash7 stuff for things. I'd say that while it's bandwidth sucks compared to other things, it's a gem for the sorts of things we're talking about here. Is it truly an unlicensed band for this use?

It is an unlicensed band almost everywhere on Earth. At least as much as the Wifi band is, which is unlicensed mostly because it's the ideal freq for microwaves, since the EM energy is resonant with hydrogen and thus dumps all of it's energy into water or hydrocarbons in a very short distance. Which is one reason that it sucks as a radio freq. Dash7 uses 433 mhz, which is reserved internationally by treaty; for emergency beacons I believe. But this also means that the freq is very narrow, and the transmission power very limited, for non-emergency beacon devices. If you have a remote control fob for your car locks, or for your garage, you almost certainly already use a low power 433 mhz device. Some 'smart' meters also use 433 mhz to communicate with the power company's passing 'meter reader' trucks.

Re: "Soundmodem" relays for amateur internet backbone

Posted: Wed Sep 14, 2011 12:41 am
by MoonShadow
Quote from beagle7 on September 13, 2011, 21:25
Check out this link (BCWARN)
They have already used wifi frequencies to do ~ 75 mile hops from Vancouver BC to Victoria.
I believe the power levels are between 1-10 watts.

I'm a ham myself, in case you couldn't tell. And the fact remains that these guys are using custom hardware and highly directional gear to make these connections. Nor do they depend upon Wifi alone to maintain the network, as they also use ham only equipment such as Pactor2 over ham radio bands. Although there isn't anything that would prevent anyone from developing a Pactor2 network over the unlicensed band that Wifi uses, there is no technical advantage to doing so. The band is what is limiting, not the Wifi technology itself. That's one reason that it's unlicensed to start with. 433 mhz is far too narrow a band to be able to use the higher bandwidth digital modes, and the narrow band digital modes common among hams (such as psk31/63/125) are very 'hands on' and don't offer technical advantages over Dash7. I'm pretty sure that Dash7 uses some variation of psk (phase shift keying) as it's base mode to start with, but just adds a layer of networking for automated devices to standardize against.

Re: "Soundmodem" relays for amateur internet backbone

Posted: Fri Sep 16, 2011 3:06 pm
by Roey
cathalgarv-eyb I hope you're not discouraged by some of the posts here, and that you do in fact explore a SoundModem broadcast setup...

While there are challenges like the limitation mentioned that most transceivers are half-duplex so you'd need to have transceivers that support full-duplex, or, hack a software defined duplex switching setup (which would be a cool project unto itself), or use four transceivers -- there are not insurmountable...

The cool aspect of this is by using SoundModem you have a transmission agnostic setup, that can work over anything that will broadcast audio if there is some hack for duplex management.

cathalgarv-eyb's idear while not without it's challenges would not only be really really fun lo-fi network to play with, it might well later be incorporated into other more ambitious and elaborate projects as a robust fall-back system.

Re: "Soundmodem" relays for amateur internet backbone

Posted: Fri Sep 16, 2011 4:03 pm
by Svartalf
Quote from Roey on September 16, 2011, 16:06
cathalgarv-eyb I hope you're not discouraged by some of the posts here, and that you do in fact explore a SoundModem broadcast setup...

Oh, we're not trying to discourage the concept. There's a minefield- and it needs to be properly navigated or you could end up with nasty fines and jail time over it. We're spelling out the parts of the minefield the rest of us know about, combined with alternatives within the space. I'm thinking of something Dash7-like with perhaps a different modulation technique, myself, for the side-step on things that'll accomplish what he's desiring and then some.

Re: "Soundmodem" relays for amateur internet backbone

Posted: Mon Nov 21, 2011 5:46 pm
by ErvKosch
Legality: You'd have to ensure that the walkie talkies were European "PMR446" compliant, NOT American ones,

There are some walkie talkies you can legally use in the US. Its the old .1 watt Space Patrol type radios. The work at 27 MHz AM or there a newer 49 mhz FM models. CB, FRS as GMRS walkie talkies are huge no-no's when it come to data transmission.

The exception seems to be Hasbro's 'Chat Now' toy. That somehow legally did voice and data in FRS band. Maybe if someone could reverse engineer the protocol you use that.

Update: I did a little more digging and found out its legal to transmit a one way text messages on FRS if the device is considered legal by the FCC. The transmission can be no longer then 1 second and there must be a 30 second gap between transmissions.


Posted: Thu Apr 25, 2013 12:31 pm
by richardski
I am fully supportive of opensource initiatives and welcome this position by DASH7. However I am concerned by the use of the 433 MHz Spectrum (433.92 MHz) which appears in ISO/IEC 18000-7. The world governing body for radio allocation is the ITU and the position is as below:

In ITU region 2 (the Americas), the frequencies that LPD433 uses are within a band allocated to amateur radio. In the United States LPD433 radios can only be used under FCC amateur regulations by properly licenced amateur radio operators. The conflicting allocations have been something of a nuisance to US amateur operators due to use of the equipment by European tourists in the U.S

So in the USA you are going to need at least a Technician class amateur license to operate in the 70 cm band where 433 MHz lives. 433 MHz is primarily for government radiolocation and secondary for amateur radio within the US.

Title 47: Telecommunication - PART 97—AMATEUR RADIO SERVICE

Subpart D—Technical Standards

§ 97.301 Authorized frequency bands.

"(a) For a station having a control operator who has been granted a Technician, Technician Plus, General, Advanced, or Amateur Extra Class operator license, who holds a CEPT radio amateur license, or who holds any class of IARP:"

UHF - 70 cm
ITU Region 2 420–450 MHz
Sharing Requirements (a), (b), (f) ... .4&idno=47

Source(s): ... lochrt.pdf

Page 27 in pdf ... ctable.pdf

Within the UK the primary user of the 430MHz to 440MHz is the military for their communications network. The secondary users are Radio Amateurs who have to accept interference from the primary user but may not cause interference to the primary user. Both these users have the capability to transmit RF power in the region of 150W to 400W within this band.

This level of RF field strength will easily deafen and render inoperative any low power receiver lacking sufficient filtering and cross modulation capacity which will result in the analogue front end RF receiver being desensitised and unable to hear its intended signal. The affected area could be of a radius from 2 to 5 miles depending on terrain and capabilities for adjacent channel rejection of the receiver .

I do hope due consideration is given to alternative frequency bands.

It is easy enough to tow away a car till it is sufficiently far enough away from a military or amateur transmitter so that it can receive a signal from its key fob etc. Not so easy if you have this problem in a fixed building especially where the transmissions are of an intermittent nature. This is probably why ZigBee and Z-Wave have avoided this band. This inband signal blocking harms the public perception of the reliability of radio control and monitoring links and so does need to be avoided.

This is a great idea but needs implementation in a more suitable frequency band.



Posted: Tue Aug 20, 2013 10:34 am
by kov314
In USA it's ISM band with unlicensed and licensed operations and "...low power communication devices must accept interference from licensed users..."
A good explanation is here:

ISM-Band and Short Range Device Regulatory Compliance Overview


Posted: Sat Dec 07, 2013 11:47 pm
by richardski
In a disaster situation or civil unrest where the government has turned off the internet and/or mobile communications then there is really only one immediate readily implemented solution that can be used by those who have access to WLAN via laptops, slates, mobile phones or even fixed base stations.

You basically have to implement, probably under difficult circumstances your own Wide area WLAN network. Replacing a damaged or turned off network has great benefits in that the end users already have the necessary Customer Premises Equipment to interact with your network Access Point.

The Raspberry PI is ideal for running an AP as it can be controlled remotely and situated on a high location with a large antenna and car battery it will run for a long time with no possibility of the state shooting the operator. If the users have SIP clients and Jabber clients installed on their CPEs then they would have easy local communication as the Raspberry PI can provide a SIP service using Asterisk and also run a Jabber server.

The 802.11b (2.4Ghz) would be ideal for the local net using a hub and spoke set up and connection to the outside world could be on a point to point using 802.11a (5GHz) where the far end is unaffected and has a connection to the Internet that can be shared. Failing that a satellite uplink if one is available.

Point to Point links using 802.11a (5GHz) and the right kit can reach 20 miles line of sight. A range of mini dishes, reasonably priced and very popular in 3rd world location are available from:
SXT 5HPnD is a low cost, high transmit power 5GHz outdoor wireless device.

The Raspberry PI is an ideal, very versatile, low cost disposable solution for difficult circumstances.

Trying to send modem tones over the audio channel of a license free 465MHz radio is a difficult proposition as the bandwidth is very narrow and the frequency repose curve is very antagonistic to data modulation requirements. Using an Amateur Band compatible Terminal Node Controller and running the AX25 or Pactor2 communications protocol, you should be able to get 300 or 2400Bd which would just about keep an old teleprinter happy. Not many people have the access to this kind of equipment or the technical knowledge to configure it. Whereas it would not take long to get many people up and running on a local WWLAN. You need to work with what is readily out there.