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Digital Repeater System Project


Note: This is a living document and will change frequently as we clarify the objective and get input from other amateur radio groups who are ahead of us in their roll-out of digital technology, and also as we get input from the local community.

Project Background

We support the migration to digital technology because of the new possibilities it has to offer.

We recognize that the majority of amateur radio operators prefer to be users of the technology rather than developers, and also that a great deal of the user level experimentation is in application development and not at the hardware development phase.

There are various digital standards in place but not a whole lot of digital ham radio equipment commercially available.

D-STAR is an open standard, developed in Japan. Icom have gotten behind the DSTAR standard and have a good portfolio of radios that are DSTAR digital capable. There are a variety of ways to integrate digital technology with dated analogue technology so that the move to digital is not overwhelmingly expensive to the end user. This way, the life of the existing analogue infrastructure can be extended, and analogue mobile equipment will be useful for a few more years.

The AOR add-on device advertised in ham magazines, uses AMBE protocol, as does DSTAR.

Icom have chosen to make a variety of VHF and UHF mixed mode radios available, which employ digital voice and a low speed data channel, and they have produced the ID-1 digital radio which employs 128kb/s data for simultaneous voice and data, has an ethernet port available, operates in the 23cm band, and also has an analogue compatibility.We are particularly interested in the higher speed data capabilities of DSTAR which permits true multimedia communication, but we recognize the importance of introducing technology which appeals to as wide a segment of the market as possible.

Icom have also developed a family of compatible digital repeater modules for VHF, UHF, as well as 23cm. All of the DSTAR modules will interconnect through the internet, while the 23cm data module will provide true medium speed internet connectivity at the front ethernet jack of ID-1 mobile radios.

This project can explore any mass market digital technology suitable for ham use but at this time the field is quite limited, and so we will focus on DSTAR. Icom has obviously put a great deal of effort behind their DSTAR portfolio and there is certainly a good opportunity for application development using their architecture.

It is rumoured that Kenwood has also bought into the DSTAR protocol and will be introducing DSTAR compatible radios in the near future.

Preliminary View of the Project


The latest system configuration in Ottawa calls for single digital VHF and digital UHF repeaters, as well as a digital voice repeater on 23cm and simplex high speed data module on 23cm. The single site will be located as high as possible on a central building in the city. This placement plan may be altered as we move along in this project.

In later phases, and only if warranted, additional 23cm repeaters may be added to improve saturated coverage throughout the Ottawa_Gatineau area.

It is believed that this configuration will provide very high signal quality thoughout most of the Ottawa area.

Why 1.2GHz?

The DSTAR standard works for VHF and UHF so why are we talking about 1.2GHz? The VHF and UHF equipment that Icom offers at this time permits relatively low speed data - this is good for messaging and digital APRS but not practical for images, live motion, and web access.

There is very light usage of the 23cm amateur radio band in the Ottawa area. There is a lot of truth in the old adage 'use it or lose it', particularly in this age of spectrum auctions where real hard cash is tied to frequencies.

The 1.2GHz band has lots of space to try slightly wider signals. And .... very important, Icom has these very nice radios (ID-1), which are compatible with both digital and analogue signals and will work either with a repeater or point-to-point.

One last thing, 1.2GHz antennas are quite small and much higher gain is possible with physically smaller antennas.

All this makes 1.2GHz a logical component of our project.

What Can we Expect on 1.2GHz?

1.2GHz will perform similarly to 440MHz. It is very much line of sight, and has good reflective properties as well as building penetration because of its short wavelength. More flutter is typically heard on 1.2GHz than on 2m. The good news is that there is no spectrum congestion, not much interference and not much intermod. Listening to digital radio is quite different from analogue radio. It either works very well or not at all. The signal quality transition is very sudden. However, at the digital level, you can repeat it forever and audio quality does not get any better or worse.

Configuration

Repeater sites will look like this.

Possible Site with 1.2GHz only:


Planned Full VHF, UHF and 1.2GHz site:


Powering the System

Most of the equipment operates on 13.8vdc. The system will be powered from commercial mains, site power. Hopefully that would include power from emergency generators. In addition, we will supply power filtering and standby power (for clean and smooth switchover) via one or more uninterruptible power modules. We will try to design the power system for 99.9% system availability, allowing for typical power reliability in the Ottawa area. That is about 9 hours of down time per year.

During emergencies, when no commercial generator is available, alternate/additional power may be possible but with some switchover delay. Access would be very much at the mercy of the site owner. To protect the licence holder, the modules will be remotely controllable. It will be possible to separately turn each module on and off.

Internet Connectivity

A DSTAR site requires a 750kb/s connection to the internet and a fixed IP. Many repeater sites already have commercial access to the internet. However, if we do not have commercial connectivity for our installation, internet access can be provided in various ways. One possibility would involve the use of 802.11g 2.4GHz client cards, and yagi or parabolic antennas. If there are multiple high speed data sites, they should connect to the same Access Point via grid type dishes. In this way, even if the internet fails, both sites would still be able to to communicate with each other, via the Access Point. While we may prefer that the internet connection be stand alone, in reality the operating cost and administrative difficulties suggest that a shared Access Point using someone's home located internet service is quite practical. Furthermore, we suspect that the load will not warrant a standalone Access Point. We are looking for ideas and suggestions in this area.

Site

We cannot over-emphasize the importance of having a good site. We require good coverage in all directions in the Ottawa area, primarily to the east, west, and south. Generally speaking this means as high a site as possible.

Because of the newness of DSTAR, we anticipate that a software specialist and a hardware specialist may need frequent and direct connectivity to the system, particularly in the early stages. Unfortunately, this may adversely impact the availability of sites.

We need good power and if possible emergency power.

The site should be heated and air conditioned as required.

The site must provide roof access to allow us to place 2 tripods with multiband, vertical, collinear antennas on them.

Since we have no recurring source of funds at this time, we are looking for a donation of physical space. If you have a source for space, please, please contact us and let us know - this is very important.

Expected Applications

  • DAPRS (i.e. Digital APRS)
  • GPS under voice (not the same as above)
  • Usage logging (who was on when)

    Frequencies

    While there are numerous VHF and UHF analogue FM repeaters in the Ottawa area, and most are missing or seldom used, the frequency charts for this area say that the spectrum is crowded (see the St. Lawrence Repeater Council's web pages). By reusing former packet frequencies, we are able to squeeze in DSTAR.

    At 23cm, Ottawa has a serious problem with radar interference. After a lot of analysis we have tentatively selected some frequencies which hopefully will be useable:

  • 23cm port A (#1) Repeater Output 1282.000MHz (digital voice and low speed data)
  • 23cm port A (#1) Repeater Input 1270.000MHz (digital voice and low speed data)
  • 23cm port A (#2) Data Radio Output 1299.200MHz simplex (high speed data)
  • 23cm port A (#2) Data Radio Input 1299.200MHz simplex (high speed data)
  • 70cm port B Repeater Output 444.850MHz (digital voice and low speed data)
  • 70cm port B Repeater Input 449.850MHz (digital voice and low speed data)
  • 2m port C Repeater Output 145.530MHz (digital voice and low speed data)
  • 2m port C Repeater Input 144.930MHz (digital voice and low speed data)

    Schedule - very preliminary

    note: there are many steps missing - this is just to get some time line in place

  • project research - June 2006 [on going]
  • grant application - July 2006 [submitted]
  • meeting with Icom - July 2006 [completed]
  • first group of ID-1's - August 2006 [revised]
  • ID-1 presentation by Icom at Carp hamfest - Sept 2006 [completed]
  • equipment orders placed - January 2007
  • partially operational - off site - February 2007
  • partially operational - on site - March 2007
  • fully operational - on site - May 2007
  • site 2 and subsequent - pending - depending on results with site 1


    This page was updated on May 14, 2010 and is Copyright © 2006-2010 by Ottawa Amateur Radio Digital Group