Presentation given to QCWA Chapter 70 on Nov. 19th, 1997
Ottawa's New Video Repeater
Bill Westbrook, VE3EKA
After four years of planning, the first video repeater is now operational in the Canadian Capital. Located at CJOH-TV, a local TV station, built by the Seniors Video Repeater Committee of the Telephone Pioneer Amateur Radio Club for the use of all amateurs within the 30 mile radius of the coverage area.
Funding was obtained from two government grants. In addition to universal medicare, in Canada we have welfare programs, including a New Horizons Program that will give a seniors group financial support for a project that gives them a reason for getting up in the morning. not bad, eh?
Planning
Bare Bones or State-of-the-Art?
When you decide to build a video repeater, there are some questions that have to be addressed. First of all, will it be bare bones or state-of-the-art? Granted, this decision will be influenced by the depth of your pockets, and technical expertise available. We were in the fortunate position of having adequate funding and committee members who worked for world renown R&D organizations where state-of-the-art is a way of life.
Reused or New Equipment?
Unlike VHF/UHF voice repeaters, a video repeater can't be built from reused taxi or telephone company radio equipment. Nor can you buy a ready built video repeater. A well designed video repeater will usually consist of equipment units, carefully selected from several manufacturers. that will meet the design requirements of the system.
AM or FM?
When we discovered that, unlike here in North America, the video repeaters in Europe were invariably frequency modulated, we did some research that turned up the following advantages fo using FM:-
Better Linearity
No Sync Signal Compression
Signal to Noise Improvement
Improved Co-channel interference Immunity
Immunity from Fading
On the downside, these advantages come at a price. FM equipment is more expensive. I was sold on FM when I compared the signal quality using VSB AM and FM over a 13 mile link.
Site Selection
Of the four sites considered, we selected downtown Ottawa location. When the Chief Engineer at TV station CJOH offered the use of their location we accepted, with alacrity. With our antennas installed 130 feet above the street and one of our committee members working there, it seemed the best choice.
Frequency Plan
Here in the frozen north, we have only one ATV frequency available at 439.25 Mhz. It was chosen for an AM input with a FM output at 914 Mhz. Later we plan to add a FM input in the 1.2 Ghz band.
Repeater Council
The frequencies chosen have been co-ordinated with the approval of the active repeater council in our area.
Industry Canada
The Canadian equivalent of the FCC agreed that 914 Mhz would be a suitable frequency for our FM transmitter.
Technical Managemnt
With government grants totalling $20,000 it was essential to keep track of, and equipped to justify all expenditures.
Funding
In addition to the New Horizons grants, we found the regional emergency measures unit to be very supportive in terms of donated equipment. Both BNR and Ericsson have made generous donations of equipment for our repeater project. Sometimes it is better to be lucky than smart!
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