Transmission - Planning a Fly-a-way

We've been given the go ahead for Rave Live, and it's to be staged in Matter. As in previous years it is our engineering goal to transmit over DTT, but that means we either have to leave the Transmission and Presentation suites back at Ravensbourne with students keeping watch, which is no good as they will then not get to meet any delegates or see the rest of Rave Live, or we can fly the kit up-to Matter.

To fly TX along with the multitude of other areas needed to make this work is going to be a major feat, but with the right amount of planning and preparation it can be done, then there is the issue of whether or not we will actually be able to transmit from Matter due to licenses/be allowed an aerial fixed to the roof etc, and there is an all round agreement that even if we can't, we will still modulate the channels and loop the feeds back into the venue over cable and onto set-top boxes to prove that we have the technological knowledge and prowess to act as a fully functioning TV center.

During a meeting yesterday we discussed the systems that we would need to take with us along with how well they would fit into rack units. We came to the conclusion that the system installed in Pres/TX at the moment is pretty much the most basic it can get, there is very little redundancy and a few pieces of equipment need to be hired/borrowed (the COFDM modulator, an IRD with an integrated RF card). It was also decided that due to the complexity of creating this fly-a-way we would need start as soon as possible, leaving spaces for the missing kit.

Instead of taking the equipment out of the TX racks and then putting it straight into a mobile rack we need to build the system on the desks in E-lab. This way cable lengths, numbering and equipment configuration can be sorted out, then the kit can be taken separately to the actual rack units, making the move much safer to both us and the kit, then installed on site.

The planned system for the Automation fly-a-way

The planned system for the TX fly-a-way

Transmission - Axis Router

Ever since our work first began in TX, the local router has not been working. All of the control panels have been unresponsive and in a state of limbo, constantly moving a green light around the buttons. After installing the timecode, we decided that this would be the next task to complete.

At the moment the unresponsive router isn't causing too much trouble, because it is only being used for monitoring. However come when Rave Live needs to be transmitted it is vital in choosing the sources that are ingested into Pharos and the feeds that go out on air. Of course these feeds can all be over patched, but it makes sense to fix the Router while we have plenty of time than to worry about it later.

The first thing to do was locate the manuals, of which the crate manual was found on Confluence (The Ravensbourne Wiki) and the control panel manuals were obtained from Snell's back catalog. After reading we decided that there was no obvious solution available through the troubleshooting sections so we went into looking to fix the fault by doing almost a complete re-install of the routing system.

The only problem was that there was no dedicated place where the control files were kept. Obviously they would have to be on a computer in TX or easily accessible from TX and a quick flick through all of the attached components to the KVM revealed that they were stored along with the programmes needed to install them on the Pharos W/S computer. After opening the router control and trying to connect with the crate we discovered that the files had been corrupted some how. This meant we had to re-install an older version which once complete enabled the router to work perfectly. After this had been done we re-instated the most up-to date version of the control files only to find that after an evening the control panels resorted back to their useless state.

The router control program, found on the Pharos W/S PC

At the moment the control file installed isn't the most up-date, but it works and all the feeds seem to be going to the correct places. This will need looking into again before Rave Live however if the kit is going to be packed into a fly-a-way and transported to Matter then the routing system will need to be dismantled and re-configured anyway. At least we know that we have a working 16x16 matrix that we can use, which should be perfect for Rave Live. More information on the Axis Router can be found here, along the manuals for both the crate and the control panels.

Transmission - Testing the Timecode Feed

The timecode has been installed in the TX suite and all thats left to do is a few minor checks and tweaks.

Initially the feed worked perfectly, the clock and VTR's remained on station time (we didn't have time to get into Pharos and check) however after returning a couple of days later we found that none of the equipment was receiving timecode anymore. After tracing the signals back we found that the problem was the SDA, so we switched the back panel over to the redundant unit and removed the original SDA.

The makeshift connectors into the back of the VTR's work really well (BNC to female XLR) which was another surprise as we all reckoned we would need some kind of impedance transformer. Ideally these connections are still only a temporary measure until we can purchase some proper connections for the VTR's. Another minor job is to properly earth the inside the krone connections, although the feeds are working fine at the moment doing this means that the project has been completed properly along with reducing the risk of things going wrong at a later date.

The biggest thing that we discovered during this installation was how a krone block works, essentially each audio feed has its own position on a krone block and jumpers are used to take feeds from one place to another. We thought that each feed was connected on the same krone block, with an input on the top connection and an output on the bottom, essentially minimising the use of jumpers, but also making the wiring a lot messier and more complex (more chance for things to go wrong).

The connection between the line from the krone block (green cable) and the makeshift connection into the back of VT18

The counter on VTR17 showing station timecode

More information on Pres, TX and this project can be found on the Presentation Suite Wiki.

Transmission - Running in Timecode

The Transmission Suite doesn't have a dedicated, manipulable feed of timecode, the aim of this installation was to provide this. During Rave on Air timecode is used in TX during tape ingest, in Pharos and also on We know that there is a feed of timecode running to Pharos control unit from the clock in CAR. To check that this was working we connected it to the unused clock and let it run for a couple of days to check that it held its time.

The original feed of timecode running into Pharos from CAR.

Once we had verified that the feed worked we began planning how to get timecode into the presentation suite. Along with running the initial signal we also wanted to achieve a few other things:

• Have timecode appear on the audio jackfield (J/F)
• Run timecode to four initial pieces of equipment; Pharos, the VTR’s 17 & 18 and the clock

The most efficient way to run the feed would be to take the original working line of timecode into Pharos and instead run it through an Analogue Distribution Amplifier (SDA) and then onto the other pieces of equipment, as with all audio, the feeds would have to run through the krone block.

The equipment needed to achieve this task would be:

• Audio multicore
• Krone Block
• SDA (in rack mount)
• Audio twisted pair cables with male XLR ends

Due to the lack of any Probell SDA cards we started looking at other spare SDA’s (Avitel and Drake). We choose to go with the Drake DA’s (# PD 7051), primarily in use for the Talkback system, but also used in CAR to deal with a lot of the analogue audio feeds. The limited space in the racks meant that we used a 1U DA Crate that can hold three cards but positions them on their sides to save space.

The installed 1U crate, below the Axis router in rack 5.

Using the back panel connector (# PD 7051) the multicore was attached to SDA while the other end was connected to a krone block.

Back panel connector (# PD 7051) with multicore attached.

Once the multicore was wired up the rest of the feeds were plotted on a basic cable diagram.

Cable diagrams showing the lines from CAR through until the SDA's outputs and the feeds running from the SDA's outputs through to the separate pieces of equipment.

The original timecode feed was passed along an audio twisted pair (#46904). The cable was relaid to appear at the krone block and its end was removed to enable it to be punched into a krone block. Both the clock and Pharos took XLR as their timecode input, so two cables were made up and run from these devices and back to the krone block (#C264, #C265). The VTR's took BNC connections as their timecode input, so as a temporary measure two BNC-Female XLR cables were used for the male XLR cables to connect onto from the krone block (#C266, #C267), these cable runs will be tested and if the BNC-XLR connections work, they will be permanently installed.