tech stuff – Page 25 – Engineering Radio

New Studio project

It is time, once again, to replace some very old Pacific Recorders BMXII consoles. The Pacific Recorders consoles were very expensive when new, but after 30 years of continuous use, have more than paid for themselves. The replacement console of choice for this installation is a SAS Rubicon. I have installed these units elsewhere and they are the modern equivalent of the PRE BMX.

The heart of the Rubicon system is the 32KD router. Routed audio systems can save a lot of time and effort in a large studio facility installation. Not having to run and terminate multiple analog and digital trunk cables between the rack room and the studio is a huge deal in a six or ten-studio installation project.

The SAS 32KD router and Rubicon console system use a serial TDM bus to communicate and transport audio around. This is a simpler system than packet-switched IP data. Basically, the console surface is a very large, fancy computer control interface. Here are some pictures of the start of the project:

This is the view from the entry door. The furniture was placed last week and the countertop was cut in for the console. The furniture is made by Studio Technology. The pile of yet-to-be-installed equipment:

For monitors, we are using the Tanoy 602p near field monitor placed on the table top above the computer screens. This studio will not have a turret. Turrets used to be necessary to hold things like cart machines and CD players. These days the CD players are used so infrequently that it was decided to put them in the side rack under the counter top. Turrets also take up a lot of counter top space that can be put to better use.

Punch blocks and power connections. The red outlets are isolated ground UPS type, the back outlets are feed by the emergency generator power panel. All electric wiring is inside of the metal conduit. The punch blocks are the inputs to the SAS RIO link unit, one 16-pair analog audio cable and ten category 5e shielded cables. The cat 5e is used for computer and TDM data buss to the router.

The SAS Rubicon console is cut into the counter top and protected by plastic sheets.

Rack room with 32KD routers. This facility has 9 studios total plus a news room with three work areas.

The SAS 32KD router. All audio from the automation systems, satellite feeds and other sources is connected directly to these units. This unit is on line for other studios that have already been converted to the SAS gear.

WBCN All digital field test results

When I said the WBCN test data may not see the light of day, perhaps I spoke too soon. For your viewing pleasure, here are the results of the WBCN all-digital HD Radio tests:

~~WBCN All-digital AM IBOC Field Test Project~~ (link has been broken, this may have been released by accident)

Well, that will teach me, won’t it.

I have given it a summary read and my first impressions were correct; from a technical standpoint (antenna, ATU) this is a very favorable test configuration. The results look pretty good on the surface, although they appear to have had some nighttime interference problems, go figure. I’ll update this post when I have time to fully read the whole paper.

Update: The link I provided earlier has been taken down. It may be that the information was not supposed to be released to the general public. Several people have asked me to upload the report to my own server so that they can download it and read it themselves. This leaves me in a bit of a quandary; the report itself is important information and its implications for the future of broadcasting are huge. On the other hand, it is the work of a private organization and not the public domain, thus if released by accident, then it should not be shared.

This story from Inside Radio is more or less accurate as to what the report contains, although it paints a somewhat favorable picture. There appear to be some issues meeting the NRSC5C mask for the MA3 (all digital) mode. That seems to be fine, however, as the NRSC5C mask can be modified to meet field conditions. How convenient is that? The information about the number of AM HD Radio stations seems a bit off, latest I have is 207 AM daytime, and 66 AM nighttime stations out of 4,659 transmitting hybrid digital-analog HD Radio, or 4% daytime and 1% nighttime respectively.

When I have time, I will do some more analysis and post my own conclusions.

Category 7 Cable

As data transfer technology progresses, so do cable types. Category 6 UTP copper cable is commonly used today in ethernet installations where 1000BaseT (or gigabit ethernet) systems are required. Cat 6 cable has a certified bandwidth of 250 MHz (500 MHz for Cat6a). Category 6 cable is a newer version of Category 5 and 5e cable wherein the wire pairs are bonded together and there is a separator to keep each pair of wires the same distance apart and in the same relationship to each other. The four twisted pairs in Cat 6 cable is also twisted within the overall cable jacket.

Category 7 cable is much different from its predecessors. It has an overall shield and individual pairs are shielded:

Shields on individual pairs are required to reduce cross-talk (FEXT, NEXT). It also requires special shielded connectors called GG45 plugs and jacks. Pinouts and color codes are the same as gigabit ethernet (Category 5e and 6) however, Category 7 (ISO 11801 Class F) jacks and plugs also have to contact the corners of the connector or jack. This allows better shielding. A small switch in the jack senses when a Category 7 type connector is inserted and switches to the corner contacts, thus keeping jacks and patch panels backward compatible with Category 5/6 cables.

Category 7 GG45 connectors, jack and plug

Category 7 cable is rated for 600 MHz bandwidth (1000 MHz for 7a) which translates to 10 GB ethernet. This was previously the domain of fiber cable. Copper cable has some advantages over fiber; lower propagation delays require less complicated equipment, copper is less expensive than fiber and more durable. It is nice to have the flexibility to use copper cable on 10 GB ethernet for runs of 100 meters or less. Longer runs still require fiber.

Category 7 and 7a cable looks remarkably similar to the older Belden multipair “computer cable” pressed into service as audio trunk cable seen so often in older studio installations.

Proper drive levels for a Harris SX series transmitters

I was working on a Harris SX5 the other day and snapped a picture of the scope while measuring RF drive levels. There are still quite a few of these units out in the field, judging from my search engine results. I thought it would be helpful to post something about it. The RF power amp boards for the Harris Gates solid-state AM series transmitters are the same design, I believe.

In order to fully drive the RF MOSFETs in this particular series of transmitters (Harris SX1, 2.5, and 5 including A models) at least 26.5 volts peak to peak is required. Less than that and the device will turn full-on and internally short. To measure RF drive, the transmitter must be in local with control voltage on, with the rear door interlock defeated (this can be safely done if the transmitter is wired with separate AC feeds for control and RF power supply). Make sure the RF power supply is defeated and will not turn on. Measure across the input of each of the toroids that feed the gates of the RF devices.

Harris SX series transmitter drive level test, 27.45 volts, 1,110,000 Hz

It should measure between 26.5 and 29.5 volts. This one measures 27.45 volts peak to peak. Each input toroid on every PA board should be measured as the toroids themselves have strange failure modes and may pass resistance and continuity tests, yet still not provide proper drive voltage to the attached devices. This has to do with core permeability. Each toroid feeds two RF MOSFETs, replace part is IRF-350.

As always when dealing with an SX transmitter, good luck.