Saturday, September 6, 2008

How We Play TWIAR On The Air In Albany

Here in TWIAR's home base, we air our news service on our flagship machine, the K2CT repeater, operated by the Albany Amateur Radio Association, on 145.190mHz. From our studios on the outskirts of Albany, it is about a twenty air mile trip to the repeater, which is situated on a mountain top in the Town of New Scotland. Our secondary, or back-up repeater is located in the same area, and is the KA2QYE machine on 147.375mHz, and is used when the primary machine is busy with club activities, or down for maintenance.

We air the full version of This Week in Amateur Radio here in our home market. (Actually the one hour Headline News version has never aired here)

Up first is the re-editing of the audio file to drop in the K2CT idents in each break point on the program. These voice id's not only identify the repeater, it also identifies our originating transmitter. This file is either saved as an mp3, or we play the original wav file.

The completed file is then loaded into our playout computer. This is a dedicated box. It is an old Dell 500 mhz desktop running Windows XP with about 250 megs of memory. The computer has two soundcards. The first, is an internal Soundblaster, and the second is an external Creative USB interface.

I use several different radio automation/live assist programs to play out the audio files. The software allows independent cueing of several audio channels while one is on the air. The audio output of the computer is fed into two Behringer DI boxes, which isolate the computer from the rest of the audio chain, helping to avoid ground loops.

The output of the DI boxes feed a dedicated Behringer UB-1622 12 channel mixer. This board receives two independent channels from the playout system, audio from a 30 second sampler, and a mic input if needed.

The sampler (and also the playout system) have CW id's of the local transmitter and the repeater, to insert into segments that run longer than the FCC's ten minute amateur ID rule. If a segment runs long, the system inserts the CW over the program audio. This ID method is independent from the repeaters own ID on the local controller.

The output of the mixer is then fed into a 24 channel analog equalizer. This device is set up for unity gain, and allows for audio sweetening. Next in the chain is a Behringer DSP processor. This adds in just a little bit of reverb which brightens the audio on the air. It also tends to bring up the average modulation. From the DSP, we go into an Optimod equivalent processor. This device splits the audio into several different bands (ie 20 to 500hz, 500-3000, etc) and adds compression and limiting on each band before reassmbling the audio at its output. A Behringer Auto-Com monitors the average audio levels from the Optimod, and has a high peak limit if needed.

The last box before we hit the transmitter is an old Shure audio master. The Shures only purpose in the chain is to drop the audio from line level to mic level for input to the transmitter.

Our transmitter, which by now has a few thousand transmit hours on it is an old Kenwood TR-7950. This particular radio, operated at low power, and equipped with a three inch external fan on the heat sink, will run forever. In fact, this particular radio has proved so reliable, we have two stand-by 7950's that we got years ago, that are still on the shelf.

The radio is fed into an eleven element Cushcraft VHF beam. The output of the repeater is monitored locally so that in the event of an emergency need for the machine while the news is played out, we can drop.

Next time, I'll go into how This Week in Amateur Radios ham service is put together each week.

Till then..73 and enjoy the programs.

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