The RARS News Hour

The RARS News Hour is heard every Sunday evening after the 8 PM net on the Raleigh Amateur Radio Society 64 repeater. The presentation material is taken from the ARRL audio news and the Amateur Radio Newsline. You can listen to the latest news from each at the following links:

Behind the Scenes

The RARS News Hour is about 45 minutes of audio news, transmitted through the Raleigh Amateur Radio Societies 146.64 MHz repeater every Sunday evening immediately after the 8 PM net. Assembling the source material and presenting the news hour is easy and in this article I'll explain how I do it. If you are interested in presenting the news hour yourself, I'd encourage you to try it. I'd be happy to answer your questions and provide any guidance you need.

News hour material comes from the American Radio Relay League
http://www.arrl.org/arrlletter/audio/
and Amateur Radio Newsline.
http://www.arnewsline.org/
Both organizations publish their news as MP3 audio files to their respective websites every Friday afternoon.  In a nutshell, presenting the news hours is simply playing MP3 audio files stored on your computer through your transmitter to the repeater. At intervals not longer than 10 minutes, you'll pause the file playback, identify your station and give others a chance to use the repeater. I'll talk more about the presentation in a moment but first let's look at the necessary hardware.

The Hardware

To send acceptable audio, you will need a direct connection between your computer and your transmitter. Avoid the temptation to use your rig's microphone to pick up the sound from your computer's speakers. The audio quality will suffer and every stray noise in the room will be transmitted. You also don't want to hold the push-to-talk (PTT) button for 45 minutes! So you're going to need a simple interface to make the audio connection, give you control of the PTT function and provide a way to identify your station. You'll also need a way to monitor your transmission. This might be headphones or a set of amplified speakers connected to your computer or a second radio listening to the repeater.

There are several of considerations for your choice of radio. Most important is that it be able to transmit continuously for at least 45 minutes without overheating.  Most ham gear is not designed to transmit continuously at maximum power. For typical hand held rigs this means operating at 1 watt or less. For 50 watt mobile rigs, 5 watts should not be a problem and ten watts may be feasible with an external helper fan blowing on the heat sink. Make sure you can still maintain a quality signal through the repeater at the reduced power level.  Another consideration is that your rig's power supply must also be able to deliver the transmit current continuously. With an HT, consider whether your battery pack will support 45 minutes of continuous transmission. If you have any doubts, use an external power supply that can deliver at least the transmit current stated in your owners manual for the power level you'll be using. Don't use the small wall wart battery charger that came with your rig. These are generally only able to supply a small charging current for the battery and won't support the transmitter. Attempting to transmit will produce mostly buzz and hum.  The final consideration is the method of interfacing to the computer and radio. Your interface must provide a direct audio connection between your computer and radio and a way to control the PTT operation. It may also provide a means to switch your radio's audio input between the computer and a microphone so you can identify your station. Let's look at each requirement.

Identifying your station can be as trivial as using a second radio. When it's time to id, pause the computer, un-key your transmitter and use the second radio to identify your station and communicate with anyone that wants to use the repeater. This is the method I use. A second radio is also convenient to monitor the presentation through the repeater. If you do monitor the repeater, the monitor antenna will likely need to be  15 to 20 feet from the presentation radio antenna. At the monitor receiver, your presentation signal is many times stronger than the repeater and even though they are on different frequencies, the local presentation signal will reduce the sensitivity of the monitor receiver enough that it may not hear the weaker repeater. This affect is called desensing and to overcome it, you have to reduce the strength of the overloading signal at the receiver. Assuming you're already transmitting with the lowest power required for good repeater signal quality, the only remedy is to increase the separation between the antennas.

I Have But One Rig

If a second rig isn't an option, you'll have to id using a microphone connected to the presentation radio. With an HT this is as simple as unplugging the interface from the radio and using the built in mic. With a mobile rig you'll have to unplug the interface and re-connect the rig's own external mic. Another mobile rig option is to enhance the interface with a switch and connector for the external mic, using the switch to transfer the rig's audio input between the computer and external mic. Also, with a single radio, you'll need a way to hear what you're sending. You can monitor the audio from your computer by using a "Y" adapter cable to connect both the interface and headphones or amplified speakers to the computer headphone jack. If you use an indoor antenna with your presentation radio and are using amplified computer speakers, rf from your transmission may produce distorted audio. The solution is just like for desense; use the minimum power necessary for a quality repeater signal and put as much distance as possible between the speaker wiring and antenna. Speakers are convenient because you can adjust the monitor volume independently of the transmitted audio but their built in amplifiers make them susceptible to rf interference.

The interface's second function is control of the PTT operation. For most radios, the transmitter is put on the air by grounding the PTT line. In the simplest arrangement, the PTT line is permanently grounded in the interface so that the rig switches to transmit just by plugging in the interface and switches back to receive when the interface is unplugged . With a single radio, this is a practical solution since you need to unplug the interface to temporarily connect a microphone to identify. If you use a second radio for identification, adding a PTT control switch to the interface may be more convenient because you can leave the interface permanently connected. This is the configuration I use.

The final job of your interface is to make the audio connection between your computer and rig. There are a couple of concerns. The first is that some radios present a DC voltage at the microphone input and if not blocked, it might cause damage to the computer. The second concern is that generally the audio signal from the computer is at a much higher level than the signal from a microphone and will need attenuation to prevent distortion caused by over driving the transmitter. The computer's volume settings may provide enough control to avoid overdriving but if not, you'll have to provide additional attenuation in the interface. The details of these solutions will depend on the characteristics of your particular radio. I'll explain my W32A interface but you will need to look at your own rig's requirements to properly design your interface. Your radio's owners manual is the first place to look for microphone and PTT connection information. You can download manuals from the following links:

For the RARS News Hour, I use a laptop computer interfaced to an Icom W32A hand held, set to 1 watt, connected to an indoor mag mount style mobile antenna. When I first started presenting the news hour, I identified my station using a second 2 meter rig and used a switch on my interface to control the W32A's PTT. Eventually I started using a simple computer audio editing program to produce a single file for transmission. This single file contains both news files and my station identifications inserted at the right times. With this one MP3 file, all I have to do is pause it and flip the interface switch to un-key the W32A to give others a chance to use the repeater. I never use the second rig unless I need to speak with someone who has asked for the repeater.

Make the Connection

Figure 1 is taken from the W32A owners manual. It shows how connections are made to an external mic and PTT switch and an external speaker. We're interested in where to connect the computer audio and how the PTT connections are made. Notice the capacitor next to the "+" terminal of the audio input plug. This is a clue that DC is present across the microphone connector, so an interface to this radio will need a similar capacitor. The other clue that DC is present is the PTT connection. When the PTT switch closes, the 33 K ohm resistor is connected across the audio lines. This causes the rig to switch to transmit by conducting a small DC current through the resistor. The radio senses this current and switches from receive to transmit. The audio from the computer is connected between the "+" and "-" input terminals. The 33 K ohm resistor is a much higher impedance than the microphone so has a negligible affect on the audio. The 3.5 volts is a separate source of DC for powering any electronics in the external mic like DTMF circuitry or a backlight and the interface will not connect to it.

Figure 2 is a schematic diagram of my interface. The terminals on the left represent the connection to the computer audio (the jack you would plug your computer speakers into). It's a standard 3.5mm or 1/8" stereo audio plug. I got mine by purchasing a patch cable of several feet and cutting it in half. On the right is the 2.5 mm plug that connects to the rig's mic connector. Since this was my first attempt at interfacing between the computer and rig, I took a conservative approach. I wanted the interface to present the same conditions to the computer as an ordinary set of headphones. I began by connecting the left and right computer audio channels together and R1 between them and ground. R1 provides a load to the computer similar to a set of headphones and its value can be anywhere from 10 to 100 ohms. C1 is included just to block any DC that may be present at the computer output. It's unlikely but If DC was present it could gradually degrade the adjustable resistor R3, which could eventually lead to noise on the audio. R2 and R3 serve as an adjustable attenuator. I wasn't sure of the audio levels I needed or if I would have enough control range through the computer volume setting so I included R2 and R3 to provide additional attenuation. After experimenting with various settings, I found that I was operating with R3 near its maximum value which translates to about 6db of attenuation, a level easily achieved from the computer volume control, so that at least for my radio, R2 and R3 aren't necessary. C2 blocks the DC present at the microphone input of the W32A. The rig's PTT operates by drawing a small DC current from the microphone connection. This is the function of S1 and R4. 

The interface I use may seem complicated but it could probably be reduced to just C2, R4 and S1. You could also leave out S1 by just connecting R4 to ground. This will switch the rig to transmit just by plugging in the interface. Figure 3 shows my interface.

Say What?

Each weekend I prepare for the Sunday presentation by downloading the MP3 files from the ARRL and Amateur Radio Newsline and preview them to find the id times. The ARRL audio lasts about 15 minutes and has 3 second pauses between the major segments and a longer 5 second pause about midway through the file. This is the time for the first id. Amateur Radio Newsline has two id breaks identified with tones. During the preview, I note the id times and then during the presentation watch the running time of the files to know when an id time is approaching. When I first started presenting the news hour I paused each file (be sure to click pause, not stop since stop rewinds the file!) and identified using the second radio. Later, when I began using a simple audio editor to produce a single news hour file I included my station identifications in the file so after the id, I just paused the file and flipped the interface PTT switch to give others a chance to use the repeater. Any software like Windows Media Player, Real Player or Quick Time that can play MP3 audio is suitable for presenting the news hour. You can use the simple script example at
Example Script
as a guide for your station id. There's no formality or strict requirements except to identify your station at least every 10 minutes. During the news hour, the repeater takes care of identifying itself so strictly speaking, you don't even have to let the repeater drop. It's just good practice in case someone needs to use it during the news hour.

Finally, the repeater normally times out after 3 minutes of continuous transmission. When I volunteered to present the news hour, I was given a timeout extension code to send to the repeater before starting the news hour. If you are genuinely interested in presenting the news hour, contact me and I will point you to the right person to obtain this information. You can reach me at wa4bpj@nc.rr.com .

Now that you've had a peek behind the curtains, perhaps you'd like to help host the news hour. I believe it's a good plan to have several capable stations to share the fun and provide mutual back up. Let me know if you'd like to help keep the news coming.