Unattended listening

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Unattended listening

Postby CPSK » Sun Sep 12, 2010 4:37 pm

Hi;
I know this may sound crazy, but have you ever been somewhere (work maybe, having a meal with your family, where scanners are "banned") where you cannot use your scanner but want to catch some activity on your favorite RR?
Well, I have just the answer. A digital voice recorder that has "VCVA" (voice activation), and an external mic input.
I just bought one (not for this purpose), and connected its external mic input to my radio's headphone output. First, I set the volume level on the radio (mine has to be turned way down) so that the level going into the VR isn't too high, then I set up the VCVA so that when the radio is not producing an output, the recorder is in standby mode.
When the squelch is broken, and the radio is producing audio output, the VCVA starts the recording (continues from the point it left off). So the result is a gap-free recording of whatever the radio was picking up.
Maybe it's too late to get the photos you wanted, but sometimes you might want to know whether a specific train passed while you were away from your radio.

My VR has USB interface, so I can upload any file to my PC, and save it, edit it; whatever I want to do. I can keep only what I want, and discard the rest using a sound editor program.

I had done unattended recording onto my laptop computer, but without VCVA, I would have to look at the sound file in my editor, and pick out the areas where there was activity. The VR is much quicker, and doesn't keep your laptop computer tied up (since you probably need it where you are, not leave it sitting home connected to the radio).
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Re: Unattended listening

Postby justalurker66 » Mon Sep 13, 2010 2:44 am

That sounds like a good idea. I wrote an app for my computer to do VOX recording ... it saves files if there is no radio traffic for a changeable length of time. But I have an extra machine that this can run on. My app has playback built in so I can scroll back to missed messages while it is still listening for new messages and play them without opening an editor. I'm still working out bugs (it crashed after four hours of the last test) and playback sounds a bit odd when dispatcher and train responses have no time between them. But a simple VOX recorder would be a lot less hassle and if you're in a state that allows scanners to be carried you could set it up in a car - away from the work/dinner environment but closer than going all the way home for the recording.
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Re: Unattended listening

Postby CPSK » Mon Sep 13, 2010 11:19 am

I think I'm going to add an attenuator to my setup. The output of the radio is 8 ohms, and the mic input on the recorder is 2K, so the volume level is too high. It's a very simple thing to do. You can wire up the resistors right into one of the plugs (at either end; doesn't matter). Do you connect your radio directly to the Line-In on your sound card, or do you use an attenuator?

I'm curious to know what method your software uses to detect a sound level. I've never worked with that type of app. Mostly I write scripts in C++ or Java, or simple VBA for Access, but never wrote anything that read signals from the sound system. It doesn't sound too difficult, if you're familiar with how Windows reads the sound card. That's one nice thing about Windows, compared to old DOS programs. If you were working in DOS, you would pretty much have to write a different driver for each sound card you wanted to support.

There was one instance where I wanted to monitor my radio unattended. It was when the RB&BB circus train was moving through town. I didn't know whether it had passed during the night or not. As it turned out, I missed the train on its first run-through, but had a chance to catch it on its second run, but was too sleepy to get out of bed <g>. I didn't miss much anyway... nothing has changed in the 15 or so years since the last time I saw the train.

I guess I could dedicate my laptop computer for radio monitoring, but its not working very well right now. The thing is nearly 9 years old.

FW
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Re: Unattended listening

Postby justalurker66 » Tue Sep 14, 2010 5:06 am

CPSK wrote:I think I'm going to add an attenuator to my setup. The output of the radio is 8 ohms, and the mic input on the recorder is 2K, so the volume level is too high. It's a very simple thing to do. You can wire up the resistors right into one of the plugs (at either end; doesn't matter). Do you connect your radio directly to the Line-In on your sound card, or do you use an attenuator?

I've been using Line-In ... the biggest issue being it is a Vista machine that doesn't allow Line-In to be fed to speakers (M$ decided we didn't need that?) so I have to record a little to set the volume. My scanner is set to about 50% output. (BTW: I tried to upgrade drivers to get the audio pass through but it didn't work. So I put an auto play in my software that repeats recorded conversations as soon as the recording is finished so I get to hear the feed on a slight delay.)

I'm curious to know what method your software uses to detect a sound level. I've never worked with that type of app. Mostly I write scripts in C++ or Java, or simple VBA for Access, but never wrote anything that read signals from the sound system. It doesn't sound too difficult, if you're familiar with how Windows reads the sound card. That's one nice thing about Windows, compared to old DOS programs. If you were working in DOS, you would pretty much have to write a different driver for each sound card you wanted to support.

I'm using an old version of Delphi (2.0) and a component named TAudio. It uses Windows system calls to talk to the sound card and one of the options is to set a threshold. Basically once recording is started it delivers captured packets of audio that are over the threshold. The component keeps sending packets until stopped (once the threshold is broken) but I keep resetting the threshold flag when a packet is accepted by the program ... so I end up with only packets that contain audio over the threshold. The component allows setting of bit rate/sample rate and size of packet. 8 bit sounds fine for radio but I've been using 16 bit 11025 SR with 1k packets. Giving small files without compression (a typical 16 second defect detector report is 367k).

There was one instance where I wanted to monitor my radio unattended. It was when the RB&BB circus train was moving through town. I didn't know whether it had passed during the night or not. As it turned out, I missed the train on its first run-through, but had a chance to catch it on its second run, but was too sleepy to get out of bed <g>. I didn't miss much anyway... nothing has changed in the 15 or so years since the last time I saw the train.

I'm mainly looking to collect a radio reports so I know what is said on that channel. The line I'm interested in uses Track Warrant control for a portion and while there are few meets being able to hear the warrants is interesting. The ability to replay the last (or a previous) exchange helps for those times where one wants to hear what was said again. I have found that some conductors and dispatchers have a personality that makes it to the radio.

There is not a lot of traffic on the channel (only 10 scheduled trains per day on the closest repeater) so the end goal is to be able to put up a good antenna that will catch as much as possible. A few weeks ago there was maintenance work underway with appropriate speed restrictions on the Track Warrants. While I like to get out the idea of railfanning from home is helpful to the budget. It would be good to catch some action without spending a tank of gas.
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