laptop audio input

[millam]

Does anyone no how to use the mic input for unitrunker. I put the disc tap audio into the mic (no line input) input and it doesn't work. I put in a regular mic and uniscope shows a normal signal. With uniscope and the disc tap audio I never can get a straight line even with the vol all the way down. It shows sharp rise and fall kinda like a rc time constant signal on top of a distorted sine wave. I have used various sized resistors in series and none seem to help. Also a capacitor. Seen places where a 1:1 transformer might help, have not tried that yet. The puter is a xp hp presario 700 laptop. Any ideas?

 

[Liverdog]

The mic input is generally the correct one to use... So, okay there. Usually, using a resistor is not helpful as you may load down the signal. Depending on the tap, you are correct to use a cap to get rid of any dc in the signal. Usually the signal should go to the tip of the plug... Make sure you bring the radio's ground to the sound card as well.

Not sure what you mean by "straight line"...

You should be seeing a cat's eye pattern using UniScope. Take a look at Rick's website for images of a proper decode...

http://www.unitrunker.com/

In my experience, laptop sound cards are quite tricky and take a lot of finesse to get the level just right. Adjust the Windows "Recording" levels for the mic input and make sure any gain is un-checked (usually under "Advanced") and turn off any "noise reduction" feature.

Post an image of what you have. Also, take note of the settings to run on UniScope (see Rick's site), and tell us what type of system you are trying to decode.

 

[millam]

laptop audio

straight line - gain at minimum, no signal. The radio and cable work on my dt. I'll check the rest and send pics later. Thanks;

Mil

 

[SkipSanders]

Have you made sure you've turned off the +20db gain boost most computers provide on mike inputs? Having it on can easily overdrive things on a discriminator output.

If there's no resistor at the discriminator tap, you may well need one in line (about 10k) to prevent loading down the discriminator, if your mike input isn't high impedance.

 

[millam]

laptop audio

I did have the leads backwards from all the component swapping that caused the severe hum, but the audio is still distorted and loads down the radio audio. I put in a 10k resistor and no help. I also turned the +20db gain off and no help. I have ordered a usb audio input device just to try. Maybe it wont load down the disc tap or what ever is going on. Also tried a 10 mic cap and no help.

Mil

 

[fmon]

You may need to install SndVol32.exe.

Check Control Panel>Sound & Audio Devices>Volume (under Sound recording). Laptops may not have this device installed.

 

[SCPD]

I put in a 10k resistor and no help. I also turned the +20db gain off and no help.

Try a larger resistor value like 47k or 100k. Please post a screen shot of Uniscope.

 

[Liverdog]

...but the audio is still distorted and loads down the radio audio.

Mil

Just so there's a clear understanding, is the 'distorted audio' something you're hearing out of the computer speakers, and the 'loading down of the radio' is your description of the audio out of the radio's speaker being diminished or absent?

Now that re-read your original post again, I see that you're saying that you cannot adjust down the mic gain; it always presents some amplitude. This happened to me with an HP laptop which had some sort of undesirable AGC circuit that I could not disable.

I think we'll be curious if the USB mic input solution works.

 

[millam]

laptop audio problem

The Griffin Imac USB audio adapter worked like a charm. The only problem may be that the gain is low. I could not get it to clip the audio with the gain control all the way up, may be the radio and disc tap that I'm using. Still it worked with Unitrunker. Bought it off ebay (buy now) for 19 bucks plus 2 bucks shipping. I would like to use it on an old dt if anybody knows how to find win98 drivers I sure like to have them.

Mil