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Author Topic: Audio Impedance Matching  (Read 452 times)
WZ6F
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Posts: 98




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« on: August 01, 2006, 06:05:03 AM »

Hello,

What is the least hassle way to match radios in general (e.g. my handheld TH-F6A) to my sound card? I did not see it using a simple forum search.

Thank you!!

73,

Alan
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N4CR
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Posts: 1672




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« Reply #1 on: August 01, 2006, 07:17:32 AM »

Steal the matching transformer from a couple of old 8 bit internal modems. You can find them in computer junk bins for about a dollar or less.

This will provide ground loop isolation and are pretty much the same transformers provided in the Rascal interface.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
KB4QAA
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Posts: 2407




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« Reply #2 on: August 01, 2006, 07:27:02 AM »

The simplest is to try plugging into the Mic and Line In jacks, and using whichever gives you acceptable audio level and least distortion.

If the result is distorted and too loud, check the Windows "Recording Control" settings for the Mic.  There is a selectable Mic boost which may be 10db, 20db or other, depending on which Windows version you are running.   And of course, check the slider controls for setting.

For a typical ham gear this should work in almost all cases.   It can be a little more problematical if you are interfacing professional audio gear or other oddities.   Of course when all else fails check the specs of your gear and computer.  

Generally, if the impedances are reasonably close, or going from high impedance into lower, things will work.  The next best choice would be to use an impedance matching transformer (Radio Shack) used to have a couple choices.   Probably the last choice would be getting into active op amp devices or such.  Often you will end up introducing more noise and distortion and losing more signal than if you just accepted a modest impedance mismatch.

I went thru a lot of this several years ago on a project which required matching TX/RX audio between military radios, PC's and professional audio equipment.

Good luck. bill

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K5LXP
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« Reply #3 on: August 01, 2006, 08:45:12 AM »

Since in this situation you have gain to burn, you could also do this with a resistor network.  Type "resistive matching" into google for some practical examples.  A transformer gives more isolation, but in most cases it's not really necessary.

Mark K5LXP
Albuquerque, NM
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W9OY
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« Reply #4 on: August 01, 2006, 01:39:10 PM »

radio sold an isolation transformer for a couple of bucks.  I don't know if they still have them or not

73  W9OY
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WZ6F
Member

Posts: 98




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« Reply #5 on: August 02, 2006, 06:37:34 PM »

Thanks to all. I will try the isolation transformer first (easiest) and potentially followed up by a simple resistor dividing circuit which will reduce the voltage. If these do not work I will try some other ideas (e.g. keeping an eye out for an old modem). Oh yes, I unfortunately already tried both line in and microphone adjusting the volume levels.

73 and thanks again!!!!!

Alan
wz6f
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