VO1GXG
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« on: May 31, 2010, 12:30:03 PM » |
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Hi All, if this topic was discussed before my apologies.
I built an interface for my computer using 2N5551 transistors. build two in a box, one for RTS and one for DTR keying, my problem is the audio coming from the computer to the radio is noisy. I'm keying a Kenwood TM-201A vhf radio via the microphone port putting the audio through there as well. The interface works fine on my TS-440 and has no noise but i am keying the radio via the 13 pin port with the audio going to the mic port. Any idea how I can fix this? someone mentioned a 1:1 transformer but i could not find any on mouser/digikey or eBay that were small.
Thanks!
Matthew.
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AA4PB
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« Reply #1 on: May 31, 2010, 01:42:24 PM » |
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How small is small? Digikey and mouser should have plenty of 1:1 (600 ohm to 600 ohm) audio transformers available.
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VO1GXG
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Posts: 57
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« Reply #2 on: May 31, 2010, 02:29:04 PM » |
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the ones i've found are fist size. now that i look closer the 5th down on mouser is the one I want. go figure! Don't go parts shopping at 2AM!
the only thing left really is will it knock out my noise problem..
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W3JKS
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« Reply #3 on: May 31, 2010, 02:31:47 PM » |
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VO1GXG
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Posts: 57
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« Reply #4 on: May 31, 2010, 06:55:53 PM » |
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Perfect John! Thanks.
with some grounding i got most of the noise gone but its still there this should kill it off!!
Cheers!!
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KB1NLW
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« Reply #5 on: June 02, 2010, 01:05:33 PM » |
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I would try clip on ferrite beads to kill RF ground loops.
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VO1GXG
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Posts: 57
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« Reply #6 on: June 02, 2010, 10:08:09 PM » |
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I grounded the radio case, the audio cable shiled and the connector ground and it got rid of the noise. Also using a TRS plug and nor a TS plug helps much.
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W5LZ
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« Reply #7 on: June 05, 2010, 05:50:31 AM » |
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Along with those 'isolation' transformers and the ferrite, you can also add a 0.01 - 0.02 cap in-line in the 'hot' audio leads. Probably won't stop that interference completely, but should help. Radio Shack used to have some very small 1:1 transformers that worked very well in this sort of application. They used to have a lot of things, so good luck with that!
Paul
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KD4SBY
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« Reply #8 on: June 07, 2010, 10:26:45 AM » |
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Radio Shack still carries a 1:1 isolation transformer (600:600 ohms) which is reasonably small.
The stock number is 273-1374.
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WI7B
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« Reply #9 on: June 07, 2010, 02:10:16 PM » |
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I agree. The Radio Shack 1:1 works well. I use one for my homebrew digital mode interface for a Kenwood TS-480S
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AE5NE
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« Reply #10 on: June 10, 2010, 10:44:15 AM » |
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Salvage the line isolation transformer from an old PC modem.
I got 4 per card from some trashed Lucent "Partner" phone system cards.... AT&T branded ones at that.
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