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Author Topic: How isolate pc from kx3  (Read 7933 times)
KG4OLW
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Posts: 168




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« on: June 26, 2013, 05:16:44 AM »

I am trying to receive some weak am radio stations on my KX3. I can tune them in on the kx3 just fine, however as soon as I plug in either the kx3 usb pc control cable, or the i/q 1/8" stereo cable, I get a loud hum on the kx3 up to s9 that knocks the signal out, additionally on the panadaptor, all the weak signals disappear. I can tune in the strong stations, but the weak stations are all gone.

I have heard of people using a ground loop isolators. Is this what I should be using in this case? Should I get one for each of the connections, one for the usb --> 1/8" cat cable as well as the i/q audio cable? Has anyone experienced similar issues? Also is the noise on the vfo frequency normal? If it is does the flex radio suffer from the same, or the other rigs with and if out that goes into an lp-pan?
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NI0Z
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« Reply #1 on: June 26, 2013, 08:09:33 AM »

This article should help:

http://roaringstar.com/index.php/articles/66-kx3-nap3-lp-brige-dm780-setup

RadioShack sales a cheap isolator and that is what I use.
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K5TED
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Posts: 747




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« Reply #2 on: June 26, 2013, 04:38:27 PM »

The ground loop isolator should take care of the I/Q connection, however, the USB hum issue is a different story altogether.

If you are getting a severe hum when connecting the PC USB to the KX3, then you have a few things to investigate.

Have you tried a completely different type of USB cable?

How are you powering the PC?

How are you powering the KX3?

Are you using a laptop with power adapter or a desktop PC with internal supply?

Have you checked this with another PC?

Have you checked the PC power supply for noise on the 5v rail?

Are the PC and KX3 power supply plugged into the same electrical circuit?
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K5TED
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« Reply #3 on: June 26, 2013, 04:46:24 PM »

Also, make sure the USB and I/Q cables aren't coiled up right next to a linear power supply. or routed underneath, next to, etc. said power supply.
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NI0Z
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« Reply #4 on: June 27, 2013, 08:09:52 AM »

I suppose it might help to say a little more here if you are still struggling.  I basically use an External USB Sound Card with my KX3 to get rid of all the hum.  You want to make sure you have a ferrite on the USB Cable as well.

The Isolator helps as well if you plan to use the I/Q signals.  So the path looks like this:

KX3, MiniJack to Stereo Jack Converter, Radio shack Isolator, RCA Jacks into USB Sound Blaster, Soublaster connected to PC via USB.

Some PC's may cause more Hum than other.  The equipment proximity advice given is also very relevant in some cases.  In others you may have a devil of a time stopping hum.  You also may want to check that your sound card settings in Control Panel are not creating a feedback loop that the KX3 aggravates when connected to the PC sound card.  Check your input and output levels.
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W4HIJ
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Posts: 367




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« Reply #5 on: June 28, 2013, 06:32:42 PM »

  You want to make sure you have a ferrite on the USB Cable as well.



A ferrite?Huh  God forbid!!!   Cheesy Cheesy Cheesy Cheesy Sorry couldn't help myself. Hope the OP get's his issues worked out! ( also that people here still have a sense of humor!)
73,
Michael, W4HIJ
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HAMMYGUY
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Posts: 85




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« Reply #6 on: July 16, 2013, 07:16:40 AM »

Google "SDR-1000 isolation" and you'll see that most of these issues have been figured out by others several years ago.  No sense reinventing the wheel just because it's a different radio. 
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W4HIJ
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Posts: 367




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« Reply #7 on: July 18, 2013, 05:35:24 PM »

Google "SDR-1000 isolation" and you'll see that most of these issues have been figured out by others several years ago.  No sense reinventing the wheel just because it's a different radio. 
Most people figured out how to deal with RFI and PC's way back when the PC became a logging tool.  Still doesn't stop some people from complaining about it and trying to make an issue of it. A properly designed and laid out ground system will nullify RFI issues regardless of whether a PC is involved with the radio or not and also regardless of the power level in use.
73,
Michael, W4HIJ
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KC4MOP
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Posts: 743




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« Reply #8 on: July 23, 2013, 05:12:10 PM »

A DJ friend of mine had same problem using a USB disc jockey hardware device.
Get a three prong adapter on the laptop charger. You are eliminating the safety ground from the computer. No issues or problems. No safety hazard. No hum!
Run your laptop on battery problem go away; then it is definitely the charger.
Fred
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ZENKI
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Posts: 960




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« Reply #9 on: August 02, 2013, 06:47:57 AM »

Galvanic isolated USB interface. I used them on all my test equipment.

http://www.herostechnology.co.uk/pages/RF_Filters/filters.html#DISO

This is a ham marketed version. There are others on the market.

A isolated USB interface should be standard on all ham equipment. As usual ham equipment manufacturers are behind   on the latest technology and trends.
These isolated interfaces are just about standard on test equipment.

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