Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Homebrew interface and Noise  (Read 2757 times)
VO1GXG
Member

Posts: 60




Ignore
« on: May 31, 2010, 12:30:03 PM »

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.
Logged
AA4PB
Member

Posts: 12899




Ignore
« Reply #1 on: May 31, 2010, 01:42:24 PM »

How small is small?  Digikey and mouser should have plenty of 1:1 (600 ohm to 600 ohm) audio transformers available.
Logged
VO1GXG
Member

Posts: 60




Ignore
« Reply #2 on: May 31, 2010, 02:29:04 PM »

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..
Logged
W3JKS
Member

Posts: 200


WWW

Ignore
« Reply #3 on: May 31, 2010, 02:31:47 PM »

Buxcomm has them on clearance for $5.97US:

http://www.buxcomm.com/catalog/index.php?main_page=product_info&cPath=37&products_id=1270&zenid=7ug198rkognlsp7b07t3oj9vi4

73,
john W3JKS/AAT3BF/AAM3EDE/AAA9SL
Logged
VO1GXG
Member

Posts: 60




Ignore
« Reply #4 on: May 31, 2010, 06:55:53 PM »

Perfect John! Thanks.

with some grounding i got most of the noise gone but its still there this should kill it off!!

Cheers!!
Logged
KB1NLW
Member

Posts: 69




Ignore
« Reply #5 on: June 02, 2010, 01:05:33 PM »

I would try clip on ferrite beads to kill RF ground loops.
Logged
VO1GXG
Member

Posts: 60




Ignore
« Reply #6 on: June 02, 2010, 10:08:09 PM »

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.
Logged
W5LZ
Member

Posts: 477




Ignore
« Reply #7 on: June 05, 2010, 05:50:31 AM »

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
Logged
KD4SBY
Member

Posts: 225




Ignore
« Reply #8 on: June 07, 2010, 10:26:45 AM »

Radio Shack still carries a 1:1 isolation transformer (600:600 ohms) which is reasonably small.
The stock number is 273-1374.
Logged
WI7B
Member

Posts: 53


WWW

Ignore
« Reply #9 on: June 07, 2010, 02:10:16 PM »

I agree.  The Radio Shack 1:1 works well. I use one for my homebrew digital mode interface for a Kenwood TS-480S
Logged
AE5NE
Member

Posts: 91




Ignore
« Reply #10 on: June 10, 2010, 10:44:15 AM »

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.
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!