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Author Topic: RF in head set cables  (Read 2634 times)
K9ZF
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Posts: 76


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« on: May 02, 2010, 03:52:15 PM »

Group,

Not sure this is the right place, but thought I would throw this out looking for ideas.

I bought a cheap head set awhile back.  This is basically a computer type head set that has been adapted to use with my FT897D.  I'm not complaining about the quality of the head set, as it was sold quite cheap, but it does need some help to work.

When ever I transmit, I get feed back into the mic.  I believe I am getting RF back into the mic, likely picked up by the head set cord.  As a 'quick and dirty' fix, I grabbed a clamp on ferrite and wrapped several turns of the cord through it.  It may have helped, but didn't solve the problem.

My next idea is to replace the cheap cord with a better, shielded, one. 

What do you think?   Will the shielded cord help?  Bypass caps?  More or different ferrites?

You can reach me direct at K9ZF, at, Yahoo, if you prefer.

Ideas appreciated,
73
Dan
--
Amateur Radio Emergency Service, Clark County Indiana. EM78el
K9ZF /R no budget Rover ***QRP-l #1269 Check out the Rover Resource Page at:
<http://www.qsl.net/n9rla> List Administrator for: InHam+grid-loc+ham-books
Ask me how to join the Indiana Ham Mailing list!

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K9ZF
Amateur Radio Emergency Service, Clark County Indiana. EM78el
The once and future K9ZF /R no budget Rover
 ***QRP-l #1269
Check out the Rover Resource Page at:
<http://www.qsl.net/n9rla>
List Administrator for: InHam+grid-loc+ham-books
Ask me how to join the Indiana Ham Maili
W3LK
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Posts: 5644




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« Reply #1 on: May 04, 2010, 09:13:16 AM »

Replacing the cord on a cheap headset is like putting lipstick on a pig. Just ditch it and get a decent headset.
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A smoking section in a restaurant makes as much sense as a peeing section in a swimming pool.
AJ8MH
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Posts: 120


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« Reply #2 on: May 05, 2010, 11:17:32 AM »

My FT-950 is sensitive to RF feedback depending on the mic and frequency
band used.  I haven't had any problems with the supplied hand mic or a modified
D104 with a electret element.  However, I've spent hours trying to eliminating
RF feedback when using my HP noise-canceling mic/headset (and others, but less
of a problem), especially when the phones are plugged into the SP-2000 external
speaker.
 
I use double shielded cable on the foot switch, external speaker, headset and
headset interface box.  I tried all the recommended “fixes” with no luck, but I
think I have finally resolved the problem.
 
Now, I just don't use the headphone jack on the external speaker with the mic/headset. 
I've shortened the leads on the headset interface box, and I installed a .0047
(junk box grab) across the jack going to the headset mic.  I also had to place a
.01 in the interface box from mic ground to the ground used for the headphones. 
(Directly connecting these two grounds together did not fix the feedback.)  I
have one core over the mic line between the interface box and the 950 and one
core at the mute switch/volume control on the HP headset cable.

By the way, the amount of feedback ranged from nothing, to a little audio distortion,
to...what sounded like squelch noise.

I hear that some ops have had RF feedback problems with expensive Heil headsets,
also.  But, I think that the cheaper headsets for computer use could be more
susceptible.  Why do I use thecheap headsets?  Because, I have them coming out
of the woodwork!

73 and good luck,
Joe
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W7VO
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Posts: 194


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« Reply #3 on: June 02, 2010, 02:42:49 PM »

I am having the exact same problem with my Heil head set, but it only occurs on 80M when the amp is at full power. I get a weird oscillation that I can change by moving the headset around. Disconnecting the earphones made it better, but it is still there. I have also tried an coaxial RF isolator, and moved grounds around, all with little success.

Today I ordered some ferrite toroids from Amidon, some Type 77 material and some Type F material. These are specifically made for low frequency (< 20 MHz) applications. I will try wrapping the mic/headset cords with these puppies and see if it makes any difference.

Just an FYI, Amidon suggests Type 43 material for applications above 20 MHz (like 10M RFI issues), and Type 77 or F for lower frequency problems. I suppose you could use both and get a broad spectrum of RFI suppression.

I will let you guys know what happens.....

73;

Mike, W7VO
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AA4HA
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Posts: 1386




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« Reply #4 on: June 03, 2010, 05:49:11 AM »

You can try bypass caps but it may reduce the frequency response of the headset. That will depend upon the value of the capacitors.

If you really like the headset (irrespective of cost) you can try to replace the cord with shielded wire. Usually headset wiring has very minimal shielding as they are trying to keep the cord flexible.

73 Tisha Hayes, AA4HA
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
W7VO
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Posts: 194


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« Reply #5 on: June 03, 2010, 01:40:05 PM »

I just looked at the Heil website, and they have a possible cure for RFI when using their headsets. Some radios (Like my Yaesu FT-2000) have a separate mic ground, and a frame (chassis) ground. In my FT-2000, those are connected internally on the mic amp board. There is a 1000pF bypass cap at the connector that is used for RF bypassing. It looks like what they are suggesting is connecting the two grounds together at the input connector. I might try that and see how it works....

Mike, W7VO
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W6GX
Member

Posts: 2482




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« Reply #6 on: June 12, 2010, 11:36:45 PM »

I have the W2ENY computer 'gaming' headset and I have been having RFI feedback on 10m.  Today I solved the problem by placing a 0.002uf cap across the mic and mic ground leads, and placing a ferrite snap on core on the cable.  Funny thing is that I would still get RFI if I just did one of these two things.  The RFI is eliminated only when both things are done.

ps many headphone cords don't actually use a shield.  They use the proven 'twisted pair' technology to achieve RF shielding.

73,
Jonathan W6GX
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K3AN
Member

Posts: 787




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« Reply #7 on: June 23, 2010, 06:58:42 AM »

Twisted pairs provide a form of shielding only when they work into a balanced load. With one lead of the pair connected directly to ground (inside the radio) and the other lead connected to an input impedance of some sort, there is NO balance and therefore NO protection against unwanted signal pickup.

RG-174 is a cheap, small coaxial cable with adequate shielding. I use it for all my interconnect cabling in the shack.
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