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Author Topic: Thumping in headphones  (Read 3285 times)
N4DSP
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Posts: 120




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« on: May 29, 2013, 05:33:24 AM »

Operating cw there is a thumping in my headphones. Using Yamaha CM-500 and not designed for amateur radio applications. What are some means to correct this?

john
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AA4PB
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« Reply #1 on: May 29, 2013, 05:37:41 AM »

Build a high pass filter for the headset connection that will prevent frequencies below about 300Hz from reaching the headset. Alternately you could purchase a communications quality headset that is designed to pass 300Hz to 3000Hz.
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G8JNJ
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« Reply #2 on: May 29, 2013, 05:42:40 AM »

Hi John,

Hi-Fi headphones are not ideal for communication purposes, because they have an extended low frequency response.

This can be distracting when listening to weak signals or with static crashes in the background.

If you radio has a receiver audio frequency equaliser. Try rolling off the gain at frequencies below 250Hz.

A simple hardware modification is to put a low value capacitor in series with the audio feed to the headphones. Something like 0.1uF is a good starting point to try.

Rolling off the high frequency end can help make listening less fatiguing too. I actually find that cheap headsets that have a limited frequency response sometimes sound better for SSB & CW QSO's.

Regards,

Martin - G8JNJ

www.g8jnj.webs.com
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N4DSP
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Posts: 120




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« Reply #3 on: May 29, 2013, 05:43:47 AM »

Build a high pass filter for the headset connection that will prevent frequencies below about 300Hz from reaching the headset. Alternately you could purchase a communications quality headset that is designed to pass 300Hz to 3000Hz.

Bob,
which headphones do you recommend? I don't need or use the combo boom mic sets since I am only cw.
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NR4C
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« Reply #4 on: May 29, 2013, 05:44:34 AM »

What radio are you using?  I use the same headset and I don't get the thumping.

Maybe your radio has some audio shaping built in that would alleviate the problem.

...nr4c bill
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N4DSP
Member

Posts: 120




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« Reply #5 on: May 29, 2013, 05:50:32 AM »

Hi John,

Hi-Fi headphones are not ideal for communication purposes, because they have an extended low frequency response.

This can be distracting when listening to weak signals or with static crashes in the background.

If you radio has a receiver audio frequency equaliser. Try rolling off the gain at frequencies below 250Hz.

A simple hardware modification is to put a low value capacitor in series with the audio feed to the headphones. Something like 0.1uF is a good starting point to try.

Rolling off the high frequency end can help make listening less fatiguing too. I actually find that cheap headsets that have a limited frequency response sometimes sound better for SSB & CW QSO's.

Regards,

Martin - G8JNJ

www.g8jnj.webs.com

Where can these headphones be found Martin? Local Radio Shacks carry hi fi sets.

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AA4PB
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« Reply #6 on: May 29, 2013, 05:59:00 AM »

I use Kenwood HS-5 headphones. They have a limited frequency response. They are also open to the outside so that they do no completely block other sounds in the room (which might not be a desirable feature for some).
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WD4CHP
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Posts: 143




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« Reply #7 on: May 29, 2013, 06:28:02 AM »

I found an "Explorer" by Telex at a hamfest for $5.

Limited frequency response and is comfortable to wear for extended use.
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VA7CPC
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« Reply #8 on: May 29, 2013, 04:53:42 PM »

Operating cw there is a thumping in my headphones. Using Yamaha CM-500 and not designed for amateur radio applications. What are some means to correct this?

john

One other possibility:

Set the rig to semi-break-in, with a long "hold time", so that it stays in TX mode between words.

If you _still_ hear the "thumping", and it "thumps" each time you go key-up (or key-down):

. . . You have "RF in the shack".

The easiest cure is to get a ferrite clamp-on choke, and run a few turns of the CM500 cable through it, as a toroid.

I find "hi-fi" headphones perfectly OK for ham use.  The receiver's IF is supposed to remove "out-of-band" signals;  it's not the headphone's job.

What rig are you using?  How far is the antenna from the rig?  What kind of antenna?

.             Charles
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K7KBN
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« Reply #9 on: May 29, 2013, 05:21:15 PM »

This problem has very little to do with the IF circuitry; it's an audio problem.  The solution is to use communications headphones (~300-3000 Hz), or building an audio filter to remove audio outside those limits.
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73
Pat K7KBN
CWO4 USNR Ret.
G8JNJ
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Posts: 473


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« Reply #10 on: May 30, 2013, 04:25:16 AM »

Hi John,

I've used all sorts of boom headsets, most costing less than £10 GBP.

Some experimentation is required to find a pair that are comfortable and sound good in this application.

Further notes / ideas can be found here.

http://g8jnj.webs.com/Boom%20headset.pdf

http://webzoom.freewebs.com/g8jnj/Clansman%20Boom%20headset.pdf

Regards,

Martin - G8JNJ

www.g8jnj.webs.com
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KE3WD
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Posts: 5694




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« Reply #11 on: May 30, 2013, 06:07:30 AM »

The OP should do something in the way of ISOLATION of the reported problem or all answers are mere conjecture. 

**Substitute another set of headphones of any kind, even cheap earbuds, just to see if the problem persists.**

**Try the several CW modes available to you, such as Full Breakin, Semi QSK, and manual to see if the problem persists in all.**

**Try it with the rig connected only to a Dummy Load with short jumper.  Vary the power level from low to high to see if that affects the reported problem as well.**

**Try it into the antenna again at varying RF power levels, see if it only happens when sending full power but perhaps does not happen at say the 5 or 10 W level, indicating an "RF in the shack" situation.


73
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AC4RD
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Posts: 1236




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« Reply #12 on: May 30, 2013, 09:24:36 AM »

What radio are you using?  I use the same headset and I don't get the thumping.
Maybe your radio has some audio shaping built in that would alleviate the problem.

I'm with Bill.  I use ordinary low-cost stereo headphones from Amazon.   My own main HF rig doesn't pass any significant amount of low-end audio, and if the very high-freq audio ever annoys me it's easy to dial in a narrower filter or use the notch control.  Maybe "communications headphones" are better, for most people, but I'm very satisfied with my $20 phones from Amazon.  Plus, I can use them for the stereo when I want to. Smiley
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KH2G
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Posts: 238




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« Reply #13 on: May 30, 2013, 08:58:10 PM »

Before diddling with the headset, try backing off the RF gain on the receiver. I suspect the "thump" is due to AGC action.
Or turn off the AGC if your rig allows it and use the RF gain for comfortablelistening.
Regards
Dick
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KE3WD
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Posts: 5694




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« Reply #14 on: May 31, 2013, 05:36:54 AM »

Before diddling with the headset, try backing off the RF gain on the receiver. I suspect the "thump" is due to AGC action.
Or turn off the AGC if your rig allows it and use the RF gain for comfortablelistening.
Regards
Dick

Very good advice from Dick here, the RF Gain Control is one of my most often used controls, backing off the receive sensitivity via the RF Gain Control once a signal is located can make a big difference in copying CW, headphones or not.  RF Gain can lower the apparent Signal-to-Noise Ratio and when the mode is CW, can make a very easy and enjoyable listen, almost like FM a lot of the time, and that can also translate to a longer time before the dreaded Ear Fatigue sets in. 


73
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