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Author Topic: Yaesu FT-450D feedback into headphone  (Read 615 times)
KE2KB
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Posts: 633




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« on: November 07, 2017, 10:18:17 AM »

Hi;
I have a new FT-450D. Everything is working fine, but I am hearing my voice - distorted, low volume - coming through the headphones when I transmit on any band. This happens when a dummy load is connected directly to the radio, and at all power levels - although the amplitude of the distorted voice is lower as I reduce output power.
I hear this mostly when the headphone is connected to the rear panel jack, but it is still there at the front panel jack (just easier to hear at the rp due to the af response there).
I do not hear anything from the radio's speaker when I transmit at any power level into the dummy load or an antenna.

The radio is pretty well grounded - a separate #6 ground conductor running from my 2nd flr shack to a ground rod (10ft 1/2" copper plated) which is also bonded to the electric service ground rod.

The rig is being powered from an Astron RS-35M power supply mounted close to the radio. I am using the Yaesu supplied power cable to connect the radio to the power supply.

This is not a real problem, as the volume level is quite low, and I have had no reports of RF feedback on my audio signal. But if it is something I can fix, then I will persue it.

Any suggestions?

Thanks
Frank
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W8WMM
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Posts: 30




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« Reply #1 on: November 07, 2017, 11:52:48 AM »

Have you tried a different set of headphones? I suspect an impedance mismatch, but that's just a hunch.
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W3TTT
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Posts: 267




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« Reply #2 on: November 07, 2017, 11:58:29 AM »

I have a new FT-891.  I set the mic preprocessor up to 100 (from the factory value of 50).  Immediately I am hearing my voice in the headphones.

YMMV.

 
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KE2KB
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Posts: 633




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« Reply #3 on: November 07, 2017, 01:32:27 PM »

Hey guys;
Thanks for your replies;
I have two pair of headphone I have tried, and I can hear my voice in both of them.
I also tried changing the mic gain. Reducing it to "low" does help a bit, but does not eliminate it completely. Setting to high makes it worse.
I guess next thing to do is play with the mic eq setting.

I also read that there may be a grounding issue between the head and the chassis, which causes an 800hz buzz in xmit and receive audio. That buzz shows up in recorded audio, so maybe I should check to find whether this feedback sound appears in the recorded audio as well.
I will play around with various controls/settings on the radio, then maybe try adding RFI filtering to the DC power line between the PS and the radio.

The fact that the problem appears even when I connect a dummy load to the radio tells me that this is not an issue with RF getting into the radio from an external source such as antenna or feedline. It appears to be an isolation problem in the TX/RX switching.
What I still need to do is determine whether or not I hear feedback when I am in CW mode. I don't have my key wired up yet, but should be able to get to it later today. I suppose that if there is feedback in CW, it will show up as a hum or click when the radio is keyed.
« Last Edit: November 07, 2017, 01:42:35 PM by KE2KB » Logged
SWMAN
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Posts: 1069




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« Reply #4 on: November 07, 2017, 06:27:59 PM »

Sounds like you have the audio voice monitor on, turn it off and see what happens.
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KE2KB
Member

Posts: 633




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« Reply #5 on: November 07, 2017, 07:05:47 PM »

Sounds like you have the audio voice monitor on, turn it off and see what happens.
I checked it and voice monitor was not on. When I did turn it on, I heard a clear voice in my phones. When it is off, I hear a low-distorted voice.
When I switched to CW mode, I could hear the CW side tone (no distortion) in the phones. When I turned the side tone vol all the way down, I heard nothing at all in the phones when I transmitted CW.
« Last Edit: November 07, 2017, 07:16:29 PM by KE2KB » Logged
VA7CPC
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Posts: 2805




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« Reply #6 on: November 07, 2017, 11:14:46 PM »

If you have any ferrite cores, try putting a few loops of your headphone cord through one, as a toroid choke. 

If the FT-450 has its chassis grounded, remove the ground wire, and see if the problem goes away.

If you were working with a real antenna, fairly close to the rig, I'd guess "RF in the shack".  But if the problem occurs with a dummy load, it might be something else.  You might also try the Yahoo FT-450 group -- I have vague memories of this being reported in the past.

.     Charles
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KE2KB
Member

Posts: 633




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« Reply #7 on: November 08, 2017, 09:52:22 AM »

If you have any ferrite cores, try putting a few loops of your headphone cord through one, as a toroid choke. 

If the FT-450 has its chassis grounded, remove the ground wire, and see if the problem goes away.

If you were working with a real antenna, fairly close to the rig, I'd guess "RF in the shack".  But if the problem occurs with a dummy load, it might be something else.  You might also try the Yahoo FT-450 group -- I have vague memories of this being reported in the past.

.     Charles
I tried everything you suggested; even tried adding a ferrite in the DC power supply cable right at the radio. Nothing changed.
This definitely appears to be an internal problem with the radio. Not a show-stopper by any means, but it is something that I would like to investigate and hopefully solve. I will check out the Yahoo user group.
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