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Author Topic: Can hear myself thro the external speaker when transmitting  (Read 4457 times)
CMS239
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Posts: 20




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« on: October 24, 2017, 01:34:29 AM »

Wondering if anyone here has experience with the BHI NEIM1031 MKII.  I have started transmitting on my Icom 7300 and noticed I can hear my transmissions through the external speaker.  Monitor is off.  Same with dummy load.  However as soon as I remove the NEIM1031 MKII the problem goes away.  Any thoughts?
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VE3PP
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« Reply #1 on: October 24, 2017, 04:41:43 AM »

Wondering if anyone here has experience with the BHI NEIM1031 MKII.  I have started transmitting on my Icom 7300 and noticed I can hear my transmissions through the external speaker.  Monitor is off.  Same with dummy load.  However as soon as I remove the NEIM1031 MKII the problem goes away.  Any thoughts?

Your speaker is picking up RF. Put some chokes on the speaker leads and ground your station.
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K0UA
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« Reply #2 on: October 24, 2017, 07:44:49 AM »

Wondering if anyone here has experience with the BHI NEIM1031 MKII.  I have started transmitting on my Icom 7300 and noticed I can hear my transmissions through the external speaker.  Monitor is off.  Same with dummy load.  However as soon as I remove the NEIM1031 MKII the problem goes away.  Any thoughts?

Your speaker is picking up RF. Put some chokes on the speaker leads and ground your station.


This ^..  Try to get as many loops of the speaker wire thru the snap on choke as you can. Of better yet use a toroidal ferrite mix 31 if you can.  But I have solved my amplified speaker problems with snap on ones.
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CMS239
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« Reply #3 on: October 24, 2017, 10:37:44 AM »

Thanks guys.

It turned out to be the BHI Noise cancelling unit causing the problem due to it getting its power from the same supply as the rig.  I am now using a separate supply which soled the problem, the diode did not.

Got this reply from BHI which may help others:

Removing RF breakthrough on Transmit               
RFI problems are normally being caused by raised levels of RF that is present in your shack when you transmit.  This obviously doesn’t help your problem so we need to help you find a fix for the problem.  External audio products added to the whole system typically have a way of showing any stray RF that may be present but wasn’t noticeable beforehand.   For your information all bhi DSP noise cancelling products are designed to have excellent RF immunity.  Having an Elevated SWR on the coax leading to your transceiver can cause transmit audio can be noticeable.  Try to match your antenna system up at the antenna feed point, and you shouldn’t hear any audio on transmit. Also make sure that there is a central Ground point for the radio, ATU, PSU etc and that any other items are adequately bonded to ground.
Try and make sure all the power cables and audio connections are routed as away from the RF cable connection as possible (I’m sure you have done this already).  Check that all coax connections are tight and secure with no loose connections and that your antenna system is matched up as best it can be at the antenna feed point.
The RF is probably getting via the common ground from the power supply that you are using to power all your equipment.  The easiest and quickest way we have found to sort this issue out is to use a separate DC power supply to power your bhi DSP noise cancelling product.   We sell a range of UK mains plug-in DC power supplies that will work with your bhi DSP noise cancelling product.  Please check them out in the accessories section of the bhi website www.bhi-ltd.com.
Alternatively if you are outside the UK try to source a suitable mains plug-in 12V DC power supply locally.  Ferrites fitted to the power and audio cables can also help with this issue, fitting them as close to the radio as possible.  Make sure that all the power cables and audio connections are routed as far away from the RF cable connection as possible.   See  FAQ Help sheet 1: https://www.bhi-ltd.com/images/docs/datasheets/Helpsheet1_Iss_B.pdf
Putting a small power diode like a 1N4002 in the ground of the bhi fused DC lead may also help by blocking the stray RF from getting in via the ground (FAQ Help sheet 2 https://www.bhi-ltd.com/images/docs/datasheets/helpsheet2.pdf).  You could also try reducing the volume/AF gain on your radio in small steps whilst increasing the volume on the bhi unit to compensate.  This has the effect of reducing the overall gain of the RF going into the bhi unit on the input side.
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KD8IIC
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« Reply #4 on: October 26, 2017, 07:37:22 PM »

  Most likely you are way over processing and overdriving the mic causing splatter by trying to sound louder or have more bass than is necessary to communicate with. Been there, done that and learned how to control myself.
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