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MD 100 Sensitivity to Background
Noise
Question: I hope this
message will be not a little bit off topic, but, probably could
be "interesting". I have a barand new FT1000 Mark V and a MD100
microphone. This microphone, unfortunately, gets a lot of
background noise, I mean when a switch my home brew linear
amplifier on the noise of its fan probably, a little bit noisy,
"enters" in the microphone causing some troubles you can easily
imagine.So my question is is there any electronic circuit to "
cut " this noise ?? Is there anybody have my same problem and
have already found the solution. Any suggestion will be
appreciated. Andy I7DFV
Response 1: Yes Andy, there
are devices to help reduce the effect of background noise
(within limits). Two types of audio equipment that are designed
specifically for this purpose are called "noise gates" and
"expanders" (or "downward expanders"). These functions are often
combined with other audio processing functions such as
equalization (boosting or cutting certain audio frequencies
relative to others) or compression, but are sometimes found as
single purpose devices. The way a noise gate generally functions
is to cut off (open) the audio path if the incoming level is
below a user specified threshold and connect (close) the path
for louder audio. You set a threshold control so that the audio
path is open (off) when there is only background noise present,
but closes (connects through) immediately when you start to
speak into the microphone. Expanders are a bit different in that
they simply reduce (not eliminate) the the output audio level
when the input level is below a threshold, and allow it to pass
unaffected when the level is above the threshold. Sometimes
complaints of "lots of fan noise" are caused by having your
microphone gain set too high causing excessive levels of ALC in
the transmitter, which effectively reduces the level of louder
audio while seemingly raising the level of softer sounds
(fans?). Adjusting mic gain for ALC indications on loud voice
peaks only will reduce the effect of the fan noise.
Of course, if the incoming level of your background noise is
very close to the level of your voice at the microphone, no
equipment (other than perhaps software noise reduction DSP
techniques) can materially change that. In that case, you'll
have to move the noise source (fans) farther away from the
microphone or perhaps put a partition of some type between the
noise and the microphone. You'll find that most of the those
hams who have hi-fidelity or "broadcast" quality SSB audio on
the air are using noise gates or expanders as part of their
audio processing chain. [No commercials, just for information:
this audio gear (new and used) is widely listed at the EBay
auction site or available specifically for hams (W2IHY).] I hope
this is useful. 73, John W2KI
Response 2: I have been test
driving a Yaesu FT-1000 MP V which has this same microphone
MD-100 and had been getting some intermittent reports of noisy
transmit audio like I may have been running the processor too
high or complaints of picking up background noise such as the
blower in the transceiver. Well, it did it again tonight and I
knew that I had not cranked up any of the controls so I noticed
that this particular Yaesu desk microphone uses the cursed RJ
style of mic connector in the rear of the mic. So I robbed the 8
pin to 8 pin mic cord from my own MD-1 mic and tried it. The
noise was all gone! I took my RJ crimping tool and recrimped the
RJ mic connector (that plugs into the back of the MD-100) and
Voila! The noise is all gone. Yaesu has been have a lot of
problems for many years with those RJ style of mic cords on
their vhf and uhf radios as they get very noisy when
transmitting and by wiggling the cord and monitoring your
transmit signal you will be able to hear it all. I usually try
and recrimp those mic cords and it will normally repair the
problem for some time. So my suggestion is to NOT use the RJ
style of mic cord on the MD-100 desk mic but rather either make
your own 8 pin to 8 pin mic cord or purchase it from Yaesu.
Best of 73's from Fern VE7GZ
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