Fixing Audio Distortion with the Mark V and MD 200 Microphone
Courtesy of Mike Schatzberg, W2AJI Administrator: 1000MP Reflector
Hello MP Fans:
Over the years my Mark V has suffered on and off with RF distorting my
audio. Certain positions of my yagi could occasionally result in audio
distortion during transmissions. I normally use my MD 200 microphone to
drive some outboard compressor/limiter with a downward expander to
control noise. As you know, this microphone was developed to work with
the Mark V specifically. I have previously needed to use ferrite
snap-ons to control the problem. The problem is especially pronounced
when running higher power with an amplifier.
Recently, I realized that the RF was entering the audio chain via the MD
200 microphone. I started to examine the microphone carefully, and here
is what I discovered:
1. The element housing is floating, and not connected to chassis ground.
It seems to act as an antenna, and picks up RF.
2. The powder coating on the housing does not permit continuity between
the upper and lower portions of the housing.
3. The vibration damping mounting bracket is not grounded to the base
4. No chassis ground is carried in the cables to the microphone board,
which is grounded to the floating housing.
5. The base of the microphone and its switching board are indeed chassis
Here's how you fix the problem:
1. At the point of attachment of the mounting bracket to the housing,
remove a small amount of the housing powder coating around the holes
which are used by the gold plated retaining pivot screws. This will
permit the mated upper and lower housing halves to be electrically
connected. ONLY REMOVE the coating from the small area around the
screws, from the surfaces where the upper and lower housings meet. When
the housings are reassembled, these contact points will not be visible
2. Remove the coating from the mounting bracket, at the very bottom,
ONLY FROM the surface that mounts onto the post which extends from the
microphone base. The post is at chassis ground already, and this change
will ground the mounting bracket also.
3. Next, the MD 200 can accept a second cartridge, there is a switch in
the base to select either the stock variable pressure element, or the
optional cartridge which you can install. This means there are two extra
wires in the microphone housing cable, which are not being used if you
DID NOT INSTALL THE ADDITIONAL CARTRIDGE. Remove the top housing and
examine the microphone board. You will see the two small pads, next to
the microphone element connector, which is white. One pad is marked, GRD
2, this is the unused microphone ground for the optional cartridge.
Solder a small gage wire to this pad, it will connect to the internal
wiring, which is connected to the base. The other end of the small wire
can be connected to the board ground, which can be obtained at the near
by pad with the mounting screw which attaches the board to the housing.
Providing this link will ground both the board to the housing, and the
housing to the base, once the other
end of the cable is grounded. Reassemble the housing.
4. Remove the base cover, you will see the small slide switch which
selects the microphone cartridge. In front of this is a row of pads
which appears to be the termination of the cable conductors. The 4th pad
from the right is the 2nd cartridge microphone ground, you can confirm
this fact now, by using your VOM to see that the cartridge housing is
common now to this pad (make sure that the upper housing is plugged into
the base of course). Tack solder another short wire to this pad, and
solder the other end to the board ground, also at the point that the
board is retained by the screw at the lower left hand corner. This board
is already at chassis ground, so completing the wiring to the housing,
makes everything common. Reassemble the base cover, and install the
cartridge mounting bracket, and the cartridge housing into the bracket.
I made some measurements and found that the housing screens are common
to the housing itself, so grounding the housing grounds the large
In my case, the RF distortion was eliminated completely, and the audio
quality was greatly improved. It is surprising that Yaesu produced a
microphone without grounded shielding for the element, with as large a
screen area as this microphone has. Obviously, take care not to damage
your microphone either electrically or mechanically during this
which does require moderate experience to complete. This modification is
done at your own risk, and no liability is assumed by the author for
errors or damage. Check your work carefully, it should work well for
I will eventually take some pictures of the mods on the two boards and
place them on my website. If you have any questions, please let me know.
73 and Happy DXing,
Administrator: 1000MP Reflector