Active Noise Cancelling headsets have other power options, maybe
running off 28V. I am not aware of 48V systems in Commercial
aviation, but I don't know everything that is out there. Carbon mics
were different but not common any more.
Maybe it was 28 instead of 48 volts ... it has been a while since I
ran into the problem of making the aviation headsets run in an "AV"
environment. I do know that the headsets in question were spec'd as
"carbon mic" equivalent and required a high voltage bias until the
resistors were reduced by a factor of about 20.
73,
... Joe, W4TV
On 3/14/2013 4:27 PM, Mark Goldberg wrote:
A standard aviation microphone approved to TSO C58 is supposed to meet
DO-214 "Audio Systems Characteristics And Minimum Operational Performance
Standards For Aircraft Audio Systems And Equipment" although not all do.
Unless you belong to the RTCA, it will cost money to see that document. The
standard is bias excitation is 8 to 16V with a 470 ohm current limiting
resistor, providing about 10 ma to what usually is an amplifier circuit in
the mic. The ac output level is supposed to be between .02 and .08 V/Pa,
where 1 Pa is 94 dB SPL referenced to 20 uPa. Normal close speech is in
the range of about 1 to 10 Pa, so this is pretty high compared to a lot of
other mics, up to .8 V. I have not tried connecting one up, but I would
think if you had a resistor that provides about 10 ma it should work, if
the rig can stand that high an input and if the bias can supply 10 ma.
Active Noise Cancelling headsets have other power options, maybe running
off 28V. I am not aware of 48V systems in Commercial aviation, but I don't
know everything that is out there. Carbon mics were different but not
common any more.
One issue is to keep the load mic preamp from disturbing the bias. I had to
filter the bias end of the series resistor on one rig with a big cap. Also,
connections vary.
Mark
On Mar 14, 2013 12:27 PM, "Joe Subich, W4TV" <li...@subich.com> wrote:
I use my headset with my K2, but would like to try it with another
rig that supplies 10v. To get my other rig voltage down to the 3-4v
region require about 12 meg ohms in series with the 10volts
supplied.
An electret does not draw current in the classic sense. 5.6K seems
to be a good value of resistor for almost anything from 5 to 8V but
12K might be safer for your 10-12V.
The "big name" aviation headsets use 33 - 48K resistors for the typical
48V aircraft system. They tend to not work well with the 3-5V ham and
computer supplies but if they are opened and the resistor removed (or
replaced with a 2K2 depending on whether the equipment already contains
a resistor), they work perfectly well at the lower voltage.
I've always used a rule of thumb of 1K/V for electret mics.
73,
... Joe, W4TV
On 3/14/2013 2:45 PM, Dr Ira J Saber wrote:
GA Everyone
I hope this has not been answered before, but I could not find my answer
in the archives, so here goes.
Can anyone tell me how much bias the microphone is able to tolerate?
Since the battery pack supplies 3v
dc, I am sure that 4-5 volts probable won't hurt. But how about 10-12v
DC?
I use my headset with my K2, but would like to try it with another rig
that supplies 10v. To get my other rig voltage down to the 3-4v region
require about 12 meg ohms in series with the 10volts supplied.
All of you guys and gals are a great source for info regardless of topic
and I wish to thank all and any of you who choose to answer my "novice"
question. I have learned something in my years on this earth, that if
you don't ask you do not get any answers.
Thanks again in advance.
73
Ira N2IS
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