Jim Brown wrote:
On 10/28/2011 6:49 AM, W8KZW wrote:
I recently elisted a computer-type headset for ham use.
I've had similar great results with some Plantronics miniature
headset/mics that I bought several years ago at the Milwaukee hamfest.
Made adapters to use them with all my rigs, which at that time included
an Omni V, k2, TS850, and IC746. All of the mics worked fine and
sounded really good with all of the rigs.
They use an
electeret element, so you need to apply about 8 volts DC through a dropping
resistor (2,200 ohms or so, value isn't critical)to protect against the
short to ground that occurs upon insertion and removal of the plug.
That's NOT why you need the dropping resistor (but you DO need it) --
the resistor prevents low impedance of the 8VDC power supply from
shorting out the audio. I'd use a higher value, more like 4.7K.
Apparently there is more than one reason for using a resistor in series
with the power supply.
You
also need to keep the DC off the mic line to the rig with a capacitor
I've never seen the need for this. Most rigs are designed to accept
electret mics that are biased in this manner.
Yes, MOST rigs have DC isolation in the mic line. That also implies
that ALL rigs don't have isolation. Why take a chance?
Very inexpensive and great results.
Yes.
Bob Heil has done lots of advertising in the ham world and sells his
very cheaply mics for a lot of money. They are no better than the Shure
mics designed for communications use, like the 444 (look for it used for
$25), or the mic in the Yamaha CM500 (about $45 new from many online
sources). The CM500 is so good that it doesn't make sense to try to add
a boom mic to another good set of headphones. I have two pairs of
MDR7506s, both of which now sit on the shelf. All you need to do to use
a CM500 (or other good headset designed for use with computers) on your
Ten Tec rig is a simple connector adapter for the mic, and a 1/8-inch to
1/4-inch adapter for the phones.
See the Solving Problems in the Shack chapter of
http://audiosystemsgroup.com/RFI-Ham.pdf and also the appendix on audio
for details on how to hook up the mic, and sources for good connectors
from a good US online source. The same info is in a power point of a
presentation I've done to a bunch of ham clubs.
http://audiosystemsgroup.com/HamInterfacing.pdf
I have to admit that spending serious money on an interface box is not
just unecessary but also silly. Almost as silly as directly connecting
a computer to a radio. While transformer isolation of audio inputs and
outputs along with opto isolated PTT lines might seem like overkill,
they do avoid possible problems caused by ground loops and electrical
incompatibilities.
|