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.
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