[ICOM] Icom Microphones

[KE5CTY Bob]

Yes Adam:

Thank you *very much* and please do send the diagrams.

73 fer nw,
Bob
KE5CTY (old calls WB5ZQU - WY5L)
10X# 37210, FP#-1141, SMIRK#-5177
http://www.qsl.net/ke5cty/
Code may be taking a back seat for now,
but the pioneering spirit that put the code
there in the first place is out front of it all.


-----Original Message-----
From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net]
On Behalf Of Adam Farson
Sent: Sunday, July 31, 2005 2:52 PM
To: 'ICOM Reflector'
Subject: RE: [ICOM] Icom Microphones


Hi Bob,

You may be able to adapt the headset microphones to your IC-728 if they
meet these conditions:

Source impedance 200 to 600 ohms

Output voltage 2 to 3 mV on voice peaks

You can get an approximate idea of the source impedance by looking at
the circuitry that the mic drives (if possible). Typically, an external
mic for a cellphone will be low-impedance (600 ohms or less). You can
check the output with an oscilloscope, if you have access to one.

A telephone headset mic has a very high output voltage, of the order of
500 mV to 1V on voice peaks. It has to be compatible with a carbon mic
in a telephone set. You will need to build an attenuator to reduce the
output to 3 mV or less.

A 0.47 to 1 uF non-polarised capacitor must be connected between the mic
or attenuator output and the mic input of the radio (Pin 1), to prevent
shorting the electret polarising voltage. 

Incidentally, any of the Icom mics with the 8-pin Foster plug except
some of the very early ones will fit any Icom transceiver fitted with
the standard 8-pin Foster socket. This includes the SM-6, SM-8, SM-10,
SM-20, HM-12, HM-14 and HM-36. There are also modular/Foster adapters
(both genders).

Here is the mic socket pinout:

http://www.qsl.net/ab4oj/icom/heilsound/icom_mic.html


You may be able to power the external mic amplifier (as needed) from the
radio's +8V supply (Pin 2. Caution! 10mA max.) The Plantronics has an
amplifier, and may require a higher voltage than 8V. I am not sure
whether the cellphone headsets require external power or not. If the
headset element is an electret, you will be able to power it from Pin 2
via a 4.7K or 10K ohm resistor between Pin 2 and the output lead (with
the capacitor between the output lead and Pin 2), or by connecting its
output to Pin 2 without the capacitor.

Hope this helps. If you would like some diagrams, I can send them to you
off-list.

Cheers for now, 73,
Adam VA7OJ/AB4OJ

-----Original Message-----
From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net]
On Behalf Of KE5CTY Bob
Sent: 31 July 2005 12:29
To: Icom Reflector
Subject: [ICOM] Icom Microphones

In talking to others, I understand that Icom Microphones are special
creatures for the Icom line of radios.

Sometimes I have noticed - you can't even swap them between Icom Models
themselves.

So I am asking this question to avoid messing something up on my rig.

I have an IC-728 and a hand microphone, I would like to be able to build
a headset microphone for it for higher quality audio output. 

I have some old Plantronics amplified headsets that were made for using
on a regular telephone and some headsets from old cell phones.

One from the cell phones (a Belkin) I especially like because of the
quality of the earpiece.

I am already using it plugged into the Headphone jack in the front of
the rig for listening.

Since I have Audio Output at the microphone jack I would like to be able
to wire this headset into the mic input for both functions of Mic and
Headset. What considerations do I need to look at to make this possible?

I don't have the money to buy a Heil or anything like that - so please
let's stay off that subject as it is frustrating for me already.

73 fer nw,
Bob
KE5CTY 


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