[ICOM] Icom Microphones

[Rolly (W7DGX) & Sandra Goodspeed]

Does anyone know about portable phone (not cell phones) headsets. How might 
they be connected to Icom's (in my case a 756 orig).

Rolly  W7DGX


----- Original Message ----- 
From: "Adam Farson" <farson at shaw.ca>
To: "'ICOM Reflector'" <icom at mailman.qth.net>
Sent: Sunday, July 31, 2005 12:51 PM
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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