Wiring up a non factory standard mic to a radio that uses a E.C.M type insert


So you just hook up the dynamic microphone or other non standard mic (like a D-104 for example) to a radio that uses a E.C.M type mic like the Yeticom Optima or the many late model pc programmable 10 meter or modern ham transceivers?:

NO!

Yeticom Optima (as an example ) supply around +8 volts DC of power up the audio line from the radio to the microphone as well as the mic audio signal going down the line into the radio. Great for powering the electret type microphone, that requires power to work, but not for a dynamic type.

 De-coupling (or blocking) this DC is a must or you will probably destroy the the 8 volts regulator and various SMT parts by connecting the mic hot wire straight to ground through the dynamic element even via the 600 ohm impedance of a dynamic or power mic (deck or mobile power preamp mic)!


What is a E.C.M mic insert :

a E.C.M mic insert (electro magnetic mic for short) is a F.E.T (field effect transistor) mic preamp insert that requires a bias voltage either feed to a third pin on the mic insert or super imposed on the mic audio line most modern e.c.m insert's only have two pins or solder pads .A E.C.M insert can not be used on a radio designed for a normal dynamic mic insert (normally) as the radio will not have a bias voltage either via a separate mic plug pin or super imposed voltage on the mic hot wire (audio wire)

All mobile phones and most handheld vhf or uhf handhelds use these e.c.m mic inserts due to the very small size and the fact they have a flat audio response and a preamp built in so not needing more complex audio preamp in the mic stage in the handheld themselves. Dynamic mics by their very nature have a peaked audio response and do not suit all situations or voices.


How is it possible to have both a audio signal and a dc voltage on the same wire :

A audio signal is AC a voltage supplied by the radio is DC voltage both can exist on the same wire at the same time by use of blocking capacitors in side the radio to prevent the dc voltage that is super imposed on the mic wire from damaging the mic stages in the rig.....most Icoms/Yeasus/Kenwoods after 1980 use this system as well as many many many vhf/uhf transceivers such as Motorola for many many years.


How do i know my radio is is a E.C.M type mic insert radio:

How do I find out if it has a DC voltage on the Mic Audio line?

It is as easy as connecting a volt meter (set for 15V DC scale) between the Mic Audio pin and Ground pin of the Mic socket on the radio (this maybe a pin rather than the socket shell, with the radio switched on. BE CAREFUL NOT TO SHORT THE MIC PIN TO GROUND!

BE CAREFUL not to touch any of the other pins with the test probes as this can damage the voltage regulator that powers the mic or the S.M.T parts connected to it , you may find that inserting an un-wired plug into the radio will give you some assistance with this.

If you have no DC voltage present then either there is no power supplied up the Audio lead or someone has been there before and blown the regulator!.

 If the radio works fine with it's own Mic then you can stop reading this page and wire up your dynamic Mic following the pin out for your radio.

If the radio does not work on it's own Mic then further investigation will be required and is outside the scope of this page.

If you have a DC voltage on the Mic Audio pin then you will need to read, understand and follow the rest of this article.


Getting rid of the "unwanted" DC by using a isolation capacitor

De-coupling the DC is as easy as fitting a 1f (105) poly or disc ceramic capacitor in the mic's hot audio lead.

Capacitor fitted in series with the mic hot wire this is easy to add inside the mic its self

you will still be able to use your stock e.c.m mic on the radio if you chose to change back to it by simply plugging it in to the radio as normal.

You can use a NON-POLARIZED Tantalum capacitor (1uF)  or a pair of back to back  Polarized Tantalums

Information on hooking up NON standard mics to radios we sell that have E.C.M type inserts

 (this will be updated in time with more radios)


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