MFJ MFJ-1272M, MFJ-1272MX, MFJ-1272MYV, MFJ-1272MZ User Manual

MFJ-1272M TNC/MICROPHONE SWITCH

Introduction

Thank you for purchasing the MFJ-1272M TNC/MIC Switch. The MFJ-1272M is designed to allow simultaneous connection of both your microphone and your TNC to the radio.

The MFJ-1272M microphone switches were designed to be used with any radio that has an 8-pin, RJ-45 modular microphone connector. Because many TNCs have different connectors, MFJ offers 5 models:

MFJ Model#	TNC and Multimodes
MFJ-1272M	All MFJ TNCs,	TAPR TNC-2 clones,	and	PK-
12/96/900
MFJ-1272MX	PK-232
MFJ-1272MYV	KAM® VHF port, KPC-9612, KPC-2, KPC-3
MFJ-1272MYH	KAM® HF port
MFJ-1272MZ	PK-88
CAUTION
Always check	your radio's	owner's manual to	see	if

there is a voltage on one of the pins of the microphone before hooking up the microphone switch. You could damage your radio by connecting the PTT line to a voltage source. Do not connect any pin labeled as a voltage source to PTT!!!!!

Warning

MFJ Enterprises, Inc. is not responsible for

damaged radios or associated equipment. It is

your

responsibility

make

sure

your

connections will not damage the radio.

MFJ-1272M Instruction Manual

KAM® is a registered trademark of Kantronics Company, Inc.

MFJ-1272M Instruction Manual

Installation

Before you install the MFJ-1272M TNC/MIC switch, you must set it up for your particular radio. The MFJ1272M comes pre-wired from the factory for Kenwood radios without RECEIVE AUDIO on the microphone jack. If you have one of these radios, the TNC/MIC switch is ready to use. If you have a Kenwood radio with RECEIVE AUDIO on the microphone jack, or if your radio is not a Kenwood, refer to the configuration section. We have given a few diagrams for placing the internal jumpers for a few popular radios on Page 8.

The MFJ-1272MYH model comes pre-wired and ready to use with the HF port on the Kantronics KAM and Icom IC706. The jumpers are setup for the IC-706 with RECEIVE AUDIO on pin 3 of the microphone plug.

Configuration

If you must configure the TNC/MIC switch for your radio, please follow this procedure.

1.Remove the two screws and top cover of the MFJ1272M.

2.Look at the writing on the unit's pc board. Please refer to Tables 1 thru 6 as to where to place the

jumpers	in relation to the pinouts on you radio.
Consult		your radio's manual and the definitions
below to		match signals.

Audio Out:

Audio to the radio from either the TNC or radio MICROPHONE.

PTT:

This is the Push-to-talk signal from either the TNC or radio Microphone.

Receive Audio:

MFJ-1272M Instruction Manual

Audio from the radio to the TNC. Please refer to the External Audio section on the following page. If you use external audio make no connection here.

MIC Audio:

Audio from mic (same # as Audio Out)

Ground:

This is the system ground on radio's mic connector. Some radios have two ground pins, MICROPHONE GROUND and GROUND. The microphone ground should not be used, due to the possibility of introducing ‘‘hum’’ into the system. Always use the pin labeled ground.

MFJ-1272M Instruction Manual

Throughs:

Connect all pins here except MICROPHONE AUDIO.

(unlabeled)

if you use external audio do not connect the radio pins for Receive

3. Header HD3 controls the RECEIVE AUDIO to the EXTERNAL SPEAKER. Place a push-on jumper on pins 2 and 3 if you want the external speaker "on" all of the time., or on pins 1 and 2 if you want the external speaker "off" when using the TNC.. Most people prefer not to hear audio during packet. Set this jumper to the positions desired, according to your own preference.

4. Replace the top and screws.

External Audio

If your radio does not have RECEIVE AUDIO on the microphone, we suggest the use of an interconnecting cable to supply RECEIVE AUDIO to the TNC/MIC switch. You would connect the cable from an External Speaker or Headphones jack on your radio, to the AUDIO IN jack of the TNC/MIC switch. Therefore no jumper connection should be made for Receive on the pc board.

Using the method above for connecting RECEIVE AUDIO to the TNC/MIC switch, will cut off the internal speaker inside the radio. In this case, you must connect an external speaker to the EXT. SPEAKER jack on the TNC/MIC switch. Otherwise you will not be able to hear any signals at all from your radio.

Jumper Configuration

Because there are so many different radio configurations, we have tried to make the MFJ-1272M as versatile as possible. With the MFJ-1272M you can virtually connect any radio pin to just about any TNC pin, just by configuring the jumpers properly. The

MFJ-1272M Instruction Manual

following tables will show how to set the jumpers, depending on the TNC functions versus the MIC pins of your particular radio. Be sure to follow the tables

closely,	with	your	radio	manual close at hand, to
verify	that	you	are not	shorting any microphone

voltages or any other microphone signals to GROUND !

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