Batboard

I plan on modding a Saber external earpiece plug into an external antenna adapter. With the standard Saber, there is NO ground ring on the set top antenna socket so you need to use the back accessory socket.

I've checked the archives but can't find a definitive answer.

How do I get the Saber to switch from the set top antenna to the back accessory antenna "socket"?

I came across a picture of a "Chinese" made Saber external antenna adapter - as well as the antenna and ground pins , there was also one pogo pin which connects to "pin 9" on the square block of 12 accessory pins (reading left to right, 1, 2, 3...on the plug side). I presume this pin is used to switch from the set top antenna to the external antenna pins - but is there a resistor or something which is connected between pin 9 and GND which then switches on the external antenna?

Thanks

To activate/changeover to an external antenna on a standard Saber you have to connect to the back of the radio where you see two connection points, one large outer ring and much smaller center connection. The radio has an internal circuit that senses the connection when it is active and sends the RF to the connection on the back of the radio. The common application is to use a public service speaker microphone which being a PS unit has an antenna mounted on its top. I don't know if connecting an external antenna straight through by itself will cause the sensing circuit to switch over; there may be additional circuitry in the spkr/mic to make this happen.

An Astro Saber, on the other hand, has a recessed pushbutton to do the same thing, located in the same area, but the RF connection is the same as on a standard Saber. However, the Astro Saber spkr/mic is different f rom the Sabers because it has a tab sticking out that pushes the transfer button when the unit is screwed to the back of the radio.

The picture of the Chinese adapter showed one pogo pin - I guess this is used to enable the Standard Saber to switch from the set top to the external antenna output...maybe by soldering a resister from the pin to GND?

On pictures of official Motorola external aerial leads, the block of 12 accessory pins all have pogo pins attached....but the "cheap" Chinese knockoff only has the mimimum required....which is sort of helpful as it helps identify which is the required pin!!!

Does anybody have a real Motorola external antenna lead which they can check the pin outs? The real Motorola external earpiece adapter which I have is very easy to open - just undo one screw.

Thanks

IIRC there is a resistor from the sel line to ground in the adapter that the Saber radio uses to determine external accessories attached.

Thanks Will

Anybody know what value resister is used?

Is it in the service manual?

g8tzl2004 wrote: Anybody know what value resister is used?

Is it in the service manual?

Believe it or not that information is available on the legacy Batlabs site: http://www.batlabs.com/saberacc.html

Thanks.

So I need to use a Zener Diode. Any idea what value is required to just switch the external antenna? ie to lower the voltage from +5v to +3.74v?

You could use a voltage divider from the 5 volt reference line dropping it down to ~3.74 volts, Mine application is a kludge to use a regular speaker mic with a added length of RG-174 coax and an external antenna on the regular speaker mic, I'm cheap and didn't want to pay for a real PSSM so i used resistive dividers.

For just the external antenna you could use a 10K resistor on the ground side and a 5 K pot to the 5 volt reference line(OPT B+), so this would set the variable pot for ~3.33K to get 3.74 volts.

Mike

I think I have this correct but you better do the math to double check: Connect OPT B+(5volts) to the top of the 5 K Pot connect the pot wiper and pot bottom lead together and then connect these two to the top of the 10k resistor and the bottom of the 10 K resistor to ground.

The junction of the Pot and 10 k resistor then goes to opt sel line, next adjust the pot for 3.33 K and then turn the radio on and it should recognize the ext antenna.


I can pull my home brew mic apart and double check these numbers later.

There is already an internal pull up to +5VDC via a 20k resistior. All you need is a single 3.74V zenner. If you can't find one use 6 silicon diodes (1N4148s or even 1N4001s) in series.

Mine was all kludged and home made with nothing in the connector end nor the mic end at all, the connector as I remember was from a KVL cable so I went the resistor route to enable options.

If his already has a 20 k pullup then a ~62K to ground at the bottom of the 20 K(OPt sel line) should do it, this gets to 3.78 volts.

Mike your idea of a pot is a good one as it would allow some experimentation on which combo of accessories the OP wanted to emulate. The zenner allows for variations in the internal resistor value from radio to radio. If you only have one Saber to hook on to then a fixed resistor is fine and cheaper than a zenner.

I was doing it cheap route and couldn't find any Zeners nor any SI diodes in any of my junk boxes, I only found resistors so that's why I went the voltage divider.

Now if I could only remember where I put that dang speaker mic.

I haven't used my saber nor 2 meters in over a year now mainly after some bad experiences on both the local Salem Oregon and then the Prescott Az 2 meter repeater I probably won't be looking too hard for the speaker mic but if he really needs some more info on my conversion then I could dig thru my boxes in the garage and confirm all of my resistor value changes.