EEVBlog #492 - Vintage Motorola MicroTAC Mobile Phone Teardown

[EEVblog]

What was technology like inside a 1994 Motorola MicroTAC GSM mobile phone?

[Legit-Design]

I think you might be wrong about the "fake" antenna. Snap the "fake" antenna in half with cutters from several places and take pictures or video? It might be just passively coupled, as long as it has something conducting inside there is a theory for it to work.

[tnt]

They're not saw filters. The "big one" is a ceramic duplexer and the second smaller one is a ceramic filter. They split the antenna signal into the "Uplink/TX" and "Downlink/RX" band, and isolate the sensitive RX stuff (that tries to receive very faint signals) from the TX stuff (which transmits like 1W or 2W of RF power into the antenna).

In more modern phones, there is no duplexer for GSM. Simply because GSM has been designed specifically so that a phone doesn't need to be full duplex. The TX and RX slot are slightly shifted in time and so modern phone just have an antenna switch. I guess back in the days those switch weren't good enough ...

And that weird module you took apart, I would guess that it's the RF Power Amplifier.

[mikeselectricstuff]

This is a GSM phone, so no duplexer.
Analogue phones had duplexers, which were usually the biggest part by far in the phone. Amazing tech - they could keep the 100s of millwatts (on a handheld)  Tx power out of the -100dbm receive signal, which was  only ISTR something like 40MHz away - serious voodoo

[JOERGG]

Hello everybody,
this is my first post. The sliding button on the side of the phone releases the full size sim card, if i remember correctly.

[JOERGG]

And i guess that the little microswitch detects, if a sim card is insertet. Remember sim cards were full size those days, approxymately 85 mm x 54 mm.

[Slothie]

Came here to say the same as JOERGG. The sim card was the size of a credit card and slid into the slot in the bottom.

[EEVblog]

There are few too many annotations on this one, so I'll just do a re-upload.

[Pippy]

Yes that little RF board you removed is the TX RF power amplifier. The bigger multi wire bonded part is the TX PA output transistor and the other smaller gold ones with wire bonds are the driver transistors.

Showing my age and background here

[gnif]

There are few too many annotations on this one, so I'll just do a re-upload.

Damn, I was just about to watch it

[senso]

Just to say that the forum link doesn't work, the link points to this:
forum: https://www.eevblog.com/forum/blog/eevblog-492-vintage-motorola-microtac-mobile-phone-teardown/

And there are more dead links..

[gnif]

Just to say that the forum link doesn't work, the link points to this:
forum: https://www.eevblog.com/forum/blog/eevblog-492-vintage-motorola-microtac-mobile-phone-teardown/

And there are more dead links..

Works fine for me.

[Stonent]

9:17 my time was 2 hours ago.

[Stonent]

I think I got it..

[EEVblog]

9:17 my time was 2 hours ago.

It'll take 3 hours to upload, then some time to process on Youtube.

[Stonent]

9:17 my time was 2 hours ago.

It'll take 3 hours to upload, then some time to process on Youtube.

Dayum.  I gotta be up in 4 hours to drive 6 hours. 

What was wrong with the first revision?

[EEVblog]

What was wrong with the first revision?

A coupla silly errors and oversights.
I started adding annotations, but it was just as easy to simply reupload. It had only been live a few hours.

[tnt]

This is a GSM phone, so no duplexer.

Oh but it _is_. Look at it :



You can clearly see the antenna pad in the middle and the uplink/downlink pads on the sides.

As I said, I know that GSM doesn't need a duplexer and you can do without. But looks like on this phone, they choose to use one.

[DaedalusYoung]

I think you might be wrong about the "fake" antenna. Snap the "fake" antenna in half with cutters from several places and take pictures or video? It might be just passively coupled, as long as it has something conducting inside there is a theory for it to work.

According to Wikipedia, the antenna really is fake:

On all models, and unlike the Motorola DynaTAC, the plastic antenna served no functional purpose, and was strictly for aesthetics.

[Telequipment]

I'm curious, I've seen those blob type ic's/controllers type devices on other things, I guess there a one off item or can they be replaced. I'm referring to that black blob behind the display.
Paul

[Legit-Design]

I think you might be wrong about the "fake" antenna. Snap the "fake" antenna in half with cutters from several places and take pictures or video? It might be just passively coupled, as long as it has something conducting inside there is a theory for it to work.

According to Wikipedia, the antenna really is fake:

On all models, and unlike the Motorola DynaTAC, the plastic antenna served no functional purpose, and was strictly for aesthetics.

http://en.wikipedia.org/wiki/Motorola_MicroTAC

Dave updated his teardown with the antenna teardown, it's not just plastic.

I've seen things with same idea for usb 3G modems. http://cdn.entelectonline.co.za/wm-43814-cmsimages/A-ADPT-026%20Datasheet.pdf claims -4 dB coupling loss. Ofcourse with usb dongle you are going to have a high gain antenna on the other end of the coupler to defeat losses.

http://www.poyntingcommercial.com/directorylisting/displaycommercial.aspx?dirid=55#prodlist=1  (horrible website, have to scroll around to middle of the product slider)



Additional Information

This device couples to the modem internal antenna signal and diverts it to a booster antenna thereby ensuring better signal reception and ultimately better data throughput. The coupler is slid over the modem (see photos). You then connect the other end of coupler to one of our booster antennas via the SMA (female) connector. The booster antenna can be mounted on the outside of the building and pointed toward your closest cellular base station to ensure good reception. Features: Works with most USB and express card Modems Lightweight Robust Application: Connecting any 3G/HSDPA modem to a high gain antenna for improved range and data throughput.


same principle with rfid inductive coupling: http://rfid-handbook.de/about-rfid.html?showall=&start=1

Original wikipedia source of the fake claim: http://web.archive.org/web/20121001035225/http://www.retrobrick.com/motomicro.html
Thats for Analogue MicroTAC

Another puzzling design feature was the retractable aerial. In fact, the aerial does absolutely nothing as it is purely for show. The unit features an internal antenna, however, the pull up plastic was added after focus groups in the US felt that any phone should have a visible aerial. But for the country who put big big heavy metal fins on their cars in the 1950's to make them seem faster, this is not really surprising.

Clearly this GSM version has a functional antenna. Becareful with wikipedia quotes

[Telequipment]

I'm curious, I've seen those blob type ic's/controllers type devices on other things, I guess there a one off item or can they be replaced. I'm referring to that black blob behind the display.
Paul

It's normally just where the board manufacturer puts the chip die directly onto the board rather than use the normal pinned/smd package. If they blow then that's it, new board required.

I see, I've noticed them before on cheap watches, and a lot of my children's toys, that have broken they all seem to have the black blob of different sizes. Thanks for replying .

[G7PSK]

I had one of those motorola phones in late 1994. It was so deaf that I could stand underneath the cell phone mast and get no signal if I did get a signal someone with a car phone could drive by and take the signal from me as they had more transmit power.

i kept it until early 96 when while doing the accounts I found that the phone company had been double charging me with two direct debits so I cancelled both of them where upon the threatened to take me to court so I told them if they wanted too I would also take them to court for duplicating the direct debit last I heard from them they asked for the phone back so I sent it to them but first I played with some high voltage and the phone, never heard from them again and I did not get another mobile until 2000 by which time there was more masts and better phones. When I got that first phone I was assured that over 90% of the country was covered by the masts but when I research that claim I found that was by population and not area so places like Norfolk were hardly covered at all and we still have black holes for phones even now.

[mikeselectricstuff]

This is a GSM phone, so no duplexer.

Oh but it _is_. Look at it :



You can clearly see the antenna pad in the middle and the uplink/downlink pads on the sides.

As I said, I know that GSM doesn't need a duplexer and you can do without. But looks like on this phone, they choose to use one.

I suspect that's for bandpass filtering, but maybe based on an old diplexer design. Analogue diplexers were at least twice this size.

[JOERGG]

If there is no need for a duplexer for GSM as mentioned before, could the showed part have the function to secure the correct impedance when two antennas are plugged in and split the RF path to the second antenna? I am sure there is an extra antenna input beside the charger plugin, used for installation in cars for example, where an antenna on the roof was possible.