EEVBlog #815 - Mailbag Teardown Bonanza

[EEVblog]

A Teardown Bonanaza Mailbag!
Fran Blanche: https://www.youtube.com/user/ContourCorsets



SPOILERS:
Lightsaber
Chinon Genesis II Film Camera
Morrow Apollo Aircraft GPS
Morrow Apollo LORAN Navigation Receiver
1970's 300A Navomatic Analog Autopilot
Thrane & Thrane GSM Satellite Phone

[max666]

I don't understand the issue with the inward curved keys of the Spectrum+, aren't practically all keyboards made that way? 

[c4757p]

I don't understand the issue with the inward curved keys of the Spectrum+, aren't practically all keyboards made that way? 

Yes, even my beloved IBM has a slight concave. I don't think that is what's wrong with the keyboard, I think it's more the small effective key size (they've got those little round circles instead of using the entire key). It really does look like an awful keyboard.

[g.lewarne]

The separate camera teardown video is marked as Private

[Don Hills]

The Spectrum keyboard doesn't use conductive rubber contacts. There are 2 sheets with metallic contacts printed on them, facing each other but with a separator sheet between them. Pressing a key pushes the contacts together.
The original 40-key board had a single such sandwich, and for some characters you had to press and hold one key then press another. On the + keyboard, the contact sandwich was "double decker". Some of the common double-key combos were mapped to single keytops. Pressing the key would press the stacked sets of contacts in the correct sequence.

[Deathwish]

Wot ! no SWMBO or Sagan appearance ?, quality is defo going downhill

[crispy_tofu]

I see your weirdly-designed keyboard and I raise you mine! 

[cpuerror]

Good video but I would have liked to see those avionics powered up.

[EEVblog]

I don't understand the issue with the inward curved keys of the Spectrum+, aren't practically all keyboards made that way? 

Slightly. It's more a combination of the deep curve and the shape. You have to feel it to get the sense of crappiness.

[EEVblog]

If nothing else the concave curve may help reduce glare from overhead light reflections. Flat keytops seem to be a very contemporary fashion though. My laptop and bluetooth keyboard have flat keytops.

My logitech has slight concave tops in the X direction, flat in the Y.

[max666]

Ah I think I understand now. The Spectrum+ has spherically concave key-caps, while modern keyboards usually have cylindrical concave key-caps, like you said "concave tops in the X direction, flat in the Y".
Yeah I can see how that might weird one out.

[crispy_tofu]

I was searching for those data cards and it looks like Garmin still sells Garmin USB Data Card Programmers, but for the newer 'legacy' models with an LCD. 

[EEVblog]

Ah I think I understand now. The Spectrum+ has spherically concave key-caps, while modern keyboards usually have cylindrical concave key-caps, like you said "concave tops in the X direction, flat in the Y".

Yeah, cylindrical concave is a better term.
The full concave really feels weird.

[Howardlong]

The patch antenna array voodoo: four patches, each fed at two points at 90 degrees, with a 90 degree (1/4 wavelength) phase shift delay made out of PCB track microstrip transmission line thus producing circular polarisation.

To maintain the right impedances, there are a bunch of 1/4 wavelength transmission line transformers, i.e., 1/4 wavelength lengths of different width PCB tracks on top of the ground plane making various different impedance microstrip transmission lines: you could use several pieces of 1/4 wavelength different impedance coax lengths if you wanted to, a transmission line is a transmission line, but it's easy and cheap to fabricate on a PCB together with the antennas. The transmissions lines are not designed to radiate, just the square patches are meant to do that!

By using a 1/4 w/l transformer, you can change the impedance in a reasonably loss free way.

For example, say you have two 50 ohm antennas you want to feed from a single 50 ohm source, if you just parallel them up you end up with 25 ohms. But by placing a 70.7 ohm 1/4 w/l transmission line in front of one 50 ohm antenna, it will look like 100 ohm. Do that twice, once for each antenna, and parallel the fwo 100 ohm presentations together, you get a single 50 ohm presentation. Bingo!

The 70.7 ohms comes from Zt = sqrt(Z1 * Z2) where Z1 and Z2 are the impedances you want to transfer from and to, and Zt is the impedance of the 1/4 w/l transmission line required. So in the example, Z1=50, Z2=100 so Z2=sqrt(5000) = 70.7 ohms.

Now, the velocity of the wave on PCB or any substrate isn't as fast as in free space. The velocity is c/sqrt(Er), so say for FR4 with Er approx 4, the velocity factor is about 0.5, so the length of the 1/4 w/l microstrip lengths would be about half that had they been made in free space.

To figure out the impedances of the transmission lines, predominently it's calculated from the width of the track, height above the ground plane and the permittivity (Er). 50 ohms is about 3mm on 1.6mm FR4, there are on line calculators for this.

FR4 might be OK to L band which this antenna looks to be judging from the size, but it becomes quite lossy much higher in frequency.

Edit: Why the foam? This is a physical mechanical separator between the patch antennas and the plastic enclosure. Because the foam's mostly air (Er=1), it won't detune the patch antennas and transmission lines, which a very close proximity plastic enclosure would do.

[max666]

Damn, awesome post! Thanks for unavailing some of the voodoo magic, Howardlong. 
I learned and understood so much more about RF just by reading your short post.

[sbprojects]

If RHCP means Left Hand Circular Polarised.
What would be the abbreviation for Right hand Circular Polarised? 

[Fungus]

Ah I think I understand now. The Spectrum+ has spherically concave key-caps, while modern keyboards usually have cylindrical concave key-caps, like you said "concave tops in the X direction, flat in the Y".

Yeah, cylindrical concave is a better term.
The full concave really feels weird.

At least they have a cutout at the top for long fingernails...

[AdamCooman]

Very nice video, I always like the two-minute teardowns, especially when there's RF stuff involved.

The power amplifier in the satellite phone is a three-stage amplifier (see attached image). The RF chip you were indicating is actually just the second stage. The big power is delivered by the final module underneath the metal bar.
I really like their design. Would it be possible to provide some high-res photo's of that PCB, I'd love to study the whole transceiver module some more. (I don't really find a mixer. could that one be on the main board?)

[@rt]

I would have liked to see the Loran and GPS receivers powered up on the bench even without antennas
(but preferably with them), or even just that old GPS module on it’s own.

[SeanB]

The autopilot brings back memories. The 1458 will be doing AC amplification, with the 4016 analogue switches being used as synchronous demodulators to detect the peak of the AC signal from the sensors that are all running from 26VAC 400Hz. The 741's will be DC amplifiers, with the one pot being used for a slight gain trim in the feedback loop, compensating for the sender being slightly variable in amplitude, and the zero will be doing an offset trim on the 741 to compensate for errors in the synchronous detectors and the opamp itself. The opamps will be selected devices, a sort during production for those with the lowest popcorn noise.

The later stages will have integrators ( big  wet slug tantalum capacitors being used as integrator caps, a foil unit is bigger than the whole unit in the value needed) with the 4016 being used as switches to connect the input samples to bias the integrator and another part being used as a zero clamp to disengage. Simply does heading control to keep you aimed to a waypoint, and you simply select it by a bearing.

[Jr460]

I don't think you are going to see that autopilot module running on 400Hz AC.

That model, what is known as a single axis model/wing leveler, was popular in small Cessnas.  Think about a 172 or 182.  (I may have even flown a 172 that had one, but I never engaged it.)  Everything on those planes is 24VDC, no AC power.

Link that gives a lot of info.  http://www.mtnflyers.com/assets/Cessna_ARC_Navomatic_300a_Blue_Highlight.pdf

(Just sold a Piper Arrow that had a two axis AP, and an HSI.  That was a joy to use, it would even capture and follow the glide slope on an ISL approach)

[Howardlong]

I was in a bit of a hurry to get out this morning when I wrote my original post above, I've since spent some time looking into this in a little more detail.

The power splitting is achieved with a cascade of 35 ohm 0.25 w/l  transformers taking 50 ohms down to 25 ohms, and then paralleling up the next two 50 ohms.

At each antenna, there are two feedpoints phased 90 degrees apart for circular polarisation each with an approximate impedance of ~25 ohms. These are transformed up to about 100 ohms with a 0.25 w/l transformer of about ~50 ohms. The resulting two 100 ohm feedlines are paralleled up to make 50 ohms and feed back into the remaining cascaded power splitters.

The additional 0.25 w/l delay in two of the 50 ohm sections is because two of the patches are being fed at different corners to the other two, an phase needs to be maintained on the wavefronts emitted from each antenna or you'll definitely not get the desired directionality and gain (think about the constructive interference pattern we're after to achive gain).

On reflection, I had missed in my haste the four parasitic copper director squares in front of the patches separated by the foam which provide more gain and directivity. The foam is there to maintain mechanical distance for the desired beam pattern. A side effect of the parasitic directors is that there will be a significant lowering of the feed impedance of the directly driven patches.

[max666]

So, what's going on with the 4.7 kOhm resistor in series with the backup battery?

[martinc]

Hi Everyone, I'm Martin. I sent in the aircraft avionics which were shown in this episode. I'm a former commercial pilot, flight instructor, aircraft mechanic, and electrical engineer (ME EE). AMA!

[martinc]

So, what's going on with the 4.7 kOhm resistor in series with the backup battery?

My totally random guess is that it serves as a current limiter for when the device is being serviced. The voltage drop across the 4.7k resistance is probably negligible for whatever currents the hardware which uses the backup battery draws. But when some traces are shorted out when someone is poking around in the case then the resistor limits the current to less than 1ma.

[rsjsouza]

Ah I think I understand now. The Spectrum+ has spherically concave key-caps, while modern keyboards usually have cylindrical concave key-caps, like you said "concave tops in the X direction, flat in the Y".

Yeah, cylindrical concave is a better term.
The full concave really feels weird.

You young whippersnapper! IBM terminal keyboards had spherical keys that were a joy to type! 

[martinc]

I don't think you are going to see that autopilot module running on 400Hz AC.

That model, what is known as a single axis model/wing leveler, was popular in small Cessnas.  Think about a 172 or 182.  (I may have even flown a 172 that had one, but I never engaged it.)  Everything on those planes is 24VDC, no AC power.

The Navomatic came out of an early 70's Cessna 206, which is sort of a 6 seat version of the 182, so you're right on with your assessment. I also agree that it's unlikely that the autopilot uses 400Hz AC, the avionics in this aircraft were exclusively DC powered. I think it was 12V, but may have been 24V. Both are pretty common in Cessna light GA aircraft. The Navomatic did have a remote power supply box, but being 70's technology I doubt that there was an inverter in there. It was a bunch of linear regulators as I recall.

I'd really like to see Dave power up the 555-based pulse width modulator daughterboard that came out of the Navomatic!

[martinc]

I would have liked to see the Loran and GPS receivers powered up on the bench even without antennas
(but preferably with them), or even just that old GPS module on it’s own.

I actually poked around with the GPS receiver module in the II Morrow (said like 2 + morrow = tomorrow) GPS unit after it was scrapped. It is a serial GPS, sends data out at 9600 baud I believe. All the hardware still works. The problem as I understand it is that the ancient firmware cannot handle the GPS week roll-over or overflow which happened in 1999 http://www.navcen.uscg.gov/?pageName=gpsweek
Even if you set the date in the UI of the unit itself, the minute it gets a satellite lock the date reverts to ~20 years ago, and all satellite signals are lost. I tried to contact the manufacturer of the GPS module to see if a firmware patch was available, and they ignored me. 

[mcgranslev]

The Thrane and Thrane phone; is a satellite phone, but as far as i know the firm is now called Cobham PLC, but they still work with communications as their main field. Both in avionics and maritime communications.

/Mike

And nice mailbag episode.

[EEVblog]

Nice work, thanks!

[TheSteve]

I was in a bit of a hurry to get out this morning when I wrote my original post above, I've since spent some time looking into this in a little more detail.

The power splitting is achieved with a cascade of 35 ohm 0.25 w/l  transformers taking 50 ohms down to 25 ohms, and then paralleling up the next two 50 ohms.

At each antenna, there are two feedpoints phased 90 degrees apart for circular polarisation each with an approximate impedance of ~25 ohms. These are transformed up to about 100 ohms with a 0.25 w/l transformer of about ~50 ohms. The resulting two 100 ohm feedlines are paralleled up to make 50 ohms and feed back into the remaining cascaded power splitters.

The additional 0.25 w/l delay in two of the 50 ohm sections is because two of the patches are being fed at different corners to the other two, an phase needs to be maintained on the wavefronts emitted from each antenna or you'll definitely not get the desired directionality and gain (think about the constructive interference pattern we're after to achive gain).

On reflection, I had missed in my haste the four parasitic copper director squares in front of the patches separated by the foam which provide more gain and directivity. The foam is there to maintain mechanical distance for the desired beam pattern. A side effect of the parasitic directors is that there will be a significant lowering of the feed impedance of the directly driven patches.

Seeing there are technically two sets of antennas would you expect the tuning is slightly different between them? I can't tell from the images but I would think one set is for TX and one set is for RX being they are 100 MHz apart with Inmarsat. If Dave gets bored and gives us precise measurements of the various transmission lines etc we would know for certain.

[cpuerror]

Funny that right after this teardown video on my feed is an aviation video showing the very same Loran C receiver in use. Never seen this receiver before today and I am generally familiar with this stuff. By the way, the Loran C system has been dismantled for some time and the receiver is now a paperweight.

[boffin]

Funny that right after this teardown video on my feed is an aviation video showing the very same Loran C receiver in use. Never seen this receiver before today and I am generally familiar with this stuff. By the way, the Loran C system has been dismantled for some time and the receiver is now a paperweight.

...Youtube of Smith Falls...

Smith Falls; a place every student pilot in the country is familiar with (when I did my license, 3 of the 4 standardized tests used a smith falls example)

[AF6LJ]

Very nice video, I always like the two-minute teardowns, especially when there's RF stuff involved.

The power amplifier in the satellite phone is a three-stage amplifier (see attached image). The RF chip you were indicating is actually just the second stage. The big power is delivered by the final module underneath the metal bar.
I really like their design. Would it be possible to provide some high-res photo's of that PCB, I'd love to study the whole transceiver module some more. (I don't really find a mixer. could that one be on the main board?)

Nice work;
You beat me to it.
As I remember that whole sat phone idea was a dream of Loral corp (my ex employer) and Motorola another company I have ties to.

[AF6LJ]

I was in a bit of a hurry to get out this morning when I wrote my original post above, I've since spent some time looking into this in a little more detail.

The power splitting is achieved with a cascade of 35 ohm 0.25 w/l  transformers taking 50 ohms down to 25 ohms, and then paralleling up the next two 50 ohms.

At each antenna, there are two feedpoints phased 90 degrees apart for circular polarisation each with an approximate impedance of ~25 ohms. These are transformed up to about 100 ohms with a 0.25 w/l transformer of about ~50 ohms. The resulting two 100 ohm feedlines are paralleled up to make 50 ohms and feed back into the remaining cascaded power splitters.

The additional 0.25 w/l delay in two of the 50 ohm sections is because two of the patches are being fed at different corners to the other two, an phase needs to be maintained on the wavefronts emitted from each antenna or you'll definitely not get the desired directionality and gain (think about the constructive interference pattern we're after to achive gain).

On reflection, I had missed in my haste the four parasitic copper director squares in front of the patches separated by the foam which provide more gain and directivity. The foam is there to maintain mechanical distance for the desired beam pattern. A side effect of the parasitic directors is that there will be a significant lowering of the feed impedance of the directly driven patches.

Seeing there are technically two sets of antennas would you expect the tuning is slightly different between them? I can't tell from the images but I would think one set is for TX and one set is for RX being they are 100 MHz apart with Inmarsat. If Dave gets bored and gives us precise measurements of the various transmission lines etc we would know for certain.

You would be correct; one antenna for transmit one for receive.
They made those phones full duplex. Somewhere in there is a is a douplexer, not on the antenna board but on the main transceiver board.
It could be one of those based on the hi-tech ceramics that were developed in the late 80s. that was the key to making the analogue cell phones smaller.
Same tech but two or so octaves higher in frequency.

Good Stuff

Thanks Dave   

[Howardlong]

I was in a bit of a hurry to get out this morning when I wrote my original post above, I've since spent some time looking into this in a little more detail.

The power splitting is achieved with a cascade of 35 ohm 0.25 w/l  transformers taking 50 ohms down to 25 ohms, and then paralleling up the next two 50 ohms.

At each antenna, there are two feedpoints phased 90 degrees apart for circular polarisation each with an approximate impedance of ~25 ohms. These are transformed up to about 100 ohms with a 0.25 w/l transformer of about ~50 ohms. The resulting two 100 ohm feedlines are paralleled up to make 50 ohms and feed back into the remaining cascaded power splitters.

The additional 0.25 w/l delay in two of the 50 ohm sections is because two of the patches are being fed at different corners to the other two, an phase needs to be maintained on the wavefronts emitted from each antenna or you'll definitely not get the desired directionality and gain (think about the constructive interference pattern we're after to achive gain).

On reflection, I had missed in my haste the four parasitic copper director squares in front of the patches separated by the foam which provide more gain and directivity. The foam is there to maintain mechanical distance for the desired beam pattern. A side effect of the parasitic directors is that there will be a significant lowering of the feed impedance of the directly driven patches.

Seeing there are technically two sets of antennas would you expect the tuning is slightly different between them? I can't tell from the images but I would think one set is for TX and one set is for RX being they are 100 MHz apart with Inmarsat. If Dave gets bored and gives us precise measurements of the various transmission lines etc we would know for certain.

Not on this one board, this is a simple single L band antenna CP parch array with nothing more than power splitters, delay lines and matching sections, there is no diplexer. Now there may be another antenna on the device, or the operation is half duplex or TDM like GSM. There is also only one feedpoint if you look, if it is full duplex then the diplexer is not on this board.

FWIW, back in the early noughties I used to design antennas for L and S band for space applications, including patch arrays on PCB like this one, the techniques here are exactly what I used then.