Author Topic: EEVBlog #815 - Mailbag Teardown Bonanza  (Read 15513 times)

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Offline rsjsouza

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Re: EEVBlog #815 - Mailbag Teardown Bonanza
« Reply #25 on: November 11, 2015, 10:04:56 pm »
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!  ;D
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Offline martinc

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Re: EEVBlog #815 - Mailbag Teardown Bonanza
« Reply #26 on: November 11, 2015, 10:08:38 pm »
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!
 

Offline martinc

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Re: EEVBlog #815 - Mailbag Teardown Bonanza
« Reply #27 on: November 11, 2015, 10:15:38 pm »
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.  :o :o
 

Offline mcgranslev

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Re: EEVBlog #815 - Mailbag Teardown Bonanza
« Reply #28 on: November 11, 2015, 11:01:57 pm »
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.
 

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Re: EEVBlog #815 - Mailbag Teardown Bonanza
« Reply #29 on: November 11, 2015, 11:10:47 pm »
 

Offline TheSteve

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Re: EEVBlog #815 - Mailbag Teardown Bonanza
« Reply #30 on: November 12, 2015, 01:03:15 am »
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.
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Offline cpuerror

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Re: EEVBlog #815 - Mailbag Teardown Bonanza
« Reply #31 on: November 12, 2015, 01:09:58 am »
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.
« Last Edit: November 12, 2015, 03:19:32 am by cpuerror »
 

Offline boffin

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Re: EEVBlog #815 - Mailbag Teardown Bonanza
« Reply #32 on: November 12, 2015, 03:19:32 am »
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)
 

Offline AF6LJ

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Re: EEVBlog #815 - Mailbag Teardown Bonanza
« Reply #33 on: November 13, 2015, 08:58:53 pm »
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.

Sue AF6LJ
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Offline AF6LJ

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Re: EEVBlog #815 - Mailbag Teardown Bonanza
« Reply #34 on: November 13, 2015, 09:04:58 pm »
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   :-+ :-+ :-+
Sue AF6LJ
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Offline Howardlong

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Re: EEVBlog #815 - Mailbag Teardown Bonanza
« Reply #35 on: November 14, 2015, 09:26:24 am »
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.
« Last Edit: November 14, 2015, 09:30:56 am by Howardlong »
 


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