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How do transmitter & receives work these days with no LC circuit?

gary350

Well-Known Member
Thread starter #1
I took old cell phone apart no LC circuit.

Weather emergency radio no LC circuit.

Wifi card no LC circuit?

How does a cell phone manage to transmit several miles on such low power?
 

JimB

Super Moderator
Most Helpful Member
#3
I found this:
https://www.elprocus.com/how-cell-phone-detector-works/

"An ordinary RF detector using tuned LC circuits is not suitable for detecting signals in the GHz frequency band used in mobile phones. "

This article says the same thing and seems to imply just a capacitor is used rather than LC and goes into it in more detail:
https://pdfs.semanticscholar.org/0c31/c7abe108213918499afce43fb500d862cbe9.pdf
I had a look at those links.
My opinion was that they are a complete joke.

As for a cell phone having no LC circuits, I think that you will find that they are there, it is just that the inductors are not obvious coils of wire but surface mount chip inductors, or etched into the circuit board.

JimB
 

Nigel Goodwin

Super Moderator
Most Helpful Member
#4
I took old cell phone apart no LC circuit.

Weather emergency radio no LC circuit.

Wifi card no LC circuit?

How does a cell phone manage to transmit several miles on such low power?
You're talking nonsense, all of those have LC circuits - just because you can't recognise them doesn't mean they aren't there.

Cell phones are also quite high power, and only transmit fairly short distances.
 

gary350

Well-Known Member
Thread starter #5
You're talking nonsense, all of those have LC circuits - just because you can't recognise them doesn't mean they aren't there.

Cell phones are also quite high power, and only transmit fairly short distances.
That is sorta what I expected and sorta what I wanted to know. I know a magnetron is not an LC circuit but it transmits a carrer way signal that can be modulated. I figured new technology has something new that I don't know about.

1970 I built 2 hand held trnasistor transceivers they transmitted a whole 200 ft. LOL

I had 2 CB walkie talkies special high power range about 1 mile.

CB car radio was 5 watt I think range was about 7 to 9 miles on a good day. A better antenna it transmitted 15 miles.

I saw a video about advancements in technology where they told, transmitters once had a limited range until we learned how to transmit several times farther with the same power. WHAT IS THAT???
 
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dknguyen

Well-Known Member
Most Helpful Member
#6
That is sorta what I expected and sorta what I wanted to know. I know a magnetron is not an LC circuit but it transmits a carrer way signal that can be modulated. I figured new technology has something new that I don't know about.

1970 I built 2 hand held trnasistor transceivers they transmitted a whole 200 ft. LOL

I had 2 CB walkie talkies special high power range about 1 mile.

CB car radio was 5 watt I think range was about 7 to 9 miles on a good day. A better antenna it transmitted 15 miles.

I saw a video about advancements in technology where they told, transmitters once had a limited range until we learned how to transmit several times farther with the same power. WHAT IS THAT???
I thought it was that receivers were more sensitive rather than transmitters could go farther.
 

cowboybob

Well-Known Member
Most Helpful Member
#7
I took old cell phone apart no LC circuit.

Weather emergency radio no LC circuit.

Wifi card no LC circuit?

How does a cell phone manage to transmit several miles on such low power?
Gary,
There are several ways to achieve electronic oscillations: some that require an LC circuit and some that don't.

Typically, these oscillations are divided into 4 general "shape" categories, as indicated.
1539550661184.png
An LC circuit is required to produce an analog Sine Wave (digitally produced sine waves do not). As the frequency desired is increased, the actual physical size of the "L" (inductor) and the "C" (capacitor) decreases (as a rule). At GHz ranges of oscillations, the L component is quite small and may even appear as no bigger that a single conductor trace (on PCBs), as JimB noted above. And the C component is, of course, equally small.

In this case of cell phone usage, less transmission power is required for successful communication because transmission distances are quite short (nearest "tower", i.e., generally "line-of-sight comms). This also allows for significant reductions in component sizing, particularly with capacitors.

As for the other wave shapes, you can google them for the various methods for producing those shapes, if you choose. They are not, as a rule, used as a carrier wave in radio transmission(s).

<<EDIT>>
Just saw your last post ;
I know a magnetron is not an LC circuit
'

Ah, but it is! A magnetron's cavity creates both the L and C needed for oscillation. The cavity's dimensions determine the resonant frequency of the magnetron.
 
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gary350

Well-Known Member
Thread starter #8
Gary,
There are several ways to achieve electronic oscillations: some that require an LC circuit and some that don't.

Typically, these oscillations are divided into 4 general "shape" categories, as indicated.
View attachment 114872
An LC circuit is required to produce an analog Sine Wave (digitally produced sine waves do not). As the frequency desired is increased, the actual physical size of the "L" (inductor) and the "C" (capacitor) decreases (as a rule). At GHz ranges of oscillations, the L component is quite small and may even appear as no bigger that a single conductor trace (on PCBs), as JimB noted above. And the C component is, of course, equally small.

In this case of cell phone usage, less transmission power is required for successful communication because transmission distances are quite short (nearest "tower", i.e., generally "line-of-sight comms). This also allows for significant reductions in component sizing, particularly with capacitors.

As for the other wave shapes, you can google them for the various methods for producing those shapes, if you choose. They are not, as a rule, used as a carrier wave in radio transmission(s).

<<EDIT>>
Just saw your last post ; '
Ah, but it is! A magnetron's cavity creates both the L and C needed for oscillation. The cavity's dimensions determine the resonant frequency of the magnetron.
That makes sense GHz range LC coil & cap would be so small they can not be seen if you don't know what to look for.

I knew that about the magnetron. England invented the magnetron early in WWII that is why Germany could never detect a radio signal from British radar. England gave the magnetron to America they wanted us to have the newest technology to beat Germany.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
#10
1970 I built 2 hand held trnasistor transceivers they transmitted a whole 200 ft. LOL
Presumably you built a 'toy' circuit, hence it's appalling performance.

I had 2 CB walkie talkies special high power range about 1 mile.
Obviously not very 'special', and not very high power.

CB car radio was 5 watt I think range was about 7 to 9 miles on a good day. A better antenna it transmitted 15 miles.
Under the right conditions CB on 27MHz easily spans the Atlantic. But 27MHz was never a good frequency anyway for CB, using crippling short aerials didn't help at all - but it was only supposed to be short range.

VHF frequencies are basically 'line of sight', and I used to regularly work North Wales from North Derbyshire using 1 watt on a 2M portable transceiver - but these are 'proper' radios. In fact, I could easily reach North Wales from my attic at home.

I saw a video about advancements in technology where they told, transmitters once had a limited range until we learned how to transmit several times farther with the same power. WHAT IS THAT???
It's basically rubbish, there's not really anything different now to what there ever was.
 

ronsimpson

Well-Known Member
Most Helpful Member
#12
2.4ghz low pass filter bottom side view.

2.4ghz band pass filter bottom side view.

Band pass filter 2.4 band pass filter. Look close: two coils and one cap you can see and probably more capacitors.

Here is a pdf from HP 1989 showing filters made on the PCB. You can make Ls and Cs and LCs etc just using copper.
2018-10-15-170128_1184x624_scrot.png
 
#13
I was an IC layout guy for National Semiconductor between 2000 and 2005 pre cell phone boom. I was part of a contracted team to build some of the chipsets for three different cell phone companies that contracted with National Semiconductor (With a company that big, if you are a layout guy, you are just a resource. Other companies contracted with us all the time). I did not design the transmitters and receivers, but I did read the schematics and build them within the IC's. Believe me they are there inside of the IC.
 

ronsimpson

Well-Known Member
Most Helpful Member
#14
I was an IC layout guy for National Semiconductor
I did a design for Silicon Labs. (cell phone IC) My part was to make the phone pick up FM radio. This IC is what we used. I put a FM band pass simple filter on the input but after that it was all software. There is a number of ICs that are exactly the same but only the program is different. You can program it for AM or short wave or FM stereo. The DSP inside has software filters. It is hard to think of decoding stereo using software.

Inside there are two micros. The 50mips 8051 is used to talk the knobs and do I/O. There is a very fast DSP that looks at the RF and decodes the audio.
 

cowboybob

Well-Known Member
Most Helpful Member
#15
Inside there are two micros. The 50mips 8051 is used to talk the knobs and do I/O. There is a very fast DSP that looks at the RF and decodes the audio.
All this (includling Wi-Fi) will soon be a t-ninsy nano chip (with no solder points) filled with 1 picogram of magic smoke.

It will be mounted (at birth) inside one of the hairs inside your ear ... o_O
 
#17
I can Google when I sleep right now. The scary thing is, I actually produce results when I look something up. .... "Let me sleep on it" has an entirely different approach with me.
 

unclejed613

Well-Known Member
#18
I know a magnetron is not an LC circuit
actually, it IS an LC circuit. the dimensions and shape of the cavities are lumped LC circuits, they just don't look like they are. the same with waveguides, especially at the lowest resonant frequency of the waveguide. i once saw a very good descriptive picture of this where a 1/4 wave stub (which is a parallel resonant LC circuit) is first stacked forming a line of 1/4 wave stubs, then doubled to create a closed waveguide. the same thing happens in cavities in a magnetron, and on circuit boards with stripline techniques. the LC circuits exist, they just aren't obvious by looking at them.

EDIT: searching frantically for the "quarter wave shorted stub-to-waveguide transformation" pictures that i know i've seen in books, but don't seem to exist on the web...
 
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unclejed613

Well-Known Member
#19
waveguide-1.png waveguide-2.png

found them, at least one set i was aware of.... there was another that showed the LC circuit portion of the 1/4 wave stub, and then proceeded to build the framework. so, here you can see, at least with waveguides (it's also applicable to other types of RF hardware such as cavities and striplines) how an actual physical object IS the LC circuit that is so elusive (can't see the forest for the trees). so, this set begins with an open wire transmission line. to the transmission line is added a 1/4 wave shorted stub (this could work as a support as shown). since there's a 90 degree phase shift from the short to the transmission line, the shorted stub looks like an open circuit, so no energy is taken away from the transmission line. then the 1/4 wave stub is duplicated on the other side, and then 1/4 wave stubs are stacked until you end up with a solid waveguide. if you're wondering where the capacitor is, it's between the long faces of the waveguide, and the inductor is the wire that the stub is made of. but wait, what about all of that capacitance in parallel? it doesn't change the resonant frequency because all the inductances are also in parallel.


so, for stuff that operates above about 300Mhz, you will find a lot of different physical objects used as resonators, transmission lines, filters, etc... because the physical objects are very convenient (as well as being pretty durable). the inductors and capacitors are there, and not so difficult to find once you know where to look. for a UHF TV transmitter, they use waveguide that looks like air conditioning ducts (quite a bit more expensive though because the inside surfaces are copper or silver plated). i just noticed the little bit of text below the last picture.... well, at least the illustration gives an idea how physical objects become LC circuits...
 
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