PLL Radio

Status
Not open for further replies.
the NE567 has a maximum operating frequency of 500khz, and as shown, it's being used with a 455khz IF (intermediate frequency). this means it has an RF amplifier, a mixer (which converts the incoming RF to the IF frequency of 455khz), and one or more IF amplifier stages in front of it. this circuit might not work well directly connected to an antenna. 455khz is a very common IF frequency for AM broadcast band and many low cost shortwave receivers. there are very few uses for an FM detector in the HF spectrum (FM may get used a bit in the amateur 10 meter band).

the AD chip is only a phase detector for a PLL, not the whole PLL. you need a complete PLL to demodulate FM. a doubly balanced mixer can be used as the phase detector. the filtered output of the phase detector is used to control the VCO, and is also the audio output when demodulating FM signals. the VCO can be "locked down" by using a fixed control voltage, and the output of the doubly balanced mixer becomes an SSB/AM audio output. the AD chip isn't well suited for such a dual use because it uses logic level signals for input and output.
 
Last edited:
hmm.. i can see how that would be a problem!

so you say the NE567 circuit wouldnt work, what is it lacking?
also i am interested in broad ranges if possible?
would there be somthing better, im just looking for simple broad range digital receiver circuit!
 
Last edited:
broad range digital receiver... actually i should say broad ranged RF reciever with digital tuneing!!: RF receiver (AM+FM+LOWER(as possible)+HIGHER(as possible), digitalty tuneable ...... i notice that the NE567 only will barely get me in to the FM band@(0.01 Hz to 500 kHz) ... the low side gets nice and low, but the high side is a little low

but for a crystal radio it is just antenna and tuning coil and headphone and thats it.... im aiming at a design that is similar in simplicity but digitally tuneable , i will be powering it with battery , and just found that schematic for template ... not sending morris codes ... maybe

I assume that the list above is the basic criteria for a receiver circuit and the NE567 already contains "RF amplifier, a mixer (which converts the incoming RF to the IF frequency of 455khz), and one or more IF amplifier stages "

.... does that mean im lacking only a final 2nd Mixer and 2nd IF Amplifier (Maybe)AF Amplifier. ? OR* I need all 5 of those of those thing on top of the NE567?
 
Last edited:

The NE567 isn't a radio chip - forget about it - it's possible to use it as a very minor part of a radio receiver, but it's basically just an audio device.

There are plenty of radio chips around, try looking those up - but a digitally tuned AM/FM wideband receiver is going to be a VERY complicated device.
 
maybe if i simplify my expectations a bit, would things be easier if i just wanted am Receiver and skip on the range and tuning?

in my mind a radio receiver works like this:
antenna --> amp(maybe) --> demodulator(PLL CHIP) --> amp --> headphones ?
 
Dr_Doggy said:
I assume that the list above is the basic criteria for a receiver circuit and the NE567 already contains "RF amplifier, a mixer (which converts the incoming RF to the IF frequency of 455khz), and one or more IF amplifier stages "
Click to expand...
Totally wrong.
The NE567 is basically a tone decoder, as Nigel said it is not a "radio chip".

Dr_Doggy said:
in my mind a radio receiver works like this:
antenna --> amp(maybe) --> demodulator(PLL CHIP) --> amp --> headphones ?
Click to expand...
A very simplistic view and wrong on several levels.
Like the man said in the film "You need to get your mind right"

Dr_Doggy said:
but for a crystal radio it is just antenna and tuning coil and headphone and thats it.... im aiming at a design that is similar in simplicity but digitally tuneable
Click to expand...
Don't forget the detector diode.
Tuning a crystal set digitally is an exercise in futility.
The selectivity of a crystal set is so broad that you will probably be receiving several stations at the same time anyway.

Actually, building a crystal set in the conventional way would be a good introduction into why they are generally never used anymore.

From your comments I think that you need to read and understand how various type of radio receiver work before considering how to tune them digitally.

JimB
 
basic reciever:


same thing, with filter:



add some amps and filters for better quality?


kinda, but dont really get this one, but this is where i would replace "Local Osc" with VCO to uC PWM:



so can i use the 3rd example, but just cut it down to :
one filter to one amp to demod to amp
also i am not understanding how we are tuning all 3 of the amps with only one capacitor tuning dial

or what if i use the 2nd example , that is where a pll can come in as demodulator?
 
Dr_Doggy said:
how we are tuning all 3 of the amps with only one capacitor tuning dial
Click to expand...
With a multi-gang capacitor:
https://www.surplussales.com/Images/Capacitors/VariableCapacitors/cav-w-305251-14_lg.jpg

Electronically, it can be done with varicap diodes.

The problem with the first two is that the selectivity is not that good; OK for basic broadcast "medium wave" etc., but no use for narrowband and VHF up etc.

The third type is a superheterodyne receiver.
With that, after basic filtering, the wanted frequency is mixed with the tunable (or synthesised) local oscillator to give a fixed intermediate frequency.

The rest of the amplification can then be done without any variable tuning and the lower IF means filtering is much easier, either with several fixed-tuned stages or with ceramic or crystal filters.

Common IFs are 10.7MHz and 455 KHz. Some receivers use double conversion, the first to make front-end selectivity easier and the second to make narrow filtering and demodulation easier.
 
ok for medium wave that means am , so no problem?
so is this superheterodyne receiver what i need for fm and up to vhf (it seems uhf will be out of the question) ?

what is the point of the mixer .. is that to inject the IF frequency? and is this why the IF amp and filter are required.... not really sure of is this the part that "decodes the FM modulations?" .... not really seeing the point of the IF ....
 
Nearly all manufactured receivers use a superheterodyne circuit. Even a very cheap AM-FM clock radio. When TV signals were analog the UHF tuner was also superheterodyne. Many LC tuned circuits are used to avoid interference from other stations. Automatic gain control is used so that the input can be very sensitive to weak distant signals but not be overloaded by strong local signals.

A crystal radio was used 100 years ago when there was only one station in town. Today my city has so many radio stations that I never counted them.
 
Dr_Doggy said:
what is the point of the mixer
Click to expand...
The mixer produces two signals, the sum and difference of the input signal and the local oscillator.

eg. If the receiver was tuned to 100MHz, the LO could be at 110.7 and the mixer outputs would be 210.7 and 10.7
The 210MHz signal is easily blocked by the IF filtering so all you get is the wanted signal

(The only thing is having enough front-end filtering to prevent "imaging" - eg. a signal at 121.4 MHz mixing with that same local oscillator will also give a 10.7MHz product, so the filtering must block a signal that far away).

That's why VHF receivers use a high first IF, it makes band filtering easier.


The IF allows the bulk of the receiver to be operated on a fixed frequency and the demodulator of whatever type is after the IF amplification - that's why your original circuit stated 455KHz as that is a common low IF for narrowband receivers such as communications types.

Things like broadcast FM / FM Stereo receivers stay at 10.7 MHz or some high IF to pass the much wider signal used.

Video receivers may use higher IFs again, to maintain linearity over the large signal bandwidths needed.
(I think some old TVs used something around 49MHz, but I may well be wrong).


Standardised IFs also make mass production cheap, as filters and tuned circuits are at the same frequency ./ frequencies regardless of receiver frequency; eg.
**broken link removed**
http://www.ebay.co.uk/i/252973687442

**broken link removed**
 
Last edited:
Dr_Doggy said:
or what if i use the 2nd example , that is where a pll can come in as demodulator?
Click to expand...

You've got to get over your PLL obsession, it's like you've heard the word (with no idea what it means) and seem desperate to use it at all costs.

You 'can' use a PLL as a demodulator, but there's not really much point when a germanium diode will work just as well.

As for the TRF block diagram, what makes it work is the multiple stages, to give you better selectivity and higher gain.

The multiple gang tuning capacitor required (plus alignment problems) is why superhets are used - which is essentially a single frequency TRF radio, with a converter on the front to convert your required frequency to the IF frequency.
 
I'd suggest you look at something like this to start with; it gives you a good ideas of the principles and components involved, and pretty much guarantees a working unit:

https://www.circuitspecialists.com/amfm-radio-kit.html

You can download the manual for it from the same page, that has the schematics and details of how each stage works and how to align it.
 

Pretty cool, nice that it's discrete rather than using an IC (the audio chip doesn't count).
 
Nigel Goodwin said:
You've got to get over your PLL obsession, it's like you've heard the word (with no idea what it means) and seem desperate to use it at all costs.
Click to expand...

thats it!!
it s my only chance to play with RF, since so far hand tuning a crystal radio is just as "FUN" as doing that LC math iv seen around

also isnt that how digital tuners work?
 
Dr_Doggy said:
also isnt that how digital tuners work?
Click to expand...

Digital tuners use a type of PLL, but NOT the one you've been talking about, and it's only a very small part of the radio.

If you want to play with digital tuning, then get the radio kit mentioned above - get it built and working - and then try to add digital tuning to it.
 
A digital tuner (or most digitally tuned radios like walkie talkies, ham transceivers, cellular phones etc..) will generally use a frequency synthesiser based around a phase-locked loop.

That's a totally different system and application to your NE567 demodulator.

(As a point of interest, you could build that 567 circuit and add it to the receiver kit above, as an alternate demodulator to it's tuned circuit discriminator).

A basic frequency synthesiser as in a receiver typically uses an RF oscillator running at the required local oscillator frequency.
That's tuned by a varicap diode to give frequency control - making it a "Voltage controlled oscillator", a VCO.

The VCO output is also fed in to a programmable divider to take it down to some reference frequency & at that point feeds a phase comparator, with the other input from eg. a crystal osc.

The phase comparator controls the voltage to the varicap, holding the RF oscillator at the desired frequency.

By changing the settings of the programmable divider, you change the VCO frequency and so the frequency the receiver (or transmitter) is tuned to.

That's just the "Local oscillator" block of the overall superheterodyne receiver, you still need all the rest.

More info here:
https://www.radio-electronics.com/i...ers/frequency-synthesiser-tutorial-basics.php


Note that you could also build an RF synth operating on the appropriate frequency to replace the LO of that receiver kit, to make that digitally tuned.
 
Last edited:
Status
Not open for further replies.

Similar threads

D
  • Question
Clock Recovery PLL
Replies
6
Views
3K
Teresad340
T
S
  • Question
RF DRIVER
Replies
1
Views
980
rjenkinsgb
E
  • Question
Building a Crystal Radio first time
Replies
16
Views
8K
edteach2
E
C
  • Question
90's Motorola Cellular radio Emulation
Replies
18
Views
10K
Chrroger
C
D
  • Question
Simple Circuit Reverse Engineering (steering wheel radio controls)
Replies
2
Views
3K
dvm
D
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…