PLL Radio

[unclejed613]

you could build a direct conversion receiver, using a digitally controlled oscillator, a balanced modulator, some RF amplification on the front-end, and an audio amplifier. the balanced modulator needs to have a lot of isolation, because the local oscillator is operating at the same frequency you are listening to. this is also called "zero IF". IIRC, there were direct conversion receiver projects in the ARRL Amateur's Handbook in the mid 1980s.

EDIT: there are a lot of different ways of making direct conversion receivers that can be found on the web. just be aware that the ultra simple demodulators (like the one that has only two diodes and uses no RF transformers) do have their limitations. the other extreme (the very complex demodulators) perform very well, but use a lot of resistors and capacitors and lots of PCB real estate. the "happy medium" demodulators generally use diodes and wideband RF transformers (or JFETs instead of diodes), and depending on the circuit you choose can work well, or barely better than the super-simple demodulator. you should be able to model these circuits in LTSpice (or other spice program) and get an idea what the pros and cons are for various demodulators. if you look at most direct conversion receivers, they either have no front end, or bandpass filters for the band of interest (many you find will be for the amateur 80 meter and 40 meter bands), a wideband RF preamp, or a preselector (RF preamp with tuning).

with a direct conversion receiver, you can have a manually tuned oscillator and use a frequency counter to indicate what frequency you are tuned to. the real key to a good direct conversion receiver, is choice of the demodulator, and the local oscillator.

 

[dr pepper]

I've played with the Ne567 recently as an Am and and Fm discriminator, despite the operating frequency of 455kc it works well as an Fm discriminiator, however its not so hot as an Am discriminator, it might have something to do with the Q comparator and oscillator not quite having a 90 degree phase shift, its more like 80 degrees.
If you want to synchronously demod Am then yes I spose you'd be better with a bespoke chip for the job.
You can do this with seperate cmos switches and a oscillator made from gates, though you need more parts.
Why do you need a pll demod?

 

[Nigel Goodwin]

Why do you need a pll demod?

He doesn't, he's read somewhere that digital radios use PLL's and expected to simply add a NE567 to a crystal set and make a digitally tuned radio.

 

[Dr_Doggy]

i will give up on the NE567, that was just an example i pulled from the web, but if there was better pll i could work with that!

"zero IF" seems like what i am looking for i will give that a look.....

what am i up to now??
well it started like this.....
**broken link removed** ... very cool
and leads to this ...

then this....
https://bio-medical.com/waveguard-connect-19-channel-eeg-cap.html
and it would be cool to mix it with some of this:
https://www.instructables.com/id/Arduino-Data-Glasses-for-My-Multimeter/
and mod one of these to include muscle wire for finger movement and accelerator-meter for 6dof:
https://pbs.twimg.com/media/ChjsK1ZXIAAhw8b.jpg:large


whatever ... just dreaming!

another totally different side project i am soon thinking of is a AM- RF trigger which will feed to a synch button on my arduino (about 200ft range)

also since i am dabbling in low bands was hoping to extend to FM ... and if possible higher bands ... just to see what i can get , whats around and how its modulated(things around besides FM) it would have been cool too if i could actually see the 2.5(2.4)ghz wifi carrier too... or a cordless phone.
Maybe have a visual demo of what FHSS is
.... what else can i see with RF receiver?
anyone know how to do this:
https://www.extremetech.com/extreme/133936-using-wifi-to-see-through-walls
or this :
https://www.engadget.com/2016/11/03/hackers-hijack-a-philips-hue-lights-with-a-drone/

whatever ... just dreaming!

But i realize now that alot of that is beyond me for now. so i just stick to am - fm .... and maybe learn some fundamentals first!
bbs with some more IF questions!!

 

[JimB]

with a direct conversion receiver, you can have a manually tuned oscillator and use a frequency counter to indicate what frequency you are tuned to. the real key to a good direct conversion receiver, is choice of the demodulator, and the local oscillator.

"zero IF" seems like what i am looking for i will give that a look.....

Be aware that the simplest of direct conversion receivers are only suited to the reception SSB and CW signals.
Reception of AM could be a bit flaky, even with a very stable local oscillator.
As for the reception of FM, as fer as I know that will be a complete non-starter.

Reception of AM using zero IF techniques, can be done successfully using a couple of I-Q type mixers.
My knowledge is a bit sketchy about this, I have never done it.

JimB

 

[dr pepper]

It would be quite a thing if you got an Ne567 to decode digital radio!
Jims right, you get an audio tone if the local and the incomming signal are not the same, even if theres a sub audio difference you get a tremelo type effect.
If you just want to listen for a minute direct conversion is fine, for a more serious application you'd want phase lock on the incomming carrier, or a very stable local osc like a crystal oscillator.
Back in the summer I put together a Vlf reciver for carrying around and listening in electrically quiet locations, it uses a Ne602 and is direct conversion.
I like IQ type mixers, the only drawback is you get a strong signal at 1/2 the local osc, and harmonics of.