I am newbie in rf - answer me Please

hello everybody!
i am try to make a wireless stereo hi-quality one-direct-trasceiver for Music.
this is my first experience about RF.
i am a programmer for microcontroller(avr) and some electronic design.

-in a pll receiver: antenna input - pll local oscillator = fm demodulate wave
if is that true , why we use IF stage to filter?

i don't like keep stereo standards (L+R,L-R,Pilot signal,etc...) , may it help to increase audio quality?


thanks

why local oscilator must be difference 10.7mhz then send to IF?

if i set local oscilator frequency equal with carrier frequency then i have demodulate signal.

Hi,
What you tell/invented is a so called "DC-RX" (direct Conversion) Receiver technique...
Newly you can find some ICs for these applications too, but I think not for FM RX.
IF has the usage that you can good selective separate the other frequencies of your wished signal.
I would say, search pleas a little bit for i.e. radio amateurs side, they writes over teenth of years good what & why better is so & not others to make...
You "DC Amp" has for example a good signal/noise distance to have, but in uV range & broad bandwidth...
Pilot & coding techniques are not so trivia for us, some are needed for transmission measurements & automatisions, other as preem/deem-phases are noise reductions & trics to better signal quality.
K.

You get some kind of demodulated signal, but not the intended base band signal, not even for AM. With "zero IF" or homodyne
receiver technique, there'a small problem with RF to LO phase relation. You may want to evaluate this in an experiment, either
with real hardware or in a simulation. That's why a homodyne receiver usually involves I/Q demodulation. With this technique,
you can handle any modulation scheme, also FM.

If you dont have L+R & L-R ("coded") modulation= you must have a two transmitter receiver system...

Pls realyse; FM-Stereo TRX technique is relative old_ca. 50 years, to the time of 60tees are the public coding & receiving techniques others possible to build as nowadays.
K.

hi
i think this fm stereo TRX as you say is over 50-60 years old,may there is better way but only for keep compatible, why you don't send L,R instead(L+R,L-R) without pilot?(for own stereo job) it is easier for a micro-controller switching between left and right and no't need pilot when use PLL synthesizer in T and R.

Hi,
Even, compatibility is an absolute law for broadcasting-consume systems, than the relative simple realisation in volume production, than to end these are price factors for us all...
As I wrote, pilot was inserted for system measurements + services. In your private solution possibly you dont/must not need/have it.
Question is for me; what needs nowadays the commercial FM-RX chip systems? If your receiver IC has/need it internal for working; you must generate/send it.
Coding with L+R/L-R is maybe a "private" thing, but if you will have a product from it: you must have some measurement instrumentations too!
Special instrumentation is very expensive if you arent compatible, than servicing will be a problem too, & they are markt-marketing & profitability problems...
Maybe somebody knows better as I; what are nowadays stereo system needs and component possibilities?
K.

may i use Am medulation for high quality stereo music in short range(max 500 meter)?
why everybody use FM ?

Hi,
AM can not categorized to high definition degre... AM is full disturbanted of all electrical & EMI noises!
Than its efficiency is relativ bad too: you must send the carrier signal as full power & the other half of transmitted Power is only your signal...
Check pls some communications theory literature for understanding that .
For HiFi you must have some better modulation system, as FM/PM or digitized as FM (FSK)/PM, event. ASK...

Tell me pls; is it a project ir idea for hobby oder for some serial production, than in both cases you have other aspects to check...
K.

i like make a wireless transceiver for business active bands. i need one stereo transmitter and 2 mono receiver for left and right channels.
and i no like use 88-108Mhz. and this is a big problem because i can't use generic fm radio ics.
at first i checked synthesizer & pll method but if i use one ic for each part of receiver then total cost will be very expensive. i don't need tuner and 3-4 solid channels is enough for me.
what can i do ?

Hi,
Nice subject!
What are the usable frequencies or band for you?
I think its use must be legal/on free/licenced freq. in Persia or other countries too?
You sayd over 2 receivers at first, to end over 3-4 solid channels; what does it mean pls?
K.

MC3371 is good for high-quality audio?

I dont have enough time yet to read it in details-sorry, but as speedy resultat:
With ceramic filters not real;I know only smallband ceramics, but you must check the types from the datasheet_maybe it exsist version for minimum+/- 15KHz too.
If not, than it can be only a middle quualiti system_or YOU MUST MAKE SELF all LC-FILTER & these isnt cheap & simple, but that have had writing at the begin too...
Thes IC is developed for "communications Rx", they arent HIFI RX systems!
They are good and selective systems, but with at i.e. 5-8 KHz bandwidth, these is cca half of your needs...
K.

http://www.silabs.com/products/audio...s/default.aspx

Look at this page, there may be some digital solutions for you...

Hi BigBoss,
This is a super thing_TNX! And the ONLY QUESTION is the PRICE!?(
I think omid_safari can not have some simpler solution...
If he does apply a premixing to hes wished Frequency/channels is a simple & smallest solution, that has hopfely a good price too...
K.

Added after 27 minutes:

Im very surprised! Mouser has it for only ca. S 6.50!
Mouser Part #: 634-SI4720-B20-GM Mfr. Part #: Si4720-B20-GM
Mfr.: Silicon Laboratories Description: RF Transceiver FM Radio Rx/Tx
RoHS: yes On stock: 207pcs, S6.51
K.

hi
sorry,i don't understand which part of this IC limit the bandidth to 5-8Khz?

Not the ICs self (and especially not the SiLabs IC_their is a super thing), but he usual ceramics filter has relative small bandwidths.
Check pls the datasheets of the filter types from circuits ....
I remember (but its an over ten years info in my head) for data at 8-10KHz max!
K.

but the ceramic filters are 10.7Mhz and 455Khz

Going back to original theory:

1. AM is prone to interference. Noise from load switching and atmospheric disturbance is in the amplitude domain, it is rarely in the frequency domain. FM receivers are able to ignore all but the most severe interference so they are preferable for audio links.

2. Zero IF (Homodyne) is not a good technique for FM. When the local oscillator is at the center frequency of the FM spectrum, it produces an equal voltage from displacement either side of the it. It makes it difficult to tell which direction the frequency moved. It IS possible but more difficult than first appears.

3. Using a superheterodyne receiver gives two advantages. Firstly, it gives better selectivity and the passband shape is easier to control. Secondly, the modulated signal can be shifted to a lower frequency where the FM deviation index is much higher as a proportion of overall frequency. This makes it easier to recover a larger voltage from the discriminator stage.

If you use a digital technique, I think the best solution is to time compress the channels. Digitize the left and right channels at rate A and send them digitally as alternate data bursts at rate 2*A. You need a small data overhead so the receiver can identify which channel it is receiving but you can also add a low rate control channel if you want to.

Brian.

thanks a lot betwixt,you make a new vision for me,i will try this method and i know that i can do it,but i have not any experience about new hi-speed low-cost technology,my best jobs on AVR and it can't handle this job.i can do it on next version surely.
now i have 2 choice:
1-use radio ic +pll ic + microcontroller.
2-use Front-end ic + IF ic + demodulator ic
i like do it out of 88-108Mhz and general radio ics can't do it.
if i found out a radio ic for work above 108Mhz and gives me bandwidth for 4-10 channels, it is enough for me(for first version).
my friend suggest me about CXA1238(Sony Radio ic).
then i was searched and find this schematic:
../imgqa/eboard/Antenna/rf-lyvaq30t4wv.gif
is there any suggestion?
thanks