RC-(remote controlled) Car

[faizanbrohi]

Hello again , i have a question how can i implement a crystal oscillator i found on the net in my modulator and replace the LC circuit  . the desciption and circuits of fundamental crystal oscillators and overtone crystals are given here http://hem.passagen.se/communication/txo.html

One more thing how can i use it as a refrence oscillator

[audioguru]

Hi Faizan,
If you use a crystal oscillator then you won't be able to frequency modulate it.
You can't get crystals with a high enough frequency anyway.

Old FM transmitters used an 11MHz crystal oscillator that was frequency modulated a little then it was followed by many frequency multiplying stages to reach 99MHz with a wide frequency deviation.
Modern FM transmitters use a low frequency crystal oscillator in a phase-locked-loop frequency synthesizer circuit then the phase-locked-loop's oscillator is frequency modulated.

[faizanbrohi]

yeah i get it , this means the TX-500 will be rock solid transmitter if it is PLL Controlled . and one more thing the IC i have for the radio is a KA22425 and also it's equivalent CXA1618M , well the PDf is attached .  i know it is not PLL Controlled but why it is stable . i also used it to check my walkie talkie and what do you know , it is quite stable also , it was also quite stable with my FM transmitters , i previously build . it also has a LED indicator to indicate if the channel is selected

[audioguru]

Those "all-in-one" radio ICs are not very good. I have a similar one in my cheap clock radio and the Sony one is in my inexpensive Sony AM-FM Walkman. My stereo and car radio tuners are much better.

Those cheap radios are "stable" because they have AFC (automatic frequency control) to coverup frequency drifting.

[faizanbrohi]

But if you can implement AFC on the reciever side , why not in the transmitter side . But i think for my project that radio is sufficient ,

[faizanbrohi]

hello again , after a long time i am back , and this time i have found two new crystal controlled IC's that suffice my needs , MC2833 FM Transmitter and MC13136/35 and MC3362 FM Reciever IC's . These IC's are crystal controlled and i think they will be fine for my Radio controlled Car. But Will it Work good for DTMF . It think it might. Although motorola does not manufacture these IC's , but these IC's Are available here in Pakistan at a very Cheap Price of Less than a Dollar . The Main Pain in the Butt is finding the crystals and the Inductors Just right and since the Transmitter is low power i have to build a Power Amplifier of 1W/0.5W for it. The Schematics and pinouts are attached.

[faizanbrohi]

Does anyone knows dbm to mW conversion . the output power of The Transmitter is +10 dbM , how much will be it in mWatts . 

[MadFalcon]

decibal gain doubles your wattage for ever +3 dB. So whatever your input wattage before the decibal gain, double that approximately 3 times. For example if your input wattage before the gain is 10mW, then +9dBm would be 80mW. (((10mw*2)*2)*2) = Final mW. Hope that helps.

[AN920]

Into a 50 Ohm load
0dBm =  1mW
10dBm = 10mW
20dBm = 100mW