audioguru Posted September 16, 2006 Report Share Posted September 16, 2006 The VHF amplifier and the power meter don't need their supply to be regulated. The output power will become reduced a little as the battery runs down. Quote Link to comment Share on other sites More sharing options...
faizanbrohi Posted September 16, 2006 Author Report Share Posted September 16, 2006 Well here is the schematic of the Power meter . i am feeling a little sleepy , will make assemble and develop the board for the oscillator and power meter , until then astalavista baby !!! Quote Link to comment Share on other sites More sharing options...
faizanbrohi Posted September 17, 2006 Author Report Share Posted September 17, 2006 Well The PCb Layouts for the power meter are made , now its time to prepare the board and practically test it . will update soon Quote Link to comment Share on other sites More sharing options...
faizanbrohi Posted September 19, 2006 Author Report Share Posted September 19, 2006 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 Quote Link to comment Share on other sites More sharing options...
audioguru Posted September 19, 2006 Report Share Posted September 19, 2006 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. Quote Link to comment Share on other sites More sharing options...
faizanbrohi Posted September 20, 2006 Author Report Share Posted September 20, 2006 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 selectedKA2245d.pdfCXA161.pdf Quote Link to comment Share on other sites More sharing options...
audioguru Posted September 20, 2006 Report Share Posted September 20, 2006 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. Quote Link to comment Share on other sites More sharing options...
faizanbrohi Posted September 20, 2006 Author Report Share Posted September 20, 2006 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 , Quote Link to comment Share on other sites More sharing options...
faizanbrohi Posted October 2, 2006 Author Report Share Posted October 2, 2006 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. Quote Link to comment Share on other sites More sharing options...
faizanbrohi Posted October 3, 2006 Author Report Share Posted October 3, 2006 Does anyone knows dbm to mW conversion . the output power of The Transmitter is +10 dbM , how much will be it in mWatts . ??? Quote Link to comment Share on other sites More sharing options...
MadFalcon Posted December 17, 2006 Report Share Posted December 17, 2006 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. Quote Link to comment Share on other sites More sharing options...
AN920 Posted December 17, 2006 Report Share Posted December 17, 2006 Into a 50 Ohm load0dBm = 1mW10dBm = 10mW20dBm = 100mW Quote Link to comment Share on other sites More sharing options...
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