i need urgent help please

Discussion in 'Wireless & RF Design' started by obiajulu, Jul 25, 2012.

  1. obiajulu

    Thread Starter New Member

    May 24, 2012
    7
    0
    i am a final student currently doing my project on a 500m fm transmitter,ihave a circuit i want to build on ,but i do not know anything about the different electronic component,also i do not know the frequency and if proper impedance was considered,please i was told that there should be a pre emphasis i do not no if it was considered.this is my attached file [​IMG]
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    And u are doing ur final?

    Some studying u been doing.
     
    BMorse likes this.
  3. TecknoTone

    New Member

    May 20, 2012
    21
    1
    I think you probably have more hurdles to overcome before you worry about pre-emphasis. Firstly, I would suggest you work with analogue circuits and gain some understanding of component identification and function in that arena before you progress to RF. A stronger understanding of English literature would be a great asset too.

    To answer your question, the carrier frequency for these component values is probably around 100MHz. It's determined by D1, C3, C4, C5, C6, L2. L2 is of course a variable component and would be used to fine tune the carrier frequency.
    Antenna impedance will be non-determinate with a circuit such as this as there is no buffered output stage.
    Pre emphasis is dependant on where you are in the world, it will be either 50 or 70 µS. This circuit is not finessed enough to take such nuances into account.
     
    Last edited: Jul 26, 2012
  4. obiajulu

    Thread Starter New Member

    May 24, 2012
    7
    0
    please if i put my resistor and capacitor as my pre emphasis before my capacitor c1 am i correct,and please i want to control the volume of my mic can i vary my R1,also please what is the function of the diode,or can someone please analyse the circuit pleassse
     
  5. WBahn

    Moderator

    Mar 31, 2012
    17,788
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    There seems to be a disconnect, since 100MHz is more akin to 3m, not 500m. So make sure that the circuit and components you are talking about are actually suitable for what it is you are supposed to be doing.

    Whatever school you are attending, you might think carefully before giving them another dime, because there is little indication that you have gotten what you have paid for, namely an education. And note that I make no judgement on your English -- it's decipherable and it is one hell of a lot better then would be my ability to communicate in your native language (no matter what it is -- unless it's actually English).
     
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  6. DickCappels

    Moderator

    Aug 21, 2008
    2,664
    634
    I suspect that the 500 meters he is talking about is the range of the transmitter.

    The values on the schematic look pretty reasonable. If you build it according to the schematic, you can probably get it to work pretty well. You aren't going to transmit music, so the pre-emphasis is not important. Really -just go ahead and build it as shown.
     
  7. WBahn

    Moderator

    Mar 31, 2012
    17,788
    4,807
    I'll buy that.
     
  8. radiohead

    Active Member

    May 28, 2009
    474
    31
    What is the purpose of D1 in the schematic?
     
  9. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    The diode D1 is performing as a varicap.(varactor diode).
    The capacitance will change with the signal from the microphone.

    Bertus
     
  10. radiohead

    Active Member

    May 28, 2009
    474
    31
    1N4007 is a rectifier diode. Shouldn't it be a 1N34A or equivalent? Maybe even an MV2109 tuning diode? If so, would that eliminate the need for C7?
     
  11. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    Even a common rectifier diode has teh capabilities of a varicap diode.
    The variation in capacitance will be not very efficient.
    There are many varicap diodes available:
    Code ( (Unknown Language)):
    1.  
    2. Varicaps en varactor diodes  1SV217      Zeer groot bereik: 39 pF @ 2V (ca. 50pF @ 0.5V),             3pF @24V SOD323 (klein smd blokje)                              0.91
    3. BA102       Speciale varicap diode voor zenders ZIE BB119                        BB105       =205 UHF stripline                                              0.90
    4. BB112       500 pF - TO92 (2 pins) 9V                                       5.90
    5. BB119       AFC varicap axiaal                                              2.90
    6. BB130       zie KV1225 BB204       =104=304 VHF 2x40pF  TO92                                       0.57
    7.              (wij hebben deze in de klasseringen wit-geel-blauw en groen) BB209       =109 VHF 40pF stripline                                         0.57
    8. BB212       neem 2x BB12                                           BB215       MELF - SMT versie van BB205                                     1.50
    9. BB221       =521AX UHF/SHF high-Q axiaal                                    0.68
    10. BB329       VHF axiaal                                                      0.68
    11. BB405       =505 UHF axiaal                                                 1.13
    12. BB409       zie BB609     BB509       zie KV1235 BB510       SMD sot23 500pF varicap 1-8V                                    0.79
    13. BB515       verbeterde BB215 smd SOD123 (blokje) 2-10pF                     1.02
    14. BB521AX     zie BB221 BB529       UHF axial                                                       0.79
    15. BB531       VHF super range 2-40 pF axiaal                                  0.79
    16. BB609       35pF axiaal                                                     1.59
    17. BB619       zie BB629 BB620       70pF! SOD23 (klein buisje)                                      1.13
    18. BB629       Wide range 2.5-38 pF smd zie BB729 BB640       Siemens SHF varicap                                             3.40
    19. BB701       0.8-8pF high-Q SMD klein blokje- low noise                      0.79
    20. BB729       Wide range 2.5-38 pF smd                                        1.25
    21. BB801       idem SOT23 SMD                                                  0.79
    22. BB809       see BB609 BB811       UHF/SHF SMD Dubus SOD123 (blokje) SOD123                        2.50
    23. BB813       TV/SAT als BB811 maar nog groter bereik: 0.6-12 pF SOD123       1.59
    24. BB833       TV/SAT als BB813, nog kleiner: SOD323                           2.50
    25. BB835       TV/SAT/SHF SOD323 0.5-9 pF                                      1.82
    26. BB909A      zie HVS303     BB814       2x40pF in SMD                                                   0.79
    27. BB911       Zeer groot bereik, axiaal,  2-55pF                              1.59
    28. BBY31       SMD UHF 10pF hi-Q prof.                                         1.34
    29. DH71010-51  0.7 - 2 pF  0.5-24V Q=4300 @ 50 MHz SOT23 Fmax= 4 GHz           5.67
    30. DH71010-53  idem dual                                                       7.94
    31. DH71020-51  1.2 - 4 pF  0.5-24V Q=3900 @ 50 MHz SOT23 Fmax= 4 GHz           5.67
    32. DH71020-53  idem dual                                                       7.94
    33. DH71045-51  3.0 - 10pF  0.5-24V Q=3000 @ 50 MHz SOT23 Fmax= 3 GHz           5.67
    34. HVS303      Wide range as BB909/910 axial glass                             1,34
    35. KV1235      550pF 9V high-Q (=KV1215,KV1236 etc.)            per diode:     5.90
    36. KV1225      550pF 25V uitverkocht - use MC500 500pF@24V 2-25VDC             9.90
    37. KV1310      40pF high-Q TO92                                                1.00
    38. MA45253     Varactor MA/COM gold plated tape ended C=1:6 Cmax=2p7 Q=3000    2.90
    39. MA4ST401    Varactor diode MA/COM smd 1-10 pF Q=250                         2.70
    40. MV1401      Motorola super-Q 30-600pF 1-10V Q=200 axiaal zie KV1235 MV2190      Motorola high Q TO92 varicap                                    3.00
    41. MV2301      Motorola high Q TO92 varicap 200pF @ 1V Q=250 6nH 0.18pF        3.50
    42.  SMV1233     Alpha SOT23 single 1,5pF @ 1V - 0,4pF @ 6V - 15V max.           6.58
    43.  
    The prices given are from a local dutch company.

    Bertus
     
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