Monday, December 8, 2014


For the 40 meter, 20 meter what type of rf pre-amp stage should be used. ,,,,

any design guidelines, examples , i have made one but i need some practical insight please..... it will be driven to the diode pdm ( product detector module).... de vu3inj...

    Dev Rama Prabhu A small 13 dB gain amp would do because of the diode DBM which is lossy!
    Normally the loss of diode DBM is around 7dB to 9dBso excess gain should not be used!
    Happy home brewing!
    By the by 12 dB gain = 4 times voltage gain!

    Kalyanasundaram Ramachandaran Around 10db will ideal.

    Indrajit Sinh should i use high ft transistor c2750 or common bc547 for 40/20 meter front end , calls A,wideband 3:1 balun transformer as load , secondary connected to dbm......

    Dev Rama Prabhu Better to go for 2N3866 as it is strong signal low noise amplifier!

    Ron Mallik 2SC3355 will easily work with 30mA of current at 9-10V Vce. Amazing noise and IP3.....2N3866 very dubious these days..."printing maal" as per local trusted dealer

    Ron Mallik Indrajit Sinh and others: IMHO the electronics is not the main problem. How skilfully you wind your magnetics, will play a big role. For example, the original designer may have carefully wound the bifilar coil with say uniform 8 twists per turn and spacing them evenly on the toroid. The novice did everything, but wound the coils randomly (anything but broadband ) and did not check for phasing: same electronics, but it doesnt work in the latter case! Designer gets bad name but HOW designer will document his skill and experience

    Ron Mallik For 40/20m BC549C is great.....10mA Ic is enough! We should not also ignore the C9018 transistor. It is a brilliant but cheap device. The vendor will make a BIG difference though.....Better to locate Fairchild/Onsemi 2N3904 instead. Atmospheric and antenna noise is much higher so do not bother about noise figure at these frequencies!

    2SC9018, 2SC9018 Datasheet, 2SC9018 AM/FM IF Amplifier, buy 2SC9018

    Indrajit Sinh i fully agree with Ron Mallik on the toroids winding. infact i have written on it in my blog. pahsing and twist no problem. will go for bc549c yes C variety.... as the rx is just for checking the local signal during the testing phase of the transitter... it will be use will similar to FSM. i will be listening on my tic tic and adjust the tx.... as for 2n3866 its a good one but in the market they sell two variety one cheap and one guranteed so not buying any2n3866
    Indrajit Sinh for the bad name :: designer has to really write two type of writings. one as a normal they are doing and one very extensive one ( like i do with writing down even a trivial thing, the process, what i thougt and what went wrong and how i got it corrected etc ). second type of writing we dont see any... that was the reason for me to re-invent wheel dialogues.... lets hope by doing thought churning something good will come out... ( i am not a designer just a reproducer, jugadu...)

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