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Thread: Amateur Radio - best place to start

  1. #1

    Default Amateur Radio - best place to start

    Hi,

    I've been interested in electronics for a couple of years now, purely as a hobby. This has recently progressed into an attraction to RF related technology and amateur radio. Although I do not have a licence as of yet (Sydney, Australia), I will definitely go down that path once I have successfully built a working transceiver or two. (I am aware of the rules that I would not be able to broadcast on various bands without a licence first.)

    I have picked up two books at this stage, the first being Basic Antennas - ARRL Hallas W1ZR, and Build your own transistor radios - R. Quan. I am in the middle of both of them and covering alot of ground.

    At this stage I am learning to put together AM radios and will try to build a TRF radio first with Antenna + filter, amplifier and detector stages.

    Some of the components in the book are obselete through hole transistors such as the MPSH10. Substituting these components require the radio to be designed with different passive components obviously.

    So to start with building an receiving antenna to detect the AM band, which in Sydney hovers around 1MHz, how would one build it? Would it be a resonant antenna with an inductor and variable capacitor? I want to detect the AM signal with an oscilloscope first, before I construct the amplifier. Would the AM signal be impossible to see on the scope, due to the fact that the signal is in the range of millivolts?

    Thank you.

  2. #2
    Super Moderator 5B4AJB's Avatar
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    Quote Originally Posted by AU30 View Post
    build a TRF radio...
    That's a great project, together with an audio amplifier - very practical.
    I helped a budding ham build a TRF trancseiver kit which needed a seperate audio amp.
    We used a scavenged TDA-type audio chip to good effect.

    Quote Originally Posted by AU30 View Post
    building an receiving antenna to detect the AM band...
    A ferrite rod with inductor wound is usually used.
    There are lots of ways to feed a receiver, but a good untuned starter antenna is a simple longwire, insulated at both ends.

    Quote Originally Posted by AU30 View Post
    Would it be a resonant antenna with an inductor and variable capacitor?
    Making the antenna resonant involves making the wire (or elements) physically longer or shorter.
    Variable inductors and capacitors can "bend" this length only so much.

    Now you are talking about an ATU (antenna tuning unit) to make the feedline together with the antenna resonant.
    Some antennas like a magnetic loop have the ability to change their resonance right at the antenna.

    Quote Originally Posted by AU30 View Post
    I want to detect the AM signal with an oscilloscope first, before I construct the amplifier. Would the AM signal be impossible to see on the scope, due to the fact that the signal is in the range of millivolts
    You'd need to have a diode on the osciloscope lead with the antenna.
    It would show all the strongest stations near the resonance of the antenna. (an audio amp connected would allow some extra "feedback" to what's going on.)


    Build a simple crystal radio receiver first, then build an audio amplifier, then build your antennas and an ATU, everything you have asked should be easy for you to work out from there

  3. #3

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    Quote Originally Posted by 5B4AJB View Post
    You'd need to have a diode on the osciloscope lead with the antenna.
    You would not need a diode to see an RF signal coming in on an antenna using an oscilloscope, oscilloscopes see AC just fine, no need to rectify it.

    Yes, the signals may be too small to see, and with all the other signals being superimposed on the one you are trying to see, the scope trace will not look like a sine wave anyhow. You may recognize a general wave-like characteristic among all the other stuff coming in if the signal is strong enough and you have the scope set up such that a wavelength is an expected number of divisions on the display. And even then, it will be hard to see the wave pattern as the other signals will make triggering the scope difficult at any particular frequency. Without triggering, the wave pattern of a signal would be all over the place.

  4. #4
    gnuuser's Avatar
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    Here is a good place to pick up kits around your neck of the woods.
    https://www.minikits.com.au/
    they offer some nice kits to build and you wouldn't have to wait very long to get them.

    while many do not have the patience to build kits Its a vital learning process to being a successful and proficient ham operator.
    Many kits out there today not only have decent instructions but explain the how and why of the critical components

    http://shop.qrp-labs.com/qcxp
    this site offers the qrp qcx transceiver kit.
    this kit you can get for the frequency band you choose and they send you the proper components.
    I selected the 40 meter band (and there are quite a few components) It is moderately easy to build providing you follow the instructions of the downloaded manual.
    you learn the calibration and alignment process (its fairly simple) but when complete you have a fully functional transceiver that will cover the entire band of your choosing.
    with a 5 watt output its cw transmission is louder than you might think.
    its a good starter radio!
    Im so old dirt was my apprentice

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