My First receiver:Recommendations-part_1

Discussion in 'Wireless & RF Design' started by froten_140, Sep 29, 2010.

  1. froten_140

    Thread Starter Active Member

    Jun 4, 2006
    30
    4
    Hello All,

    I'm planing to start building my first project in RF circuits, a SW radio receiver (3-30MHz). I have small experience with RF design so I'm trying to get some help through this forum.

    In this post I would like to get some recommendations on the overall design, building blocks, suggested circuits, links and projects.

    Since it is the first receiver, it doesn't have to be a high performance, can be Battery or line power operated, and all transistor since IC's are difficult to optain in my city. Any idea is welcome.

    Thanks in advance for any help.
     
  2. bertus

    Administrator

    Apr 5, 2008
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  3. Randolf777

    New Member

    Sep 30, 2010
    1
    0
    I would consider using a superhetrodyne radio. It is easy to build an oscillator with today's circuits which include diodes acting as variable capacitors. In this way you don't have to use filtering on the front end that is adjustable and tracks. If you don't really care whether or not you are going to pick up "image" signals, then simply change the frequency into a mixer and run the output through a fixed filter. This is much easier and I used to listen to aircraft using this method with a simple potentiometer connected to the varacter to control the frequency of the oscillator. Images were usually not a problem up in the commercial aircraft band since we live in a part of the country where there is limited aircraft traffic. If you want a schematic can throw one together for you that will probably give you the range you need. You may need to switch your oscillator to make the different bands, but that is easy to do and if you have a good antenna you may pick up some images and other interference, but you will still have a good first receiver that will tune the band you are looking for. By the way, do you need single-side-band, AM, FM or what kind of detector are you looking for? The single-side-band detector can be more complex than the rest of the radio if you don't have access to Integrated Circuits.

    I hope this helps some. My background is ground-to-air/satellite and missile communication from the RF point of view and I have designed a lot of receivers and transmitters, including high-power broadcast transmitters.

    Have a good day.
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    For a beginner there are lots of options. What part of the world are you (you mention lack of parts)? Most folks order mail order, but packages crossing international boarders can be a hassle, this I understand.

    You will note most of the old hands have their location and time zone as part of their profile, in such a way to be displayed in the upper right hand corner. Parts is a major reason for this, there will probably be other members from that region who can help.

    Have you had much experience wiring circuits? RF in particular is another world, things that don't matter with lower frequencies (the word is negligible) are suddenly critical.

    Two techniques for prototyping I recommend are the Dead Bug technique, and the Manhattan Construction for RF (go down the page to find it). Your chances for the project to work go up using either or both of them with RF.

    I will disagree with Randolf777 a little, unless you have the right test equipment (or access to same) superheterodyne is not for a beginner, mainly because tweaking of the values is critical. It is more sensitive and simpler in many ways, the test equipment needed is my main objection. A simple 3 transistor receiver with tank circuits between them is probably a lot simpler to build.

    The web, particularly HAM sites, are a fantastic source for articles and ideas. I would suggest if you find a circuit you like post the link here so it can be vetted. Not all schematics on the web work (in fact, I tend to agree with AudioGuru, most don't). Feel free to send me a PM if you post here again.
     
  5. froten_140

    Thread Starter Active Member

    Jun 4, 2006
    30
    4
    Thanks all for all the help.

    I have done some RF circuits in the past and read a lot of text books and web pages put still lacking practical experience, therefore I'm starting with this project at the transistor level.

    I have downloaded many old receiver circuits (two links are attached bellow) which I'll try to build a similar receiver (with NPN transistors). I choice these circuit because of low parts count, low current and because I understand the circuit theory of operation. and I'm starting with the mixer circuit.

    any advises are welcome.

    appreciate ant help.

    http://techpreservation.dyndns.org/s...al_8V1_14.djvu
    http://techpreservation.dyndns.org/s...TP-30_157.djvu
     
  6. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I could read the first one.
    The second one gave a black screen.

    My comments on the first one:
    The transistors are Germanium transistors, the Vbe is much lower as with Silicium transistors.
    The conversion from PNP to NPN will not be that easy, the working points need to be changed.
    The powersupply must also be reversed.

    Bertus
     
  7. froten_140

    Thread Starter Active Member

    Jun 4, 2006
    30
    4
    Thanks for the help. I'm aware there will be many changes.

    I would like to know:

    1) What is the sensitivity required to build a SW receiver? or what is the expected RF signal value at the input of the mixer? is it in the range of 1uV, 100uV or 1m?

    2) What is required gain from the mixer to the detector? 60db,80db or more?

    3) What is minimum RF signal value at the detector diode? do we need more 0.7V for the diode to work?
     
  8. bertus

    Administrator

    Apr 5, 2008
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  9. Wendy

    Moderator

    Mar 24, 2008
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    The graphic standards used by most people are .gif, .pdf, .png, etc. If you want other people to see your work you need to use a standard graphics format. I can not participate simply because the graphics standards are not in my library (and I'm not going to add a new program unnecessarily). I'm not the most experienced user, I only have 24 years with Collins Radio and another 15 years experience as a hobbiest and in armature radio.
     
  10. davebee

    Well-Known Member

    Oct 22, 2008
    539
    46
    I would suggest that you consider starting by buying and assembling a kit.

    For about $45, you can get a kit that builds a radio that's just about what you described:

    http://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&key=SR2C

    There is so much to learn about receiver design that I don't think you'd be losing any educational opportunities by starting with a kit instead of building your own design.
     
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