RF Transistor in an Amazing Ham Transmitter

Discussion in 'Wireless & RF Design' started by Willen, Jan 1, 2016.

  1. Willen

    Thread Starter Member

    Nov 13, 2015
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    Hi,
    I am new here but not a VERY beginner guy (a life long learner hobbyist).

    I am pretty curious in RF electronics from my starting days. It's wireless so it seems like a magic! I already made many toy FM transmitters and a microcontroller controlled PLL FM transmitter too. Being engage with transmitter, I knew that
    FM normally transmits in VHF band and for VHF RF amp, a special 'RF power transistor' is needed. But Ham radios transmit in few MHz. And few links shows that using a very simple 'medium power transistor' they transmit around 100km far! Amazing!
    Designer says this one with SL100 transistor, he transmitted 80km-
    http://www.flashwebhost.com/circuit/dsb_transmitter_for_hams.php

    But I never read and thought about few MHz RF amplifier and its transistor's essential transient frequency and gain. He also said FETs like IRF850 etc also work there. Almost many general power transistor or mosfet work for few MHz RF amp to achieve 100s of KMs?
     
    Last edited: Jan 1, 2016
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    RF propagation is different at HF than at VHF.
     
  3. Willen

    Thread Starter Member

    Nov 13, 2015
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    Hi Mike, Yes due to ionosphere too. I want to focus about transistors here.
     
  4. sailorjoe

    Member

    Jun 4, 2013
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    Hi, Willen. I think you'll find that there are lots and lots and lots of different types of transistors, suitable for all kinds of applications. Some transistors are designed for low power, some for high power. Some are designed for low frequency work, others for high frequency, even up through the 50 GHz range. If you think about a modern microprocessor chip, it runs at around 2.4 GHz. That means a lot of the transistors in the chip have to handle very high frequencies. In the circuit you provided, I was surprised to see the 2N2222 used as the rf preamp stage, but I can see that it would work just fine. In fact, the SL100 is considered a medium power transistor, with a max power dissipation of only 0.8 Watts. Wait until you build a radio with 100 Watts!
    Does that answer your question?
     
  5. Willen

    Thread Starter Member

    Nov 13, 2015
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    Hi Sailorjoe,
    I mean it's harder to get RF power transistor around me as other consumer parts.
    If 2N2222 would work just fine then why you was suprised? (confused on your sentence)

    Confused again! :) Please tell me the fact if 'general power transistor' is efficient to handle few MHz ham radio transmitters, as the link says?

    Same as IRF510, any mosfet used in SMPS like IRFz44 also can handle few MHz too?
     
    Last edited: Jan 2, 2016
  6. Papabravo

    Expert

    Feb 24, 2006
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    General purpose transistors are not well characterized for RF work. The equipment to do this might cost as much as a small house. The alternative to this is to depend on manufacturers for the data which can be a hit or miss proposition. This is less critical in HF applications (3-30 MHz.), but more critical in VHF and UHF (30 MHz - 3 GHz) applications. As the frequency goes up layout becomes a critical feature of a design along with microstriplines.
     
  7. Willen

    Thread Starter Member

    Nov 13, 2015
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    Hi again, So I am trying to learn about just HF, which not critical as VHF. Ham and its transmission range is amazing than VHF transmitters!
     
  8. Papabravo

    Expert

    Feb 24, 2006
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    Willen likes this.
  9. Willen

    Thread Starter Member

    Nov 13, 2015
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    Hi Papa,
    Thank you so much for your amazing links! It seems that it's VERY useful specially for amature radio operator or a person who have a ham radio in hand. In my whole country there are approx 10 or little more amature radio operator and maybe few have radio. I wish I also could be one! :)

    but now I am just starting to understand it- specially about its output transistor. Link I posted at first post is amazing (using general power transistor) so!
     
  10. Papabravo

    Expert

    Feb 24, 2006
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    Do you know what it would take in your country to get a license? I'm curious to know what obstacles there might be.
     
  11. Willen

    Thread Starter Member

    Nov 13, 2015
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    I have not asked to the government about the process. I just became surprised by seeing some its output transistor like SL100, BD139 etc general power transistor, and they said it's fine for 7MHz SSB transmission.
     
  12. sailorjoe

    Member

    Jun 4, 2013
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    Sorry, Willen, I didn't mean to confuse you. To clarify, I was surprised to see a 2N2222 transistor because they're usually only used in audio frequency applications, and in logic circuits. So I had to back to the specs for the transistor and verify that it had enough gain at the frequency of the radio to be useful, and it does. So it's a good choice. There are better choices, but they're likely more expensive for you.
    Every transistor has specific characteristics. That's why there are so many to choose from!
    It turns out that 7 MHz, the frequency of the radio, is high but not too high to use general purpose transistors, and that's what the radio circuit designer has done.

    You can always get the datasheet for a transistor and look at and compare specifications. Take a look at these. One is for the IRF510, and the other is for the IRFz44. What do see is different about them, and what is the same?
    http://www.vishay.com/docs/91015/sihf510.pdf
    http://www.vishay.com/docs/91291/91291.pdf

    And this is how to get a license. http://www.moic.gov.np/upload/documents/Radio-Communication-License-Regulation-2049-eng.pdf
     
    Last edited: Jan 2, 2016
  13. Willen

    Thread Starter Member

    Nov 13, 2015
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    Hi again,
    Thank you for clarify! I am little familier with transistor and many transistor's datasheets have its 'max transient frequency' and some datasheet have its 'frequency versus AC current gain graph' too. But problem is: every datasheet do not have Frequency Vs AC gain graph and it makes me hard to assume how it works in different frequency range. (like 7MHz RF, 27MHz RF, 100MHz RF etc)

    And I am vary unfamiliar with MOSFETs. I think datasheet of FET has no 'Max transient frequency' as transistor. Maybe I need to assume by its gate capacitance or ON OFF speed like in nS or uS etc. And which is hard to me. (Thank you datasheet but now I am out of my home and my poor cellphone is not able to decode it. Will see it this evening in my PC.)

    Do not worry about license, I may not operate a ham radio station. Just the transistor factor making me amazing.
     
    Last edited: Jan 3, 2016
  14. sailorjoe

    Member

    Jun 4, 2013
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    You are right that data sheets don't always tell you exactly what you want to know. Partly that is because transistors designed for specific uses don't get qualified (measured) for other uses. For example, a transistor designed for switching may not be qualified for linearity. Or a transistor designed for linear power control may not be qualified for switching speed.
    I appreciate your amazement at all this, and your willingness to learn more. If you Google search for "transistor fundamentals", you'll find lots of free books about transistors and how to use them.

    By the way, today I found a number of articles explaining how ham radio operators in Nepal and from India were instrumental in helping get aid to Nepal after the April earthquake. Sometimes a person with a battery, a radio set, and knowledge can help his country when everything else fails. Consider getting your license. You will become part of a wonderful community of amateur radio enthusiasts who will help you develop your knowledge and skills, and someday, you will be ready to be of service.
     
    Last edited: Jan 3, 2016
  15. bertus

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  16. Willen

    Thread Starter Member

    Nov 13, 2015
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    Hi sailorJoe,

    Exactly you found the point! When I heard an Amature operator of Nepal carried a battery and his transmitter and antenna and went to remote hill area which was badly affected by earthquake and had set antenna in a tree and started rescue. Inspiring! :) after then I became crazy with amature operator and its community!


    Hi Bertus,

    I am going to be mad hearing about its output power! 60 watts!? IRF840 is in my near shop and IRF830 is in my hand! :) Can you show/tell me some parameter in the datasheet of IRF840 which says 'it works at 7MHz with enough gain' as RF amp? (Maybe IRF830 has little less power than IRF840)
     
  17. bertus

    Administrator

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    Hello,

    The datasheet of the 840 claims a low input capacitance.
    In the datasheet there is also a switching test for 1 Mhz.
    In the 830 datasheet, I can not find the claim, but the capacity graphs look the same.

    I have attached both datasheets from IRF.

    Bertus
     
  18. BR-549

    Well-Known Member

    Sep 22, 2013
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    Hello Willen. Because of your physical location, you have another option to explore.

    You should consider VHF and UHF. About 40 years ago, I worked for a private commercial radio company. We installed private repeaters in the western part of the US.

    Our two main problems were getting to the peak and the power supply. There were no practical solar panels at that time.

    We would wait until winter. Until the snowpak got to 10-15 foot. This would allow a snow cat to travel over fences and fallen trees, rocks, etc. And get to a mountain peak with relative ease. We would pull and tack a couple thousand feet of 110V power line to trees, up to peak. If we were above treeline, we would lay wire right on the ground. If we had enough voltage left to run a battery charger, we called it a success.

    These were VHF and UHF repeaters, most were about 5 watts and an omni antenna. These repeaters covered hundreds of square miles. This was tube equipment.

    Now days, with solar panels and solid state, this would be much easier and more reliable and cheap.

    Nowadays, one can talk clear across the country on low power repeaters.
     
  19. bertus

    Administrator

    Apr 5, 2008
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  20. Willen

    Thread Starter Member

    Nov 13, 2015
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    Hi again,

    I did many experiment with toy VHF transmitter. But getting VHF or UHF power transistor is not possible in my case, to experiment. Amazing ham sounds really amazing, due to its simplicity and purpose.

    - Can you tell me in basic or place any link of a simple page about SSB, DSB, CW, QRP, Ham, Amature? (introduction/distinguish)

    - As bertus said, QRP transmits far with less power, it is just because of efficient antenna or ?
     
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