SMD Transmitter

Discussion in 'The Projects Forum' started by radiohead, Jul 18, 2011.

  1. radiohead

    Thread Starter Active Member

    May 28, 2009
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    This is my first stab at an all-SMD transmitter. It operates from 1.5 to 5 volts. It draws 14 mA using a SAFT LSH 20 (13,000 mAh) 3.6 volt battery, so I should get about 928 hours (38 days) from the one battery. This one oscillates at 1.065 GHz using an MRF-901 microwave transistor. The antenna is 1/2λ and I got about 150 meters or so in an open field. Not bad for something smaller than a dime!

    The tiny capacitors are hard to hold in place with a knife blade. Are there any better ways to hold these micro components in place for soldering?
     
  2. radiohead

    Thread Starter Active Member

    May 28, 2009
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    Here is a better schematic image.
     
  3. KJ6EAD

    Senior Member

    Apr 30, 2011
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    In your quest for miniaturization, you made the first schematic too small to read. :D

    There's a member of the forum called "nsaspook". You should P.M. him to see how many transmitters he wants to buy from you. ;)

    Yes, most experienced SMD solderers use hooked fine-point non-magnetic stainless steel tweezers to place the component, bump it into place and clamp it down to the PCB with light pressure from both tips together on the top center of the component. Some will use a hooked pick in a similar manner but this means changing tools during the operation. See the video link below.

    Tweezers: http://www.cooperhandtools.com/brands/CF_Files/model_detail.cfm?upc=043127608896

    Video: http://www.youtube.com/user/SolderingGeek#p/u/39/66GV4OuShzI
     
    Last edited: Jul 18, 2011
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    I much prefer these:
    http://www.cooperhandtools.com/brands/CF_Files/model_detail.cfm?upc=043127608865
    I just find the longer hooked tweezers to be a bit awkward, and tend to amplify any shaking due to over-imbibing on coffee. ;) Also, the mechanical advantage is better; the longer hooked jaws have a bit too much flex for my taste.

    Once you've mangled the points, you can easily file them back down to make them a bit more rugged. I like to keep several pairs on hand. The new ones I use for small SMD's, the ones I've reworked are more general-purpose.
     
  5. KJ6EAD

    Senior Member

    Apr 30, 2011
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    Just say "no, I have to solder tomorrow" to coffee refills. :rolleyes:
     
  6. radiohead

    Thread Starter Active Member

    May 28, 2009
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    Thanks for the tips. I do have some tweezers, I will mod them to suit my needs.

    I am purchasing sme 0805 size capacitors and 0805 size resistors. The caps I have now are much, much too small. I think they're 01005 or 0201 size. I will use the tiny ones until they all spring off the CCA, get stuck on the soldering iron tip or actually get soldered in place... :)
     
  7. radiohead

    Thread Starter Active Member

    May 28, 2009
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    For the test, I used one Yaesu and two Icom receivers. Each with a different freq. I used a Rhode-Schwartz spec-A and came up with the frequency I posted. If you build one, be advised that your frequency will change with the diameter of your hairpin turn as well as the length of your antenna.

    You can use through hole components, but I found that for some reason, the frequency will drift upward until the transistor stabilizes. I don't know why but it does. The frequency drift is almost nil with the SMD.

    My guess is because of the extremely short lead lengths that may act as antennae.

    any thoughts on this theory?
     
  8. radiohead

    Thread Starter Active Member

    May 28, 2009
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    "bumping" the ultra-micro component into place requires both patience and skill. I used a small dab of paste flux to add as an 'adhesive' but in the end, the wire bit I used to jockey it to where I wanted it usually made the component stick to the wire bit or the knife blade (magnetized).

    AAARRRGH!! This is frustrating!!!
     
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