Just finished my Pixie 2 transceiver (pics)

Discussion in 'Homebrew and Kit Projects' started by VK2ZYZ, Jul 13, 2008.

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  1. WA6MHZ

    WA6MHZ Ham Member QRZ Page

    These are WONDERFUL examples of Homebrew!!! Wish more Hams would do it!
    One of the ways I try to do it is with isolated pads on a PCB. That way, I have a good ground plane and easy bypassing. I have a device called a Whitney punch that punches out holes in metal, or in this case, round chunks of PCB material. The disks are superglued to the main copper ground plane and then the parts soldered to these. Works great! Also cut out rectangular chunks to put under ICs so the IC is floating above the board and allows easy bypassing, grounding or soldering wires and parts to the floating leads. To assure they won't break off (I usually use Surface mount parts) I encapsulate the floating parts in Hot Glue to keep them safe. (after they have been thoroughly tested and aligned!) Its alot of trouble to take the hot glue off, but saves broken wires and parts. Wish you would detail your great homebrewing efforts over on the HAMRADIOHOMEBREW Yahoo group so the folks over there would be as inspired! I am still building a 6M SSB xcvr, but got waylayed with Vintage radio restorations and antenna work. I need to be retired so I have more time to work on projects!
     
  2. AG3Y

    AG3Y Guest

    I've seen the pads isolated in a couple of different ways. One way is to use a leather punch or similar device that will cut out little circles of PC board that you can CA glue to the baseboard. Another is to actually cut through the top layer of copper to result in an isolated circle of copper. The difference is that one way results in little lifted "islands" of copper CB material, the other just has the copper circles at surface level.

    Radio Shack used to ( I don't know if this is still true ) have small circuit board chips that had a foot pattern of a DIP IC already etched into the board. The problem with RS boards is that the glue used to hold the copper on to the substrate is VERY poor quality ( well, what isn't from RS ? ? ? ) and getting a pad just a LITTLE too warm will result in it lifting freely from the board. A real hassle!

    Ugly construction may not look like anything but . . . well ugly! , but it is a very good way of quickly building a one-time project !

    73, Jim
     
  3. AB8RO

    AB8RO Ham Member QRZ Page

    I bought a bunch of little irregular shaped square pads from Dan's small kits. They aren't as pretty, but they work well enough.
     
  4. AG3Y

    AG3Y Guest

    Can you believe that sometimes in my job, I would end up etching out the circuit paths with a small cut-off tool in a Dremel machine ? Takes a deft touch to be able to cut only as deep as necessary to isolate the path, and not cut through to the other side of the board !
     
  5. WA6MHZ

    WA6MHZ Ham Member QRZ Page

    I also make PCBs here at work using copper tape. I lay down a layer of copper tape on the fiberglass, and then, using a sharp Xacto, cut the traces and remove the copper tape that would not be needed, leaving nice traces. They dont stick too well, but once parts are applied, seems to work FB. This works for even very narrow traces I need for SMT ICs.
     
  6. K5UOS

    K5UOS Ham Member QRZ Page

    Charley,

    I am always late to comment. Your scratch homebrew construction looks excellent….like you have done it many times before.

    I like using a simple marker for labeling knobs and other controls. There are a lots of pretty homebrew rigs that look better than they work.

    I can tell you are very excited. Building a working receiver is very exciting even if you have done it many times before. Simple receivers seem to thrill me, too.

    There should be a Pixie night once a year. There must be thousands(?) of the little rigs built.


    72 K5UOS
     
  7. KC4UMO

    KC4UMO Ham Member QRZ Page

    Heck, I going to build me one!

    All the scematics I found use an IC chip...
     
  8. K5UOS

    K5UOS Ham Member QRZ Page

    Buddy,

    This is simplified. Performance of a minimalist rig like the Pixie is best understood up front. Using IC's is different and not necessarily better or worse.

    The early DC receivers used an unbalanced or singly balanced device like a dual gate mosfet or a BJT as a detector.
    Detection of local and strong in-band AM BC stations were particularly irritating with these systems. The reasons can be quite complex.

    In the 70's balanced diode mixers became popular to address some of the problems associated with DC receiver i.e. BC interference, hum, etc.
    A separate outboard oscillator and audio amp was necessary. Shielding the oscillator, decoupling the
    power supply and isolating the front end improved the performance. See W7EL's Optimized Transceiver.

    In the 80's the NE602 IC provided a simple means for onboard VBFO, mixer and audio preamp in a single device.
    The NE602 can suffer from strong BC band interference but the simplicity of building a VFO controlled minimalist receiver
    with just two IC's (NE602 and LM386) makes this a popular choice for 1st receiver projects.

    My guess is the Pixie can be (is) overwhelmed with strong 40M BC band interference like some of my early DC transceivers.
    I used them a lot in the daytime when the problem was not as great.

    Just note that Pixies may represent the lowest limit of functional receiver design. That is why they are so popular with
    minimalist ham operators who thrive on these simplest of rigs. All done with a handfull of parts.

    I have a preference for simple receivers built with SBL-1's, passive audio filtering (diplexer), a 2N2222A preamp and an LM386 audio amp.
    Coupled with a grounded gate pre-amp with low pass filters this setup makes for a cheap receiver for a portable CW or DSB rig.
    I have seen many designs for a weekend receiver project with similar configurations. Great 2nd receiver/tranceiver projects.

    K5UOS
     
    Last edited: Jul 14, 2008
  9. KC4UMO

    KC4UMO Ham Member QRZ Page

    Donald,
    Thanks for the info. I think I may have a few LM386's around in the junk box. I am a nut for building things with junk parts. Specially when you don't have to buy anything

    I was thinking of building the Funster 40:
    http://www.qrp.pops.net/funster.asp
    but I want to build one of Pixies first.

    I think these are great learning projects.

    BTW, I have to compliment you again on that shiny rig in your bio...
     
  10. AB8RO

    AB8RO Ham Member QRZ Page

    I agree. I think a problem is that so many projects use toroids. I have a draw full of them so it isn't an issue for me but I remember when I was a kid that mail order parts were a show stopper. That was part of why the tuna tin 2 was so great, you could built it with parts from radio shack.

    I really like projects that can be built entirely from something common and discarded. Old VCRs are great because they often have single sided PC boards which makes de-soldering components easy even if you don't have special tools.
     
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