20M Rockmite ][. A several evening project.

Discussion in 'QRP Corner' started by VE7WAX, Sep 9, 2016.

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  1. VE7WAX

    VE7WAX Ham Member QRZ Page

    This project was quite an endeavour. After being out of HF for several years, I decided to get back into the game with something small --- a QRPme Rockmite ][. I ordered the kit from Rex, and it arrived two weeks later.

    The kit contained the board, components, and all the hardware necessary to install the radio in an enclosure, including pots for volume and speed controls, a DC receptacle and switch, a momentary push-button switch, wires, and an LED. The kit also included 12 header pins (more on these below). I purchased the enclosure and a pot knob at a local supplier.

    The builder's guide and builder's help documents on Rex's website are concise, and were quite sufficient to help this novice through construction. By the end of the second evening the board was complete, and wired for installation into the enclosure.

    As you can see above, I followed the builder's help advice and installed header pins in the Y1 and Y2 sockets to enable crystal switching (the kit comes with crystals for both 14050 KHz and 14060 KHz). I also installed header pins under Q6 to make replacing or upgrading the PA transistor easy.

    After completing the board, I put it aside and focused on the enclosure. Because I intended to bolt the board to the roof of the enclosure, there was no room on top of the radio for any fittings. My priority was to keep all fittings on the short ends of the radio. I knew I wanted at least a volume control. But try as I might, I just couldn't find room for a key speed knob without ruining the clean lines of the enclosure. The radio's PicoKeyer chip has a speed menu. So to me the speed pot seemed redundant, and I omitted it.

    Measuring and drilling precise holes in the the enclosure was more challenging than I expected. After permitting the drill bit to grab the enclosure from my hands and thrash it around my drill press for a few seconds, I resolved to slow down and work more carefully. Fortunately the damage was slight, and only cosmetic---a permanent sign of an important lesson learned.

    With the holes drilled, it was time to fit the power receptacle, the switch, and the power indicating LED. A diode between the receptacle and switch protects the radio against reversed polarity.

    Some twinlead feeds the LED with DC directly from the switch through a 1K resistor. The Rockmite ][ kit comes with soldering pads. Super glue holds these to the enclosure walls. Handy stuff!

    The BNC was connected to the board with a length of coax, both of which were included with the kit.

    With the radio assembled, it was time for the smoke test. I plugged in my headphones and keyer, hooked up the dummy load, and plugged in a 12V battery. I flipped the switch and, magically, the radio came to life. Unfortunately, the sidetone which so many complain about being super harsh in the Rockmite, was nearly inaudible. Furthermore, the frequency offset did not flip with short button presses as it ought to. Despite these, the radio keyed, transmitted, and received nicely (even on dummy load I could hear CW stations!).

    Following the troubleshooting section in the builder's help, I confirmed all the voltages coming off the keyer. The results were interesting. Pin 3 did not shift voltage with short button presses, which explained why the T/R offset wouldn't change. But even stranger, the pin that controls the transmit/receive/muting circuit was giving off a 1900 Hz square wave. An oscilloscope trace of the radio's RF output confirmed that the signal was coming out in 1900Hz pulses of RF.

    Unfortunately, during further troubleshooting I toasted a MOFSET with my multi-meter probe, which also toasted the adjacent zener diode.

    Time to email Rex. He was amazing. Over the next few days he went above and beyond to try and help me, and gave me several avenues to troubleshoot. I told him that I suspected I might have ESDed my keyer chip. So he shipped a new and MOFSET and PicoKeyer chip to me at a very modest price. But after I installed the new keyer chip, the radio displayed identical faults. After some head scratching on both ends of our email chain, Rex discovered another customer was having identical problems as me. Eureka!

    Rex realized he programmed a batch chips for a different kit, but sent these out with some Rockmites by mistake. Bam. He immediately shipped a new chip, properly programmed this time. It arrived four days later. I installed it and everything worked properly. And yes, that side tone is harsh. A 33 uF cap across the audio leads softened it nicely. It cuts a bit of the high end off the receive audio too. We'll see how that works out.

    On eight AA batteries my radio puts out about 8.8V peak to peak into a 50 ohm dummy load---750mW! Now I await my Emtech ZM-2 tuner so I can take the radio outside and make a few QSOs.

    A big thanks to Rex for being very patient with this novice kit builder.

    Overall, I am impressed with the Rockmite. It is a mature kit, with a large following. I really enjoyed assembling it.

    Thanks for looking.


    Note the damage on the left side of the enclosure. Be careful with your drill press!






    Last edited: Sep 9, 2016
    KC8YLT, W7UUU, K4YND and 1 other person like this.
  2. N6RGR

    N6RGR Premium Subscriber QRZ Page


    Nice work! I am thinking about trying a milliwatt QRP rig as well. Several small kits that look and perform decently. I need to get back to practicing my CW.

    73, Roger KK6IVD
  3. K4YND

    K4YND Ham Member QRZ Page

    bravo. keep sharing your builds
  4. KL7KN

    KL7KN Premium Subscriber QRZ Page

    I must say, your photo work is as or more impressive than the kit build.

    Care to share any details? Camera, lens, lighting, etc?

    As far as the rig goes - pretty sanitary, as they say, nicely done!
  5. W7UUU

    W7UUU Principal Moderator Lifetime Member 133 Administrator Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    Very nicely done indeed!

    You'll most definitely need to post more about making contacts - nice project! :)

  6. VE7WAX

    VE7WAX Ham Member QRZ Page

    Thanks for the kind comments guys.

    I await an Emtech ZM-2 tuner kit in the mail which should arrive any day now. I'll snap a few shots while I assemble it.

    As far as the camera goes, nothing fancy, just my cellphone. I zoomed in for some of the closeups. Lighting is from two desk lamps that adorn my bench and a ceiling light.

  7. KP4SX

    KP4SX Premium Subscriber QRZ Page

    Excellent! I recently ordered a little kit so this piqued my interest even more to get started.
  8. K8JD

    K8JD Ham Member QRZ Page

    What about an antenna ?
    I suggest a 3 element HyGain monobander for a QRP rig. Gauranteed Results !
  9. VE7WAX

    VE7WAX Ham Member QRZ Page

    Well, I took it out last weekend and set it up on a local hill with an end fed antenna in an inverted vee over a 20 foot collapsible fishing pole.

    Heard LOTS of stations. But I wasn't able to snag a contact. I think I will switch out the power transistor and a resistor to up the power to over a watt and try again.
  10. KB4MNG

    KB4MNG Ham Member QRZ Page

    I don't have the patience or time to try to make a contact with less than a watt.
    KB9LXP likes this.

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