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Thread: My Rock-Mite 40M

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  1. #1

    Default My Rock-Mite 40M

    Hey guys,

    After thinking about getting into Ham Radio for a couple years, I finally got around to taking the exam and now I'm licensed! I just find it fascinating that I can solder something together and use it to talk to people hundreds of miles away. I haven't used this transceiver yet (still waiting on my dipole to come in the mail), but I just finished building this Rock-Mite 40M QRP CW rig. It was a relatively cheap option, and it definitely fulfilled my need to apply some of my college physics courses. I'm almost finished learning CW, so hopefully my antenna will come soon.

    RM1.jpg
    RM.jpg
    Really worked on my soldering skills putting this together! Drilled some holes into an altoids tin for the enclosure.
    RM2.jpg

    Quick question: if an antenna isn't connected to the radio, does the radio transmit any sort of signal if I practice with my key?

    Thanks and 73,

    Andrew

  2. #2
    Join Date
    Aug 2004
    Location
    Ash Fork, AZ - 60 miles south of the Grand Canyon, off of Route 66.
    Posts
    725

    Default

    Quote Originally Posted by KB3YLI View Post
    Quick question: if an antenna isn't connected to the radio, does the radio transmit any sort of signal if I practice with my key?
    I'm not trying to be snarky but it is called a "transceiver" not a "code practice oscillator" (CPO). If you use it as a CPO you should connect a 50 Ohm dummy load to the antenna terminal. I believe that Radio Shack has, or use to have, 50 Ohm 1-2 Watt non-inductive resistors. Just wire then across a connector and plug them into the antenna terminal.

    But it's also pretty easy to build a separate CPO for learning CW. There are dozens of CPO drawings available on the internet. For example here is one, at http://hamslife.com/?p=18, that uses parts that are available at Radio Shack. You can get a little pre-drilled prototype board at RS. There are many more just like it on the internet.

    When you finally put it on the air, you will need a lot of patience. When you are very low power, it often takes a bit of work to make a contact. I have a HW-8, HW-7, and 40 Meter Vectronics TX/RX for QRP work. They are a lot of fun to use, but they are often a lot of work. Just don't get discouraged when no one seems to be answering. Sooner or later you will be heard and someone will give you a call.
    73, Martin, K7MEM
    Ash Fork, AZ
    [URL]http://www.k7mem.com[/URL]

    In my area, it seems that every pickup truck or SUV comes with one or more dogs. It's so common that I can only assume that the dog(s) must come with the vehicle. So logic tells me that, if you want to keep the truck for a long time, go for the multi-dog option. Otherwise, if the dog dies, you have to buy a new truck. I have five dogs (4 dogs as of 4/4/2013, RIP Katie), so I'm set for a few years.

  3. #3

    Default

    Yes, but make a dummy load first. Hopefully your nearby rat shack has a couple of 200 ohm half watt resistors, tie four of them together in paralell and hook them up to the antenna jack. When you transmit, you should be able to hear the "sidetone" in the headphones.

    Btw, you could fabricate a nice portable antenna with a long piece of lamp cord. Split the cord partway so each leg is approx 33 ft (use the formula) and use the unsplit part as the feedline. This works much better than you might think .

    Have fun with your little rig, i usually listen for those when the nasty psk guys aren't plugging up the bands with thier howls.

    73 m/4

  4. #4

    Default

    Quote Originally Posted by AB9LZ View Post
    Btw, you could fabricate a nice portable antenna with a long piece of lamp cord. Split the cord partway so each leg is approx 33 ft (use the formula) and use the unsplit part as the feedline. This works much better than you might think .
    Lampcord? That's pretty cool. I guess the main reason I'm interested in amateur radio is hearing the stories of WWII soldiers building radios out of scrap bits and pieces, just whatever was laying around, and I figured, heck I could do that too. I still don't quite understand how antenna's work, but that's why I'm getting into building my own equipment, I want to be able to understand all this stuff!

  5. #5

    Default

    A lampcord dipole works out to an approx 75 ohm impendence depending how high it's hung, a close enough match for most rigs, including the rock mite, to work just fine without any need for an external tuner. I've used one several times while backpacking with an sw+, I've since switched to an end fed halfwave, but only because it's easier to hang (lampcord is pretty bulky too, space is at a premium in my pack). All in all I've managed about a dozen blue ridge to europe Qrp qso's with the lampcord.

    73 m/4

  6. #6
    Join Date
    May 2009
    Location
    Millsap, Texas
    Posts
    495

    Default

    Nice first build! As others have stated, build some sort of dummy load before keying the transmitter. If not, even
    at such low power levels, you could damage the output transistor keying it without an antenna or a dummy load.
    Patience is the key with QRP!!
    Have fun!
    james
    WD5GWY

  7. #7
    Join Date
    Feb 2004
    Location
    Bakersfield, CA
    Posts
    4,604

    Default

    I just cringe everytime someone says they are buying a dipole antenna. It's just wire and sometimes you add a balun (it will work without one) and the feed line. The measurement to make a 1/2 wave dipole is 468/F = Feet. F is the frequency in Mhz. From this formula you can get the diminsions of every dipole antenna that is a 1/2 wave. When you get the wire measured fold it in half (or if you want to be picky, measure it) and cut it. The length is usually a bit too long for immediate use. You would trim the length to obtain a low SWR (1.5:1 is good). Don't forget you need to have the center and the ends insulated from contact with anything. Your insulators can be anything non-conductive, pieces of plastic are a good source, PVC pipe works and you can buy them. Just use your imagination. Zip cord can vary in impedance, one QST article measured it 100-110 ohms.
    There is a good source of information you can download at; http://ok1ike.c-a-v.com/soubory/ant_...toolkit_2e.pdf. Everything is in metric so you would need to covert it or use a metric measuring system.
    Hope this helps
    73
    Gary

  8. #8

    Default

    It's a good thing I don't bother with QST anymore, else none of the stuff I do would actually work

    My impedance bridge (it's homemade, so may not be perfectly accurate) measured my lampcord antenna under a typical deploy... thrown over a low branch, at 67 ohms.

    If you liked the rockmite experience, you may want to try the sw+, it has a good filter a usable vfo and enough additional power to make it a daily user. I used one from a London hotel room over a three week period (used an end fed wire thrown over the edge of the balcony), was able to work russia, north africa, and lot lot of middle eastern countries that i don't normally see. I made a jig so i could power it from my work provided laptop battery.

    73 m/4

  9. #9
    Join Date
    Feb 2004
    Location
    Bakersfield, CA
    Posts
    4,604

    Default

    The QST article was really a long time ago. It was kind of amusing. It started off with the measurements of various zip cord then it announced "Anybody that needs a 110 ohm feedline this is it!!". Then it asked "So who needs a 110 ohm feedline?". There were fewer manufacturers of zip cord back then and it was usually made the same way at each plant. The zip cord today is all over the place. So yes you can get different impedance just by looking for zip cord that has different spacing or insulation. There is one place where a 110 ohm feedline is good and that would be on a full wave loop. Zip cord works well on the lower bands but as you go higher the losses become very high.
    Have fun
    73
    Gary

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