40m Pixie kit convert to 70cm

Discussion in 'Homebrew and Kit Projects' started by KN4BSH, Apr 14, 2017.

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  1. KN4BSH

    KN4BSH Ham Member QRZ Page

    This might have been discussed before; however, cannot find it or articulate my search correctly.

    However, is it possible to put a 70cm crystal in the 40m Pixie kit and use the lower side of the 70cm band plan for CW?
  2. KI6J

    KI6J Ham Member QRZ Page

    "The faster you go, the rounder you get".
    - Ken Kesey
  3. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    No. At the very minimum you would also need to change the inductor to achieve a resonant circuit, just as you do when changing between 40m/80m.

    The rest of the circuit, components as well as the actual circuit board would need to be analyzed. At V/U lead lengths and circuit board traces become critical.

    I don't know whether fundamental frequency crystals are available, or practical at 400Mhz due to crystal properties. Often at VHF and above 'overtone' (harmonic generating) crystals were used, or multiplier circuits using lower frequency crystals.

    Much more than swapping one or two components is probably required. Many designs are available in QST and 73 Magazine archives from the 1960's onward for basic V/U Rx/Txcver's.
    Last edited: Apr 14, 2017
  4. KN4BSH

    KN4BSH Ham Member QRZ Page

    Hi KB4QAA good to be discussing another topic with you.
    Much appreciate your input - Thank you for the direction for QST and 73 Magazine. I will look into those magazine, and see if I can find anything. Where I live 2meter is a little problematic; however, I have been having better luck with 70cm. Due to the latter, was brainstorming about the 40m Pixie kit (you already know I am building) and an idea about 70cm project.

    KB4QAA likes this.
  5. VK3YE

    VK3YE Ham Member QRZ Page

    While not 'pure homebrew' another possibility could be just to get a cheap Chinese handheld, mute the microphone, and attach a key to the PTT.
  6. N7EKU

    N7EKU Ham Member QRZ Page

  7. VK3YE

    VK3YE Ham Member QRZ Page

    You're right.

    Tried it on a Baofeng. There was a raspy note for about 1/2 sec after the PTT was released. So it would work at slow speeds (eg 5wpm) but not much more.

    A possibility could be to key the antenna lead.

    However it would be desirable to have some load not too far from 50 ohm (100 ohm resistor across the antenna socket?) to avoid transmitting with no antenna.

    This will be inefficient (heating the resistor) but could work in a pinch. Keying an external RF power amplifier is another possibility.

    While cumbersome all have better prospects than modifying a minimalist rig that as it is only just works on HF.
  8. KN4BSH

    KN4BSH Ham Member QRZ Page

    I like the idea, and I have thought about it myself; however, correct me if I am wrong - wouldn't that still operate in FM and roughly between 10-15kHz of bandwidth? CW only uses 150Hz of bandwidth. Now the reason I bring this up is out of curiosity - if I operate on FM @147.430 but on/off the power/PTT to run CW does that mean I am taking up RF 147.430-147.450, since FM is roughly 10-15kHz of bandwidth?

    Does bandwidth convert to the frequencies I see on my radio's dial?
  9. N7EKU

    N7EKU Ham Member QRZ Page

    Yes unless you were able to modify the rig, it would occupy a wide bandwidth,

    That's why in the linked post they said you need to find a way to disable FM modulation.

    You bring up another problem in that I don't know how you would enable a 700Hz offset between transmit and receive...

    I'm not sure how much active CW there is on 70cm? On 40m you would see a lot more I think!


  10. IZ3NYT

    IZ3NYT Ham Member QRZ Page

    just use a saw resonator
    73 Andrea

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