Selecting and buying cables and test leads

Discussion in 'General Electronics Chat' started by ozmo, Dec 15, 2009.

  1. ozmo

    Thread Starter New Member

    Dec 15, 2009
    10
    0
    hey all, this is my first post here, hope you're all doing fine.

    I need to buy cables and test leads for my novice lab setup, but I'm not sure about what to get (ie, what quality i need)

    I need some combination of banana-to-banana patch cables, alligator clips, BNC-to-BNC and BNC-to-testleads to hook up the breadboard, powersupply, oscilloscope, DMM, and so on.

    My interest is in projects that'll be in the 144-440MHz range, but I'm not which cables would be appropriate for this range. Do I even need to consider frequency effects? I checked out Allied Electronics, and the datasheets for their patch cables don't make any reference to frequency usage (http://www.alliedelec.com/test-equipment/test-leads/).

    I did some searching in this topic and didn't find anything recent that matched my question. Thanks.
     
    Last edited: Dec 15, 2009
  2. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    Hi,
    for working with any signals at that range of frequencies, you need RF grade coaxial cable for anything other than extremely short lengths.

    Breadboards will not work well (if at all) due to the connecting lead lengths and stray capacitance etc.

    The best practical methods are either ground-plane matrix board or plain copper clad board and build in 'dead bug' style.

    Scope leads must be used in 'x10' mode, as the high value probe resistor then isolates the circuit you are working on from the lead capacitance.

    You can use any normal wire for general power connections, but any grounds between sections of circuit mut be short and heavy (hence ground plane whenever possible).

    Be aware that audio screened cable is very lossy at VHF and should be avoided. RF coax is rated for a specific impedance and generally uses different insulation.

    440MHz is not easy to work with for prototyping, a piece of plain wire about six inches long, without any capacitive loading, is a resonator (1/4 wavelength).
    With the added capacitance of circuit connections etc., a connecting wire an inch or less could be self resonant - you MUST keep all connections incredibly short and everything very well decoupled.

    Have a look at some ham radio sites for examples of building gear for those frequencies, it could save you a lot of hassle.
     
  3. ozmo

    Thread Starter New Member

    Dec 15, 2009
    10
    0
    thanks for the info, ill do some reading into the items youve mentioned and try to get a better handle on what i need.

    i edited the topic and original post a bit to make the topic of the thread a bit more focused, hopefully some others will find it helpful
     
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