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Re. 2 VHF units with Dummy load

Discussion in 'General Electronics Discussion' started by Puno, Mar 21, 2011.

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  1. Puno

    Puno

    29
    0
    Feb 25, 2011
    After the last chat on here, I set out to test them with the dummy load sit next to each other and didn't pick up at all. I would say they are very good dummy load. Now I am thinking of trying my other idea to build dummy load (2 25 watts resistor in parallel for each unit inside a die cast aluminium case with input BNC panel socket and see what happens.

    Any suggestions are welcome...
     
  2. davenn

    davenn Moderator

    13,833
    1,950
    Sep 5, 2009
    ok you have to consider 2 things.

    1) max freq of use

    2) type of resistor

    #2 will have a significant effect on #1.

    Altho lower wattage rating, carbon resistors are normally used so that you dont have a hi inductive reactance problem that would occur if you were using hi wattage wire wound resistors. This inductive reactance problem increases with frequency

    You will need multiple resistors to produce a) the wattage capability you need and b) to still end up with a 50 Ohm load.
    Have "been there done that" in years gone by as many of my fellow amateurs have.

    There are much easier ways these days that werent available a way back then....
    there are now 50 Ohm terminating resistors available capable of at least 100W when correctly heatsunk.

    here's an example www site showing what they look like

    http://www.innovativepp.com/resistors.html?gclid=CKiRoZDv4KcCFQXybwodYQ599A

    cheers
    Dave
     
  3. Puno

    Puno

    29
    0
    Feb 25, 2011
    re. VHF dummy loads

    just check out these resistors I am going to use as dummy loads for each unit. They are the RCH25 100R, non inductive or very little inductance and good in high frequencies application, so if you have a moment check them out and see what you think. These are more readily available locally. Each VHF unit max tx power is 25W.
    appreciate your input in this matter.
     
  4. davenn

    davenn Moderator

    13,833
    1,950
    Sep 5, 2009
    ok..
    just keep in mind you will need 2 in parallel to get 50 Ohm.
    I wouldnt go much above 150 - 200 MHz with them because of their wire connection style
    High Frequency = HF not Very High Frequency = VHF ;)

    The type I showed you in that link are specifically designed for RF use and for terminal connection direct
    to RF connector or short length of PCB track between them and the connector
    They are not the only manufacturer there are a variety available :)

    cheers
    Dave
     
    Last edited: Mar 22, 2011
  5. Puno

    Puno

    29
    0
    Feb 25, 2011
    cool Dave will let you know the outcome of this. appreciate all comments and advise.

    cheers
    puno
     
  6. Puno

    Puno

    29
    0
    Feb 25, 2011
    re. VHF dummy load tested

    4 dummy loads were mounted inside a 150x200mm diecast case with each load of 50ohms(2 100 ohms 25w in parallel) compactly packed with polystyrene foam to prevent interefering with each other and with BNC panel sockets connectors. The result is perfect on pwr tx on 1W and 25w but units normally set on low pwr.

    So appreciate all the help from you guys for making this project a success.

    cheers
     
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