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Duplexer or Antenna Switch?

Discussion in 'General Technical Questions and Answers' started by 2E0RPS, Sep 11, 2008.

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  1. 2E0RPS

    2E0RPS Ham Member

    I'm using two Transceivers.

    One for HF and the second for VHF/UHF. My multiband aerial will cover all these bands.

    If i connect the aerial to the two transceivers (one antenna to two transceivers) should i use a Duplexer or a 2 way antenna coax switch?

    Many thanks in advance

    73 de Rod /2E0RPS
     
  2. G3TXQ

    G3TXQ Ham Member

    Rod,

    You need the 2-way coax switch.

    By the way, I'm intrigued to know what antenna you have that's giving you HF, VHF and UHF coverage?

    73,
    Steve
     
  3. 2E0RPS

    2E0RPS Ham Member

    Thanks Steve,

    I've got a 2way coax switch but it think it was designed for CB only not sure if i can use it on HF/VHF/UHF bands.

    In regard to the antenna I'm using a Sandpiper MV6+3 multiband vertical made in Britain.

    in reality the antenna is designed to cover 80 to 6m. However with the addition of counterpoise wire it works well on all HF bands including 2m and 70cm in the sense that i can engage all city repetaers with an overall VHF/UHF SWR below 1.7.

    73 de Rod / 2E0RPS
     
  4. WB2WIK

    WB2WIK Premium Subscriber

    I disagree. You can use a 2-way switch, sure, but then you'd be on "either" HF or VHF/UHF and you couldn't use them both at the same time.

    With a duplexer, you can use both rigs simultaneously, up to the power limitation and isolation rating of the duplexer.

    I have some from Comet rated 600W PEP on HF and 200W PEP on VHF-UHF and they are essentially lossless and have >60 dB isolation HF:VHF. As such, just as efficient as a "switch," but allows operation with both rigs and a common antenna at the same time.

    The duplexer is likely to cost more, but not that much more. A very good coax switch that's low loss and high isolation at UHF is in the $80 range ($USD). A duplexer to do this job is in the $100 range ($USD), so the premium is not large for the added versatility.

    WB2WIK/6
     
  5. WB2WIK

    WB2WIK Premium Subscriber

    ::Thought I'd give you a reference. I see Comet now has a "600W" model that does exactly what you're looking for, and it's cheap:

    Model CF-360A:

    HF/6M-440MHz Duplexer
    Band Pass
    1.3-30MHz
    49-470MHz
    Ins. Loss
    0.2dB
    0.2dB
    Max Power
    600w PEP
    600w PEP
    Isolation:
    More than 45dB
    CONNECTORS:
    Output:
    PL-259
    Low In:
    SO-239
    High In:
    SO-239

    73

    Steve WB2WIK/6
     
  6. K3ACE

    K3ACE Ham Member

    Isn't the correct term a "diplexer"? I thought a duplexer was used when simultaneously transmitting and receiveing on the same antenna...ie a repeater.
     
    Last edited: Sep 11, 2008
  7. 2E0RPS

    2E0RPS Ham Member

    Thanks for your input WB2WIK

    I see your point. Obviously the possibility to use the rigs simultaneously without switching is a better option.

    73 de Rod /2E0RPS
     
  8. WB2WIK

    WB2WIK Premium Subscriber

    ::In this case, the term "duplexer" is appropriate, as you can indeed transmit and receive simultaneously using one: You can transmit on HF and receive on VHF (duplex); or the other way around (duplex); or you can receive on both bands (diplex); or you can transmit on both bands (diplex).

    I think "duplexer" is a perfect description of what these little units truly are.

    WB2WIK/6
     
  9. K3ACE

    K3ACE Ham Member


    Didn't think of it that way. Of course you can listen to a subband while txing on the primary. I am that much smarter now.
     
  10. 2E0RPS

    2E0RPS Ham Member

    Thanks again.

    The antenna will be connected to a Yaesu FT920 (HF to 6m) and an IC 706MKIIG (2 to 70cm) in few words the duplexer has to cover 1.3 to 50mhz / 144-440mhz. Will have to be a different model than the one you mentioned. in anycase i understood what i need now..many thanks 73 de Rod /2E0RPS


     
  11. AC0FP

    AC0FP Ham Member

    diplexer

    You are correct the duplexer term is sometime misused, splitting HF and VHF/UHF requires a diplexer. The CF-360A specification indicates it is a diplexer.

    73,

    Frank:)
     
  12. G3TXQ

    G3TXQ Ham Member

    The terminology confused me, too! Wikipedia has quite a good explanation of the terms:
    http://en.wikipedia.org/wiki/Diplexer

    Steve
     
  13. G3TXQ

    G3TXQ Ham Member

    Just for my education, is it really possible to transmit at 600 Watts on HF and simultaneously receive on VHF through a duplexer with 45dB isolation?

    I guess I'm unfamiliar with how a VHF receiver responds to a +13dBm HF signal across its input?

    Steve
     
  14. WB2WIK

    WB2WIK Premium Subscriber

    +13dBm = 1.0Vrms. This is not a very strong signal at all. My most sensitive GaAsFET and MESFET preamplifiers can handle at least 2V without degradation or damage (+19 dBm), most stuff can handle more.

    In fact, when doing intercept point and IMD testing on receivers, one of the applied signals is almost always > +13 dBm.

    WB2WIK/6
     
  15. WB2WIK

    WB2WIK Premium Subscriber

    ::Also, I should mention: My Comet stuff are "rated" 45 dB, but actually measure >60 dB -- always. The 45 dB seems to be an extremely conservative and pessimistic rating, must be allowing for some wild deviations that don't seem to really occur.

    WB2WIK/6
     
  16. G3TXQ

    G3TXQ Ham Member

    Thanks for the info - duplexers are not something I've ever played with.

    By the way, I think the Comet model Rod needs might be the CF-706A/B.

    73,
    Steve
     
  17. WB2WIK

    WB2WIK Premium Subscriber

    ::I disagree with Wikipedia. As you probably know, you or I or anyone can create a Wikipedia definition: It's open source and unverified, uncorroborated information that becomes more and more accurate as more contributors refine it. I have contributed many Wiki definitions over the years, and most are still there, uncontested, although a few have been altered.

    In this case, I think the definition given is taken from a commercial diplexer manufacturer and it's just their definition. In reality, the term depends on the application. If you use a diplexer to operate full duplex in split bands, isn't this then a duplexer? Diplexing usually refers to only transmitting and not receiving, as is the case with broadcast stations.

    Anyway, here is exactly the right product for the application described, and it's from Diamond Antennas and not Comet:

    http://www.rfparts.com/diamond/mx62m.html

    You might note Diamond calls it a "DUPLEXER.":)

    WB2WIK/6
     
  18. 2E0RPS

    2E0RPS Ham Member

    Thanks Steve,

    this unit will be perfect for my needs. Initially i was considering in purchasing the following: MX-62M Diamond HF & 6m/2m/70cm Duplexer but in term of Frequency coverage the one you mentioned is better tailored for my IC706 and FT920.

    73 de Rod / 2E0RPS

     
  19. AI3V

    AI3V Ham Member

    Not even close Steve,

    The very best receivers will use a -23dbm as one signal.......

    http://www.arrl.org/tis/info/pdf/020708qex046.pdf

    Maybe a MIXER would be tested at +13dbm.....

    To the OP:Rod, a +13 dbm signal is probably not going to damage the rig, but you can count on more or less complete desense, I would be surprised if you would be able to hear anything on vhf/uhf while you are transmitting hf.

    There may be band combos that will work, but there will be some that don't.

    Rege
     
  20. K3ACE

    K3ACE Ham Member

    If I could ask a quick question. What device would you recommend for using a single antenna on a uhf/vhf rig with individual outputs. I would like to be able to monitor uhf and vhf repeaters via a single discone with my TS-790A
     
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