One radio, 2 antennas, duplexer question

Discussion in 'Mobile Radio Systems' started by KI6GEA, Oct 14, 2021.

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  1. KI6GEA

    KI6GEA Platinum Subscriber Platinum Subscriber QRZ Page

    Hey guys, I'm pretty new at this stuff so please bear with me... I'm currently active on 2M as a technician, but am studying for my general to get into HF.

    I'm setting up my mobile rig, which currently consists of an IC-705 which just has the single antenna port. I have a mag mount on the roof with a Diamond dual band for VHF/UHF.. I also just ran a Diamond K400 mount to the hood, because of the grounding capability and lower mounting point for my HF antenna. I tried the Diamond HV7A in that spot, which would have been ideal as it hits 20m (my target HF band) as well as 2m/70cm... However this antenna is too large/unstable on this mount for the type of driving I do. So I'm back to seeking a dedicated 20m antenna for the hood and keeping my VHF/UHF on the roof. FYI I also have the ICOM AT-705 antenna tuner in the mix on the HF antenna.

    I'm looking at the Diamond duplexers, as it seems the logical and most convenient solution to my dual antenna issue... However all of the documentation I can find on these duplexers implies they are for 2 radios to one antenna, not vice versa... I'm not opposed to a manual antenna switch either, but I love the idea of being able to switch or scan multiple bands on the fly without having to operate a switch. Will the Diamond or any other duplexer work in this way? What would you recommend as a solution?

    TIA and 73,

  2. W4EAE

    W4EAE XML Subscriber QRZ Page

    Those diplexers work in either direction. You can use one antenna and two radios (provided isolation is good enough), or two antennas with one radio.
  3. KI6GEA

    KI6GEA Platinum Subscriber Platinum Subscriber QRZ Page

    Thanks. I called HRO to order one, and they told me that they don't work that way... So I didn't order it. And I can't find any reference anywhere on a setup like this. Not sure what to do...

  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    HRO's advice is nuts.

    These duplexers (or diplexers) are nothing more than passive filters. The VHF side is a high-pass, the HF side is a low-pass. Commonly used for two antennas and one radio, I've done that for 35 years using Diamond or Comet (they are similar) units.
    PU2OZT likes this.
  5. W4EAE

    W4EAE XML Subscriber QRZ Page

    @WB2WIK is correct. I use one of these on my roof to allow a single run of coax for both an HF rx antenna and a VHF tx/rx antenna.

    If there were any 'danger' in using one of these, the greatest risk would be in the two-radios-one-antenna setup as opposed to the other way around.
    WF7A likes this.
  6. WF7A

    WF7A Subscriber QRZ Page

    To do a good deed, e-mail Diamond's Tech Support, ask them about duplexer installation (to back up 'WIK's post), then e-mail the salesperson at HRO (or the manager of the store) to diplomatically say, "I did some research and thought you might be interested in what Diamond had to say about duplexer installation. You almost lost a sale because of incorrect advice on your part." This would be a goodwill gesture on your part to help educate salespeople since who knows who else he told (incorrectly) about duplexer, or even triplexer, installation. After all, we need to do our part to prevent others from dispensing erroneous information--that's my job. : )
    PU2OZT likes this.
  7. KC4YDY

    KC4YDY Ham Member QRZ Page

    I use a VHF/HF diplexer all the time in my truck and in my wife's minivan. In my RAM truck I use a separate radio (FT-2400) and antenna for VHF and an FT-100 and ATAS-120 for HF. I use a diplexer so I can run VHF on the FT-100/ATAS if I want to but usually only use the FT-100 for HF.

    When we travel I'll pull the ATAS and FT-100 out of my truck and install it in pre-installed mounts in her Toyota Sienna. Feed the FT-100's two outputs into the diplexer, output of the diplexer goes to the ATAS mount. VHF and HF in one stick. Have been using this setup for years. I don't remember the part number of the diplexer but know it is a Comet. Not saying HRO is FOS, but their sales tech gave you incorrect info.

    73 de Paul, KC4YDY

  8. N1IPU

    N1IPU Ham Member QRZ Page

    Sounds like you got a fuddy salesman. Your install will be fine.

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