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multiple antennas, one feedline?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by WA7ZAF, Jan 4, 2019.

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  1. WA7ZAF

    WA7ZAF Ham Member QRZ Page

    I'm considering making some changes to my antenna system, so I've been doing a lot of thinking. I know, that was my first mistake. Anyway, I typically work three bands in my local area, and I have never had any trouble getting into any station that I want to talk to, either via repeater, or simplex. I currently have only one antenna, a homebrew tribander for 2m/220/440.

    The problem that I am facing right now is that I am starting to get into DSTAR, and the only DSTAR repeater near enough to me is not quite in range. Sometimes I get in ok, but other times during the same qso, I get reports that I have "fallen off the cliff," and my signal has dropped off (R2D2). I believe that I could easily fix this with a dedicated 70cm yagi pointed at the repeater.

    The design of my house does not allow for me to easily bring another feedline in. I would have to either make the current hole in the wall bigger, or drill another hole in the wall. I don't like either of those options so I was wondering if it would be possible to connect the tribander and the yagi to one feedline using a tee. How would this affect my signal on all three bands? I am guessing that the 2m signal would find the 2m radiator and the 220 signal would find the 220 radiator. What would the 70cm signal do? Would it split and radiate with lower power to both antennas? Could the tribander and the yagi somehow possibly be phased for increased gain?
     
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    A "T" adapter won't work well.

    I'd use a remote relay which won't necessarily require any new wiring, as the power to activate the relay can go through the coax; then you'd just need a "switch" in the shack (along with a bias-T) to switch from the triband omni to the 70cm beam.

    That would require both a good relay that works well at UHF and a good bias-T system that also works well at UHF.

    Some stuff about homebrewing this and some commercial products: http://www.karinya.net/g3txq/temp/020506qex052.pdf
    http://huprf.com/huprf/bias-tee-dc-injector-for-vhf/

    Lots more stuff on line about this concept, which I use, myself, quite a bit.

    A good coaxial relay would be required. The Tohtsu stuff works fine; this one's good to 500 MHz with just about zero loss and excellent SWR: https://www.rfparts.com/cx520d.html

    Cheaper to drill another hole and use a second coax line, with a simple 2-position UHF-rated coaxial switch in the shack, but using a remote relay and a bias-T injector saves the hole and the second run of coax.
     
  3. AK5B

    AK5B Ham Member QRZ Page

    All you need is a diplexer; about $45 or so online. Comet and Diamond are two manufacturers that make different models for diffrent bands and coax connectors.
     
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    That won't work because he's using two antennas that both work on the same band (70cm).

    The only way to use a diplexer would be to use the 3-band omni only on 144/222 and then use only the beam on 70cm, rendering the omni inoperable on 70cm.
     
    AK5B likes this.
  5. AK5B

    AK5B Ham Member QRZ Page

    Right; I didn't think of that when I posted my recommendation. I started to advise a remote switch at first but when I saw it was for VHF/UHF I figured a simple diplexer would suffice---thanks for correcting me. If it was me I'd just drill another hole and run separate coaxes, but...

    73,

    Jeff
     
    W4IOA likes this.
  6. W4IOA

    W4IOA Ham Member QRZ Page

    Holes are easy to fix. There are lots of things I hesitate to do but drilling a hole for coax isn't one of them.
     
    N1VAU and AK5B like this.
  7. WA7ZAF

    WA7ZAF Ham Member QRZ Page

    This might actually be a good option, because there are only 2 440 repeaters that are local to me, and I can hit both of them with 50mw on an ht from inside my house. I'm pretty sure that I'll be able to get into them, even off the back of the beam if I'm running the 5 watts of low power on my base radio. There are about 30 440 repeaters in the direction of the DSTAR repeater that I will be using, so I'll probably be able to add many of those to my scan list when I get the yagi.
     
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Then, just do that.

    It's easy and cheap, and just use the 440 beam for everything and forget about the omni on 440.
     

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