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Remote Antenna Switch Box

Discussion in 'Home Brew' started by caspear1978, Mar 12, 2012.

  1. caspear1978

    caspear1978 Member

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    So I was sitting in the radio room today deciding on what my next project will be.

    As I was looking at my previous homebrew switch box i decided since ill be putting up an Astro-Plane for local talking and still running a Pdl-2 for dx.

    Why not make a remote switch box so i don't have to have 3 runs of coax coming out of the house.

    I got to looking around the room at my spare parts and found that i have most of what i need to do it, I can salvage the SO-239s from the previous switch box or just take out the switch I have in there and just install the relays in that box.

    I have 2 relays, 2 switches, 4 SO-239s, and the box i used before. i found a 12 volt wall wart in a box of spare parts so there's the power source. I know I can run the power through the coax, but haven't figured out how to do that and don't understand how it works. So for now Ill just run a cord out the window and to the box.

    I'm already going to be running a Rotor cable out the window this week once I get my rotor setup so ill just run the power cable for both at the same time and then ill be done with any antenna work for the summer.



    I'll post pictures during the build and after the build.
     
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  2. pro151

    pro151 KB4RMA

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    Someone please tell me how to run a 12VDC power source through the same coax feeding an antenna without wreaking havoc with the radio.

    This is a concept that I have obviously missed over the years.
     
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  3. wavrider

    wavrider W9WDX Amateur Radio Club Member

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    http://www.ameritron.com/pdffiles/RCS-4X.pdf

    Been around for years.
     
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  4. wavrider

    wavrider W9WDX Amateur Radio Club Member

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    I use 30amp SP DT relays 12vdc automotive type.

    I also do not like the idea of voltage on the coax from an external source so I use wire to the switch. 24g is not expensive and works well.

    I use a five position band switch to select the antenna I want to use.

    I have swept this with the antenna analyzer and have no issues.

    One run to the tower of coax, then up to five antennas can be connected to the home brew switch, works great.

    Source for 30 amp relays are automotive salvage yards. Hard to beat a 30 amp relay for $1.00
     
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  5. pro151

    pro151 KB4RMA

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    Well how about that! Out of all of the crap I have seen, built and done over the years, this is the first time I have heard of or seen this mentioned.

    Thanks for the lesson! (y)
     
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  6. caspear1978

    caspear1978 Member

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    this is one of them things I'm shocked that more people haven't built. or they have and just never talked about it.

    Wavrider, you are correct its hard to beat useful relays at a junkyard. I actually have 2 relays out of an old amp some one dropped off with me for parts, the pills were bad and i never had any plans on getting it back up and running, so there's the relays i needed. i just hope the hold up. if not then ill switch them out to the ones you've used and be done. i do have a question for you,, do you run any kind of power and if show how much do you believe the relays will hold up to?
     
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  7. caspear1978

    caspear1978 Member

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    Relays are wired in. now power hooked up yet that will be done tomorrow.

    First test tonight was to see how the swr looked. so far so good. no change in swr.

    I'll post pictures tomorrow of how it looks tonight. and after I hook up power to the relays. It doesn't look pretty but it works and thats what matters most.
     
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  8. wavrider

    wavrider W9WDX Amateur Radio Club Member

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    I have used full legal limit 1500 Watts during testing of the switch box. No issues.

    The reason I use automotive relays, they are sealed, I.E. weather proof (y)
     
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  9. wavrider

    wavrider W9WDX Amateur Radio Club Member

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    You are welcome but I never would put any voltage on my coax as it is just another problem that may happen.
     
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  10. Captain Kilowatt

    Captain Kilowatt Professional Amateur Staff Member

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    I have no problem with injecting a DC control voltage on my coax cable if it is done proberly with the right blocking capacitor on each end and the series coil for the DC to flow thru while preventing RF from getting back into the power source. The only issue is that you are very limited in the number of relays you can switch this way. Typically you are limited to three antennas with one being on when the power is off, one operates from a pos. voltage and the other from a neg. voltage.
     
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  11. wavrider

    wavrider W9WDX Amateur Radio Club Member

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    If the blocking cap fails what would the result be to the transceiver?

    I just prefer not to take the risk of adding a potential problem that would result in catastrophic damage to a transceiver or associated equipment. One less thing to worry about.

    Other ops do run the control voltage on the coax.
     
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  12. Captain Kilowatt

    Captain Kilowatt Professional Amateur Staff Member

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    Most radios already have series blocking caps in the output filter sections already and they already have shunt coils to ground so any failure of multiple caps would result in the DC voltage flowing thru one of those coils to ground possibly burning out the coil and causing it to open up. This of course assumes that the operator was irresponsible enough to power the relays from an unfused high current power source. Normally one would use fuses and/or a low current power source like a wall wart cube to power the relays.
     
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  13. wavrider

    wavrider W9WDX Amateur Radio Club Member

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    Fair enough and all that was said is true, most radios have the safety components.

    The discussion about using control voltage on the coax or separate is moot.
    Either way works, one just has more risk than the other.
     
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  14. Captain Kilowatt

    Captain Kilowatt Professional Amateur Staff Member

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    True, I will grant you that one in a million is a much greater chance than zero. (y) :laugh:
     
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  15. caspear1978

    caspear1978 Member

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    Ok got a quick question. Trying to figure out what wire to use to run up to the switch box to power the relays. Im thinking about running one wire for ground and then 2 for the power. the relays say 2 amps on them and i will be running 12 volts to them. Would rotor wire handle 12 volts passing through it to power the relays and have them stay on or would i need something thicker? What would you all recommend for this project?

    Thanks in advanced. Mark
     
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