Coax entrance with HVAC wires/tubing

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by K5TZA, Jul 4, 2021.

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  1. K5TZA

    K5TZA Premium Subscriber QRZ Page

    Hello everyone. I've not been able to find info from searches so I thought I'd ask the collective wisdom of the ham's here. I'm setting up my ham shack in the garage and trying to figure out how to run my coax through the exterior wall without too much destruction. Fortunately (or unfortunately) for me, the HVAC condensers are immediately outside my desk location and there is already an opening in the brick for the wires and tubing that runs to them. This begs 2 questions in my mind, but maybe more after some feedback:
    1. Is this a good or bad idea? Has anyone tried this? I'm only running 100W max on HF, but I do worry about causing issues with the A/C units. I don't want to fry any sensitive sensors or circuits.
    2. Should I use double-shielded cable to prevent any interference with the A/C electronics? What type is best for this application? RG-214 from DXEngineering looks amazing but very expensive. Would RG-400 be suitable for this application?
    Thanks for any feedback or help you can provide! 73 -- Tom, K5TZA
    K5JAZ likes this.
  2. AK5B

    AK5B Ham Member QRZ Page

    As long as your ac service panel is nearby (and you run ADUs bonded to its ground electrode---and put some coax-wound ferrite chokes on your feedlines close to antenna feedpoints---you should be good to go. RG400 is a very good coax to use (it's double shielded with PTFE dielectric), Mix 31 ferrite toroids and Polyphasers/Alpha Delta/Morgan/etc. are your friends.
    KU3X likes this.
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    What kind of outdoor A/C unit has "active electronics" in it?

    Maybe some do, I really don't know. Mine doesn't, and I've never had any like that. All the "control circuitry" with lots of active electronics is in the indoor part, along with the heating system, blower and all else. My outdoor "Carrier" unit is dumb as rocks and has a big electromagnetic contactor to power it on and off, and a big starting capacitor, and a motor turning a big fan to pull air through the coils and blow the hot air out the top. No actual control circuitry, no ICs, no anything that RF would interfere with. It's not very old.

    As such, unless they're making them more complicated now, I wouldn't worry about anything.
  4. K8JD

    K8JD Ham Member QRZ Page

    Unless your antennas are poorly designed and installed, the SWR should be low and feedline radiation will not be enought to mess with the motor starting/running capacitors or relays in an AC heat exchanger outside unit !
    That's all that is in my Janitrol made, outside unit here.
    Take off the cover and check it out !@! :rolleyes:
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    That's all that's in every A/C unit I've ever seen.

    Unless recently "they" started adding active electronics, which I think would be a crappy idea due to heat and WX concerns, that's probably what they all are.

    All the active stuff is inside the house, which in my case is about 65 feet horizontally away from the outside compressor system.
  6. K5TZA

    K5TZA Premium Subscriber QRZ Page

    Thank you all for the input!! It gives me enough confidence to try it out and see if anything happens.

    As for my antennas, I'm starting out with a hamstick dipole setup, tuned to each band I'll use. I've been testing out the 20 m version and can get down to about 1.2 SWR in the middle of the band. It's enough to make contacts in Europe with FT8, which is as good as I can hope for within the HOA restrictions we have here. Don't expect that setup will generate much interference from the feedline.

    AK5B: thanks for the tech details. I already have several Mix 31 ferrites for my coax, but need to add the lightning arresters now that I'll have a permanent cable running outside.

    Thanks again for all the help!
    AK5B likes this.
  7. WB4MDX

    WB4MDX Ham Member QRZ Page

    I’ve have done this for 15yrs from my third floor shack to my crawl space. Rg213 has no problem from RFI. No issues with HVAC as well.
  8. KI5FJ

    KI5FJ Ham Member QRZ Page

    In addition to Common Mode Currents on the feed-line you must consider the distance from the Antenna to the Temperature Control.
    High RF Field Strength can be troublesome. Be Well & 73, Joe O, K I 5 F J, NNNN
  9. WA4SIX

    WA4SIX Ham Member QRZ Page

    If you have a variable speed compressor & blower, you may get interferance. Most of the higher seer AC systems have them.

  10. K5TZA

    K5TZA Premium Subscriber QRZ Page

    Thanks, Joe. I saw this happen once using an EFHW too close to the house…shut down the A/C unit whenever I transmitted. My “permanent” setup is a hamstick dipole on a telescoping mast about 40 feet from the house. Haven’t seen any issues with it interfering with any electronics in the house yet.

    Thanks again for all the help!

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