Grounding for my temporary setup / low power transmit

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KD2RWV, Apr 19, 2020.

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  1. KD2RWV

    KD2RWV Ham Member QRZ Page

    I'm a newbie, and don't have a dedicated spot for my radio yet. I have been setting up my end fed 10/20/40m dipole, putting the radio on the living room desk, and running 25' coax through the window to the antenna when I want to listen. I tear it all down when I'm done. I know the radio chassis should be grounded (in addition to the 3rd prong on the power cord) and there's a lug on the back for it, but I'm not sure how / where to ground it since my living room desk is all the way around the house from the electrical service ground point. I am not at risk of lightning because I would tear it all down if a storm came through, but I am getting ready to try transmitting for the first time and I thought maybe I should get it grounded for that? I'm limited to transmitting 25W by the antenna, but I don't think the transmit power matters, it should still be grounded, right? I am concerned that pounding a ground rod in near the transceiver is a bad idea, as I should probably tie to the common house ground point if I'm going to ground it at all?

    Any thoughts are welcome.

    On a side note, do you think it'd be smart to use a choke at the end of the feed line to avoid the coax ending up radiating? If I did that, would I still need to ground the chassis of the transceiver?
     
  2. WA9UAA

    WA9UAA Ham Member QRZ Page

    Hi OM,
    We probably need to know more about the antenna and it's matching network. There is a chance it needs a counterpoise wire attached to the box as well as the radiator. An end-fed wire will need a return path for the radiator or it will use the coax as you suggested above. Wait on the choke, you may not need it.
    73,
    Rob
     
  3. K7TRF

    K7TRF Premium Subscriber QRZ Page

    If your radio is grounded with a three wire electrical cord you do not need to ground it with the ground stud on the chassis.

    To be compliant with the NEC you should ground your coax shield where it enters the building and any extra ground rods you drive should be bonded back to the main AC service ground. The best way to satisfy that condition is to route your coax outside the building to where your AC service enters your home and bond the coax shield to the main ground right there, enter the building and then do any routing to your shack indoors (e.g through a crawl space or attic).

    Assuming you deploy a complete antenna system that includes its own RF return which includes dipoles, yagi's, verticals or inverted-Ls with radials/counterpoise or even an end fed half wave with either a short counterpoise or some coax feed line to serve that role you don't need any other in the shack grounding. But you do need that coax shield ground outside your home to be compliant with electrical codes.
     
    W6KCS and WB5YUZ like this.
  4. KD2RWV

    KD2RWV Ham Member QRZ Page

    It's a PAR EndFedEZ. It'll be trimmed for minimum SWR at the desired operating points in each band, and per the documentation "Maximum efficiency and absolute minimum feedline radiation will occur when the antenna is tuned." That doesn't say no feedline radiation ...

    The matching is described as "a wideband 9:1 transformer wound on a binocular core," there's a schematic attached here. Also per the docs: "No ground plane or counterpoise is needed," this is a link to an article on the subject: https://www.hamradio.me/antennas/of-fields-and-feedpoints.html

    Believe it?
     

    Attached Files:

  5. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Nope

    There are two basic forms of End Fed antennas, the half wave resonant form and the non-resonant form. The former uses a wire cut to approximately half wavelength on the lowest supported band and uses a 49:1 or 64:1 matching transformer. Those can be run with either a very short piece of counterpoise wire or even intentionally use some of the coax shield as the small counterpoise it needs.

    The latter are similar to the popular 43 or 33 foot verticals. They're cut to be non-resonant on any of the HF ham bands and typically use a 9:1 matching transformer. The transformer (UNUN) doesn't really assure a perfect 50 ohm match on any band but it tends to lower the SWR50 sufficiently that the coax sees a pretty low SWR which minimizes coax losses. The final SWR for these is cleaned up with a tuner in the shack or even a good wide range tuner in the rig. These definitely need some form of counterpoise or radials. If you don't include counterpoise then a combination of your coax shield and even your home's internal ground wiring will serve that role which isn't ideal.

    The marketing for non-resonant end feds 'matched' with a 9:1 UNUN may say no counterpoise is needed but physics says otherwise.
     
    WA7ARK and KX4O like this.
  6. AA4PB

    AA4PB Ham Member QRZ Page

    If the antenna is end-fed and has no other type of radials, then the coax shield has to be acting as the radial and will be radiating some RF energy. Since your installation is temporary (i.e. you disconnect the coax from the radio and put it outside the house when you aren't operating) then I wouldn't worry about ground rods and bonding to the electrical system. A ground rod shouldn't make any difference in performance. On a permanent installation it is required by code for lightning protection and if the ground rod is used then it must also be bonded to the home's electrical system ground.
     
  7. KX4O

    KX4O Ham Member QRZ Page

    That's my schematic of the LNR transformer from the 40-20-10 model as reviewed here. It's much higher than 9:1 and is suitable for feeding a half-wave antenna at its high impedance end.

    Par (and LNR) are good products.
     
  8. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    You want to either get it high off the ground, 30 ft or more and the higher the better, or configure it as an inverted "L" fed at the high end with the far end dropped. 25W and a low horizontal antenna is going to be a tough row to hoe, at least on sideband.

    On the other hand, if you're going to work only FT 8, throw it up however and have at it.
     
  9. KD2RWV

    KD2RWV Ham Member QRZ Page

    That's a nice writeup, thanks. Reading this it's clear the design is intended to use the coax as the counterpoise, which also may explain a bit about why the antenna is recommended to be tuned not at the antenna, but at the other end of the coax you plan to use to feed it.

    So it sounds like a choke to prevent coax shield currents will probably render the antenna useless. I'm curious now whether my coax feed cable is long enough? I'm also curious as to whether I can choke the coax to keep the currents away from the radio, while employing a traditional counterpoise wire on the ground. The antenna "matchbox" doesn't provide a lug to attach an external counterpoise...
     

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