Counterpoise for MFJ-9000 series.

Discussion in 'QRP Corner' started by W4WVW, Jan 5, 2020.

ad: L-HROutlet
ad: l-rl
ad: abrind-2
ad: Left-2
ad: L-MFJ
ad: Left-3
ad: Subscribe
  1. W4WVW

    W4WVW Ham Member QRZ Page

    I have a 9015 with a vertical mobile whip. Your suggestion for a counterpoise and how to attach it.
     
  2. W6KLD

    W6KLD Ham Member QRZ Page

    Attach a lug to a rear panel screw making sure an electrical connection to ground (metal to metal) exists.
     
  3. K7TRF

    K7TRF Premium Subscriber QRZ Page

    If the whip is attached directly to the rig then the advice above is good. Attach one or several pieces of wire, each approximately 11 feet long directly to the rig's chassis. A drilled hole with a machine screw and wing nut would allow an easy connection to ground radials for this installation scenario.

    If the whip is at some distance from the rig and fed with coax then the counterpoise/radials should be out at the whip and at the far end of the coax. In that case attach some kind of wing nuts or other fasteners to the coax shield side of whatever mounting bracket you're using to support the whip and attach one or better yet 3 or 4 radials each 8 to 11 feet long to that bracket. If you can get the feed point up even five or six feet on a tripod or some other kind of raised supports and slope the radials down and outwards it's better than having them actually lie on the ground. The length of the radials isn't critical but should be somewhere around .15 to .25 wavelengths long and should ideally all be the same length. You may have to adjust the length of your whip for best SWR as you change the length of your radials.

    For instance I often use antenna mirror mount brackets to build homebrew vertical antennas. I drill four holes in the corners of the top plate of one of these brackets and use bolts and nuts to connect radials to the top plate of the bracket and the whip to the insulated center post. The bracket can be easily attached to a support mast and elevated for use and a coax jumper just screws into the connector on the underside of the bracket. Here's what the unmodified bracket (no holes drilled for radials or radial connection bolts added) looks like:
    [​IMG]
    The rear clamping plate is square and can be rotated to a vertical which is convenient for clamping to a mast or can be used in the horizontal position to clamp to something like a railing.

    In a minimalist installation you could run roughly 11 feet of coax to the whip and let the shield of the coax serve as counterpoise, it's not ideal in terms of common mode RF back to the rig but with a QRP rig it could work as a quick deployment setup.
     
  4. W4WVW

    W4WVW Ham Member QRZ Page

    Thanks! I have a PL259 to SO239 right angle adapter so the whip is directly mounted to the rig with no coax run. I'll mostly be operating from my patio and I can't have any "permanent" outside transmitting antennas due to deed restrictions. What about a large alligator clip clamped onto the outside of the right angle adapter? I've also heard of guys clamping to a tape measure for a counterpoise.
     
  5. N7EKU

    N7EKU Ham Member QRZ Page

    Hi,

    What is your whip? Is it made for 15M?

    73,


    Mark.
     
  6. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Yup, either of those solutions could work. Basically you just want somewhere around 1/4 wavelength (roughly 11 feet on 15 meters) of conductive material electrically connected to the chassis of your MFJ-9015. A big alligator clip could work and a metal tape measure could work as well as could a piece of wire.
     
  7. W4WVW

    W4WVW Ham Member QRZ Page

  8. N7EKU

    N7EKU Ham Member QRZ Page

    I see,

    With your wanting to mount the antenna on your rig, you will need to have tuned radials. At least one, but three or four would be better. They will need to be somewhere close to 234'/21.1 MHz = 11.1' (maybe start with 11' - 2") each. If you have an SWR meter or antenna analyzer, it would be good so you can check it and tune the radials a bit more.

    73,


    Mark.
     
  9. W4WVW

    W4WVW Ham Member QRZ Page

    I do have an SWR/wattmeter I can use for tuning. I wondered about the tape measure counterpoise as it would be easiest to adjust for proper length.
     
  10. N7EKU

    N7EKU Ham Member QRZ Page

    Sure,

    I think a dedicated tape measure would work. To make a good contact, you would want to bare the metal to make good contact as the normal hook probably doesn't (it sits in a loose rivet so that it can slide in a bit for inside measurements). What would be nice is it would be easy and quick to store when not in use.

    73,


    Mark.
     

Share This Page