Callsign
Page 1 of 2 1 2 LastLast
Results 1 to 10 of 19

Thread: MFJ 931 "artificial earth." Does it work worth a darn?

ad: L-HROutlet
ad: l-assoc
ad: l-innov
ad: l-tentec
ad: l-gcopper
ad: l-rl
ad: l-WarrenG
ad: l-Waters
ad: l-Heil

Contribute
to QRZ

  1. #1
    Join Date
    Sep 2008
    Location
    DM13
    Posts
    19

    Default MFJ 931 "artificial earth." Does it work worth a darn?

    Does that device really work in place of ground radials?

    TNX.
    "Happy hour is the hour after everyone leaves happy hour."

  2. #2
    Join Date
    Feb 2002
    Location
    Right here
    Posts
    13,007

    Default

    Yeah, it works but you still need a wire. All it does is tune the wire to resonate on whatever band you're working. But yes, it really does work and no, it doesn't work as well as a number of resonant ground radials.
    I'm sorry you don't have the experience or understanding to realize that others possess a skill set that you seem to dismiss as fantastical.

  3. #3

    Default Wire lengths and numbers

    The MFJ-931 certainly works. Try putting many wires onto artificial ground output terminal, all the same length and all at the same time, and spread them out. Voila! Plural radials.

    Another trick is to connect wires of different lengths, all at the same time on the output terminal. That way you get multi-band tuning. I use approximate quarter waves for all of the bands I use. Exact fine tuning of the ground wire can be achieved using the MFJ-931.

    Not just for Verticals. A tuned ground is a must for long wires and particularly random wires. The MFJ-931 can resonate the "other half" of the antenna. Use an ATU for the antenna and the MFJ-931 for the counterpoise, and watch the signal strength soar!

    Finally, a ground tuner such as the MFJ-931 is really a cut down ATU. Make, beg or borrow and RF ammeter, put an ATU where you would put the MFJ-931, adjust it the same way for maximum current reading in the ground wire, and see if it works OK for you. Please note that the SWR reading of the ATU is to be totally disregarded for this exercise. Only the RF ammeter reading counts. Watch you do not overload any meters.

    Enjoy. 73

    John

    G4ALA

  4. #4
    Join Date
    Mar 2003
    Location
    3763 Lyle Avenue, North Pole, AK 99705
    Posts
    23,050

    Default

    Quote Originally Posted by AI6DX View Post
    Does that device really work in place of ground radials?

    TNX.
    It does scoot the current distribution around, and can solve certain "R.F. in the shack" problems when you have no other options. But it is NOT a replacement for a ground radial system. Is it worth having? Certainly.

    eric
    "The more you know, the less you don't know."

  5. #5
    Join Date
    May 2007
    Location
    Etna PA
    Posts
    2,883

    Default

    It's a band-aid.

    Spend the $$ instead to erect a antenna that does not require the artificial "Ground".

    Rege
    Now my mistakes travel at the speed of light!:cool:

  6. #6
    Join Date
    Sep 2008
    Location
    DM13
    Posts
    19

    Default

    Quote Originally Posted by ai3v View Post
    It's a band-aid.

    Spend the $$ instead to erect a antenna that does not require the artificial "Ground".

    Rege
    Rege, I do agree with you 100% about the good antenna. BUT, when one doesn't have the ability to erect a proper antenna, the artificial ground may be the only viable (and last resort) option.

    Tim
    "Happy hour is the hour after everyone leaves happy hour."

  7. #7
    Join Date
    Feb 2002
    Location
    Right here
    Posts
    13,007

    Default

    Quote Originally Posted by AI6DX View Post
    Rege, I do agree with you 100% about the good antenna. BUT, when one doesn't have the ability to erect a proper antenna, the artificial ground may be the only viable (and last resort) option.

    Tim
    They can also be put to good use for portable operating setups where running a large ground system is not possible.
    I'm sorry you don't have the experience or understanding to realize that others possess a skill set that you seem to dismiss as fantastical.

  8. #8
    Join Date
    Oct 2003
    Location
    Middle Georgia USA
    Posts
    7,722

    Default

    Quote Originally Posted by AI6DX View Post
    Does that device really work in place of ground radials?

    TNX.
    1.) It cannot move current around in the ground. That is electrically impossible.

    2.) It cannot transform or decrease ground resistance.

    The only thing it can do is cancel reactance in the ground lead. If you have a ground lead that has 629 -j1100 ohms impedance with a current maxima 10 feet from the radio and you tune for maximum ground current, the very best result will be some resistance over 629 ohms j0 with maximum current 10 feet from the radio.

    It is electrically impossible for it to do anything other than this, because the only thing it can do is add a series reactance (along with some loss resistance) to the connection point.

    73 Tom

  9. #9

    Default Too High

    629 Ohms? Sounds way too high to me. Any measurements I have made indicate more like 40 or 50 ohms, the radiation resistance of the counterpoise wire. Do not be put off!

    73

    John
    G4ALA

  10. #10
    Join Date
    Apr 2004
    Location
    Grid Sq EN90pv
    Posts
    580

    Default

    What no one has said is that the MFJ unit is a solution for people in apartments who are too high above actual ground. It that situation, a piece of wire to the real earth may be a DC gound but is no RF ground. If you are at or near 'real' earth, use it.
    "Our Country! In her intercourse with foreign nations may she always be in the right; but our country, right or wrong." Stephen Decatur

    ex WN8MFO,DL4MO, DA2MP, AJ3YJ (AF MARS)

Page 1 of 2 1 2 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •