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   Home   Help Search  
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Author Topic: Help please.....How to setup and use an MFJ-934  (Read 1072 times)

Posts: 6

« on: April 22, 2017, 08:10:07 AM »

Can anyone please help me with how to setup and use the artificial ground side of my MFJ-934. Current setup:

Yaesu FTDX 3000
50' RG8X
Super Antenna MP1 with SW1 vertical on my 3rd floor balcony
Counterpoise at 33' connected to the Super Antenna UM2 Mount
Mounted to my Wodden Banister

Currently only using the Antenna Tuner side of the MFJ 934 and bought it for the artificial ground.

I've check online for video on how to set it up and can't find anything. I'm usually a pretty smart guy but in this instance I'm lost. I don't seem to understand the instructions. When I connect a wire to the artificial ground nothing happens. Should my counterpoise be connected to the 934?  Should my chassis be connected to it?  I don't know what I'm doing.

Help please


Posts: 284

« Reply #1 on: April 22, 2017, 05:54:00 PM »

Go here.....

All you seek, and much, much more.


Posts: 7285

« Reply #2 on: April 23, 2017, 04:22:39 PM »

With the MP1 the MFJ-934 artificial ground feature is not used. If used it will tend to steal current from the 33' counterpoise wire by causing RF current along the coax shield and the building AC power system, and/or along the "GND" wire attached to the MFJ-934.

An exception is if the MFJ-934 is placed right at the MP1 antenna with a very short coaxial cable (1' for example). Then the counterpoise wire is connected to the MFJ-934 artificial GND section and is tuned for maximum current. Trying to tune the MP1 and the artificial GND (they will interact) would be a challenge.

The MP1 uses a counterpoise wire and the antenna system should be setup to cause most of the antenna return current to take the path of the counterpoise wire or wires. To that end, the counterpoise wire(s) should be 1/4 wavelength long for each band. If that is not possible - and only one wire is used - a ferrite choke should be placed at the coax-to-antenna point to reduce coaxial cable shield current and force the current to take the path of the counterpoise wire. The bands where a 33' wire will be quite ineffective are 14 MHz and 28 MHz. On these bands the 33' wire presents an impedance of thousands of ohms the antenna return current will take some other path.  

The chart by G3TXQ shows several feedline chokes that can be used.

Note that the MP1 with a 33' counterpoise forms an asymmetrical dipole with the counterpoise doing most of the radiating. At 7 MHz the counterpoise wire "current-area" is about 23 amp-ft while the MP1 is about 4 amp-ft. On this band the counterpoise will do 85% of the radiating and should be placed as one would place a radiating antenna wire.

  KH6AQ, formerly WX7G
« Last Edit: April 23, 2017, 04:38:06 PM by WX7G » Logged

Posts: 62

« Reply #3 on: April 24, 2017, 06:17:17 AM »

What is an artificial ground?

I use real grounds, copper water pipes, radials, 8-foot long copper rod driven into the ground, even bonded to the electrical provider's ground.

« Last Edit: April 24, 2017, 06:20:48 AM by KC4ZGP » Logged

Posts: 7285

« Reply #4 on: April 24, 2017, 09:34:08 AM »

The MJF "artificial ground" refers to a device that will resonate the GND path with the aim being to provide a low ground impedance at the MFJ artificial ground. doing this can reduce the common-mode RF potential on the equipment (think getting bit by the mic) and reduce RF ground current taking other paths. It maximizes the current on the ground connection (wire).

In the case of the MP,1 maximizing current on the MFJ-934 ground connection is exactly what one does not want to do. The current should be maximized on the MP1 "counterpoise."
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