MFJ-931 Artificial RF Ground

[K4EET]

Does anyone have experience with the subject MFJ-931 Artificial RF Ground? My shack is on the second floor and about 35 feet from my 10-foot ground rods. I'm wondering if the MFJ-931 would really improve my RF Ground. Comments?

From the MFJ Catalog and:
MFJ Enterprises Inc.

Thanks in advance!

73, Dave K4EET

 

[K4EET]

FYI, I posted this question seeking comments from RadioReference members and also to let others know that such an animal exists. I have reviewed these reviews at eHam.net:
MFJ-931 Artificial RF Ground Product Reviews
but I am still debating on whether to get this or not. I don't really have any RF/RFI problems but if it could improve reception then it would be worth it. Just seeking additional comments...

Thanks in advance. 73, Dave K4EET

 

[K7MEM]

If you don't have any real issues, why do you need it?

Are you using a End-Fed antenna with a random length counterpoise?

My current shack is at ground level. It's in the barn and about 300 feet from the main house. Electrical wiring consists of a single 15 Amp circuit coming from the house electric supply. The only time I ever had issues with RF in the shack was when I was running a End-Fed antenna. I fixed that by switching to a different type of antenna.

But before that I operated for over 20 years from a second story room. I didn't use any extra grounding, other than what the house provided. Never had any issues with RF in the shack or RFI.

There is no guarantee that it will improve reception, so what are you trying to fix?

 

[902]

My impression is that this is a tuner that can reduce or eliminate RF coming back down your transmission line. My current station and my original stations are on the second floor and have a 20 - 25 ft. run to the point where I've bonded everything together outside.

I use a B&W 90 for NVIS on all HF frequencies and a DXE 6BTV vertical that has traps for 8 bands. I've used coax and open-wire feeds, and my original station was a random length "Inverted-L" with a wire feed going up the side of the house. There were some "hot" situations on some bands that I solved with bonding and moving further away from the antenna, but I haven't ever felt that I needed one of these.

I've picked up MFJ nifties, but haven't always found the things to be useful or necessary unless I had a unique situation.

Are you getting RF back into your equipment? Maybe have a hot key or knobs on the tuner?

Got to echo K7MEM. What makes you think you need one?

 

[K4EET]

If you don't have any real issues, why do you need it? <snip> There is no guarantee that it will improve reception, so what are you trying to fix?

Reading the eHam reviews, some have said reception was improved by lowering the noise floor. I have mitigated most RFI problems, e.g. where the computer would freeze, but on some bands I still have to run 50 watts input versus 100 watts. So perhaps if this box really works as advertised, a few more "loose ends" could be improved upon. I'm just trying to find as many users as I can to see what their experiences are using this artificial ground.

73, Dave K4EET

 

[K4EET]

<snip> Got to echo K7MEM. What makes you think you need one?

See my most recent post...

73, Dave K4EET

 

[kj3n]

Unless I missed it (possible), I don't see any mention of type of antenna(s) being used, distance from operating position, or if the RFI problems are band specific.

The mention of a computer freezing would indicate to me, an antenna less than 40 feet from the operating position. If that's the case, then it's probably a simple matter of fundamental overload. A situation that I highly doubt the MFJ device will mitigate to any significant degree.

IMO, devices like the artificial ground "solve" problems (more like mask them) that exist due to poor antenna installations, or poor choice of antenna. For example, end fed antennas are notorious for having RFI problems due to lack of a sufficient counterpoise and/or RF ground system. OCF dipoles are also problematic in this regard, although not as bad as the end fed design.

 

[K4EET]

Unless I missed it (possible), I don't see any mention of type of antenna(s) being used, distance from operating position, or if the RFI problems are band specific.

You did not miss it. I had not said any specifics of the operating environment.

The mention of a computer freezing would indicate to me, an antenna less than 40 feet from the operating position. If that's the case, then it's probably a simple matter of fundamental overload. A situation that I highly doubt the MFJ device will mitigate to any significant degree.

I have an Alpha-Delta DX-LB Plus; a loaded 160/80 Meter dipole with 40 Meter dipole and 20/10 Meter fan dipoles underneath. The station is about 50 feet from one end of the dipole affording fair isolation. I have a FLEX-6500 (100 Watts) with built-in antenna tuner running barefoot. Being disabled and in a wheelchair, things are pretty simple here so as to not be a burden to other hams that help me with the setup. I have chokes on most critical signal cables including the power cords. The only bands that I have to reduce power by 50% are 160 Meters and 10 Meters. The main thing that is missing is a good RF ground.

IMO, devices like the artificial ground "solve" problems (more like mask them) that exist due to poor antenna installations, or poor choice of antenna. For example, end fed antennas are notorious for having RFI problems due to lack of a sufficient counterpoise and/or RF ground system. OCF dipoles are also problematic in this regard, although not as bad as the end fed design.

Like I said, the fact that I am on the second floor without a good RF ground is my biggest issue. That is why I am considering the MFJ-931 Artificial RF Ground...

73, Dave K4EET

 

[kj3n]

I have an Alpha-Delta DX-LB Plus; a loaded 160/80 Meter dipole with 40 Meter dipole and 20/10 Meter fan dipoles underneath. The station is about 50 feet from one end of the dipole affording fair isolation. I have a FLEX-6500 (100 Watts) with built-in antenna tuner running barefoot. Being disabled and in a wheelchair, things are pretty simple here so as to not be a burden to other hams that help me with the setup. I have chokes on most critical signal cables including the power cords. The only bands that I have to reduce power by 50% are 160 Meters and 10 Meters. The main thing that is missing is a good RF ground.

Being 50 feet from the end of a dipole isn't much isolation at the lower bands, especially 160m. The ends of a dipole are high voltage points, so there's significant RF energy there. You'd probably have less trouble if you were positioned at the center of the dipoles.

Like I said, the fact that I am on the second floor without a good RF ground is my biggest issue. That is why I am considering the MFJ-931 Artificial RF Ground...

You're running dipoles. Dipoles are balanced antennas and do not require an RF ground. I think you're barking up the wrong tree. Does the coax run parallel to one end of the dipole? If so, how much separation is there between the dipole and the coax?

I'm betting there's significant coupling between the dipole and the coax, with RF traveling down the shield and into the shack. An isolation balun or choke balun might be a better solution.

 

[K4EET]

Being 50 feet from the end of a dipole isn't much isolation at the lower bands, especially 160m. The ends of a dipole are high voltage points, so there's significant RF energy there. You'd probably have less trouble if you were positioned at the center of the dipoles.

You're running dipoles. Dipoles are balanced antennas and do not require an RF ground. I think you're barking up the wrong tree. Does the coax run parallel to one end of the dipole? If so, how much separation is there between the dipole and the coax?

I'm betting there's significant coupling between the dipole and the coax, with RF traveling down the shield and into the shack. An isolation balun or choke balun might be a better solution.

The coax is pretty much perpendicular to the dipole coming into the shack wall. I might try your suggestion of an isolation balun / choke balun first. That I've not tried other than a big coil of coax acting as an open-air choke of sorts.

73, Dave K4EET