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Posted: 8/23/2010 4:34:31 PM EDT
I picked up my Tech and General tickets last month and have the basics of a rig built around a mobile radio. As it now stands the most likely spot for my "shack" will be our second floor bedroom, which given our walkout basement below puts me almost 2 floors above ground floor. The good news is I have a 15x15 deck at that level that I can use for raising and lashing down a Buddipole system and gaining some decent altitude for a portable antenna. The bad news is figuring out how to ground my rig.

Since I learned studying for my ticket that a long ground wire can become resonant and should be avoided, I'm at a bit of a loss as to how to approach this. Suggestions?

––Gene, KC9SYL
Link Posted: 8/23/2010 5:20:29 PM EDT
I suggest getting a grounding buss bar , and running it to your rig location and then running two large grounding cables to the earth ground and using two ground rods 6 ft in the ground.. being sure to use good copper ground clamps and run the ground rods away from each other to get better coverage.


congrats.. on the new ticket
Link Posted: 8/23/2010 8:25:38 PM EDT
[Last Edit: 8/23/2010 8:28:20 PM EDT by targetworks]
What band(s) are you considering operating?

I haven't looked into this stuff for a long time, but it's likely that there are certain lengths of ground wire that are fine for certain bands. Somehow I'm remembering that 23 feet was a "magic length", but I could be misremembering. It almost certainly depends whether the ground wire length is roughly 1/4 wavelength, or 1/2 wavelength (and so on) - the impedance of the ground wire at rf frequencies can be "good to go" or "infinitely bad for you" depending on the length - choose correctly and it works fine, choose wrongly and you have rf in the shack, distorted signals, and a shocking experience when you transmit....

ETA:

In fact, I believe that you can use a 23 foot ground wire without even connecting it to a ground rod (for certain hf bands) and it acts as a counterpoise or virtual rf ground. But as I say,. I haven't looked into it for a long time, so I could have it wrong...
Link Posted: 8/23/2010 10:22:43 PM EDT
High rise grounding.

Isolate and protect the equipment. ALL connections (100%, no exceptions) to the equipment go to a ground buss mounted surge protector, then to the gear. Antennas and such on the building need a low impedance path to ground on the outside of the structure preferably... 12" wide aluminum roof flashing would be one idea. Ground buss should connect to that ground path at or near the feedline entry point.

Use better antenna designs that don't require an "earth" ground RF sink.
Link Posted: 8/24/2010 9:30:00 AM EDT
Thanks for the assistance, guys. I think the frequencies I'll be running will end up being determined by what I can make work. I understand the need to ground everything to a common ground in the shack; it's the final run to an outside ground where everything gets difficult. To keep the ground line less than 1/4 wavelength at 10m gives me 8-9 feet to work with, which won't even get me halfway to ground.

I've got a copy of the ARRL antenna book amongst the pile of reading material on my desk; I've read elsewhere they have some grounding suggestions there, so I'll start perusing that soon. (Working on studying for my Extra license this Saturday.) I've just been trying to put all the pieces together, and have gotten somewhat stuck at this point. I may need to rearrange my house to get my shack closer to ground level, but that will require some additional input from the spouse. (That would be the same spouse who has flower beds all around the foundation of the house where I'll need to be laying out RF ground wire.) Hmmm...

––Gene
Link Posted: 8/25/2010 8:12:46 AM EDT
[Last Edit: 8/25/2010 8:34:54 AM EDT by Gamma762]
Originally Posted By grflick:
it's the final run to an outside ground where everything gets difficult. To keep the ground line less than 1/4 wavelength at 10m gives me 8-9 feet to work with, which won't even get me halfway to ground.

As I sorta mentioned before, you're not going to have an RF ground. Just have to be more selective with the antenna & feedline systems that you use and it won't be a problem. If you don't have any antennas on the house you really don't need much in the way of a ground system as your grounding efforts should be at ground level in that case.
Link Posted: 8/25/2010 8:26:58 AM EDT

Originally Posted By Gamma762:

As I sorta mentioned before, you're not going to have an RF ground. Just have to be more selective with the antenna & feedline systems that you use and it won't be a problem. If you don't have any antennas on the house you really don't need much in the way of a ground system as your grounding efforts should be at ground level in that case.

I'm still up in the air (no pun intended) about putting an antenna on the house. We are surrounded by woods, so I'd *like* to get something up on the roof, but only if I'm not going to create an RF grounding nightmare.

Can you point me in a direction on "better antennas that don't require an *earth* ground RF sink"? I can't say that I've seen that feature advertised in any of the material I've read to date, but that doesn't mean much. It may have just been worded using different terminology and I didn't put 2 and 2 together at the time.

Thanks!

––Gene
Link Posted: 8/25/2010 8:44:07 AM EDT
[Last Edit: 8/25/2010 8:47:19 AM EDT by Gamma762]
RF grounds are needed for HF when running antenna systems which put a lot of stray RF onto the feedline shield/back to the shack... things like random long wires, any OCF dipole, etc. Dipoles with no baluns and verticals with insufficient ground plane and/or too much feedline coupling may also need attention. Almost anything that requires a tuner is suspect... if that's what you have in mind, best to get a remote tuner mounted at ground level at the antenna.

Some examples of antennas which should be problem-free would be a resonant dipole with a decent balun and a ground plane (vertical) antenna with sufficient ground plane (and probably a few ferrites on the coax for a ground mounted antenna). Commercial yagis, rotatable dipoles, etc should also be fine. My usual suggestion for an easy, low cost HF antenna is a fan dipole resonant on the more common bands. If you're next to a wooded area you should have a lot of supports handy for a variety of antennas.

With almost any antenna system (to include tuner) you can get your RF ground by just running the feedline to ground level, then to the house, ground at the entry point to the house (or wherever it leaves ground level) then up to the shack. That's good practice for a variety of reasons if possible.
Link Posted: 8/25/2010 9:06:25 AM EDT
Thanks, Gamma. Very helpful info to get me pointed in the right direction on workable options. I wasn't even aware that someone was making remote tuners that could be placed separate from the shack, so that might open up some options. (I told you I'm new at this!) Given our trees, a Carolina Windom was on the short list of possibilities, but I had figured out somewhere along the line that that could present RF-grounding issues. Your suggestion of a fan dipole may be much more reasonable.

––Gene
Link Posted: 8/25/2010 9:13:04 AM EDT
tag. I'm on a second floor, and am working on my grounding also. I have a tuner at the station, that is grounded via the bus method. Coax runs about 50 feet to a ladder line balun. The coax ground is tied to a ground system at that point.

So far so good. Far from ideal, but better than nothing.
Link Posted: 9/4/2010 1:04:32 PM EDT
From the University of Hawaii Ham Radio Club Website:


http://www.chem.hawaii.edu/uham/radials.html


Above Ground Solutions

If you are stuck on the second floor of a wood frame house, you can often use a tuned ground wire. A half wavelength of wire will replicate the impedance at the other end. At 15 meters that is about 23 feet. Also there are ground wire tuners available that series tune a random long ground wire to series resonance at any operating frequency. These can be extremely useful where you have to go down the side of a building to an outside groundstake or water faucet two or three floors below. The tuner will allow you to make any length of wire look like the "magic" series tuned length and get rid of any reactance due to the wire length.

But, keep in mind that such a wire will radiate and that radiation will be added or subtracted from the radiation from the antenna, changing its pattern, maybe for the better, probably for the worse.

In fact you can use a series of quarter wavelength wires, one for each band, attached to your tuner to fake a ground. These should be insulated wires since they will be hot with RF. They will be REALLY hot at the far end! I use teflon tape over the end and slip the ends in a section of insulating tubing, leaving the tubing going several inches past the end of the wire. These counterpoise wires can be laid about the floor of a condo apartment many floors up, or wherever you need to fake a ground.

One long one can be used with a ground wire series tuner like made by MFJ Enterprises and usually called an "artificial ground". Keep in mind the wires must be left floating at the far end in this particular application. In this case the artificial ground will be tuning them as an odd quarter wave multiple, not a half wave multiple as is the case if the end is grounded.

The artificial ground tuners can also be used with grounded wires that have to go a long way to find a decent RF ground, such as dropping out a second floor window to a cold water faucet outside at ground level. In this case they will tune the wire to an electrical 1/2 wavelength and effectively "eliminate" the wire length from the circuit. Though there still can be radiation from this long ground lead to alter antenna patterns, etc.

All these mechanisms replace the missing part of antennas like the end fed random length wire and the quarter wave vertical or the end fed half wave wire. If possible a symmetrical antenna like a center fed dipole, either horizontal or vertical, or a center fed symmetrical random wire using good twin lead or ladder line, will decrease the demands on the station ground and any radial system.

Link Posted: 9/5/2010 5:15:15 PM EDT
A Buddipole is a balanced antenna and (at resonance) not dependent on a RF ground. Of course nothing is perfect and you can have common mode currents in the feedline and RF in the shack, and it's really a separate issue from your station ground. Google "ugly balun" or "choke balun" for a cheap and easy way to eliminate common mode currents and "RF in the shack" associated with that. Mobiles & portables almost always operate completely above ground and it is not an issue - except as someone else said, and "ungrounded" ground system, such as elevated radials used with a vertical and other similar counterpoise systems, are going to be hot relative to the true earth ground. You should still have a DC ground for safety, as described elsewhere in this thread, but it is unlikely to affect your RF performance.

All of that having been said, in your circumstances I think you could do a lot better than a Buddipole. Buy some wire, dude! Outdoor low voltage lighting cable (a black zip-cord) is great for quick & cheap wire antennas. And don't be afraid of that Carolina Windom.
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