In a long thread about Ken Cartwright's grounding situation I posted the following:
In a long thread about Ken Cartwright's grounding situation I posted the following:
This could easily be a new forum thread, but it also follows the grounding subject on this thread, so here we are.
I once described how I use a six-foot foot aluminum window frame as an indoor/outdoor antenna, as follows: The SS Tran is on the floor below the window with a 2.5-ft. wire straight up and screwed to the inside bottom of the metal window frame. Outside on the porch another 2.5 ft. of wire is screwed at the top of the window frame and run up the wall underneath the overhanging roof. This arrangement gives good indoor/outdoor coverage, but there's no ground.
Right under the floor is the home's 100-ft long steel I-Beam. What if that were attached as a ground plane? It's more or less at ground level and it's under the floor as if "underground."
Would that I-Beam radiate from the side like a horizontal wire antenna, or out the ends?
The biggest obstacle to simply testing it is finding a way of attaching a good electrical connection to such hard metal. Ideas?
That is the end of my earlier posting. Now today's results which may interest anyone wanting to experiment with an I-Beam or other metallic object.
At the hardware store I found a "Beam Clamp" 1/4-20 Malleable Iron. It has two screw slots for adding "Aluminum Mechanical Grounding Lugs" for copper or aluminum conductors, the same type of ground lug that can be added inside a service box, and of course a proper machine screw to combine the Lug with the Clamp.
In this experiment I am assuming that the home's I-Beam is the same as "underground" since it is below the floor, and I'll ground a Part 15 transmitter and run the remaining length vertically up above the floor as an antenna (described above).
Down at the other end of the building will be a 2nd transmitter using the same I-Beam.
The I-Beam stands on two vertical iron struts which anchor firmly on the concrete floor, so this is probably earth ground.
Full report of results will follow.
In this experiment I am assuming that the home's I-Beam is the same as "underground" since it is below the floor, and I'll ground a Part 15 transmitter and run the remaining length vertically up above the floor as an antenna (described above).
Remaining length of what? -- I'm a little confused. I'm struggling with what you're trying to do. Grounding the antenna will make it unable to radiate. The antenna and the RF ground are separate things. The RF ground is an 'unintentional radiator' in a monopole antenna situation, so it does emit, but... well, if you run a wire from the TX' RF ground connection to ground and another wire from the TX' antenna connection as your antenna, what you have is a kind of dipole.
The I-Beam won't necessarily form a ground 'plane'. It's one long heavy metal thing. Further, unless it's buried and at least some portion of it or something to which it's electrically bonded goes deep into the ground, it's not an Earth ground ... certainly not just because it's under the floor. Earth ground is electro-mechanical in nature.
Down at the other end of the building will be a 2nd transmitter using the same I-Beam.
I don't see a problem with them sharing the same RF ground, but it's effectiveness as a counterpoise and/or safety ground might be in question.
The I-Beam stands on two vertical iron struts which anchor firmly on the concrete floor, so this is probably earth ground.
Not unless it's bonded to something which goes deep into the ground, like a ground rod. Does the I-Beam go around the entire house? Where and how is your house ground made. I don't know what the ground conduction index is at your location, but if it isn't so good, you'll need a deep ground rod. The I-Beam may have so much mass it will form a fair ground ... like the engine block in a car. Whether or not it will make a good safety ground as well seems disputable.
But keep on experimenting ... 😉
Ken Norris your input came at the exact time I was trying the idea.
While I was not planning to "ground the antenna" to the I-beam, I did describe the I-beam as a place to attach the transmitter's ground.
This has been accomplished and, true to your predictions, there was no improvement whatsoever in coverage area, despite a 100' horizontal metal beam on the ground side of the circuit.
Much work has lead to zero results, in the true spirit of Part 15 broadcasting.
Thank you for sharing thoughts.
Carl,
I had my ham radio stations in a mobile home for over 20 years. Here is what I learned.
Mobile home frames are made of iron I-beams and/or large iron channel iron, usually welded together into long stringers and shorter cross members. The frame is usually required by law to have its own service ground at the breaker box and directly to earth. At the breaker box, the AC neutral, service ground and frame ground are all connected together.
In my home, I decided connecting to the frame was redundant considering the ground connection at the breaker box. I did run a station counterpoise out the window, down and around the base of the home. In addition, I sank an 8-foot ground rod and connected it to the station ground and connected it to all the other grounds. All of the plug in connectors had 3-prong to 2-prong adapters to isolate the equipment from the service AC ground for safety and to reduce ground loops that can cause hum. All station equipment went directly to earth ground. I have even used a similar hook-up to the aluminum window frame. The window frame antenna didn't work because of the metal straps that wrap around the walls of the home (underneath the siding) to hold it together during transport.
Finally, most wall-wart power supplies, and even linear and switching power supplies, usually have the negative side of the supply hooked to neutral or ground. Most times, RF signal out of phase with the antenna, attenuates the signal coming out of the final network of the transmitter. So, a separate counterpoise is most likely necessary. Remember to keep the antenna and the ground separate as well. The greater the voltage potential between the antenna and the ground (over simplified) the greater the signal.
All those years of playing with QRP ham radio comes in handy.
You're not alone, I'm sure 😉 What was the attempt? I think, if you can, you should drive ground rods at each end of the house, one for each TX. If you still want to use the I-Beam, clamp it to a ground rod.
But what about the common claim that the ground side of a transmitter circuit radiates on a long wire (or I-beam) for which reason the length of a ground lead is considered part of the 3-meter length? Therefore, why isn't my 100' I-beam causing a dramatic increase in horizontal radiation? As I said, it has no observable affect either good or bad.
I don't know about mobile homes, but this would be a mistake in many cases:
At the breaker box, the AC neutral, service ground and frame ground are all connected together.
For example, in a marine situation at least, you do not want the green wire (ground) and white wire (neutral) to be connected to each other anywhere ... that would be a bad idea. If you plug a tester into a receptacle it will show a ground fault. In addition to the neutral, you would also be using the bonded ground as a return path for AC current, which means a portion of it (at least) is trying to get back to the circuit through the water because the boat's ground (usually the motor and any metal through-hulls) is connected to it, and serves as DC return path. This is what nearly fried my computer, which must use a 3-wire connector. It's expecting a free Earth ground, not a connection to neutral ... it already has that.
In a saltwater environment, corrosion is the enemy ... I've had it carry current right across the plastic surface of an AC receptacle and short out (smoke and fire), and can even more easily carry stray current from neutral to ground. This is what was causing a problem with my (expensive) marine battery charger, which I had to disconnect until I can figure out how to avoid continuity where I don't want it.
It's a very common mistake. On boats, the battery charger/inveter system is highest among the usual suspects.
People unknowingly think it will prevent galvanic action if they don't ground the system separately, but the proper solution for that is a galvanic isolator. Check it all out:
http://members.cox.net/pc-usa/station/marine%20grounding.htm
After half-a-day's work, I can't charge my battery until I track down the problem with it, but the AC circuit is safe. The tester shows Correct on all the receptacles, and DVM tests at the shore power connection vacillates between .01 - .02 volts of leakage, which is acceptable.
HTH ...
Finally it's cool and not so cold. That's why I took a radio outside to wander the yard and noticed what might be the only advantage gained by the "I-beam connection."
The yard around here is about 60'-wide by 200'-long. The longer length is from downhill to uphill at a steep angle. Previous (to the I-beam connection) the AM signal at 1640 kHz was about gone by the mulch pile up top, and pretty weak down in front on the low side.
Now, however, the AM 1640 signal is fairly uniform over the entire yard, which suggests an advantage gained of several feet.
To prove this I will disconnect and reconnect the I-beam connection under scientific scrutiny.
In remodeling my mobile home several years ago, the electrical inspector gave special attention to the grounds in the home, including the frame. The frame is required, in most states, to have an earth ground. The frame ground was inspected separately from the rest of the home. The inspector said it was for "fire safety". In the breaker box, the service ground and neutral are connected together to make sure that the "ground interrupter" outlets work properly. They are required in the kitchen, laundry room, outside outlets and bathrooms. I seem to also remember, the 220volt AC circuits wouldn't work right or pass inspection without a particular ground/neutral configuration in the breaker box.
Putting ground rods at either end of the homes frame won't provide any particular advantage. The size and area of the frame provides most of the positive effect on the transmission system and signal. The location and distance of the transmit antenna from the frame will affect the signal to some degree.
Anyway, I am glad you have found an advantage to connecting to the frame.