grounding for those without access to dirt ground

ground lead issue solved. see illustration. any sort of highly shielded coax can be used. rg6qs is probably best when small flexiable lead is needed, hardline or lmr for large elevated outdoor installs that use a direct connection to ground and don't require routing around objects to attain ground.

illustration

RFB/Krocks deserves the credit for this idea. i just took his idea tweaked it slightly and illustrated it.

For some time many people have been asking about how to obtain a decent ground in situations where the dirt is 2 levels or more below. Then discussing your situation which is similar, the biggest concern was preventing a long ground conductor from radiating but maintaining the RF return path to the TX while observing the "ground lead" debate/issue.

Then I started thinking about balanced to un-balanced and back and thought why not try it with something like this.

Looks like it will work. Keep us up to date!

RFB

fry has already chimed in via email but since he's not too keen on replying to questions via email i don't know if his nec2 calculations take into account the inner and outer conductors being at two differing ground potentials or if his nec graph is for two similar ground potentials.

in my situation the electrical ground is on backside of building while hot water pipes enter on the totally opposite side of building.

two completely isolated grounds.

if you see this fry i would like to see nec calculations for the scenario i posed using two differing ground potentials separated by 40ft on opposite sides of building.

i could be wrong, but would like to see a simulation based on that.

you could put your thinking cap on as well and try to help with the situation.

we need a grounding solution for cliff dwellers that will pass fcc scrutiny and still allow us to ground our transmitters with a compliant grounding system.

apartment/condo dwellers don't own property so we don't have in most situation dirt level access where we can securely place out part 15 transmitters.

this is the issue, not trying to skirt the law.

Robert,

A shielded cable will not prevent RF radiation unless the current in the inner conductor is equal to and opposite of that in the outer shield. Do you think this is the case with your system?

It is rare that this is the case since the radiated field from the antenna induces current in the outer conductor upsetting the balance between this and the inner conductor current hence radiation from the coax.

Neil

neat thing is i have a fim. i can test my theories. when i get the energy to.

Hi Neil,

You said:
"A shielded cable will not prevent RF radiation unless the current in the inner conductor is equal to and opposite of that in the outer shield."

Hmmm ... Do you mean opposite polarity? Modulation phase? .... What?

i think in a coax, the shield is the RF return. it in exact opposite phase of the center conductor.

was a shot in the dark idea.

Well, we know cable TV cables emit signals, but because of spurious effects like proximity to other wiring, unequal signal relationships, unintended contact with metallic objects, etc., much of it ends up as EMI/RFI stuff, but cable for TV is for reception, so the ground shield is to help absorb it and send it to ground before it gets to the TV's jack.

Otherwise, twisted wire would work, too. That's mostly true of audio, hence the telco twisted pair wiring concept. But I'm not at all sure the effect of preventing unintentional radiation via bal-unbal can be achieved.

And yet, in my particular situation where I do indeed use 75Ω TV cable, I could detect no difference in radiated output between a 3' cable and a 20' cable, maybe 70% horizontal. None, 0, zed, zip ... and we're talking about close proximity (3' from the antenna system) measurements on the digital meter of fractions of microvolts (uncalibrated).

I wonder if and under what conditions good TX' ground via counterpoise-only return path coupling takes precedence over a wired-to-pipe, ground grid, or radial system. I recall getting a tuned signal out quite a bit more than expected with no ground (other than the audio and PS connection to house wiring), very possibly because of rebar rods.

Hmmm ... Do you mean opposite polarity? Modulation phase? .... What?

The current in the outside shield and the current in the inner conductor have be be equal and opposite in direction for cancellation of the radiated RF fields. The thing that upsets this balance is the appearance of RF current in the outside conductor which comes from the field radiated from the antenna. This is the same effect which happens in a radial system...the current is collected and returned to the transmitter. The "collecting" conductor can be a wire or the shield of a coax and the effect is the same.

Regarding cable TV leakage, the RG6 used in CATV is 100% shielded with foil material. From my readings on this subject, the leakage generally happens at the connectors and from the internals of the attached equipment. This would explain your observation that the cable length didn't affect the observed leakage.

Neil

is there an accepted way to obtain a good ground return while still being part 15.219 legal when living in an apartment or condo where a dirt level install is not possible?

or do people in apartments just have to run under radiated emissions rules under 15.209?

this is what my issue is. no ground level access.

what i have now is a horizontal 15ft ground that runs from the tx on porch to hot water pipe indoors and enters building through wall unit a/c. i'm at far end of property on bottom floor above a parking garage and ground wire runs from tx in a direction that heads in a direction pointing to interior of property to put most of signal toward interior of the property. i had a reading of 8mV @ about 400ft on my nems clarke 120E but i have yet to match it up to a potomac for accuracy and i'm not used to using it yet and might be messing up on one of the steps. i use tx's with a series tuned internal toroid / cap network to tune a 102" whip to resonance. in my case porch is 8ft of clearance floor to ceiling so i can't fit a full 102" vertical whip. that 8mV was from a point off the side with the radial/ground in middle of property.

I am fairly sure I have heard that grounding is best to a cold water pipe for several reasons. The cold water pipe goes most directly to earth ground.

The hot water pipe takes a long path all the way through the water heater, and I think hot water pipes are more likely to corrode at pipe joins.

Perhaps others have an opinion about this.

cold water pipes are also most like going to have pvc somewhere in line as the metal goes bad they get replaced with pvc. central HW systems would melt pvc so it's guaranteed to be copper through out.