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Author Topic: Best grounding practices???  (Read 911 times)
KG6IBW
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Posts: 13




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« on: March 12, 2002, 01:13:19 PM »

Givens:

I have an IC-718 located about 15 feet from the ground (and a new 8'
ground rod).  The chassis is grounded by a 25' piece of 6 gauge 1x19
copper between them.  The antenna is a HighSierra vertical screwdriver
whose base is about 8' above the radio.  It has a counterpoise of 14
gauge stranded wire radials emanating from the base and sloping downward
(32', 16', 2x 8').  The radio is driven off a lead acid cell and is
isolated from the house AC.

Questions:

What (if anything) should I change to adhere to best grounding
practices?  I am assuming that from 60Hz and dc point of view I am
grounded well.  Should the ground rod be tied to the house wiring?  What
about RF ground?  Is the 6 ga useless?  Do I need a wide braid or copper
sheet ground?  What about counterpoise issues?  Is the connection from
the transceiver chassis to the counterpoise via the coax outer braid in
the feedline adequate?  Should a low reluctance connection be made from
the base of the antenna to the ground rod?  Any other changes?  I am
adding a linear driven off  the house AC, would this make any other grounding
changes advisable?
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WB2WIK
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Posts: 20611




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« Reply #1 on: March 12, 2002, 01:43:49 PM »

You've raised a lot of questions, and given a good bit of detail regarding your setup and plans.

What's a "6 gauge 1x19 copper?"  I'm familiar with 6 ga. copper wire; what's the "1x19" mean?  Never heard such an expression.  Did you mean "7x19" (seven strands of 19 gauge wire)?

In any case, a 25' length of #6 ga. does not an RF ground make.  That's waaaay too inductive to be effective on the higher HF bands, although it may do something on 80 meters.  On 40, it may start to look like an RF choke, as it's approaching 1/4-wavelength long, and odd increments of 1/4-wavelengh at any frequency is not a good length for grounding, as it transforms a low impedance (earth) to a high impedance (equipment).

It also sounds as though you have only four radials on the base of the HS Screwdriver.  Is that true?  I'm surprised it works.  My experience with the HS Screwdriver (considerable) is that it required a minimum of 3-4 radials per band if installed on anything other than an automobile.  Thus, to use it on all bands 80-10m, you'd want about 24 to 32 radials.  If you have just four radials, one each at 32' and 16' and two at 8', sounds like possibly you're trying to work only 40, 20 and 10 meters.  Is that true?

I am concerned about your statement "adding a linear driven off the house AC."  No problem with amplifiers, although I wouldn't recommend running one during the tuning process of the HS Screwdriver -- this can cause failures.  But if you're intending an amplifier, and the antenna is only 8' above the rig as you stated, that's mighty close.  Biohazard exposure alarms go off in my head, on that one.  8' is only a tenth of a wavelength or so on 20 meters -- this is too close for daily operation, especially at higher power.  Not to mention that operating with anything more than "barefoot" power, when using an antenna so close to the transmitter, is very likely to cause "RF feedback" problems (radiated RF getting back into the rig's circuitry, mike line, etc and causing problems).

While I have no idea what your station setup is like or how much space you have, my recommendations for improved performance as well as safety would be:

1.  Get that antenna farther away from you and your equipment.

2.  Add more radials to the base of the HS Screwdriver.

3.  Change the #6 ga wire to 6"-12" wide copper flashing.  Use a very short #6 ga jumper (1" or 2" long) to connect the flashing to your equipment, and a few such short jumpers on the ground rod end to connect the flashing to the ground rod.  If possible, add a second (and a third) ground rod about a foot or two away from the first one, and run them all in parallel using a couple of paralleled #6 ga copper wires between them.

4.  Whether you connect the base of the antenna to the ground rod or not is up to you, but I wouldn't bother.

5.  If and when you add the amplifier, ground its chassis to the same point as the IC718's ground, which will preferably be as described in #3, above.

6.  And if you can't get the antenna 25' away from your operating position, I wouldn't add the amplifier.

WB2WIK/6
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KG6IBW
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Posts: 13




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« Reply #2 on: March 12, 2002, 03:05:47 PM »

WB2WIK Steve, thanks so much for your thoughtful reply.  1x19 is like 7x19 except instead of each of the 19 strands having seven substrands, each of the 19 is solid wire.  The HS vertical with four radials seems to work, I QSOed Queensland with it (about 7000 miles) and Warsaw (6000 miles).  Also Jim at HS seems to like the radial config ok, but I will follow your advice and add more.   I usually work 10 and 20 m.  

As far as RF hazard goes, I used the UTAustin page on the web and am OK for controlled even with 100% transmit time (which I never come even close to) and even at 10m.

Thanks for your recommendations.  

Moving further away from the antenna is quite difficult.  I will consider it further.
I will add more radials.
I will try to get in some copper flashing.  Should it go to the amplifier chassis or to the antenna counterpoise attachment point or both?
Would it be wise to try to shield the operating position from the antenna?  Can I trust the UT page?
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KB9BQN
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Posts: 3


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« Reply #3 on: March 12, 2002, 04:09:53 PM »

Hello,

Another alternative to 6ga copper is 1/2" or 1" tinned copper braid.  Cable X-Perts sells it in bulk or with the ring terminals installed.  Check out www.cablexperts.com.  They also offer the product through AES and HRO stores.

73's Chuck
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WB2WIK
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Posts: 20611




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« Reply #4 on: March 12, 2002, 04:25:00 PM »

7 x 19 means 7 strands of #19 gauge wire.  It's just 7-strand wire.  1 x 19 would mean 1 strand of #19 gauge wire and thus would only be #19 gauge, overall.

The "seems to work" of course is great but always a subjective term.  What's most important for most of us is "works compared with what?"  I have worked (no kidding) Ohio using a 40W light bulb as an antenna, while operating (along with the bulb) below ground in my parents' basement.  25W output, 40m CW.  I've also worked a fellow in Bulgaria using an FT817 barefoot with a whip antenna, just 1-1/2 weeks ago during the ARRL DX Phone contest.  Assuming his antenna probably had -20dB "gain" on 20 meters, that's about 120,000 miles per Watt (to explain the distance covered vs. power used).  The trick was that on _my_ end, I was using stacked 5 element 36' long boom Yagis at 65' and 95' above ground, so the other station didn't need to do much except be there.

A lot of the enjoyment of HF work, for me and I think for most of us, is in doing everything we can within reason to have an effective station capable of global DX on a moment's notice.  To that end, we can all continually improve.

Of course, we all have fun in our own way.  Since the HS antenna tunes 12 and 17 as well as 10 and 20, and those bands (12 & 17) are less densely populated and therefore less competitive, I'd think you might want to use them.  Although I have a tower-mounted 6 element beam that covers 14 through 30 MHz and does quite well on all five bands, I find myself using 17m in preference to 20m, simply because it's easier.

If you follow that line of thinking, you might want to add radials for those bands and see what you can do, there.

Copper flashing is readily available anywhere home building materials are sold, including Home Depot.  I'd run it between a good, solid earth ground and the chassis of the amplifier (as well as the chassis of the IC-718).  Since your vertical is elevated above ground, earthing its base (counterpoise attachment point) theoretically won't do anything.  It probably won't hurt, but it also should not help.  It _might_ hurt, if the earthing happens to be 1/4-wavelength long on any frequency you operate.  That would be a very bad length indeed; as such, it's probably best to avoid this connection altogether.

As far as trusting the UT page, I haven't even looked at it, so I can't comment.  I'll go take a look.  But having knowledge of physics, and electromagnetic theory, and an understanding of the inverse square law, it seems impossible to me that you'd want to be operating within 1/10-wavelength of your antenna.

Prior to releasing the revision of Part 97 which requires amateurs to perform their own analysis of radiation safety based on guidelines introduced about a decade ago, I and several other local hams I know (N6NB and N6VI come to mind) were part of the FCC Office of Engineering and Technology (OET) field study, where FCC engineers actually visited our stations and made measurements using elaborate equipment calibrated to NIST standards to determine what might be -- and might not be -- safe operating practice for typical amateur HF stations.  

The FCC team visited my home during the summer of 1990, as I recall, and this was arranged and facilitated by N6NB, who was doing research for the FCC on this matter.  It was determined that my transmitting at 100W into a sloping dipole antenna hanging from a tree in the yard, about 60' from my operating position, created some very nasty secondary radiation from the steel bed frame in our Master Bedroom, which happened to be closer than the "shack" to the antenna, and more at its same elevation (since the bedroom was upstairs, about 20' above the "shack" location).  Very nasty secondary radiation -- actually stronger than the primary signal from the antenna itself, and probably due to a resonance in the bed frame.  That level of radiation greatly exceeded what are now considered safe standards.

You might say it was a "glowing report" on how bad things can get, and unfortunately what all the calculations, charts and spreadsheets cannot predict because people don't plug in such variables as bed frames.

WB2WIK/6
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WB2WIK
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Posts: 20611




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« Reply #5 on: March 12, 2002, 05:53:44 PM »

I checked the following website, which I assume is the pointer for the calculator you used:

http://n5xu.ae.utexas.edu/cgi-bin/rfsafety.cgi

That's a calculator made from the BASIC program written by N6NB, and I see no reason not to trust it; however, again, it is useful only for free-space calculations as required by the FCC for MPE analysis and does not include any provision for reradiated emissions, etc.

Based on your situation, with the center of the antenna 11 feet away (8 feet + 3 more feet to get to the center of the HS) and 300W average power, on 10m, you'd be more than 2x over the MPE of .23mW/cm2.  I just guessed at the 300W average power, but that's about right for a 600-800W PEP amplifier using processing/dynamic ALC.  The calculator yields a figure of .5437mW/cm2, a pretty big number.

If you're planning an amplifier, I really recommend you get that antenna farther away...or leave the antenna where it is, and move your operating position farther from it.

WB2WIK/6
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AG4DG
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Posts: 537


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« Reply #6 on: March 12, 2002, 06:13:49 PM »

Are you sure the transceiver needs an RF station ground?  While I can see the need for the RF ground plane of a vertical antenna, using RF chokes and improving the RF ground plane are easier ways to reduce RF feedback.  The idea of an RF ground rod is to provide the common mode RF current (the cause of RF feedback) an alternative to you as the path.  I think it's easier to just minimize the stray RF in the first place.  I have written more at:

http://www.jasonhsu.com/ham_radio-technical.html
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K0XU
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Posts: 294




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« Reply #7 on: March 12, 2002, 10:30:47 PM »

If you have a perfect ground on the antenna, perfect connections all the way, don't wander away from the resonant frequencies, never have a bad connection develope unexpectedly in the middle of a QSO, rain or snow doesn't detune you system or any of the other real world thing that happen at my station, you might be able to get by without an RF ground. But I feel a lot better having one. And my rig quit biting me when transmitted on the wrong antenna on 40 meters;-)

On the subject of minimalist antennas, I once made a contact on 40M phone loading up the I-beam in the basement of the house. (I was trying out a new tuner I had built and I was alone in the house). The path was probably 3-400 miles. As the discussion came around to antennas, the other fellow asked me what kind of antenna I was using and I replied "a beam". He then asked what kind of beam, to which I replied "Just a big old I-beam down here in the basement". He never came back to me after that. Oh well.

Jim
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WB2WIK
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« Reply #8 on: March 13, 2002, 11:26:37 AM »

K0XU: This has nothing to do with "grounding," but here's another story (absolutely true)...

1966, 2 meter AM contact with Mark, WB2WHC, who lived about 6-7 miles from me, across two towns.  Mark's in the attic of his parents' house, where he has his "shack" set up to minimize feedline losses (a good idea), and just completed construction of a new 2m antenna, a phased colinear array.  He also has a 2m beam (homebrew) with a folded dipole driven element.  The antennas are both about 200-300 Ohm feedpoint Z, so he's using twin lead to feed them, and an old-fashioned "knife" switch to switch between them.

I was watching his signal strength to see which was stronger at my end, the beam or the colinear.  Mark switched while transmitting (Gonset Communicator, bulletproof) and talking.  "The is the beam.  This is "nothing" (meaning the position where the knife switch was making no contact with either of the antenna feedlines).  This is the colinear."

Which was strongest?

"Nothing."

WB2WIK/6
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RobertKoernerExAE7G
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Posts: 1435




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« Reply #9 on: March 13, 2002, 03:12:48 PM »

Was that where the commonly used term was developed Steve?

He was using the knife, and thus had a cutting edge antenna--cutting edge technology?
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W7NMC
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Posts: 8




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« Reply #10 on: March 14, 2002, 07:31:37 PM »

Hello, I've been doing plenty of Web research on grounding practices. An informative Web site is www.polyphaser.com. There is much information on grounding on this site. One thing I have learned in almost a year of doing research on grounding is this: you will get as much conflicting information as there are opinions on pizza, using both Ham and other Web sites. So, I have decided to use a "common sense" approach to grounding:  to weed out the obvious misinformation and use the information that keeps coming up as repetitive.  Even commercial Web sites that offer to contract your grounding needs will offer differing opinions as to proper grounding.  My advice:  do plenty of research on this subject, and then come to your own conclusions. Good luck.  Howard
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W0FM
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« Reply #11 on: March 15, 2002, 05:10:33 PM »

For Steve, WB2WIK:  Interesting concept on the re-radiating bedsprings.  (Not that different that the garbage we experience on high density RF sites when dissimilar metals react and re-radiate.)

But, it pains me to think of the money my wife has wasted on her electric blanket when the radiating bedsprings could have done the same job!  "Good night honey, sleep well....I'll go down and fire up the linear"   :-)  

Terry, WØFM  
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KL7IPV
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« Reply #12 on: March 19, 2002, 05:25:18 PM »

Oh, that WAS bad.
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