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Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1079
Registered: 9-2004
| | Posted on Monday, January 23, 2006 - 12:09 am: | 
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i ran across this article in my searches for antenna designs. (tonight was a sterba curtain)
i found it interesting because it sounds very logical, and yet some parts differ with the advice most of us give and get.
so, anyone and everyone feel free to post your reactions and comments about this article.
AS IF I WASNT CONFUSED ENOUGH ALREADY!!!
Rf grounding is considerably different than surge grounding. First thing is you are working with RF. Since it is an AC signal it has impedance. The length of the ground runs has much more to do with the fraction of a wavelength at the frequency involved than the DC resistance of the wire. While the DC resistance of a ground wire may be only a fraction of an ohm, the impedance (or the AC resistance at RF frequency) can easily be hundreds or thousands of ohms on the same wire. This can make it pretty difficult to get an effective RF ground. Remember an RF ground wire is just a short antenna! We want to make it as LOUSY an antenna as possible! We really don’t need it radiating extra RF inside our shack. It is supposed to remove this stuff not cause it. An effective RF ground needs to be less than a quarter wave length at the highest frequency used. As you can see there is no such thing as an effective ground for VHF or UHF. We will concentrate our efforts to 10 meters and above. This means our ground wire from radio to ground must be about 9 feet or less! This is still pretty difficult. All radios, tuners, meters, etc in radio system should be grounded in a star ground configuration. The common point should be at the tuner if one is used, otherwise a ground bus bar can be purchased at an electrical house. All Connections to radios should be with either insulated or bare wire with as few strands as possible. RF likes smooth surfaces best. DO NOT USE braid for RF connections. This is an old wives tale! Your ground run should go directly to the ground where you should have a ground rod for the connection point, (which will be connected to all your other ground rods in the system as discussed above). This run must be less than nine feet to be effective. If you are on the second floor this will make this length impossible. Use of a shielded ground* wire can stop radiation of the ground wire but you will still have a lousy ground. Nothing can change this. Ground wire tuners only turn your ground wire into a counterpoise for your antenna, meaning it WILL radiate. This will only ensure that the low voltage point of your antenna will be at your radio. Next we need to form our RF counterpoise outside at our ground system. You will next need to add some bare copper wire at the RF feedpoint where your shack ground wire connects to. I prefer to use bare 8 gauge copper ground wire here. It is single conductor, bare copper and easily bent and run around house. Single strand is best but it should definitely be bare even if you have to strip insulation off wire. Run it around the house or anywhere it will stay out of the way fo lawn equipment but not buried deeper than ½”. This is CRITICAL. RF will not penetrate soil deeper than this at these frequencies. Those bonding wires you have between ground rods and ground rods do not exist to the RF! Burying this wire under wood chips or similar non conductive landscaping, etc is the way to go. This counterpoise should be as long as the wire antennas you have in the air. For most hams this will be about 130 feet. Longer is better. I run all the way around my house. I have found the eight gauge will push into the spacing used between driveway and foundation when persuaded with the proper tool, (READ HAMMER). You can connect the loop back on itself at the feed point. This can add several S units to the receive signal and dramatically reduce noise on the signal, though nothing will help all the noise on 80 or 160 meters. Years ago I installed a long wire antenna that was about 250 feet long and about 50 feet in the air. This should work fantastic you say. I had three ground rods outside window of shack with single ott solid copper ground wire direct to tuner. Ground wire length was only six feet. All three rods were spaced about eight feet apart with connecting bare wire interconnecting them….in other words, a really good surge ground. What I did not realize at that time was how lousy my RF ground was. We could not tune the antenna on most frequencies and we kept getting zapped from the radio or microphone when we transmitted. Also, our signal reports were lousy. SO, after consulting some experts, I added 250 feet of counterpoise around the building consisting of some bare 6 gauge copper wire I had. The radio was on while I rolled it out and a friend was listening to the broadcast on 40 meters, (OK it was night time---best time to do antenna work right!) Anyway he reported the broadcast was only about S 4-5 on meter. As I rolled out the counterpoise it rose to 40 over S9 and came in much clearer. We were able to tune everything easily now and SWR was rock stable. When we did a signal test, the station we had talked to before accused us of running a contest amplifier. We could not convince them it was only 100 watts, same as before and the same antenna!
SUMMARY.
Don’t underestimate the importance of a good ground system.
i know, its long.
what do you think?
matt |
Road_warrior
Senior Member
Username: Road_warrior
Post Number: 1187
Registered: 7-2004
| | Posted on Monday, January 23, 2006 - 6:08 am: |
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Everything made sense up until the part
about running a RF counterpoise around the house.
And adding all that extra recieve in his radio.
I'm not a ham and have never tried it, so, i don't know.
I am having trouble of my own in hooking up
a RF ground that doesn't radiate, even though
i'm using the less than 9 ft. (7.6ft) bare
copper ground wire to outside rod. |
Hollowpoint445
Senior Member
Username: Hollowpoint445
Post Number: 1039
Registered: 6-2004
| | Posted on Monday, January 23, 2006 - 9:09 am: |
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In the story the antenna used was a random wire on 40 meters. They require quite a good ground to work decently. Essentially what he did by rolling out the wire was to create a counterpoise for the random wire radiator.
The CB equivalent would be to plug a 9' piece of wire into the center of your CB's SO239, and then add another 9' piece to the threads or chassis to act as the counterpoise. |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 2303
Registered: 7-2004
| | Posted on Monday, January 23, 2006 - 10:38 am: |
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how do you know if you have a bad rf ground?
mic bite, possibly tvi, and maybe poor peformance from your station are signs.
i have read & been told 'K-I-S-S' when it comes to grounding your CB. more involved RF grounding & bigger problems are more prevalent when a multiacre antenna farm is feeding a dozen bands with multiple transmission modes and feedlines running hundreds of feet & more back to large amplifiers & such.
who 'told' me? names include not just joe-cber or ted-ham, but locals who build & design for the coast guard auxiliary, BC stations, as well as those who have written for periodicals & books, those who may have contributed to this forum, or been mentioned in it. what books? well, i've probably read every one in the arrl library since about 1975.
you know what kid? not only does some of that info differ from what has been spread across the land by this & other forums, but some of it differs from book to book!!! written by the same people in some instances! i suppose even the experts re-think their theories & update them from time to time.
while the answer to 'how do you know' may be a bit oversimplified, if you can say NO to mic bite & tvi, you are probably close to being 'good' already.
poor shielding on coax, poor installation of connectors, poor shielding of equipment can allow rf to escape & radiate from all wires involved, including ground wires, electrical cords, etc. if your station's performance does not seem to be what it should be, that may be a sign of a poor rf ground.
mic bite in a mobile usually requires some slight rethinking & reworking of a MINIMAL amount of grounds, not a mile of wire, to resolve the unground problem.
a cb radio, even with a small amplifier, a filter, a meter & an antenna with lightning protection & ground rod should not require so much thought.
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Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1081
Registered: 9-2004
| | Posted on Monday, January 23, 2006 - 4:20 pm: |
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hollowpoint makes a very good point about what type of antenna he was using.
i guess i glossed over that fact too quickly.
i like the way you explained that.
pat, yeah, i definitely adhere to the KISS principle.
this article actually made me chuckle a bit as i read it. he sounds intelligent in the beginning, and then at the end he sounds just like a CB'er!
"my buddies meter went up to +30!"
anyway, good clarification guys; anyone else wonder about the "dont use braid for an RF ground" part?
matt |
Marconi
Advanced Member
Username: Marconi
Post Number: 553
Registered: 11-2001
| | Posted on Monday, January 23, 2006 - 7:26 pm: |
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Hea Kid, are the words in your piece above, your words or the word of another. The look very familar, as though I had read these same words somewhere before. The way I read in the first time I thought they were about your experience and your words. Just curious. |
Road_warrior
Senior Member
Username: Road_warrior
Post Number: 1190
Registered: 7-2004
| | Posted on Monday, January 23, 2006 - 9:13 pm: |
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Eddie, i've read that article on the web
before. LOL...You probably have too.
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Road_warrior
Senior Member
Username: Road_warrior
Post Number: 1191
Registered: 7-2004
| | Posted on Monday, January 23, 2006 - 9:12 pm: |
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Eddie, i've read that article on the web
before. LOL...You probably have too.
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Tech833
Moderator
Username: Tech833
Post Number: 1165
Registered: 8-2002
| | Posted on Monday, January 23, 2006 - 10:08 pm: |
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Everything in that article is accurate ecept the part about not burying your radials deeper than 1/2 inch. It is O.K. to bury your radials as deep as you want. Most systems I build have radials between 18 and 24 inches deep.
As long as everything in your system is bonded, you will not get mic bite.
The lower you go in frequency, the more important your ground becomes. It is very possible to get the signal improvement in the article with a good ground system vs. a poor one. My tower has over a mile of bare copper wire in the ground fanning out in all directions in lengths varying from 25 to 120 feet long. I have one of the biggest signals on 80m with only a wire antenna and a 100 watt radio. Some of you guys even hear me with the Radio Shack mobile CB on the CEF nets on that same longwire despite my calculated -14 dB gain on 11m with it.
On 11m- It's all in the ground and your takeoff angle. The lower you go, it's all about your ground system and the ground losses. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1084
Registered: 9-2004
| | Posted on Tuesday, January 24, 2006 - 12:58 am: |
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good info 833, what do you think about his views on using braid?
marconi, as you've probably guessed by now, i found this on the web.
matt |
Wildrat
Advanced Member
Username: Wildrat
Post Number: 706
Registered: 12-2003
| | Posted on Tuesday, January 24, 2006 - 8:28 am: |
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Kids first sentence was ( I found this article while doing my searches )
He did not plagiarize
Mark |
Road_warrior
Senior Member
Username: Road_warrior
Post Number: 1192
Registered: 7-2004
| | Posted on Tuesday, January 24, 2006 - 11:35 am: |
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Well, it's nice to know that it's accurate
information.
Thanks for explaining about the lower
freq and ground losses. |
Marconi
Advanced Member
Username: Marconi
Post Number: 556
Registered: 11-2001
| | Posted on Tuesday, January 24, 2006 - 12:49 pm: |
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Your are right Wildrat, I missed that part about his searches.
The piece is long and after reading it again, it just seemed that I had heard some of those words and ideas before, so I asked.
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Tech833
Moderator
Username: Tech833
Post Number: 1166
Registered: 8-2002
| | Posted on Wednesday, January 25, 2006 - 12:02 am: |
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There is nothing wrong with using braid for flexible ground connections (like to bond a beam boom to a tower when using a rotor). However, it is good engineering practice to use strap whenever possible due to the lower skin resistance and higher velocity factor. |
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