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Post by sparepart on May 29, 2018 17:27:26 GMT
Looking for clarity on the 3 meter antenna and ground length limitation: 3 Meters is 118.11 inches. A Procaster has a 104 inch antenna. Based on that logic, my RF ground lead can only be 14.11 inches in length?
Our Procaster is mounted on a 12 foot tall cyclone fence that is several hundred feet long.
I can make a 14 inch long bonding jumper and bolt it to the fence post, however would prefer to run a wire to a driven ground rod.
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Rich
Full Member
RF Systems Engr (retired)
Posts: 112
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Post by Rich on May 29, 2018 17:49:55 GMT
The nearest location of a true r-f ground would be where/if the bottom of the fence post you attach your "ground lead" to is in electrical contact with the Earth.
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Post by sparepart on May 29, 2018 18:32:30 GMT
The nearest location of a true r-f ground would be where/if the bottom of the fence post you attach your "ground lead" to is in electrical contact with the Earth. Where I am getting hung up is the ground lead length being regulated by the FCC as an active part of the antenna system (counterpoise vs. protective ground). Mounting the TX on a 3 foot pole driven into the dirt with a 14" ground wire to to a driven ground rod can't be what the intent of the regulation is |
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Post by part15engineer on May 29, 2018 18:37:09 GMT
you might be better off (if you have a flat roof), putting your pro caster up on the building roof on a 6ft mast over a symmetrical ground radial set as many and as long as you can afford to make them and space permits. the radials must be symmetrical and flat or they will radiate violating the 3m rule.
as for lightning grounding a MOV at the base of the mast joining the tx to an actual earth ground should off lightning protection. it is my understanding there is no connection to ground until there is a large charge on the line. also putting MOV surge protector on the incoming power and audio lines is a good idea since lightning looks for the best way to earth ground.
a direct hit you will lose the TX but at least your studio investment will be safe.
a fence post is not the best location for a procaster or rangemaster.
better yet if you want to provide me the address either here or in a PM i can google earth the location and give you a good idea of the best location.
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Post by sparepart on May 29, 2018 19:05:29 GMT
you might be better off (if you have a flat roof), putting your pro caster up on the building roof on a 6ft mast over a symmetrical ground radial set as many and as long as you can afford to make them and space permits. the radials must be symmetrical and flat or they will radiate violating the 3m rule.
as for lightning grounding a MOV at the base of the mast joining the tx to an actual earth ground should off lightning protection. it is my understanding there is no connection to ground until there is a large charge on the line. also putting MOV surge protector on the incoming power and audio lines is a good idea since lightning looks for the best way to earth ground.
a direct hit you will lose the TX but at least your studio investment will be safe.
a fence post is not the best location for a procaster or rangemaster.
better yet if you want to provide me the address either here or in a PM i can google earth the location and give you a good idea of the best location.
No joy on a flat roof, and the site is on the National Register of Historic places to boot.... From a protection perspective, the aerial feed cable between the transmitter and coupler is protected by a Polyphaser IX2T (646444249317) on both ends of the cable. The mounting plate for the Procaster and IX2T are welded to the fence post (location is recycled from a previous use). I'm fairly familiar with NEC, R56, and, GR core for grounding. Hence the tradeoff on sacrificing the TX by locating it on the fence. We know the fence is a compromise location, however it's the only option at the moment. |
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Deleted
Deleted Member
Posts: 0
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Post by Deleted on May 29, 2018 21:13:15 GMT
Bonus Lengths
I can arrange an extra 1.89-inches for sparepart, based on the original part 15 rules of the 1960s which allowed antenna length of 10-feet (120-inches).
When the gov switched to metric measurement they rounded down to the nearest whole-numbers, which gave us the 3-meters of today.
Perhaps we can look elsewhere for clues in the rules which might help...
As I recall, licensed stations are permitted a certain tolerance above the 100% assigned power... a whole 5%
Doesn't that give another 6-inches?
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Post by Admin on May 30, 2018 4:52:23 GMT
I don't think any of us really KNOW, but based on all that I have read, if you are not causing interference, and if you are running an otherwise clean installation, it seems that the FCC will cut you some slack if your length is just slightly over. To put a point on it, this is just my opinion. Bonus LengthsI can arrange an extra 1.89-inches for sparepart, based on the original part 15 rules of the 1960s which allowed antenna length of 10-feet (120-inches). When the gov switched to metric measurement they rounded down to the nearest whole-numbers, which gave us the 3-meters of today. Perhaps we can look elsewhere for clues in the rules which might help... As I recall, licensed stations are permitted a certain tolerance above the 100% assigned power... a whole 5% Doesn't that give another 6-inches? |
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Post by Admin on May 30, 2018 9:26:35 GMT
Maybe replace one of the fence posts with a 12 foot copper pipe driven 8 feet into the ground?  Looking for clarity on the 3 meter antenna and ground length limitation: 3 Meters is 118.11 inches. A Procaster has a 104 inch antenna. Based on that logic, my RF ground lead can only be 14.11 inches in length? Our Procaster is mounted on a 12 foot tall cyclone fence that is several hundred feet long. I can make a 14 inch long bonding jumper and bolt it to the fence post, however would prefer to run a wire to a driven ground rod. |
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