Scanner Antenna Problems
- Thread starter scottie84
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dbox1
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Scott,
I fear I'm going to show my age here, but I first got into radio way back when tubes were the rage, back when you had to have a FCC license for Citizens Band radio. I have been a long time SWL'r for ever, and enjoy the hobbie of radio. From VLF to sat, count me in.
A lot of folks confuse "bonding" with "grounding" and when it comes to antenna performance and protection, a good strategy is worth a ton of prevention. Are you looking to utilize earth as lightning protection or as an integral part of your antenna scheme?
I fear I'm going to show my age here, but I first got into radio way back when tubes were the rage, back when you had to have a FCC license for Citizens Band radio. I have been a long time SWL'r for ever, and enjoy the hobbie of radio. From VLF to sat, count me in.
A lot of folks confuse "bonding" with "grounding" and when it comes to antenna performance and protection, a good strategy is worth a ton of prevention. Are you looking to utilize earth as lightning protection or as an integral part of your antenna scheme?
Well I guess I have never thought about it that way, but I would have to say both. Lighting protection as in a path that most of a direct hit would follow to keep my house from burning down, I know my gear is gone no matter what for the most part. I would think a single 8ft ground rod would be sufficient for my antennas and radios. Whats your take on it? I really don't know what the advantages to having the grounding system I described would be. Oh and I finally "after all this rain" got my grounding rod all the way in, it still had about 2 feet sticking out, this ground is hard! Also I heard that you can not have two grounds to meet code, is my ground rod for my shack considered as a second ground, or do they just mean for the home electrical system?
Scott
Scott
dbox1
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Scott,
A single ground rod driven 5' down, on average, will end up with around 110 ohm resistance to true earth. That same rod driven just 5 more feet, will yield about 65 ohm resistance. (this is why i stated before a 10' rod minimum) If you are lucky to live someplace where you have a well for example, the galvanized casing extending below 50 foot will yield a true resistance of around 5 ohm, and that's about as low as it gets until you get to a real deep earth ground over 100 feet deep. Having said that you can now see that a single shallow ground rod, in most cases doesn't provide adequate protection for towers and shacks. Most lightning protection company's will always provide multiple paths (ground rods) for protection. Usually at opposite ends or all 4 corners of the structure.
Now comes the issue of bonding in your home to meet code. Bonding to ground is used to protect you, as a consumer, from being electrocuted by your appliances. If the neutral fails, grounding is provided as an alternate path for the AC, and provides an extra measure of protection to you. But bonding is not to keep you safe from lightning. You should never have multiple ground bonds on your service entrance for ground loop reasons. Most new construction doesn't allow you to gain access to the service entrance grounding rod, but if you can, then you add additional rods extending from it as long as they all bond at the same point at the service entrance. Also notice, that code is abiguous on the condition of multiple ground rods for the purpose of bonding. They are pretty clear on the first, but the second rod I guess, they assume follows the same as the 1st.
Your ham tower and equipment are a story all together different, and one of the most crucial of all, since you have this magic lightning rod hangin out there with the presense of your tower/antenna mast. A single rod is not considered enough to protect from lightning for the reasons of resistance stated above. Once the initial strike is forming, it will certainly seek another path of smaller resistance, and that can be through anything, including your equipment via the neutral, since it's not protected by breakers, and grounded at every OG&E pole. Knowing one rod, driven down a few feet, isn't enough, you add more rods and bring them all to a common connection point to the tower/shack. Whether chained, or triangulated, the point in which you connect all the stuff should be a one point to help prevent ground loops. How many do I think should be used? No less than 2, and 3 isn't a bad idea. Space them at least 8~10 feet apart and use a minimum of 6 guage copper to connect them all.
If you are using the earth for VLF operations and using earth as a ground plane, then I would use plate material rather than rods.
A single ground rod driven 5' down, on average, will end up with around 110 ohm resistance to true earth. That same rod driven just 5 more feet, will yield about 65 ohm resistance. (this is why i stated before a 10' rod minimum) If you are lucky to live someplace where you have a well for example, the galvanized casing extending below 50 foot will yield a true resistance of around 5 ohm, and that's about as low as it gets until you get to a real deep earth ground over 100 feet deep. Having said that you can now see that a single shallow ground rod, in most cases doesn't provide adequate protection for towers and shacks. Most lightning protection company's will always provide multiple paths (ground rods) for protection. Usually at opposite ends or all 4 corners of the structure.
Now comes the issue of bonding in your home to meet code. Bonding to ground is used to protect you, as a consumer, from being electrocuted by your appliances. If the neutral fails, grounding is provided as an alternate path for the AC, and provides an extra measure of protection to you. But bonding is not to keep you safe from lightning. You should never have multiple ground bonds on your service entrance for ground loop reasons. Most new construction doesn't allow you to gain access to the service entrance grounding rod, but if you can, then you add additional rods extending from it as long as they all bond at the same point at the service entrance. Also notice, that code is abiguous on the condition of multiple ground rods for the purpose of bonding. They are pretty clear on the first, but the second rod I guess, they assume follows the same as the 1st.
Your ham tower and equipment are a story all together different, and one of the most crucial of all, since you have this magic lightning rod hangin out there with the presense of your tower/antenna mast. A single rod is not considered enough to protect from lightning for the reasons of resistance stated above. Once the initial strike is forming, it will certainly seek another path of smaller resistance, and that can be through anything, including your equipment via the neutral, since it's not protected by breakers, and grounded at every OG&E pole. Knowing one rod, driven down a few feet, isn't enough, you add more rods and bring them all to a common connection point to the tower/shack. Whether chained, or triangulated, the point in which you connect all the stuff should be a one point to help prevent ground loops. How many do I think should be used? No less than 2, and 3 isn't a bad idea. Space them at least 8~10 feet apart and use a minimum of 6 guage copper to connect them all.
If you are using the earth for VLF operations and using earth as a ground plane, then I would use plate material rather than rods.
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Thanks so much for the info, I did not know the facts about resistance in regards to depth, I'll be sure to add at least one more rod, I don't know if I can stand pounding 2 more in, that might just kill me before the lightning. I'll tie them together with large gauge wire, and attach all my grounds to it. Thanks again.
Scott
Scott
dbox1
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The real problem with just one rod, is that as the inital strike starts, it saturates the ground around the first rod and the remaining current while not as "hot" as the inital flash, will not be able to go down the first rod, you will need more rods, or it will flash over to the next path of least resistance. It is commonly reported that 7~10 rods may be required and on towers that are used in broadcast (which are extremely high and very susceptable to lighting) can use more as well as sustain repeated strikes with very little or no damage to equipment at all.
I have had a spur of a direct strike hit my antenna back in the 60's and it followed neutral and took out a pole with it. It was not properly grounded and I lost equipment because of it. But I have also had a direct lightning strike at my previous shack (Chickasha) with adequate grounding and my equipment suffered no loss. (4 ground rods in series spaced at 10' intervals)
I have had a spur of a direct strike hit my antenna back in the 60's and it followed neutral and took out a pole with it. It was not properly grounded and I lost equipment because of it. But I have also had a direct lightning strike at my previous shack (Chickasha) with adequate grounding and my equipment suffered no loss. (4 ground rods in series spaced at 10' intervals)
gcgrotz
Member
scott4957 said:
Dbox, you are right on the money there. I see big towers hit all the time with little or no effect. In fact, if you have a big broadcast tower, say 500ft, you can pretty much guarantee that it will get hit, usually several times every season. Also, a general rule seems to be that the more users - cellular, multiple broadcasters, etc - there are on a tower; the more the strike current is divided into multiple paths to ground with less damage to anyone. I hardly ever see damage at sites with 20-30 feedlines, maybe a rare phone line gets blown or something.
Multiple ground rods should be spaced no closer than a distance equal to their length for maximum effectiveness because of that field that will exist during a strike. Closer spacing is wasting a good ground rod, not to mention the effort it takes to pound it in.
It also depends on what you want to accomplish. If it is maximum lightning protection, most wireless companies specify a buried ring around the shelter or pad with at least 6 rods connected with welded connections using #2 solid wire. Of course that is a little impractical for the average homeowner.
I always try to bond my radio grounds to the main electrical ground with a minimum #6 copper wire, and I try to make the antenna grounds physically close to the main ground. I see no problem with a triangle or a straight line, just keep some spacing. Also, using a compound like "copper shield" or a no-ox will help the connections last longer. I have also been known to drill into the rod and tap it for a 1/4-20 bolt for my connection instead of a ground clamp.
Find a book on grounding such as one from Polyphaser Corporation. I think Universal carries it and it is a good investment.
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Well everyone, the LMR400 didn't do the job either. I ordered 100 feet with the ends already installed. Although there is better reception, I'm still not receiving what I was first intending to. Another new problem is that now I just get constant squelch on about 5 frequencies that didn't do it before. I don't suppose I have any other options?? Thanks!
scottie84 said:
65 miles seems like a long way to receive anything. I know I can't receive anything 65 miles away from my location; I doubt I could receive 35 miles away!
Anyway, the only thing I would do at this point is to raise the height of the antenna as high as you can safely get it. Aside from an amplifier, which I don't recommend because they also amplify noise and interference, the only other thing I could see you trying is a directional yagi or log periodic antenna, pointed in the direction of interest.
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