Surge / Ground / Lightning
in [Home Built PC]
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From: phil-news-nospam on 6 May 2008 20:27 In alt.engineering.electrical Eric <me(a)nomail.com> wrote: | phil-news-nospam(a)ipal.net wrote: |> In alt.engineering.electrical Eric <me(a)nomail.com> wrote: |> |> | I can attest to vhf/uhf content in lightning strikes. I worked for a |> | communications outfit. We owned and maintained a number of comm sites |> | with towers and antennas. One strike on an antenna destroyed the LDF rf |> | cable all the way to the polyphaser at the bottom of the tower. It had |> | blowouts at about 1 foot intervals all down it's length suggesting a |> | 1/2 wave of about 1 foot or approx 460 mhz. That's one hell of a lot of |> | energy at that frequency.. |> |> Apparently you had some kind of resonance involved. Maybe the antenna itself |> can cause that. Or the output tank circuit in the transmitter. Once you have |> the resonance to narrowband the energy, it would only take a reflection back |> up the line and you turn a propogating surge into standing waves. |> | Pretty much what we determined. Also in another thread I stressed that | the rise time by itself does not determine frequency content. One needs | to know the rate of change, or slew rate, to determine that. A | lightning pulse may have a rise time of 1.2 microseconds but in that | short time the current can rise to thousands of amps, generating a large | amount of vhf,uhf energy. In some plots of voltage rises I've seen in the past, the rise was not at all a smooth one. It went up in steps. Of course if one _thinks_ there will be no VHF or UHF energy and does measurement with a ssytem only capable of lower frequencies, that would smooth out how the rise appears. -- |WARNING: Due to extreme spam, I no longer see any articles originating from | | Google Groups. If you want your postings to be seen by more readers | | you will need to find a different place to post on Usenet. | | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |
From: Eric on 6 May 2008 13:08 phil-news-nospam(a)ipal.net wrote: > In alt.engineering.electrical Eric <me(a)nomail.com> wrote: > > | I can attest to vhf/uhf content in lightning strikes. I worked for a > | communications outfit. We owned and maintained a number of comm sites > | with towers and antennas. One strike on an antenna destroyed the LDF rf > | cable all the way to the polyphaser at the bottom of the tower. It had > | blowouts at about 1 foot intervals all down it's length suggesting a > | 1/2 wave of about 1 foot or approx 460 mhz. That's one hell of a lot of > | energy at that frequency.. > > Apparently you had some kind of resonance involved. Maybe the antenna itself > can cause that. Or the output tank circuit in the transmitter. Once you have > the resonance to narrowband the energy, it would only take a reflection back > up the line and you turn a propogating surge into standing waves. > Pretty much what we determined. Also in another thread I stressed that the rise time by itself does not determine frequency content. One needs to know the rate of change, or slew rate, to determine that. A lightning pulse may have a rise time of 1.2 microseconds but in that short time the current can rise to thousands of amps, generating a large amount of vhf,uhf energy. Eric
From: phil-news-nospam on 4 May 2008 20:20 In alt.engineering.electrical "nobody >" <usenetharvested(a)aol.com> wrote: | phil-news-nospam(a)ipal.net wrote: |> In alt.engineering.electrical Timothy Daniels <SpamBucket(a)nospamplease.biz> wrote: |> |> | Would you please sum up what you believe to be prudent |> | protection (for electronic equipment) from nearby lightning strikes? |> | I'm thinking of both in single-family homes and in condo/apartment |> | buildings. What would you do to protect from in-house (or in-building) |> | surges, such as elevator motors suddenly shorting out, or welding |> | equipment in use? |> |> How much money are you willing to spend? |> | | The only thing I can think of that comes close is to have a heavy | motor/generator set with a HUGE flywheel sitting in the basement. How about driving a generator in the basement with either a heavy fiberglass axle rod driven at some distance by a (sacrificial) motor, or by a fluid that does not conduct electricity through a turbine system, similarly driven by a motor/pump at some distance. -- |WARNING: Due to extreme spam, I no longer see any articles originating from | | Google Groups. If you want your postings to be seen by more readers | | you will need to find a different place to post on Usenet. | | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |
From: phil-news-nospam on 4 May 2008 20:28 In alt.engineering.electrical VWWall <vwall(a)large.invalid> wrote: | phil-news-nospam(a)ipal.net wrote: |> In alt.engineering.electrical VWWall <vwall(a)large.invalid> wrote: |> |> | Actually, a real current will flow until the line's capacitance is |> | charged to the source voltage. When the source is removed, the energy |> | involved will remain until it is leaked off through the inter-wire |> | resistance. If the source is AC, no net energy will "flow", except that |> | lost in the inter-wire resistance. If the line length is long enough at |> | the frequency involved, reflections from the end of an incorrectly |> | terminated transmission line will return to dissipate energy in the |> | source resistance. |> |> That reflection even happens with DC. When the switch closes, you have a |> rising wavefront leading the chargeup of the line. Unless the far end has |> a perfectly matched load, that wavefront will reflect back. This is in |> fact how a lot of very early radio transmissions were tuned, with the |> "switch" being a noisy spark gap, and the "line" being a long wire antenna |> cut to a specific length. You don't even need to have 2 conductors. | | That's because a switch closure is not really DC. Resolve a step | function into a Fourier series, and it has an infinite number of AC | components. In the case of a single wire, you do need to consider EM | theory. Electromagnetic, yes. Electromotive (as someone else suggested), not really. -- |WARNING: Due to extreme spam, I no longer see any articles originating from | | Google Groups. If you want your postings to be seen by more readers | | you will need to find a different place to post on Usenet. | | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |
From: phil-news-nospam on 4 May 2008 12:52
In alt.tv.tech.hdtv Mike Tomlinson <mike(a)jasper.org.uk> wrote: | The same thing said eight times. Part of w_tom's modus operandi - | repeat something enough times and it must be true. That's a common MO of anyone arguing any point where the other party is not accepting it. It happens on all sides. Nothing significant from this bit of "info". Move along. -- |WARNING: Due to extreme spam, I no longer see any articles originating from | | Google Groups. If you want your postings to be seen by more readers | | you will need to find a different place to post on Usenet. | | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) | |