I've used my lightning filter for 15-20 years now without losing any electronics connected to the phone line. YMMV. I've made several variations of this filter over the years (due to lightning destroying parts of the filter) and ALL variations have worked. I do have a slow country line and seldom get more than 24000 baud but I have never seen the filter slow it down any and I have looked. Some years we get a lot of lightning and some just a bit. I have had a lot of experience keeping electronics (electronic gate opener, vehicle detector, and other misc items) working out in the weather far from any building. My filter design is probably overdone, but after losing several answering machines and electronic telephones I didn't want to take any more chances. This was before I went on the internet. I build the filter on an open board taped or glued to the concrete wall so I can inspect/test/repair it easily and there is no box to build up heat. Respect lightning, it is bad shit. I also put telephone connectors on the input & outlet of the filter so I have the option of using the filter, bypassing the filter, or removing the filter entirely for testing purposes. Amazingly those tiny jacks seem to survive intact when heavy ZNRs etc downstream disintegrate.
The filter; you start with tip, ring and ground at a point as close to ground as you can get. Real earth ground is IMPORTANT, you should be within 8 feet of earth via a short fat copper cable. If you are in an apartment or cannot get close to ground, do the best you can and good luck. I start with putting some small resistance in series with the tip & ring connections. It doesn't take much, it's just to protect the next stage. I've used 12 volt light bulbs, 1-10 ohm wirewound power resistors, and low value wirewound air core chokes with equal sucess. A fuse would also probably work, these elements all blow out with a lightning strike. Have replacements handy. Next I use a delta connection of plain Radio Shack 120vac ZNR surge supressors. #276-568B 130 vac 70 joules. Don't use anything small. They will blow up when a bad lightning bolt comes down the line. Wire them tip to ground, ring to ground, and tip to ring. I also usually use small high voltage (mica) condensers across each ZNR to short out the really high frequency stuff. These caps will also detonate with a bad strike. Be sure to write down what components you used, there won't be enough left to read after a bad strike. The next stage is another small inductance/resistance stage. It's intention is to hold down the surge to its following stage while the first 2 stages fry in a strike. I usually dig something out of my junkbox; currently I am using a common mode rejection choke. Looks like a small open transformer, resistance less than one ohm. Low voltage light bulbs also work nice, the spiral fillament gives them enough inductance to do the job. I don't calculate these things, I just slap something together and rely on the multiple layers to work. The next stage is another delta stage just like stage 2 described above. It never blows, that's why the filter works. I usually don't bother bypassing the ZNRs with caps in this stage. WHAT DIDN'T WORK; I initially tried to use a delta of 6 25 watt zener diodes carefully chosen to be just above the measured voltages between tip-ring-ground. Bad idea, zener diodes cannot absorb the surges that ZNR varistor surge supressors can. They blew quickly. I also experimented using neon lamps, also chosen to be just above normal ringing voltage. They seemed to work but wore out and blackened very quickly, and I also doubt they could take the high currents required in a strike. Occasionally my phone line shorts out to the (7kv) power line in the 1/2 mile trip thru the woods to my house so current handling is important to me. Nick Committees of Correspondence Web page: http://www.geocities.com/CapitolHill/5357/ - free men own guns, slaves don't -- PCI-PowerMacs is sponsored by <http://lowendmac.com/> and... Small Dog Electronics http://www.smalldog.com | Refurbished Drives | -- Sonnet & PowerLogix Upgrades - start at $169 | & CDRWs on Sale! | Support Low End Mac <http://lowendmac.com/lists/support.html> PCI-PowerMacs list info: <http://lowendmac.com/lists/pci-powermacs.shtml> --> AOL users, remove "mailto:"; Send list messages to: <mailto:[EMAIL PROTECTED]> To unsubscribe, email: <mailto:[EMAIL PROTECTED]> For digest mode, email: <mailto:[EMAIL PROTECTED]> Subscription questions: <mailto:[EMAIL PROTECTED]> Archive:<http://www.mail-archive.com/pci-powermacs%40mail.maclaunch.com/> Using a Mac? Free email & more at Applelinks! http://www.applelinks.com
