Return-Path: Received: from rly-dd10.mx.aol.com (rly-dd10.mail.aol.com [172.19.141.157]) by air-dd10.mail.aol.com (v123.4) with ESMTP id MAILINDD102-ba049e4749729f; Tue, 14 Apr 2009 07:33:58 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by rly-dd10.mx.aol.com (v123.4) with ESMTP id MAILRELAYINDD102-ba049e4749729f; Tue, 14 Apr 2009 07:33:44 -0400 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1Ltgsz-0000LP-2S for rs_out_1@blacksheep.org; Tue, 14 Apr 2009 12:33:05 +0100 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1Ltgsy-0000LG-EC for rsgb_lf_group@blacksheep.org; Tue, 14 Apr 2009 12:33:04 +0100 Received: from blu0-omc1-s38.blu0.hotmail.com ([65.55.116.49]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1Ltgsw-0004nX-M3 for rsgb_lf_group@blacksheep.org; Tue, 14 Apr 2009 12:33:04 +0100 Received: from BLU146-W5 ([65.55.116.7]) by blu0-omc1-s38.blu0.hotmail.com with Microsoft SMTPSVC(6.0.3790.3959); Tue, 14 Apr 2009 04:32:35 -0700 Message-ID: X-Originating-IP: [221.198.51.73] From: Laurence BY3A-KL1X China To: Date: Tue, 14 Apr 2009 03:32:35 -0800 Importance: Normal MIME-Version: 1.0 X-OriginalArrivalTime: 14 Apr 2009 11:32:35.0428 (UTC) FILETIME=[B52A9A40:01C9BCF4] X-Karma: unknown: X-Spam-Score: 0.9 (/) X-Spam-Report: autolearn=disabled,HTML_10_20=0.945,HTML_MESSAGE=0.001 Content-Type: multipart/alternative; boundary="_47fca9e1-f5b6-4240-8f5d-92ed8bacf9c0_" Subject: LF: Arcs and sparks - user beware X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.0 required=5.0 tests=FORGED_HOTMAIL_RCVD, HTML_MESSAGE autolearn=no version=2.63 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-AOL-IP: 193.82.116.20 X-Mailer: Unknown (No Version) --_47fca9e1-f5b6-4240-8f5d-92ed8bacf9c0_ Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable =20 Having seen and been given a few nasty jolts in my formative years - Im now=20= very cautious working on the LF and MF arrays - especially when transmitting= , but my thoughts of static and painful discharges normally relate to larger= (sic) vertrical arrays and similar, I didnt think I would be thrown across=20= the field and have that nasty metallic taste in my mouth again. =20 Heres the scenerio - (Its got a bit of MF in it honest) : - Location about=20= 5000 ft asl Central America - Date - About a month ago. =20 Ive up a commercial wideband dipole at 40 foot and the RG213 is due replacem= ent - I disconnect from the radio end - so the coax in the shack exactly 80m= away is left floating..... I move to the antennae site I dig out the coax f= rom the ground under the antennae which is buried just for a couple of feet=20= (just vegetation over growth) and pull down the coax and antennae, (which by= design is DC grounded via a transformer - I wont call it a Balun/un) I stri= p off the insulation (self amalgamating and pvc tape overlay) -=20 =20 I disconnect the antennae (which is laying mostly on the ground) from the co= ax plug holding the outer of the pl259 - I drop the cable to ground (its dry= ) and sort out the antennae for 5 mins.=20 =20 I then pick up the cable and my hand touches between the inner pin of the PL= 259 and the outer - there is a massive White flash and bang, I see Green, Im= thrown backwards and look like Ive had too much Merlot (again) - Sheri come= s bounding across the field in here Green Wellies (Hunters of course) and pu= lls me up -- " What the......etc?" My first shock for over 30 years in radio= . =20 But what could have caused this - it wasnt stormy - its wasnt that dry eithe= r really and Im in the middle of a field with only the far off steaming and=20= ash visible from the Turrialba volcano. =20 I check the far end and short it to ground using insulated tools - nothing -= I check insulation resistance etc... so Im guessing the inner and its diele= ctric and the capacitive affects of the cable produced a viable storage cap.= Im guess I got a Kv or two, but moreover it had a punch so quite a bit of c= urrent flowed too. =20 Just a warning about old dogs learning the hard way - never presume an open=20= circuit long length of piece of coax - even if its laying on the ground may=20= not have a residual static charge build up between the outer and core. Its a= new one on me. =20 In the Antarctic and Arctic the charges on the outers of coaxs can be quite=20= amusing to watch - I had two RG58s spaced about 6 inches apart hanging/dangl= ing with about a 1m length - as the charge built up on the cables from the p= assing dry snow grains outside (blowing 50 and -50 to boot) - the cables st= arted to oscillate and be attracted to each other gradually gaining momentum= till there was a big flash and band and the coaxs went back to their restin= g position. =20 I did say there would be something relevant to LF/MF in this - one of the co= axs went to a NDB! =20 Last story - that NDB had an intermittent open circuit/high SWR trip and I c= ouldnt figure it out till I went outside and saw an Arctic fox jump from a n= earby piece of blue ice and snap with her jaws onto the coax going up to the= antennae and then her whole body idly swing to and fro for a few secs befor= e letting go and then jumping back onto the ice block and doing it again and= again. Very amusing and no wonder the coax has given a short where the tee= th had push the outer and inner together. New coax required and raised the c= oax off the ice a bit more... =20 Laurence By3a kl1X _________________________________________________________________ Windows Live=99 SkyDrive: Get 25 GB of free online storage. http://windowslive.com/online/skydrive?ocid=3DTXT_TAGLM_WL_skydrive_032009= =3D --_47fca9e1-f5b6-4240-8f5d-92ed8bacf9c0_ Content-Type: text/html; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable  
Having seen and been given a few nasty jolts in my formative years - Im now=20= very cautious working on the LF and MF arrays - especially when transmitting= , but my thoughts of static and painful discharges normally relate to larger= (sic) vertrical arrays and similar, I didnt think I would be thrown across=20= the field and have that nasty metallic taste in my mouth again.
 
Heres the scenerio -  (Its got a bit of MF in it honest) : - Location a= bout 5000 ft asl Central America - Date - About a month ago.
 
Ive up a commercial wideband dipole at 40 foot and the RG213 is due rep= lacement - I disconnect from the radio end - so the coax in the shack exactl= y 80m away is left floating..... I move to the antennae site I dig out the c= oax from the ground under the antennae which is buried just for a couple of=20= feet (just vegetation over growth) and pull down the coax and antennae, (whi= ch by design is DC grounded via a transformer - I wont call it a Balun/un) I= strip off the insulation (self amalgamating and pvc tape overlay) -
 
I disconnect the antennae (which is laying mostly on the ground) from the co= ax plug holding the outer of the pl259 - I drop the cable to ground (its dry= ) and sort out the antennae for 5 mins.
 
I then pick up the cable and my hand touches between the inner pin of t= he PL259 and the outer - there is a massive White flash and bang, I see Gree= n, Im thrown backwards and look like Ive had too much Merlot (again) - Sheri= comes bounding across the field in here Green Wellies (Hunters of course) a= nd pulls me up -- " What the......etc?" My first shock for over 30 years in=20= radio.
 
But what could have caused this - it wasnt stormy - its wasnt that dry eithe= r really and Im in the middle of a field with only the far off steaming and=20= ash visible from the Turrialba volcano.
 
I check the far end and short it to ground using insulated tools - nothing -= I check insulation resistance etc... so Im guessing the inner and its = dielectric and the capacitive affects of the cable produced a viable storage= cap. Im guess I got a Kv or two, but moreover it had a punch so quite a bit= of current flowed too.
 
Just a warning about old dogs learning the hard way - never presume an open=20= circuit long length of piece of coax - even if its laying on the ground may=20= not have a residual static charge build up between the outer and core. Its a= new one on me.
 
In the Antarctic and Arctic the charges on the outers of coaxs can be quite=20= amusing to watch - I had two RG58s spaced about 6 inches apart hanging/= dangling with about a 1m length - as the charge built up on the cables from=20= the passing dry  snow grains outside (blowing 50 and -50 to boot) - the= cables started to oscillate and be attracted to each other gradually gainin= g momentum till there was a big flash and band and the coaxs went back to th= eir resting position.
 
I did say there would be something relevant to LF/MF in this - one= of the coaxs went to a NDB!
 
Last story - that NDB had an intermittent open circuit/high SWR trip and I c= ouldnt figure it out till I went outside and saw an Arctic fox jump fro= m a nearby piece of blue ice and snap with her jaws onto the coax going= up to the antennae and then her whole body idly swing to and fro for a= few secs before letting go and then jumping back onto the ic= e block and doing it again and again. Very amusing and no wonder the co= ax has given  a short where the teeth had push the outer and inner toge= ther. New coax required and raised the coax off the ice a bit more...  
Laurence By3a kl1X

Windows Live=99 SkyDrive: Get 25 GB of fre= e online storage. Check it out. =3D --_47fca9e1-f5b6-4240-8f5d-92ed8bacf9c0_--