SWR bridge diodes
Locked
 
|
Hi,
The other night I left my K2/100 and KAT100 still attached to the antenna, and we must have had a thunderstorm or the like pass through. I had been using the rig before I hit the sack, and everything was fine, but in the morning I got the dreaded "Hi Cur" warning if I tried to transmit anything higher than 10w. Subsequent testing proved the SWR bridge diodes in both the KPA100 *and* the KAT100 had changed from being diodes to short-circuits. A trip to the local (dead loss) Electronics store to get some more 1N1755 diodes produced 1 diode ! ( typical) What's a bloke going to do with the Christmas postal rush in full swing and Elecraft thousands of miles away? In the end I replaced the 4 diodes with common old 1N4148's and everything appears to be working fine......which brings me to the question......why are the 1N5711's used anyway? does their being Shottky diodes make them any better in this application? I did wonder if the slightly larger forward resistance of the 1N4148 might cause a slightly lower VRFDET, but that doesn't seem to be the case. To add to this saga......after finding the diodes being faulty, I had the end of the antenna draped over a certificate on the wall to keep it out of the way. A sudden rain storm went through accompanied by strong winds, and there was a spark jumping across the ends of BNC fitting on the end of the antenna as if it had been connected to a cars spark coil. A grounding switch is now being installed.... I have lost the odd SWR bridge diode in my 40 or so years as an Amateur, but this is the first time I have actually seen why.... (the antenna is a 80/40/20m set of 1/2 waves arranged as inverted "V's" up 13m in the center,and single coax fed.) 73.....Ron ZL1TW -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.432 / Virus Database: 268.15.15/581 - Release Date: 9/12/2006 3:41 p.m. _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
|
|
Ron,
2 reasons for the use of 1N5711 diodes rather than 1N4148 (or even 1N34A) - 1) the 1N5711s have been shown to produce a more consistent voltage over the frequency range than any of the others, and 2) the Shottky design has a low diode drop (the 1N34A does too) which will produce readings that are more correct at low powers (less than 2 watts). With the KPA100 installed, the low power factor may not be a large consideration for you, so the 1N4148s could stay, but if the greater frequency dependency produces a problem, swap back to the 1N5711s. Yes, keep those antennas shorted when not in use and when thunderstorms approach. 73, Don W3FPR > -----Original Message----- > Hi, > The other night I left my K2/100 and KAT100 still attached to the > antenna, and we must have had a thunderstorm or the like pass through. I > had been using the rig before I hit the sack, and everything was > fine, but > in the morning I got the dreaded "Hi Cur" warning if I tried to transmit > anything higher than 10w. > Subsequent testing proved the SWR bridge diodes in both the KPA100 > *and* the KAT100 had changed from being diodes to short-circuits. A trip > to the local (dead loss) Electronics store to get some more 1N1755 diodes > produced 1 diode ! ( typical) > What's a bloke going to do with the Christmas postal rush in full > swing and > Elecraft thousands of miles away? > In the end I replaced the 4 diodes with common old 1N4148's and > everything > appears to be working fine......which brings me to the question......why > are the 1N5711's used anyway? does their being Shottky diodes > make them any > better in this application? > No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.432 / Virus Database: 268.15.15/580 - Release Date: 12/8/2006 12:53 PM _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
|
|
OK Thanks Don and Tom,
QRP below 5w is rarely used here on the K2. I pull the K1 out for those events..... Anyway, I will get a bundle of 1N5711's off Elecraft next time I put an order in just to bring everything up to standard. I'm sure I will need more eventually with the memory I have, even with a disconnect/grounding switch installed ....unless I make it switch automatically when I turn the K2 off [G] 73 ......Ron ZL1TW At 07:53 a.m. 10/12/2006 -0500, you wrote: >Ron, > >2 reasons for the use of 1N5711 diodes rather than 1N4148 (or even 1N34A) - >1) the 1N5711s have been shown to produce a more consistent voltage over the >frequency range than any of the others, and 2) the Shottky design has a low >diode drop (the 1N34A does too) which will produce readings that are more >correct at low powers (less than 2 watts). > >With the KPA100 installed, the low power factor may not be a large >consideration for you, so the 1N4148s could stay, but if the greater >frequency dependency produces a problem, swap back to the 1N5711s. > >Yes, keep those antennas shorted when not in use and when thunderstorms >approach. > >73, >Don W3FPR > > > -----Original Message----- > > > Hi, > > The other night I left my K2/100 and KAT100 still attached to the > > antenna, and we must have had a thunderstorm or the like pass through. I > > had been using the rig before I hit the sack, and everything was > > fine, but > > in the morning I got the dreaded "Hi Cur" warning if I tried to transmit > > anything higher than 10w. > > Subsequent testing proved the SWR bridge diodes in both the KPA100 > > *and* the KAT100 had changed from being diodes to short-circuits. A trip > > to the local (dead loss) Electronics store to get some more 1N1755 diodes > > produced 1 diode ! ( typical) > > What's a bloke going to do with the Christmas postal rush in full > > swing and > > Elecraft thousands of miles away? > > In the end I replaced the 4 diodes with common old 1N4148's and > > everything > > appears to be working fine......which brings me to the question......why > > are the 1N5711's used anyway? does their being Shottky diodes > > make them any > > better in this application? > > >-- >No virus found in this outgoing message. >Checked by AVG Free Edition. >Version: 7.5.432 / Virus Database: 268.15.15/580 - Release Date: 12/8/2006 >12:53 PM > > > >-- >No virus found in this incoming message. >Checked by AVG Free Edition. >Version: 7.5.432 / Virus Database: 268.15.15/581 - Release Date: 9/12/2006 >3:41 p.m. No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.432 / Virus Database: 268.15.15/581 - Release Date: 9/12/2006 3:41 p.m. _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
«
Return to Elecraft
|
1 view|%1 views
| Free forum by Nabble | Edit this page |