Re: [Elecraft] [K3] Kite antennas and static protection
On 6/14/2010 3:15 AM, Tom W8JI wrote: > The most important thing in this is to always have a dc leak path to earth > on the antenna side of any "T" network or anything else that might add a > series capacitance. (Some lighting suppressors are a bad design with "dc > isolation" by a series capacitor on the center conductor.) We never want > series capacitance that prevents or blocks a bleed-off path to earth. The popular ICE lightning suppressors do have a DC blocking capacitor, but there is a toroidal RF choke to ground (with a DC resistance of about half an ohm) on the antenna side. They also appear to have a drain with a resistance of about 130K on the radio side. -- Vic, K2VCO Fresno CA http://www.qsl.net/k2vco/ __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] [K3] Kite antennas and static protection
The most important thing in this is to always have a dc leak path to earth on the antenna side of any "T" network or anything else that might add a series capacitance. (Some lighting suppressors are a bad design with "dc isolation" by a series capacitor on the center conductor.) We never want series capacitance that prevents or blocks a bleed-off path to earth. >From my measurements here on a 300-foot tall well-insulated tower, the current is microamperes even in inclement weather. The ground path doesn't have to be low resistance to hold the antenna to reasonable voltages. It's the charging of antenna and any feeder or equipment capacitance (like the antenna capacitor in a T network) that is the big problem, because when voltage gradually builds and eventually becomes high enough to arc over, that charged capacitance can dump a lot of current into other equipment. This fast dumping of charge buildup is the major cause of damage to diodes in SWR detectors and directional couplers. In a T network tuner it is the output capacitor that charges and eventually dumps a spike back though the other components. The bleeds on the radio input ports are a great idea for stations with poor or non-existent charge drains on antennas, but won't do anything once an antenna tuner or some other series capacitance is in line. A small high impedance RF choke, or even a 10K to 100K resistor (careful of normal operating voltage and dissipation) is an adequate drain according to measurements I made on a 300-ft very well insulated tower. (Without a drain that tower would charge enough to knock me on my backside in just a very gentle breeze on a nice clear day!) 73 Tom > GW0ETF wrote: >> Does the K3's built-in protection (surge arrestor and bleed resistor on >> each >> rx input) obviate the need for external protection when using a big kite >> antenna? >> >> If it does, and in view of the inevitable advice *to* arrange for a DC >> path >> to earth at receiver input whenever using a kite, I suppose an implied >> question isis the K3 unusual in providing static protection at it's >> inputs? >> >> 73, >> >> Stewart Rolfe, GW0ETF __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] [K3] Kite antennas and static protection
Stewart, Because a kite antenna can develop quite a charge from wind static if nothing else, I would not trust any radio to reduce that charge. Give some thought to the situation where yourself or someone else could touch the wire - a DC path is not only for the radio protection, it is for people and pet protection as well. Besides, you do not want the COR protective devices in the K3 to fire for any purpose - consider them as you would a fire insurance policy - something you hope you never have to use. 73, Don W3FPR GW0ETF wrote: > Does the K3's built-in protection (surge arrestor and bleed resistor on each > rx input) obviate the need for external protection when using a big kite > antenna? > > If it does, and in view of the inevitable advice *to* arrange for a DC path > to earth at receiver input whenever using a kite, I suppose an implied > question isis the K3 unusual in providing static protection at it's > inputs? > > 73, > > Stewart Rolfe, GW0ETF > __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] [K3] Kite antennas and static protection
- Original Message - From: GW0ETF To: elecraft@mailman.qth.net Sent: Monday, June 14, 2010 1:20 AM Subject: [Elecraft] [K3] Kite antennas and static protection Does the K3's built-in protection (surge arrestor and bleed resistor on each rx input) obviate the need for external protection when using a big kite antenna? If it does, and in view of the inevitable advice *to* arrange for a DC path to earth at receiver input whenever using a kite, I suppose an implied question isis the K3 unusual in providing static protection at it's inputs? 73, Stewart Rolfe, GW0ETF -- G'day Stewart, I for one would never use a rig on its own, I would (and do) always use a dc ground on my kite antennas. That goes for Elecraft or any other brand of radio, no matter how much 'protection' they might have built in. Jeff Cochrane VK4BOF Innisfail QLD Australia Elecraft K3 #4257 __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
