Re: Topband: [TowerTalk] What's heating up ?
The problem with doorknobs capacitor is the dielectric. Class one or NPO does not change capacitance with temperature and has low loss on 1.8 MHz, however the max capacitance you can find is 170pF. Most 500pf doorknobs are N750 and can be used up to 3 amp on 80m, but only 1.5 amp on 160m, with the dissipation of loss in heat and they change capacitance. A simple solution is to parallel several small capacitors NPO. The small capacitor below cost US1.00/each. CERA-MITE - 564CC0GAA302EL620J - Capacitor, ceramic. 62pF 3,000V Capacitor, ceramic. 62pF 3000V. Type: NPO, epoxy coated. Tolerance: 5%. Package: radial disc. Dimensions: 16.9mm D x 3.8mm with 5.8mm lead spacing http://www.electronicsurplus.com/cera-mite-564cc0gaa302el620j-capacitor-cera mic-62pf-3-000v I used 20 in parallel for several years tuning my Folded Unipole with no problems, very stable, just do not let one disc to touch each other. Regards JC N4IS -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Lennart m Sent: Monday, March 13, 2017 1:29 PM To: k2av@gmail.com; 'Gary Schafer' <garyscha...@largeriver.net>; 'Jim Kennedy' <kenned...@cableone.net>; 'Steve London' <n...@arrl.net> Cc: 'Topband' <topband@contesting.com> Subject: Re: Topband: [TowerTalk] What's heating up ? Hi all, There are some good, fixed EU caps that were used in coast to ship radio transmitters. One of the outstanding onses were manufactured by "Rosenthal", also famous for the production of extremely high Q porcelain used in dishes. Otherwise I would follow the advice from Guy. 73 Len SM7BIC -Ursprungligt meddelande- Från: Topband [mailto:topband-boun...@contesting.com] För Guy Olinger Skickat: den 13 mars 2017 17:41 Till: Gary Schafer <garyscha...@largeriver.net>; Jim Kennedy <kenned...@cableone.net>; Steve London <n...@arrl.net> Kopia: Topband <topband@contesting.com> Ämne: Re: Topband: [TowerTalk] What's heating up ? Once you know the problem is the cap, then you need to get really serious about the cap. Caps in RF tuning networks are stressed applications. Decide if you ever want to use it for anything except short and separated cycles, like calling DX. If you get into contests, or ragchew for hours with relatives or friends, you need to beef up. Use your junkbox to tune up the network at 25 watts so you know what the values are, and then go get something serious that will take what your model says is needed for 5 kW, something with dissipation, etc, way in excess of "ideal conditions" predicted by a network model. Do **not** just barely cover 1.5 kW in your calculating. Caps in tuning networks can wind up carrying many times the current specified in models, as you tune away from "center" frequencies, or experience wandering environment, like Z moving with wind, or rain saturated ground, or trying to move up the band by switching a tuner in the shack. If you do QRO, get a vacuum cap or create the value with three or four parallel ceramic doorknobs of the HEC HT50 variety for values of 500 pF or less. The Russian flat doorknobs are probably the best for 3300 or 2200 pf specifications. Most of the pictures have kBap (kVA) numbers on them. If you can't locate **manufacturer** current ratings or Russian kBap numbers, then don't use or don't buy. Invest in caps you KNOW are rated. A contest will find you out if you go cheep, and heat often is run-away, where increasing heat increases resistance. And then you're toast, because the heat has quite possibly changed the value and characteristics of the cap. Prices have been going up on caps, and you may easily spend $100 or more to get fixed caps that will do the job without heating up. Don't ask me how I know this. :>) But I won't ever go cheep on tuner caps again. 73, Guy K2AV On Mon, Mar 13, 2017 at 9:42 AM Steve London <n2ica...@gmail.com> wrote: > The characteristics of the doorknob are unknown. It's a junk box > special, with all of the lettering faded. Found an interesting article > on the web by I0IJ on RF vs. HF capacitors. I'll have to try > experimenting with more caps from the junk box. > > Thanks for the suggestions. > > 73, > Steve, N2IC > > > On 03/12/2017 11:01 PM, Jim Kennedy wrote: > > Garys suggestion is right on. I assume from the the cap you describe > that its a doorknob type. If so be sure it is RF rated and not a HV > type used in power supplies, Total different characteristics. > > > > Jim > > W7ouu > > > > - Original Message - > > From: "Gary Schafer" <garyscha...@largeriver.net> > > To: n...@arrl.net, "Topband" <topband@contesting.com>, > towert...@contesting.com > > Sent: Monday, March 13, 2017 4:00:42 AM > > Subject: Re: [TowerTalk] What's heating up ? > > > > Probably the capacit
Re: Topband: [TowerTalk] What's heating up ?
Hi all, There are some good, fixed EU caps that were used in coast to ship radio transmitters. One of the outstanding onses were manufactured by "Rosenthal", also famous for the production of extremely high Q porcelain used in dishes. Otherwise I would follow the advice from Guy. 73 Len SM7BIC -Ursprungligt meddelande- Från: Topband [mailto:topband-boun...@contesting.com] För Guy Olinger Skickat: den 13 mars 2017 17:41 Till: Gary Schafer <garyscha...@largeriver.net>; Jim Kennedy <kenned...@cableone.net>; Steve London <n...@arrl.net> Kopia: Topband <topband@contesting.com> Ämne: Re: Topband: [TowerTalk] What's heating up ? Once you know the problem is the cap, then you need to get really serious about the cap. Caps in RF tuning networks are stressed applications. Decide if you ever want to use it for anything except short and separated cycles, like calling DX. If you get into contests, or ragchew for hours with relatives or friends, you need to beef up. Use your junkbox to tune up the network at 25 watts so you know what the values are, and then go get something serious that will take what your model says is needed for 5 kW, something with dissipation, etc, way in excess of "ideal conditions" predicted by a network model. Do **not** just barely cover 1.5 kW in your calculating. Caps in tuning networks can wind up carrying many times the current specified in models, as you tune away from "center" frequencies, or experience wandering environment, like Z moving with wind, or rain saturated ground, or trying to move up the band by switching a tuner in the shack. If you do QRO, get a vacuum cap or create the value with three or four parallel ceramic doorknobs of the HEC HT50 variety for values of 500 pF or less. The Russian flat doorknobs are probably the best for 3300 or 2200 pf specifications. Most of the pictures have kBap (kVA) numbers on them. If you can't locate **manufacturer** current ratings or Russian kBap numbers, then don't use or don't buy. Invest in caps you KNOW are rated. A contest will find you out if you go cheep, and heat often is run-away, where increasing heat increases resistance. And then you're toast, because the heat has quite possibly changed the value and characteristics of the cap. Prices have been going up on caps, and you may easily spend $100 or more to get fixed caps that will do the job without heating up. Don't ask me how I know this. :>) But I won't ever go cheep on tuner caps again. 73, Guy K2AV On Mon, Mar 13, 2017 at 9:42 AM Steve London <n2ica...@gmail.com> wrote: > The characteristics of the doorknob are unknown. It's a junk box > special, with all of the lettering faded. Found an interesting article > on the web by I0IJ on RF vs. HF capacitors. I'll have to try > experimenting with more caps from the junk box. > > Thanks for the suggestions. > > 73, > Steve, N2IC > > > On 03/12/2017 11:01 PM, Jim Kennedy wrote: > > Garys suggestion is right on. I assume from the the cap you describe > that its a doorknob type. If so be sure it is RF rated and not a HV > type used in power supplies, Total different characteristics. > > > > Jim > > W7ouu > > > > - Original Message - > > From: "Gary Schafer" <garyscha...@largeriver.net> > > To: n...@arrl.net, "Topband" <topband@contesting.com>, > towert...@contesting.com > > Sent: Monday, March 13, 2017 4:00:42 AM > > Subject: Re: [TowerTalk] What's heating up ? > > > > Probably the capacitor. Try 2 or 3 smaller values in parallel to > > make > your > > 2200pf. Then see if the drift is the same. > > > > Or the coil wire size is too small. > > > > 73 > > Gary K4FMX > > > >> -Original Message- > >> From: TowerTalk [mailto:towertalk-boun...@contesting.com] On Behalf > >> Of Steve London > >> Sent: Sunday, March 12, 2017 10:42 PM > >> To: Topband; towert...@contesting.com > >> Subject: [TowerTalk] What's heating up ? > >> > >> I am experimenting with the N4KG reverse feed method for 160 meters > >> on a tower with a lot of stuff already on it. I like the > >> possibility that elevated radials will be an improvement over my > >> terrible, dry, mountaintop ground characteristics. > >> > >> As I transmit, the SWR creeps up, pretty significantly. Something > >> is clearly getting warm. > >> > >> Possibilities: > >> > >> - I am matching the 160 feedline with an L-network (series L, shunt C). > >> TLW says 7 amps through the capacitor, with 3 watts of dissipation. > >> The capacitor measures 2200 pf, the usual transmitting capacitor, > >> cylindrical, abo
Re: Topband: [TowerTalk] What's heating up ?
For a while I was cooking vacuum variables in my 160 meter Omega match network as well as SO-239's es "N" female connectors... I couldn't figure out what the problem was?. So I checked the line from the shack to the network... It was a 1/4 quarter wavelength line... The problem was due to a voltage/current node at the line termination.. This is a well known phenomenon in electromagnetic theory. I added about 20 feet to the line and the problem disappeared! * /Standing waves/are waves of voltage and current which do not propagate (i.e. they are stationary), but are the result of interference between incident and reflected waves along a transmission line. * A/node/is a point on a standing wave of/minimum/amplitude. * An/antinode/is a point on a standing wave of/maximum/amplitude. * Standing waves can only exist in a transmission line when the terminating impedance does not match the line’s characteristic impedance. In a perfectly terminated line, there are no reflected waves, and therefore no standing waves at all. * At certain frequencies, the nodes and antinodes of standing waves will correlate with the ends of a transmission line, resulting in/resonance/. * The lowest-frequency resonant point on a transmission line is where the line is one quarter-wavelength long. Resonant points exist at every harmonic (integer-multiple) frequency of the fundamental (quarter-wavelength). Since I fixed the problem the network tunes more smoothly. The 1000 pfd vacuum variable to ground is tuned with a reversible 12 VDC, 1 RPM motor. The other 1000 pfd vacuum variable is in series with the OMEGA arm and is only adjustable locally 73, John, W4NU K4JAG, 1959 to 1998 On 3/13/2017 12:41 PM, Guy Olinger wrote: Once you know the problem is the cap, then you need to get really serious about the cap. Caps in RF tuning networks are stressed applications. Decide if you ever want to use it for anything except short and separated cycles, like calling DX. If you get into contests, or ragchew for hours with relatives or friends, you need to beef up. Use your junkbox to tune up the network at 25 watts so you know what the values are, and then go get something serious that will take what your model says is needed for 5 kW, something with dissipation, etc, way in excess of "ideal conditions" predicted by a network model. Do **not** just barely cover 1.5 kW in your calculating. Caps in tuning networks can wind up carrying many times the current specified in models, as you tune away from "center" frequencies, or experience wandering environment, like Z moving with wind, or rain saturated ground, or trying to move up the band by switching a tuner in the shack. If you do QRO, get a vacuum cap or create the value with three or four parallel ceramic doorknobs of the HEC HT50 variety for values of 500 pF or less. The Russian flat doorknobs are probably the best for 3300 or 2200 pf specifications. Most of the pictures have kBap (kVA) numbers on them. If you can't locate **manufacturer** current ratings or Russian kBap numbers, then don't use or don't buy. Invest in caps you KNOW are rated. A contest will find you out if you go cheep, and heat often is run-away, where increasing heat increases resistance. And then you're toast, because the heat has quite possibly changed the value and characteristics of the cap. Prices have been going up on caps, and you may easily spend $100 or more to get fixed caps that will do the job without heating up. Don't ask me how I know this. :>) But I won't ever go cheep on tuner caps again. 73, Guy K2AV On Mon, Mar 13, 2017 at 9:42 AM Steve Londonwrote: The characteristics of the doorknob are unknown. It's a junk box special, with all of the lettering faded. Found an interesting article on the web by I0IJ on RF vs. HF capacitors. I'll have to try experimenting with more caps from the junk box. Thanks for the suggestions. 73, Steve, N2IC On 03/12/2017 11:01 PM, Jim Kennedy wrote: Garys suggestion is right on. I assume from the the cap you describe that its a doorknob type. If so be sure it is RF rated and not a HV type used in power supplies, Total different characteristics. Jim W7ouu - Original Message - From: "Gary Schafer" To: n...@arrl.net, "Topband" , towert...@contesting.com Sent: Monday, March 13, 2017 4:00:42 AM Subject: Re: [TowerTalk] What's heating up ? Probably the capacitor. Try 2 or 3 smaller values in parallel to make your 2200pf. Then see if the drift is the same. Or the coil wire size is too small. 73 Gary K4FMX -Original Message- From: TowerTalk [mailto:towertalk-boun...@contesting.com] On Behalf Of Steve London Sent: Sunday, March 12, 2017 10:42 PM To: Topband; towert...@contesting.com Subject: [TowerTalk] What's heating up ? I am experimenting with the N4KG reverse
Re: Topband: [TowerTalk] What's heating up ?
Once you know the problem is the cap, then you need to get really serious about the cap. Caps in RF tuning networks are stressed applications. Decide if you ever want to use it for anything except short and separated cycles, like calling DX. If you get into contests, or ragchew for hours with relatives or friends, you need to beef up. Use your junkbox to tune up the network at 25 watts so you know what the values are, and then go get something serious that will take what your model says is needed for 5 kW, something with dissipation, etc, way in excess of "ideal conditions" predicted by a network model. Do **not** just barely cover 1.5 kW in your calculating. Caps in tuning networks can wind up carrying many times the current specified in models, as you tune away from "center" frequencies, or experience wandering environment, like Z moving with wind, or rain saturated ground, or trying to move up the band by switching a tuner in the shack. If you do QRO, get a vacuum cap or create the value with three or four parallel ceramic doorknobs of the HEC HT50 variety for values of 500 pF or less. The Russian flat doorknobs are probably the best for 3300 or 2200 pf specifications. Most of the pictures have kBap (kVA) numbers on them. If you can't locate **manufacturer** current ratings or Russian kBap numbers, then don't use or don't buy. Invest in caps you KNOW are rated. A contest will find you out if you go cheep, and heat often is run-away, where increasing heat increases resistance. And then you're toast, because the heat has quite possibly changed the value and characteristics of the cap. Prices have been going up on caps, and you may easily spend $100 or more to get fixed caps that will do the job without heating up. Don't ask me how I know this. :>) But I won't ever go cheep on tuner caps again. 73, Guy K2AV On Mon, Mar 13, 2017 at 9:42 AM Steve Londonwrote: > The characteristics of the doorknob are unknown. It's a junk box > special, with all of the lettering faded. Found an interesting article > on the web by I0IJ on RF vs. HF capacitors. I'll have to try > experimenting with more caps from the junk box. > > Thanks for the suggestions. > > 73, > Steve, N2IC > > > On 03/12/2017 11:01 PM, Jim Kennedy wrote: > > Garys suggestion is right on. I assume from the the cap you describe > that its a doorknob type. If so be sure it is RF rated and not a HV type > used in power supplies, Total different characteristics. > > > > Jim > > W7ouu > > > > - Original Message - > > From: "Gary Schafer" > > To: n...@arrl.net, "Topband" , > towert...@contesting.com > > Sent: Monday, March 13, 2017 4:00:42 AM > > Subject: Re: [TowerTalk] What's heating up ? > > > > Probably the capacitor. Try 2 or 3 smaller values in parallel to make > your > > 2200pf. Then see if the drift is the same. > > > > Or the coil wire size is too small. > > > > 73 > > Gary K4FMX > > > >> -Original Message- > >> From: TowerTalk [mailto:towertalk-boun...@contesting.com] On Behalf Of > >> Steve London > >> Sent: Sunday, March 12, 2017 10:42 PM > >> To: Topband; towert...@contesting.com > >> Subject: [TowerTalk] What's heating up ? > >> > >> I am experimenting with the N4KG reverse feed method for 160 meters on a > >> tower with a lot of stuff already on it. I like the possibility that > >> elevated radials will be an improvement over my terrible, dry, > >> mountaintop ground characteristics. > >> > >> As I transmit, the SWR creeps up, pretty significantly. Something is > >> clearly getting warm. > >> > >> Possibilities: > >> > >> - I am matching the 160 feedline with an L-network (series L, shunt C). > >> TLW says 7 amps through the capacitor, with 3 watts of dissipation. The > >> capacitor measures 2200 pf, the usual transmitting capacitor, > >> cylindrical, about 3/4" in diameter. > >> > >> - The M2 balun feeding the 40 meter beam on the same tower. I monitored > >> the SWR on the 40 meter beam while transmitting on 160. No change in 40 > >> meter SWR. > >> > >> - The M2 balun feeding the KT-36XA on the same tower. I monitored the > >> SWR on the KT-36XA while transmitting on 160. No change in KT-36XA meter > >> SWR. > >> > >> - Gamma match on homebrew 15 meter beam. Gamma match is just a piece of > >> RG-8 dielectric/center conductor inside aluminum tubing. > >> > >> Suggestions on how to troubleshoot this ? Start by disconnecting the > >> feedlines to the baluns ? And once I determine which component is > >> heating, what then ? > >> > >> 73, > >> Steve, N2IC > >> ___ > >> > >> > >> > >> ___ > >> TowerTalk mailing list > >> towert...@contesting.com > >> http://lists.contesting.com/mailman/listinfo/towertalk > > > > ___ > > > > > > > > ___ > > TowerTalk mailing list > >