Topband: de n7dd
i am in need of the connections for the Clark Electronics KB-2 beverage antenna switch box. There are 3 wing nut connections on the back of the box and I need to know what the input to each is. Help would be appreciated. Please email direct to pace...@aol.com thanks, larryn7dd _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: de n7dd
Issues of a fixed capacitor as seen in this thread have been a similar problem for a network two-banding an 160m Inv L over FCP. k2av.com has a section on this problem how to do 500 with three 170 pf barrel style HEC caps. The section also has links to HEC reference material on how to derate those capacitors, also links to a number of suppliers. Click on green index button "160+80 on One L/FCP". Do a find on "80M Capacitor". The calculations in the k2av.com text are at 3.5 MHz. The reference material will need to be exercised for 1.8 MHz. The HEC 170's seem fairly plentiful with better prices than other cap values. 73, Guy K2AV On Fri, Jan 10, 2020 at 2:22 PM Mike Waters wrote: > An air variable is exactly what I was thinking, Dave. > > My 160m inverted-L tuner uses just two air variables. I padded the HV > variable with a small 100 pf N1500 (or two) doorknob with no problem. > > I use those same doorknobs as padders in my HB legal-limit amplifier, but > they do cause the tuning to drift. :-( > > I have also seen fixed-value HV vacuum capacitors at hamfests. > > 73 Mike > W0BTU > > On Thu, Jan 9, 2020, 3:15 PM David Olean wrote: > > > > > ... What about an air variable in a wx proof box? > > > > > _ > Searchable Archives: http://www.contesting.com/_topband - Topband > Reflector > _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: de n7dd
An air variable is exactly what I was thinking, Dave. My 160m inverted-L tuner uses just two air variables. I padded the HV variable with a small 100 pf N1500 (or two) doorknob with no problem. I use those same doorknobs as padders in my HB legal-limit amplifier, but they do cause the tuning to drift. :-( I have also seen fixed-value HV vacuum capacitors at hamfests. 73 Mike W0BTU On Thu, Jan 9, 2020, 3:15 PM David Olean wrote: > > ... What about an air variable in a wx proof box? > > _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: de n7dd
"MaxGain Systems has a surplus Jennngs 500pF/20KV cap for about $350" This is the one being used on my T and no problems at 1.5KW. 73, Ted: W1GL --- Original message --- Subject: Re: Topband: de n7dd From: Paul Christensen To: topband Date: Thursday, 09/01/2020 10:25 AM does anyone know of a HV (20KV) capacitor with a value of approximately 500 pf that has a NPO value? Once you get above about 100pF, NP0 options are very limited. Be mindful of the RF current magnitude in the application. Small doorknobs can heat and change in value. In fact, I am dealing with this issue now on a 160m T vertical. My hope was that a paralleled pair of HEC doorknobs would work in a NEMA 4x4x2 enclosure at the base. The fit is fine, but the caps are overheating in FT8/RTTY modes. The fix will involve replacement with a vacuum cap in a larger enclosure. MaxGain Systems has a surplus Jennngs 500pF/20KV cap for about $350. Also consider transmitting mica capacitors. Both will be quite large but will meet your NP0 requirement. Kintronic Labs sells a new 500pF/20KV mica for about $650. These are typically used in AM broadcast installations. In time, you can likely find these at lower prices. The most common used mica will be manufactured by Sangamo. If you're in a rush, be prepared to pay more. Paul, W9AC _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: de n7dd
You can try several paralleled doorknob caps to lower ESR, thus minimize cap heating. In my case, one vacuum variable will replace the HEC doorknob pair. In the alternative, an air variable in a WX-proof enclosure should work fine. You can compute the peak voltage across the cap as well as average current in TLW software that's included in recent editions of the ARRL Antenna Book. Once the peak operating voltage is known, you can obtain an air-variable cap with adequate plate spacing. Polycarbonate tool boxes from Lowes or Home Depot make great weatherproof enclosures when base-feeding an antenna. The side walls are sturdy and many models have a gasketed rubber seal that forms around the lid's perimeter. Paul, W9AC -Original Message- From: David Olean Sent: Thursday, January 9, 2020 4:15 PM To: Paul Christensen ; 'topband' Subject: Re: Topband: de n7dd Hello Paul, I am dealing with the same overheating problem. I need a 475 pf capacitor to shunt feed my 160 tower. I just happened to have a 500 pf 15 KV doorknob almost the size of my fist. It did work for awhile, (several years) but now seems to heat up and the VSWR climbs to 2:1. The unit is definitely heating. I measured about 95 degrees when the outside air temp was 12 F. I tried a single red Sprague plastic doorknob and it starts to run away with 500 watts of power. My next plan was to put four NEC caps together to get 475 pf: 2X 200 PF, 1X 50 PF, and 1X 25 PF. It sounds like maybe this is not going to work either. I guess I need a bigger box and a vacuum capacitor. My amplifier is capable of 1500 watts output. There is not a lot of voltage as it is a 50 ohm input. 6 amps at 300 volts RMS would be 1800 watts at 50 ohms. What about an air variable in a wx proof box? Dave K1WHS On 1/9/2020 3:24 PM, Paul Christensen wrote: >> does anyone know of a HV (20KV) capacitor with a value of >> approximately > 500 pf that has a NPO value? > > Once you get above about 100pF, NP0 options are very limited. Be > mindful of the RF current magnitude in the application. Small > doorknobs can heat and change in value. In fact, I am dealing with this > issue now on a 160m T > vertical. My hope was that a paralleled pair of HEC doorknobs would work > in a NEMA 4x4x2 enclosure at the base. The fit is fine, but the caps > are overheating in FT8/RTTY modes. The fix will involve replacement > with a vacuum cap in a larger enclosure. > > MaxGain Systems has a surplus Jennngs 500pF/20KV cap for about $350. > Also consider transmitting mica capacitors. Both will be quite large > but will meet your NP0 requirement. Kintronic Labs sells a new > 500pF/20KV mica for about $650. These are typically used in AM > broadcast installations. In time, you can likely find these at lower > prices. The most common used mica will be manufactured by Sangamo. > If you're in a rush, be prepared to pay more. > > Paul, W9AC > > _ > Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: de n7dd
Hello Paul, I am dealing with the same overheating problem. I need a 475 pf capacitor to shunt feed my 160 tower. I just happened to have a 500 pf 15 KV doorknob almost the size of my fist. It did work for awhile, (several years) but now seems to heat up and the VSWR climbs to 2:1. The unit is definitely heating. I measured about 95 degrees when the outside air temp was 12 F. I tried a single red Sprague plastic doorknob and it starts to run away with 500 watts of power. My next plan was to put four NEC caps together to get 475 pf: 2X 200 PF, 1X 50 PF, and 1X 25 PF. It sounds like maybe this is not going to work either. I guess I need a bigger box and a vacuum capacitor. My amplifier is capable of 1500 watts output. There is not a lot of voltage as it is a 50 ohm input. 6 amps at 300 volts RMS would be 1800 watts at 50 ohms. What about an air variable in a wx proof box? Dave K1WHS On 1/9/2020 3:24 PM, Paul Christensen wrote: does anyone know of a HV (20KV) capacitor with a value of approximately 500 pf that has a NPO value? Once you get above about 100pF, NP0 options are very limited. Be mindful of the RF current magnitude in the application. Small doorknobs can heat and change in value. In fact, I am dealing with this issue now on a 160m T vertical. My hope was that a paralleled pair of HEC doorknobs would work in a NEMA 4x4x2 enclosure at the base. The fit is fine, but the caps are overheating in FT8/RTTY modes. The fix will involve replacement with a vacuum cap in a larger enclosure. MaxGain Systems has a surplus Jennngs 500pF/20KV cap for about $350. Also consider transmitting mica capacitors. Both will be quite large but will meet your NP0 requirement. Kintronic Labs sells a new 500pF/20KV mica for about $650. These are typically used in AM broadcast installations. In time, you can likely find these at lower prices. The most common used mica will be manufactured by Sangamo. If you're in a rush, be prepared to pay more. Paul, W9AC _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: de n7dd
> does anyone know of a HV (20KV) capacitor with a value of approximately 500 pf that has a NPO value? Once you get above about 100pF, NP0 options are very limited. Be mindful of the RF current magnitude in the application. Small doorknobs can heat and change in value. In fact, I am dealing with this issue now on a 160m T vertical. My hope was that a paralleled pair of HEC doorknobs would work in a NEMA 4x4x2 enclosure at the base. The fit is fine, but the caps are overheating in FT8/RTTY modes. The fix will involve replacement with a vacuum cap in a larger enclosure. MaxGain Systems has a surplus Jennngs 500pF/20KV cap for about $350. Also consider transmitting mica capacitors. Both will be quite large but will meet your NP0 requirement. Kintronic Labs sells a new 500pF/20KV mica for about $650. These are typically used in AM broadcast installations. In time, you can likely find these at lower prices. The most common used mica will be manufactured by Sangamo. If you're in a rush, be prepared to pay more. Paul, W9AC _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: de n7dd
Larry, It will be hard to find. You can find HEC HT75 100 or 200 pF, 15 kV with -750 tempco. You could parallel them to get 500 pF. Alternatively, there are Russian 470 pF, 15 kV, -1500 tempco caps around. GL and 73, George, AA7JV On Thu, 9 Jan 2020 04:35:12 + (UTC) Larry via Topband wrote: does anyone know of a HV (20KV) capacitor with a value of approximately 500 pf that has a NPO value? thanks in advance. larry/n7dd _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: de n7dd
Larry, I understand most modern doorknobs (e.g. HEC's) at or below 170pF are NPO. I think 3 170pF's in parallel may work if you truly need NPO. Matching network or blocking capacitor? Tim N3QE On Wed, Jan 8, 2020 at 11:35 PM Larry via Topband wrote: > does anyone know of a HV (20KV) capacitor with a value of approximately > 500 pf that has a NPO value? > thanks in advance. > larry/n7dd > _ > Searchable Archives: http://www.contesting.com/_topband - Topband > Reflector > _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Topband: de n7dd
does anyone know of a HV (20KV) capacitor with a value of approximately 500 pf that has a NPO value? thanks in advance. larry/n7dd _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Topband: de n7dd
hi all, can anyone tell me if there is common grey line between Kuwait and Tucson, Arizona? especially where SR/SS match. if so what dates? thanks, larry n7dd _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: de n7dd
hi bob (DU7ET), you have done an outstanding job on top band this season. thank you for your devotion. you have given many a new country on 160. have a safe voyage and may you have following seas. see you next season. 73, larry n7dd _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: de n7dd
Conditions were awful from Arizona during the contest weekend. two and three days BEFORE the contest they were excellent to Europe. Guess that "Murphys Law" was in full effect. Too bad. The first night only produced a handful of EU and the second night there were NO EU to be heard. Look at the YouTube video that was sent to me by IK0IOL. You may find it interesting. https://www.youtube.com/watch?v=3mes-Wf7BpU Would like to say it was fun but it was not this year. 73, larry n7dd multi by n7dd and w8tk _ Topband Reflector Archives - http://www.contesting.com/_topband
