Topband: Voltage at top of vertical and scaling?
I'd also put RF chokes in series with the DC relay lines, at the base of the vertical antenna to further keep RF off it but also to break it up so the relay line doesn't detune the 80 m. vertical, perhaps with another pair at the shack entrance. All this sure seems like a lot of work which is why I simply hung a wire for 160 inverted L from a 3 foot standoff at the top of my 80 m. mast and did my dual band that way, using the same ground system for both. 73 Rob K5UJ _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Voltage at top of vertical and scaling?
On 4/17/2019 1:40 AM, Ulrich Weiß wrote: Would like to know how to feed the relay at the top of the vertical... regards Uli, DJ2YA Run a single insulated wire from the bottom to the top of vertical. Connect a 0.1 uF bypass capacitor from the wire to the vertical at the top. Connect another bypass capacitor from the wire to the vertical at the bottom. Connect the coil of the relay across the upper bypass capacitor. I like to spiral the wire around the vertical just to hold it in place. You can also use cable ties or electrical tape to hold it. Wind a bifilar choke on a large high permeability (EG #33) toroid. Connect one end of the twisted pair across the bypass capacitor at the bottom of the vertical. The other end of the twisted pair from the toroid should also have a bypass capacitor across it. The conductor in the pair that is connected to the vertical should be connected to ground at the other end. This provides a DC ground for static drain purposes. The other conductor is where you feed in the coil voltage. The reason for this arrangement is that the DC currents due to the relay coil in the bifilar wires are equal and opposite. Therefore, the DC does not excite the toroid and saturate it or magnetize it. It also avoids generating any voltage spikes when the coil voltage is switched off. About 25 turns on the toroid will work (not critical). Rick N6RK _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Voltage at top of vertical and scaling?
Would like to know how to feed the relay at the top of the vertical... regards Uli, DJ2YA -Ursprüngliche Nachricht- From: Richard (Rick) Karlquist Sent: Wednesday, April 17, 2019 2:47 AM To: Jim Miller ; topband@contesting.com Subject: Re: Topband: Voltage at top of vertical and scaling? On 4/16/2019 5:38 AM, Jim Miller wrote: Is there some zener like ionization at the top that limits the voltage? jim ab3cv Supposedly, if you run a kW to a mobile whip on 80 meters, and the whip has only a 1/4 inch metal ball on the top, you can get corona discharge, like a Tesla coil. I have seen this problem fixed by adding a copper toilet float ball atop the whip. Air has a known electric field for breakdown, but it is a complicated problem to calculate voltage by integrating the electric field from the tip of the vertical to "infinity". If interested in the details, see articles on Telsa coils. A quarter wave vertical would have MUCH less voltage on top, of course. If it's still too high, it is easily reduced by adding a top hat. I have a relay at the top of my 80 meter vertical. As described in my QST article, I increased the spacing of the contacts to 1/2 inch. I have never had any trouble with this arrangement even at 1500W. Nor have any readers of the article reported to me that their relays arc'ed over. It is far easier to simply overkill the voltage problem rather than attempt to determine exactly how much voltage is generated. Rick N6RK _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Voltage at top of vertical and scaling?
When I was KA1DQG and in an apartment in Bridgeport, CT & not allowed to have antennas... I had two Hustler mobile sections I used opposed, as a short dipole on 80M that was on the carpet floor. Rig was a Kenwood 820S & the amp was a SB-221. I am here to say I smelled the smoke before I saw the two large burnt areas at each of the ball ends where the corona ripped the carpet a pair of new ones. Luckily there was some unused carpet in the basement & I did the equivalent of a hair plug transfer and all was well. Corona at the ball end? Oh ya... 73, Gary KA1J > On 4/16/2019 5:38 AM, Jim Miller wrote: > > > Is there some zener like ionization at the top that limits the > > voltage? > > > > > jim ab3cv > > Supposedly, if you run a kW to a mobile whip on 80 meters, and the > whip has only a 1/4 inch metal ball on the top, you can get corona > discharge, like a Tesla coil. I have seen this problem fixed by > adding a copper toilet float ball atop the whip. Air has a known > electric field for breakdown, but it is a complicated problem to > calculate voltage by integrating the electric field from the tip of > the vertical to "infinity". If interested in the details, see > articles on Telsa coils. > > A quarter wave vertical would have MUCH less voltage on top, > of course. If it's still too high, it is easily reduced by > adding a top hat. > > I have a relay at the top of my 80 meter vertical. As > described in my QST article, I increased the spacing of > the contacts to 1/2 inch. I have never had any trouble > with this arrangement even at 1500W. Nor have any readers > of the article reported to me that their relays arc'ed over. > > It is far easier to simply overkill the voltage problem > rather than attempt to determine exactly how much voltage > is generated. > > Rick N6RK > _ > Searchable Archives: http://www.contesting.com/_topband - Topband > Reflector > _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Voltage at top of vertical and scaling?
On 4/16/2019 5:38 AM, Jim Miller wrote: Is there some zener like ionization at the top that limits the voltage? jim ab3cv Supposedly, if you run a kW to a mobile whip on 80 meters, and the whip has only a 1/4 inch metal ball on the top, you can get corona discharge, like a Tesla coil. I have seen this problem fixed by adding a copper toilet float ball atop the whip. Air has a known electric field for breakdown, but it is a complicated problem to calculate voltage by integrating the electric field from the tip of the vertical to "infinity". If interested in the details, see articles on Telsa coils. A quarter wave vertical would have MUCH less voltage on top, of course. If it's still too high, it is easily reduced by adding a top hat. I have a relay at the top of my 80 meter vertical. As described in my QST article, I increased the spacing of the contacts to 1/2 inch. I have never had any trouble with this arrangement even at 1500W. Nor have any readers of the article reported to me that their relays arc'ed over. It is far easier to simply overkill the voltage problem rather than attempt to determine exactly how much voltage is generated. Rick N6RK _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Voltage at top of vertical and scaling?
I used a W1W relay at the top of mine for years without incident. 73/jeff/ac0c alpha-charlie-zero-charlie www.ac0c.com On 4/16/19 7:22 PM, Jim Miller wrote: Thanks all for your help on this. It sounds like my 15Kv relay at 53ft on the 68ft vertical is safe. It's never hot switched and provides connection to a 160 "tail" to give me my inverted L there. Best I can do on my limited size, no tree property. 73 jim ab3cv On Tue, Apr 16, 2019 at 7:52 PM HP wrote: Just for grins - did a EZNEC free space - perfect ground - with 80 m vertical of #12 wire resonant at 3.55 mhz then put another #12 quarter wave resonant wire at right angles to the top thru 1 megohm -1500 watts in to the vert (says its 36.42 + j 0 at source ) says there is 3042 volts at angle -92.56 deg across the 1 meg resistor . If go to 10 megs it says 3051 at -93.6 deg and base goes to 36.23 +J 0.02 at 10K its says 1245 v at -29.7 deg and base goes to 41.62 + J 8.2 FWIW and grins -- Hank K7HP - On Apr 16, 2019, at 6:38 AM, Jim Miller wrote: Is there any data on what the voltage might be at the top of a full size 80m vertical at 1500w input? Is there some zener like ionization at the top that limits the voltage? If so is there a way to estimate the voltage at lower points along the vertical? I assume the scaling wouldn't be linear since starting at the bottom on 36 ohms (sorta) and going to "infinity" at the top would preclude that. Thanks jim ab3cv _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Voltage at top of vertical and scaling?
Thanks all for your help on this. It sounds like my 15Kv relay at 53ft on the 68ft vertical is safe. It's never hot switched and provides connection to a 160 "tail" to give me my inverted L there. Best I can do on my limited size, no tree property. 73 jim ab3cv On Tue, Apr 16, 2019 at 7:52 PM HP wrote: > Just for grins - did a EZNEC free space - perfect ground - with 80 m > vertical of #12 wire resonant at 3.55 mhz > then put another #12 quarter wave resonant wire at right angles to the top > thru 1 megohm -1500 watts in to the vert > (says its 36.42 + j 0 at source ) says there is 3042 volts at angle -92.56 > deg across the 1 meg resistor . > > If go to 10 megs it says 3051 at -93.6 deg and base goes to 36.23 +J 0.02 > > at 10K its says 1245 v at -29.7 deg and base goes to 41.62 + J 8.2 > > FWIW and grins -- > > Hank K7HP > > - On Apr 16, 2019, at 6:38 AM, Jim Miller wrote: > > Is there any data on what the voltage might be at the top of a full size > 80m vertical at 1500w input? > > Is there some zener like ionization at the top that limits the voltage? > > If so is there a way to estimate the voltage at lower points along the > vertical? I assume the scaling wouldn't be linear since starting at the > bottom on 36 ohms (sorta) and going to "infinity" at the top would preclude > that. > > Thanks > > jim ab3cv > _ > Searchable Archives: http://www.contesting.com/_topband - Topband > Reflector > > _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Voltage at top of vertical and scaling?
Is this an intellectual exercise or Jim do you want to do something at the top of this vert - like hang a vac relay there to engage some 160m top hat cap loading wires? 73/jeff/ac0c alpha-charlie-zero-charlie www.ac0c.com On 4/16/19 6:52 PM, HP wrote: Just for grins - did a EZNEC free space - perfect ground - with 80 m vertical of #12 wire resonant at 3.55 mhz then put another #12 quarter wave resonant wire at right angles to the top thru 1 megohm -1500 watts in to the vert (says its 36.42 + j 0 at source ) says there is 3042 volts at angle -92.56 deg across the 1 meg resistor . If go to 10 megs it says 3051 at -93.6 deg and base goes to 36.23 +J 0.02 at 10K its says 1245 v at -29.7 deg and base goes to 41.62 + J 8.2 FWIW and grins -- Hank K7HP - On Apr 16, 2019, at 6:38 AM, Jim Miller wrote: | Is there any data on what the voltage might be at the top of a full size | 80m vertical at 1500w input? | Is there some zener like ionization at the top that limits the voltage? | If so is there a way to estimate the voltage at lower points along the | vertical? I assume the scaling wouldn't be linear since starting at the | bottom on 36 ohms (sorta) and going to "infinity" at the top would preclude | that. | Thanks | jim ab3cv | _ | Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Voltage at top of vertical and scaling?
Just for grins - did a EZNEC free space - perfect ground - with 80 m vertical of #12 wire resonant at 3.55 mhz then put another #12 quarter wave resonant wire at right angles to the top thru 1 megohm -1500 watts in to the vert (says its 36.42 + j 0 at source ) says there is 3042 volts at angle -92.56 deg across the 1 meg resistor . If go to 10 megs it says 3051 at -93.6 deg and base goes to 36.23 +J 0.02 at 10K its says 1245 v at -29.7 deg and base goes to 41.62 + J 8.2 FWIW and grins -- Hank K7HP - On Apr 16, 2019, at 6:38 AM, Jim Miller wrote: | Is there any data on what the voltage might be at the top of a full size | 80m vertical at 1500w input? | Is there some zener like ionization at the top that limits the voltage? | If so is there a way to estimate the voltage at lower points along the | vertical? I assume the scaling wouldn't be linear since starting at the | bottom on 36 ohms (sorta) and going to "infinity" at the top would preclude | that. | Thanks | jim ab3cv | _ | Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Voltage at top of vertical and scaling?
Hi Jim, Let me take a crack at this based on some online reading I just did, and the examples I found were based on treating the antenna as a transmission line (W8JI as well as others treat it this way). I would estimate the voltage at the tip of 1/4 wave vertical running 1500 watts to be 3437 Vrms = 4861 Vpeak. This is just an estimate using some general assumptions. Full Details: The above assumes the feedpoint impedance is 35 ohms, and that the characteristic impedance of a single wire vertical acting as a transmission line is considered to be between 400 to 650 ohms (I used the average value of 525 ohms). Using 525 ohms as the characteristic impedance of the single wire vertical transmission line, this would translate into an impedance at the tip of the 1/4 wave wire to be 7875 ohms which appears to fall into the range of expected tip of antenna impedance values stated online (easy to transform the feedpoint impedance to the tip of the antenna since we are dealing with a 1/4 wavelength but you have to take a leap of faith that the characteristic impedance of the single wire antenna acting as a transmission line is 525 ohms). If you then treat the single wire vertical as a lossless transmission line, the voltage at the tip of the antenna calculates to be 3437 Vrms (4861 Volts Peak) when running 1500 watts. The online examples I saw were lacking a lot of detail, and some included some obvious errors. Therefore I had to take the best of each example to come up with my above approximation (assuming the online examples were on the right track). I hope others will step in and correct me if they feel I have not interpreted things correctly. I'm probably sticking my neck way out on this one :) 73, Don (wd8dsb) On Tue, Apr 16, 2019 at 8:38 AM Jim Miller wrote: > Is there any data on what the voltage might be at the top of a full size > 80m vertical at 1500w input? > > Is there some zener like ionization at the top that limits the voltage? > > If so is there a way to estimate the voltage at lower points along the > vertical? I assume the scaling wouldn't be linear since starting at the > bottom on 36 ohms (sorta) and going to "infinity" at the top would preclude > that. > > Thanks > > jim ab3cv > _ > Searchable Archives: http://www.contesting.com/_topband - Topband > Reflector > _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Topband: Voltage at top of vertical and scaling?
Is there any data on what the voltage might be at the top of a full size 80m vertical at 1500w input? Is there some zener like ionization at the top that limits the voltage? If so is there a way to estimate the voltage at lower points along the vertical? I assume the scaling wouldn't be linear since starting at the bottom on 36 ohms (sorta) and going to "infinity" at the top would preclude that. Thanks jim ab3cv _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
