Re: Topband: Fw: Short Bogs
The very act of laying an insulated conductor on the earth lowers its velocity factor. I forget how much, but the reduction in VF for a BOG is significant. This has been discussed at length here; you might find some helpful info in the list archives. 73, Mike www.w0btu.com ___ Stew Perry Topband Distance Challenge coming on December 29th.
Re: Topband: Fw: Short Bogs
If youre building a Beverage/BOG as the thread title indicates, resonance does not matter, it is a nonresonant slow wave antenna. For a resonant antenna up in the air and used for transmitting the insulation adds 3-5% to the electrical length. Carl KM1H - Original Message - From: Bruce k...@myfairpoint.net To: topband@contesting.com Sent: Sunday, December 30, 2012 1:15 PM Subject: Topband: Fw: Short Bogs . If we want to make an antenna electrically longer through cable velocity factor, it can't be done by the insulation slowing the wave inside the shield. 73 Tom In my experience, external insulation (through synthetic covering or frost) lowers the resonant frequency of wire antennas of a given length and height above ground. For example, I typically use 453/F as a starter length for insulated wire dipoles...it's higher for bare wire of the same AWG diameter. It may not be due to velocity factor (not sure of the reason), but it is observable and repeatable. 73, Gary NL7Y I also have had insulated wires of the same AWG diameter resonate lower in frequency than bare ones of the same length. Think we need multiple people experiment: Put up an antenna with covered wire. Measure the frequency, then cut the insulation away (of this same piece), and re-measure the frequency. If we get different results from different people, then we can start looking at the insulation. Is it economy grade made for 60 cycles (600 volts), or is it the good stuff ??? 1. If it is low grade insulation with resistance at 1.8, 3.5 MHZ, then it may be making the wire appear to be fatter. If true, then that would be valid reason. 2. If the insulation is high quality at HF radio frequencies, and IF the frequency changes, then we need to look further 73 Bruce-K1FZ www.qsl.net/k1fz/ ___ Stew Perry Topband Distance Challenge coming on December 29th. - No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1430 / Virus Database: 2637/5497 - Release Date: 12/30/12 ___ Stew Perry Topband Distance Challenge coming on December 29th.
Re: Topband: Fw: Short Bogs
Well. it's not really the quality of the insulation -it's its relative permittivity - relative to the permittivity of free-space (or a vacuum) The dielectric loading of having a layer of higher permittivity material surrounding the wire causes waves propagating down the wire to travel a bit more slowly, thereby increasing its electrical length. Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Bruce Sent: Sunday, December 30, 2012 1:15 PM To: topband@contesting.com Subject: Topband: Fw: Short Bogs . If we want to make an antenna electrically longer through cable velocity factor, it can't be done by the insulation slowing the wave inside the shield. 73 Tom In my experience, external insulation (through synthetic covering or frost) lowers the resonant frequency of wire antennas of a given length and height above ground. For example, I typically use 453/F as a starter length for insulated wire dipoles...it's higher for bare wire of the same AWG diameter. It may not be due to velocity factor (not sure of the reason), but it is observable and repeatable. 73, Gary NL7Y I also have had insulated wires of the same AWG diameter resonate lower in frequency than bare ones of the same length. Think we need multiple people experiment: Put up an antenna with covered wire. Measure the frequency, then cut the insulation away (of this same piece), and re-measure the frequency. If we get different results from different people, then we can start looking at the insulation. Is it economy grade made for 60 cycles (600 volts), or is it the good stuff ??? 1. If it is low grade insulation with resistance at 1.8, 3.5 MHZ, then it may be making the wire appear to be fatter. If true, then that would be valid reason. 2. If the insulation is high quality at HF radio frequencies, and IF the frequency changes, then we need to look further 73 Bruce-K1FZ www.qsl.net/k1fz/ ___ Stew Perry Topband Distance Challenge coming on December 29th. ___ Stew Perry Topband Distance Challenge coming on December 29th.
Re: Topband: Fw: Short Bogs
The characteristics of #12 THHN and such vary all over the map. It is not being made for use at RF. The insulation not only changes the velocity factor, but it also adds loss. This too varies all over the map. Wireman has various wires with UV resistant black PE insulation. That stuff seems to be predictable and stable. I personally don't know of any THHN with PE insulation. YMMV, of course. Neither of the guys at Home Depot and Lowes have any idea what I'm talking about if I mention PE insulation. Apparently plastic is plastic :). 73, Guy On Sun, Dec 30, 2012 at 4:55 PM, Charlie Cunningham charlie-cunning...@nc.rr.com wrote: Well. it's not really the quality of the insulation -it's its relative permittivity - relative to the permittivity of free-space (or a vacuum) The dielectric loading of having a layer of higher permittivity material surrounding the wire causes waves propagating down the wire to travel a bit more slowly, thereby increasing its electrical length. Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Bruce Sent: Sunday, December 30, 2012 1:15 PM To: topband@contesting.com Subject: Topband: Fw: Short Bogs . If we want to make an antenna electrically longer through cable velocity factor, it can't be done by the insulation slowing the wave inside the shield. 73 Tom In my experience, external insulation (through synthetic covering or frost) lowers the resonant frequency of wire antennas of a given length and height above ground. For example, I typically use 453/F as a starter length for insulated wire dipoles...it's higher for bare wire of the same AWG diameter. It may not be due to velocity factor (not sure of the reason), but it is observable and repeatable. 73, Gary NL7Y I also have had insulated wires of the same AWG diameter resonate lower in frequency than bare ones of the same length. Think we need multiple people experiment: Put up an antenna with covered wire. Measure the frequency, then cut the insulation away (of this same piece), and re-measure the frequency. If we get different results from different people, then we can start looking at the insulation. Is it economy grade made for 60 cycles (600 volts), or is it the good stuff ??? 1. If it is low grade insulation with resistance at 1.8, 3.5 MHZ, then it may be making the wire appear to be fatter. If true, then that would be valid reason. 2. If the insulation is high quality at HF radio frequencies, and IF the frequency changes, then we need to look further 73 Bruce-K1FZ www.qsl.net/k1fz/ ___ Stew Perry Topband Distance Challenge coming on December 29th. ___ Stew Perry Topband Distance Challenge coming on December 29th. ___ Stew Perry Topband Distance Challenge coming on December 29th.
Re: Topband: Fw: Short Bogs
On Sun, 2012-12-30 at 20:53 -0500, Guy Olinger K2AV wrote: The characteristics of #12 THHN and such vary all over the map. It is not being made for use at RF. The insulation not only changes the velocity factor, but it also adds loss. This too varies all over the map. Wireman has various wires with UV resistant black PE insulation. That stuff seems to be predictable and stable. I personally don't know of any THHN with PE insulation. YMMV, of course. Neither of the guys at Home Depot and Lowes have any idea what I'm talking about if I mention PE insulation. Apparently plastic is plastic :). 73, Guy I got my THHN at the depot and the guys in there told me I can't have grey wire. Grey wire is not on the agenda for wiring appliances. I hope they don't come here to investigate THHN abuse! I um... didn't use in an appliance. Now lets see about this wireman guy. I'll try Google first. 73, Bill KU8H ___ Stew Perry Topband Distance Challenge coming on December 29th.
