Re: Topband: 160 Shunt-Fed Tower Readings
You're quite welcome, Larry! Hope it helped! You're certainly on the right track and doing some good work! FB on the Beverages!! Wish I had real estate for beverages, but I live on a city lot, so I had to resort to terminated receiving loops that, surprisingly, worked quite well and enabled me to hear LOTS that I had been missing on 160. Generally, with my inverted-L and 500-600 watts, if I could hear 'em, I could work 'em! My problem before putting up the KAZ loops was hearing! The terminated loops were great receive antennas on 80, 40 and 30m also. The Beverages should help you a LOT! Have fun and have a Merry Christmas! 73, Charlie, K4OTV -Original Message- From: Larry K4AB [mailto:larry.k...@gmail.com] Sent: Wednesday, December 10, 2014 8:23 PM To: Charlie Cunningham Cc: topband@contesting.com Subject: Re: Topband: 160 Shunt-Fed Tower Readings TU, Charlie on a great explaination for us non-engineers! The topband reflector is a great resource for guys like me trying to understand this band, even after decades in the hobby. And yes, I'm working on the Beverages, as we speak! Thanks, again! 73, Larry K4AB On 12/10/14, Charlie Cunningham wrote: > Hi, again, Larry, > > Well, first of all the shunt feed, being a shorted transmission line, > < 1/4 wavelength in extent, would present an inductive resent at the > feed point that you are correctly cancelling with the 1000 pF series > variable capacitor. You missed ever so slightly and you are showing a > series reactance of j5.6 ohms! Trivially small and negligible!! DON'T > bother trying to improve it!! You would pick up more reactance than > that by just changing frequency a few kilohertz!! It's PERFECT! The > 15893 pF is the equivalent series capacitance that would produce -j5.6 > ohms of capacitive reactance - so the message is that the equivalent > series capacitance is NEGLIGIBILY LARGE!! (LARGE is GOOD!) If you > had measured at a frequency where the reactance cancellatio was exact > and perfect, the driving point impedance would be pure real, with 0 > reactance that would correspond to infinite capacitance or 0 > inductance. > > The real part of your driving point impedance is 59.5 ohms real, > resulting in a VSWR od 1.23:1!! So near a "perfect match" that you > won't improve it significantly, even if you did an AWFUL LOT of work > to make a trivially small change in the tap point of your wire cage!! > The mismatch loss at > 1.23:1 VSWR is essentially 0, and the excess loss in a feedline > operating at 1.23:1 VSWR is essentially 0, and the loss in even a very > long run of coax would be essentially equal to the "flat' loss - that > is: the loss in a "flat" line operated at 1:1 VSWR. > > So, Larry, you've done a GREAT job on your TX antenna. And do keep in > mind that you have 24 feet of boom up there that's top-loading that > 94' of Rohn 25! Just congratulate yourself on a job well done, and > ENJOY!! If you want to worki on topband antennas - work on Beverages > or terminated loop receive antennas to help you HEAR better! > > Great job! Have fun and enjoy! > > BTW - I AM an RF engineer and I have spent q lot of my career > designing and measuring antennas > > 73, > Charlie, K4OTV > > > > -Original Message----- > From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of > Larry K4AB > Sent: Wednesday, December 10, 2014 6:14 PM > To: Charlie Cunningham > Cc: topband@contesting.com > Subject: Re: Topband: 160 Shunt-Fed Tower Readings " line >>Why do you feel a need to improve it? > > Thanks for the response, Charlie! > > I'm concerned about a few things: > > 1) I'm thinking the antenna is electrically too short. After all, the > Yagi at the top really isn't adding too much top loading. And I'm > thinking adding a couple of top loading wires connected to the tower > might be beneficial. > > 2) What exactly is the analyzer telling me when it says C:15893pF? > I'm far from an engineer, but something tells me that's way high. Or > is it? > > 73, > Larry K4AB > > > On 12/10/14, Charlie Cunningham wrote: >> From your description and your measured data, Larry, I don't see how >> you could improve the antenna noticeably! Why do you feel a need to >> improve it? >> I appears to be resonant, well-matched and it appears to have an >> excellent ground image system! I think you might be kidding yourself >> if you change anything! As the old adage says n "If it ain't broke >> -don't fix it"! >> >> 73, >> Charlie, K4OTV >> >> -Original Message- &g
Re: Topband: 160 Shunt-Fed Tower Readings
TU, Charlie on a great explaination for us non-engineers! The topband reflector is a great resource for guys like me trying to understand this band, even after decades in the hobby. And yes, I'm working on the Beverages, as we speak! Thanks, again! 73, Larry K4AB On 12/10/14, Charlie Cunningham wrote: > Hi, again, Larry, > > Well, first of all the shunt feed, being a shorted transmission line, < 1/4 > wavelength in extent, would present an inductive resent at the feed point > that you are correctly cancelling with the 1000 pF series variable > capacitor. You missed ever so slightly and you are showing a series > reactance of j5.6 ohms! Trivially small and negligible!! DON'T bother > trying > to improve it!! You would pick up more reactance than that by just > changing > frequency a few kilohertz!! It's PERFECT! The 15893 pF is the equivalent > series capacitance that would produce -j5.6 ohms of capacitive reactance - > so the message is that the equivalent series capacitance is NEGLIGIBILY > LARGE!! (LARGE is GOOD!) If you had measured at a frequency where the > reactance cancellatio was exact and perfect, the driving point impedance > would be pure real, with 0 reactance that would correspond to infinite > capacitance or 0 inductance. > > The real part of your driving point impedance is 59.5 ohms real, resulting > in a VSWR od 1.23:1!! So near a "perfect match" that you won't improve it > significantly, even if you did an AWFUL LOT of work to make a trivially > small change in the tap point of your wire cage!! The mismatch loss at > 1.23:1 VSWR is essentially 0, and the excess loss in a feedline operating > at 1.23:1 VSWR is essentially 0, and the loss in even a very long run of > coax would be essentially equal to the "flat' loss - that is: the loss in a > "flat" line operated at 1:1 VSWR. > > So, Larry, you've done a GREAT job on your TX antenna. And do keep in mind > that you have 24 feet of boom up there that's top-loading that 94' of Rohn > 25! Just congratulate yourself on a job well done, and ENJOY!! If you want > to worki on topband antennas - work on Beverages or terminated loop receive > antennas to help you HEAR better! > > Great job! Have fun and enjoy! > > BTW - I AM an RF engineer and I have spent q lot of my career designing and > measuring antennas > > 73, > Charlie, K4OTV > > > > -Original Message----- > From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Larry > K4AB > Sent: Wednesday, December 10, 2014 6:14 PM > To: Charlie Cunningham > Cc: topband@contesting.com > Subject: Re: Topband: 160 Shunt-Fed Tower Readings > " line >>Why do you feel a need to improve it? > > Thanks for the response, Charlie! > > I'm concerned about a few things: > > 1) I'm thinking the antenna is electrically too short. After all, the Yagi > at the top really isn't adding too much top loading. And I'm thinking > adding a couple of top loading wires connected to the tower might be > beneficial. > > 2) What exactly is the analyzer telling me when it says C:15893pF? > I'm far from an engineer, but something tells me that's way high. Or is > it? > > 73, > Larry K4AB > > > On 12/10/14, Charlie Cunningham wrote: >> From your description and your measured data, Larry, I don't see how >> you could improve the antenna noticeably! Why do you feel a need to >> improve it? >> I appears to be resonant, well-matched and it appears to have an >> excellent ground image system! I think you might be kidding yourself >> if you change anything! As the old adage says n "If it ain't broke >> -don't fix it"! >> >> 73, >> Charlie, K4OTV >> >> -Original Message- >> From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of >> Larry K4AB >> Sent: Wednesday, December 10, 2014 2:41 PM >> To: topband@contesting.com >> Subject: Topband: 160 Shunt-Fed Tower Readings >> >> The antenna is a 94' Rohn 25, with a Force 12 24'boom Delta 6BA on top. >> Note >> that the elements are insulated from the boom. The base of the tower >> is grounded. >> >> 73 radials are attached to the base ranging in length from 130'-250'. >> 15,000 feet of radials, average length of ~200'. >> >> It is fed through a series 1000pF 10KV Jennings vacuum variable. >> The shunt is a 4 wire cage about 3" in diameter and attached at ~45' >> level. It is spaced about 3' from the tower. >> >> Here are the readings I get from a RigExpert AA-30 at the feedpoint: >> >> 1.830 kHz >> Series model: lZI: 59.7 Ohms >> R:59.5 Ohms >> SWR: 1.23 >> X:5.6 Ohms >> C: 15893 pF >> >> What are these reading telling me,and how can I improve the antenna? >> >> Thanks, in advance! >> >> 73, >> Larry K4AB >> _ >> Topband Reflector Archives - http://www.contesting.com/_topband >> >> > _ > Topband Reflector Archives - http://www.contesting.com/_topband > > _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: 160 Shunt-Fed Tower Readings
N0!! That's the equivalent series capacitance that correspond to -j5.6ohms capacitive reactance! It would be much clearer if the analyzer would present it in that form, since it clearly has determined the sign - since it's indicating an equivalent capacitance. Anyway, I stand by what I wrote you, Larry. I'd leave that TX antenna alone! 59.5 ohms real with 1.23;1 vswr IS JUST FINE! IMO Have Fun! 73, Charlie, K4OTV From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Larry K4AB Sent: Wednesday, December 10, 2014 7:10 PM To: topband@contesting.com Subject: Re: Topband: 160 Shunt-Fed Tower Readings >I would like to know how you can get 15893pf from a 1000pf capacitor. That >has to be a mis-read value there...gary maybe rounded off to 159pf?? That's a great question. Where is the analyzer actually getting that reading? 73, Larry K4AB On 12/10/14, Tom W8JI wrote: >> I'm concerned about a few things: >> >> 1) I'm thinking the antenna is electrically too short. After all, the >> Yagi at the top really isn't adding too much top loading. And I'm >> thinking >> adding a couple of top loading wires connected to the tower >> might be beneficial. > > If you run any power, you will likely start to have problems with arcing at > > the Yagi antenna elements where they cross the boom. > > This is because of the poor insulation, and because of the high voltage at > the boom when on 160. > > The cure for that is to ground the elements to the boom though air coil > inductors. Just five or ten uH would work OK, and not upset the antenna > operation. This would also add 160 top loading. > > >> 2) What exactly is the analyzer telling me when it says C:15893pF? >> I'm far from an engineer, but something tells me that's way high. Or is >> it? > > It is meaningless. It just means you are measuring almost where the antenna > > is resonant. > > 73 Tom > > _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: 160 Shunt-Fed Tower Readings
Hi, again, Larry, Well, first of all the shunt feed, being a shorted transmission line, < 1/4 wavelength in extent, would present an inductive resent at the feed point that you are correctly cancelling with the 1000 pF series variable capacitor. You missed ever so slightly and you are showing a series reactance of j5.6 ohms! Trivially small and negligible!! DON'T bother trying to improve it!! You would pick up more reactance than that by just changing frequency a few kilohertz!! It's PERFECT! The 15893 pF is the equivalent series capacitance that would produce -j5.6 ohms of capacitive reactance - so the message is that the equivalent series capacitance is NEGLIGIBILY LARGE!! (LARGE is GOOD!) If you had measured at a frequency where the reactance cancellatio was exact and perfect, the driving point impedance would be pure real, with 0 reactance that would correspond to infinite capacitance or 0 inductance. The real part of your driving point impedance is 59.5 ohms real, resulting in a VSWR od 1.23:1!! So near a "perfect match" that you won't improve it significantly, even if you did an AWFUL LOT of work to make a trivially small change in the tap point of your wire cage!! The mismatch loss at 1.23:1 VSWR is essentially 0, and the excess loss in a feedline operating at 1.23:1 VSWR is essentially 0, and the loss in even a very long run of coax would be essentially equal to the "flat' loss - that is: the loss in a "flat" line operated at 1:1 VSWR. So, Larry, you've done a GREAT job on your TX antenna. And do keep in mind that you have 24 feet of boom up there that's top-loading that 94' of Rohn 25! Just congratulate yourself on a job well done, and ENJOY!! If you want to worki on topband antennas - work on Beverages or terminated loop receive antennas to help you HEAR better! Great job! Have fun and enjoy! BTW - I AM an RF engineer and I have spent q lot of my career designing and measuring antennas 73, Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Larry K4AB Sent: Wednesday, December 10, 2014 6:14 PM To: Charlie Cunningham Cc: topband@contesting.com Subject: Re: Topband: 160 Shunt-Fed Tower Readings " line >Why do you feel a need to improve it? Thanks for the response, Charlie! I'm concerned about a few things: 1) I'm thinking the antenna is electrically too short. After all, the Yagi at the top really isn't adding too much top loading. And I'm thinking adding a couple of top loading wires connected to the tower might be beneficial. 2) What exactly is the analyzer telling me when it says C:15893pF? I'm far from an engineer, but something tells me that's way high. Or is it? 73, Larry K4AB On 12/10/14, Charlie Cunningham wrote: > From your description and your measured data, Larry, I don't see how > you could improve the antenna noticeably! Why do you feel a need to > improve it? > I appears to be resonant, well-matched and it appears to have an > excellent ground image system! I think you might be kidding yourself > if you change anything! As the old adage says n "If it ain't broke > -don't fix it"! > > 73, > Charlie, K4OTV > > -Original Message- > From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of > Larry K4AB > Sent: Wednesday, December 10, 2014 2:41 PM > To: topband@contesting.com > Subject: Topband: 160 Shunt-Fed Tower Readings > > The antenna is a 94' Rohn 25, with a Force 12 24'boom Delta 6BA on top. > Note > that the elements are insulated from the boom. The base of the tower > is grounded. > > 73 radials are attached to the base ranging in length from 130'-250'. > 15,000 feet of radials, average length of ~200'. > > It is fed through a series 1000pF 10KV Jennings vacuum variable. > The shunt is a 4 wire cage about 3" in diameter and attached at ~45' > level. It is spaced about 3' from the tower. > > Here are the readings I get from a RigExpert AA-30 at the feedpoint: > > 1.830 kHz > Series model: lZI: 59.7 Ohms > R:59.5 Ohms > SWR: 1.23 > X:5.6 Ohms > C: 15893 pF > > What are these reading telling me,and how can I improve the antenna? > > Thanks, in advance! > > 73, > Larry K4AB > _ > Topband Reflector Archives - http://www.contesting.com/_topband > > _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: 160 Shunt-Fed Tower Readings
>I would like to know how you can get 15893pf from a 1000pf capacitor. That >has to be a mis-read value there...gary maybe rounded off to 159pf?? That's a great question. Where is the analyzer actually getting that reading? 73, Larry K4AB On 12/10/14, Tom W8JI wrote: >> I'm concerned about a few things: >> >> 1) I'm thinking the antenna is electrically too short. After all, the >> Yagi at the top really isn't adding too much top loading. And I'm >> thinking >> adding a couple of top loading wires connected to the tower >> might be beneficial. > > If you run any power, you will likely start to have problems with arcing at > > the Yagi antenna elements where they cross the boom. > > This is because of the poor insulation, and because of the high voltage at > the boom when on 160. > > The cure for that is to ground the elements to the boom though air coil > inductors. Just five or ten uH would work OK, and not upset the antenna > operation. This would also add 160 top loading. > > >> 2) What exactly is the analyzer telling me when it says C:15893pF? >> I'm far from an engineer, but something tells me that's way high. Or is >> it? > > It is meaningless. It just means you are measuring almost where the antenna > > is resonant. > > 73 Tom > > _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: 160 Shunt-Fed Tower Readings
I'm concerned about a few things: 1) I'm thinking the antenna is electrically too short. After all, the Yagi at the top really isn't adding too much top loading. And I'm thinking adding a couple of top loading wires connected to the tower might be beneficial. If you run any power, you will likely start to have problems with arcing at the Yagi antenna elements where they cross the boom. This is because of the poor insulation, and because of the high voltage at the boom when on 160. The cure for that is to ground the elements to the boom though air coil inductors. Just five or ten uH would work OK, and not upset the antenna operation. This would also add 160 top loading. 2) What exactly is the analyzer telling me when it says C:15893pF? I'm far from an engineer, but something tells me that's way high. Or is it? It is meaningless. It just means you are measuring almost where the antenna is resonant. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: 160 Shunt-Fed Tower Readings
>Why do you feel a need to improve it? Thanks for the response, Charlie! I'm concerned about a few things: 1) I'm thinking the antenna is electrically too short. After all, the Yagi at the top really isn't adding too much top loading. And I'm thinking adding a couple of top loading wires connected to the tower might be beneficial. 2) What exactly is the analyzer telling me when it says C:15893pF? I'm far from an engineer, but something tells me that's way high. Or is it? 73, Larry K4AB On 12/10/14, Charlie Cunningham wrote: > From your description and your measured data, Larry, I don't see how you > could improve the antenna noticeably! Why do you feel a need to improve > it? > I appears to be resonant, well-matched and it appears to have an > excellent > ground image system! I think you might be kidding yourself if you change > anything! As the old adage says n "If it ain't broke -don't fix it"! > > 73, > Charlie, K4OTV > > -Original Message- > From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Larry > K4AB > Sent: Wednesday, December 10, 2014 2:41 PM > To: topband@contesting.com > Subject: Topband: 160 Shunt-Fed Tower Readings > > The antenna is a 94' Rohn 25, with a Force 12 24'boom Delta 6BA on top. > Note > that the elements are insulated from the boom. The base of the tower is > grounded. > > 73 radials are attached to the base ranging in length from 130'-250'. > 15,000 feet of radials, average length of ~200'. > > It is fed through a series 1000pF 10KV Jennings vacuum variable. > The shunt is a 4 wire cage about 3" in diameter and attached at ~45' > level. It is spaced about 3' from the tower. > > Here are the readings I get from a RigExpert AA-30 at the feedpoint: > > 1.830 kHz > Series model: lZI: 59.7 Ohms > R:59.5 Ohms > SWR: 1.23 > X:5.6 Ohms > C: 15893 pF > > What are these reading telling me,and how can I improve the antenna? > > Thanks, in advance! > > 73, > Larry K4AB > _ > Topband Reflector Archives - http://www.contesting.com/_topband > > _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: 160 Shunt-Fed Tower Readings
>From your description and your measured data, Larry, I don't see how you could improve the antenna noticeably! Why do you feel a need to improve it? I appears to be resonant, well-matched and it appears to have an excellent ground image system! I think you might be kidding yourself if you change anything! As the old adage says n "If it ain't broke -don't fix it"! 73, Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Larry K4AB Sent: Wednesday, December 10, 2014 2:41 PM To: topband@contesting.com Subject: Topband: 160 Shunt-Fed Tower Readings The antenna is a 94' Rohn 25, with a Force 12 24'boom Delta 6BA on top. Note that the elements are insulated from the boom. The base of the tower is grounded. 73 radials are attached to the base ranging in length from 130'-250'. 15,000 feet of radials, average length of ~200'. It is fed through a series 1000pF 10KV Jennings vacuum variable. The shunt is a 4 wire cage about 3" in diameter and attached at ~45' level. It is spaced about 3' from the tower. Here are the readings I get from a RigExpert AA-30 at the feedpoint: 1.830 kHz Series model: lZI: 59.7 Ohms R:59.5 Ohms SWR: 1.23 X:5.6 Ohms C: 15893 pF What are these reading telling me,and how can I improve the antenna? Thanks, in advance! 73, Larry K4AB _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: 160 Shunt-Fed Tower Readings
You may be able to improve the antennas performance by taking the out side insulated elements at the center to the boom with hand wound chokes that pass only below 5 Mhz or lower to provide some top loading without impacting the Force 12 performance. You may also be able to get a better feed impedance by employing a cage of three or four wires taped to the tower itself at or near the sweet point. Usually if the Q is to high the bandwidth will suffer. Having a lower series "C" will make you well better as well. Herb Schoenbohm, KV4FZ On 12/10/2014 3:41 PM, Larry K4AB wrote: The antenna is a 94' Rohn 25, with a Force 12 24'boom Delta 6BA on top. Note that the elements are insulated from the boom. The base of the tower is grounded. 73 radials are attached to the base ranging in length from 130'-250'. 15,000 feet of radials, average length of ~200'. It is fed through a series 1000pF 10KV Jennings vacuum variable. The shunt is a 4 wire cage about 3" in diameter and attached at ~45' level. It is spaced about 3' from the tower. Here are the readings I get from a RigExpert AA-30 at the feedpoint: 1.830 kHz Series model: lZI: 59.7 Ohms R:59.5 Ohms SWR: 1.23 X:5.6 Ohms C: 15893 pF What are these reading telling me,and how can I improve the antenna? Thanks, in advance! 73, Larry K4AB _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: 160 Shunt-Fed Tower Readings
The antenna is a 94' Rohn 25, with a Force 12 24'boom Delta 6BA on top. Note that the elements are insulated from the boom. The base of the tower is grounded. 73 radials are attached to the base ranging in length from 130'-250'. 15,000 feet of radials, average length of ~200'. It is fed through a series 1000pF 10KV Jennings vacuum variable. The shunt is a 4 wire cage about 3" in diameter and attached at ~45' level. It is spaced about 3' from the tower. Here are the readings I get from a RigExpert AA-30 at the feedpoint: 1.830 kHz Series model: lZI: 59.7 Ohms R:59.5 Ohms SWR: 1.23 X:5.6 Ohms C: 15893 pF What are these reading telling me,and how can I improve the antenna? Thanks, in advance! 73, Larry K4AB _ Topband Reflector Archives - http://www.contesting.com/_topband
