Re: Topband: Compromise vertical loading questions
Thanks for all the input received. In short it seems like lifting the coil would not do much difference. Raising/increasing the angle of the top loading spokes might be the better option. Then of course moving the antenna to the water and improving the radials including some going into the water should make the most improvement. Unfortunately I can not move the antenna much more. Putting it on the beach would be hassle as it had to come down every morning and go up again in the evening. To much activity on the beach in daytime :) I will see what I can do with the top loading spokes. The wind has changed today, it might help or it might not. Thanks again for all the input received on the reflector and in private. 73 from the Maldives de Björn, SM0MDG 8Q7BM SE0X On 29 Jan 2014, at 12:47, Björn SM0MDG bj...@sm0mdg.com wrote: Here are some question for anyone with more tech skills than me; My compromise vertical at 8Q7BM is made of thin wire attached to a DX-Wire 15 meter glass fibre pole. The vertical wire goes all the way up, but as the pole’s top sections are very thin/weak the three top loading spokes (each 12 meter long) are attached at about 13 meter. The antenna has a 1/4 elevate radial towards the water at 2-3 meter height. The whole structure is within 1/4 wave of the water line. The antenna is self resonant at 2.2 MHz and I use a coil wound on a water bottle to bring it down to 1.8. The coil appears to be about 8-10 uH according to online calculators. My questions are; How much I can improve by moving the coil up. What improvement should I expect if center loading at about 7 meter? How about moving the coil all the way up to the top loading spokes? Is it worth the effort? (the pole won’t support much up there). My top loading spokes are sloping more than the recommended angle. According to the ON4UN Low Band book I got the impression that the difference should be minimal when close to salt water. I have tried to slope them less, but easily get in trouble with the weak pole in the wind. And there are pats to the beach every where so options are few. Which one of the two above actions would be the most beneficial? Move the loading coil higher up or rearrange the top loading spokes for a better angle? 73 de Björn, SM0MDG 8Q7BM SE0X _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Compromise vertical loading questions
Hi, Bjorn Well I would expect that moving the loading coil higher would be more beneficial than improving the top loading spokes, as it would move the high current portion of the antenna higher aboveground (the radial) and there would, hopefully, be less loss In the loading coil by having it in a lower current region of the antenna. Improving the top loading spokes might be helpful also, but I think less than moving the loading inductance higher. Of course, since the loading inductance will be in a lower current region of the antenna, it may require a bit more inductance to resonate the antenna. Good luck! Have fun! 73, Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Björn SM0MDG Sent: Wednesday, January 29, 2014 2:48 AM To: topband@contesting.com List Subject: Topband: Compromise vertical loading questions Here are some question for anyone with more tech skills than me; My compromise vertical at 8Q7BM is made of thin wire attached to a DX-Wire 15 meter glass fibre pole. The vertical wire goes all the way up, but as the poles top sections are very thin/weak the three top loading spokes (each 12 meter long) are attached at about 13 meter. The antenna has a 1/4 elevate radial towards the water at 2-3 meter height. The whole structure is within 1/4 wave of the water line. The antenna is self resonant at 2.2 MHz and I use a coil wound on a water bottle to bring it down to 1.8. The coil appears to be about 8-10 uH according to online calculators. My questions are; How much I can improve by moving the coil up. What improvement should I expect if center loading at about 7 meter? How about moving the coil all the way up to the top loading spokes? Is it worth the effort? (the pole wont support much up there). My top loading spokes are sloping more than the recommended angle. According to the ON4UN Low Band book I got the impression that the difference should be minimal when close to salt water. I have tried to slope them less, but easily get in trouble with the weak pole in the wind. And there are pats to the beach every where so options are few. Which one of the two above actions would be the most beneficial? Move the loading coil higher up or rearrange the top loading spokes for a better angle? 73 de Björn, SM0MDG 8Q7BM SE0X _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Compromise vertical loading questions
How much I can improve by moving the coil up. What improvement should I expect if center loading at about 7 meter? How about moving the coil all the way up to the top loading spokes? Is it worth the effort? (the pole won’t support much up there). The coil does not do much at all to current distribution. The spokes pretty much set the current distribution in the antenna, so moving the coil would have almost no effect. My top loading spokes are sloping more than the recommended angle. According to the ON4UN Low Band book I got the impression that the difference should be minimal when close to salt water. I have tried to slope them less, but easily get in trouble with the weak pole in the wind. And there are pats to the beach every where so options are few. The slope of the spokes has virtually the same effect on current distribution over earth as over sea water. The downward slope, in effect, shortens the vertical. This is because when folded down the current into the spokes opposes current in the vertical, subtracting from effective height. The cancelation is a cos function as well as ampere-feet (or ampere-meters), so it rapidly becomes worse at smaller angles. It actually deals with EM field intensity and direction as the fields from the wires and radiator interect at differing angles. Which one of the two above actions would be the most beneficial? Move the loading coil higher up or rearrange the top loading spokes for a better angle? The coil would have almost no effect. The loading wires effect would depend on angle. 73 Tom 73 de Björn, SM0MDG 8Q7BM SE0X _ Topband Reflector Archives - http://www.contesting.com/_topband - No virus found in this message. Checked by AVG - www.avg.com Version: 2014.0.4259 / Virus Database: 3681/7041 - Release Date: 01/28/14 _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Compromise vertical loading questions
Hi, Bjorn Well, I can't argue with JC. With my first ever inverted L for 160, I had similar experiences as did his friend, AA7JV with; submerged radials. In my case, the inverted L was on the dam of a lake behind my house. Not salt water, of course, but the lake had been treated with some amount of copper sulfate to control vegetation growth. I cut perhaps 8 1/4 wave radials of bare 14 gauge stranded wire and weighted the ends with bricks. I then used my canoe to fan the radials over nearly 180 degrees of semi -circle and submerged them in the lake. Like AA7JV, I could see the driving point impedance drop and the VSWR bandwidth of the antenna system decrease as I added radials, reducing the ground losses. One of my earlier QSOs wasn with Jacky, 3B8CF, on Mauritius around my sunset, but I also worked VK3, VK6, JA etc. - all with about 400W. So, if you could move that antenna nearer the water's edge, and submerge that radial in salt water, I expect you might see some improvement. In any case, GL and have fun!! 73, Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of JC N4IS Sent: Wednesday, January 29, 2014 8:39 AM To: 'Björn SM0MDG'; topband@contesting.com Subject: Re: Topband: Compromise vertical loading questions Hi Bjorn How much I can improve by moving the coil up. What improvement should I expect if center loading at about 7 meter? How about moving the coil all the way up to the top loading spokes? Is it worth the effort? (the pole wont support much up there). . Not much, changing the loading would increase the signal 5-10% , it is around 1 db, however if you can get close to salt water and get the radials wet your signal can increase 10db or more. AA7JV can comment better on that, but close to the water is not good, in the water is unbelievable better. George used get several wires tied with a stone and through it into the water, as you increase the number of the wires, you can see the impedance changing. You will may lose some of the radials and they need to be replaced. The radials could be very short and thin but they will work if in the water. I can hear you almost every day with the antenna you are using now. Regards JC N4IS _ 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: Compromise vertical loading questions
One additional point about this that I might not have expressed in enough detail. When a top hat with significant capacitance compared to distributed capaciatnce along the radiator is involved, current tends to become very linear throughout the radiator no matter where any loading inductance is inserted. Bjorn has a particularly extreme example for this, because the SRF of the vertical without any inductor was 2.2 MHz. The antenna is self resonant at 2.2 MHz and I use a coil wound on a water bottle to bring it down to 1.8. The coil appears to be about 8-10 uH according to online calculators. He only has 100 ohms of reactance-cancelling inductance, which further proves his statement that the antenna SRF is 2.2 MHz. While the amount of reactance has no direct bearing on distribution, the fact it is so low means current is pretty much all flowing into the hat wires. Series reactances do not change distribution above the reactance because it is a series system. Shunting capacitances or reactances do. The only way current can change is through an electric field and displacement currents. The significant capacitance, in his case, is the hat. The only two places where significant changes are possible without a significant height increase are: 1.) reducing foldback of the hat 2.) improving the ground system 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Compromise vertical loading questions
On Wed, Jan 29, 2014 at 07:54 AM, Tom W8JI wrote: How much I can improve by moving the coil up. What improvement should I expect if center loading at about 7 meter? How about moving the coil all the way up to the top loading spokes? Is it worth the effort? (the pole won’t support much up there). The coil does not do much at all to current distribution. The spokes pretty much set the current distribution in the antenna, so moving the coil would have almost no effect. 73 Tom Here we go again, Tom spreading misinformation. IT IS important where the coil is placed in the loaded antenna. See the discussion at http://www.k3bu.us/loadingcoils.htm Also, QEX finally started publishing Barry's, W9UCW articles in QEX Jan/Feb 2014 issue describing actual measurements and results of their experiments. Interesting, that Tom admits that there is cos (diminishing) distribution of current along the straight wire - radiator, but when you roll that wire into a coil - magic - current becomes constant across the coiled wire according to Tom. The suggestion about loading coil placement to improve efficiency of (resonant 1/4 wave) antenna (trying to maintain maximum length of radiator with highest current) is to place the coil furthest away from the feed point. The further we go, impedance along the wire increases and number of required turns increase in order to maintain resonance for the length of wire, while having high current portion of the radiator the longest - stronger radiated field. My most effective mobile 160m antenna was fender mounted Hustler mast with loading coil on the top and loading wire going to the short mast on the front bumper of 1972 Buick LeSabre. Yuri, K3BU.us www.MVmanor.com _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Compromise vertical loading questions
The discussion is about the placement of an additional loading coil and its influence while the radiator is already loaded by a capacitance hat. So who spreads misinformation? -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Yuri Blanarovich Here we go again, Tom spreading misinformation. IT IS important where the coil is placed in the loaded antenna. _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Compromise vertical loading questions
Yes no doubt, it seems if a persons personal agenda precedes their ability to read with any comprehension on this reflector so many times, here we go again. The discussion is about the placement of an additional loading coil and its influence while the radiator is already loaded by a capacitance hat. So who spreads misinformation? -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Yuri Blanarovich Here we go again, Tom spreading misinformation. IT IS important where the coil is placed in the loaded antenna. _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Compromise vertical loading questions
Amen Merv, You hit the nail on the head ! ! 73 Price W0RI Yes no doubt, it seems if a persons personal agenda precedes their ability to read with any comprehension on this reflector so many times, here we go again. The discussion is about the placement of an additional loading coil and its influence while the radiator is already loaded by a capacitance hat. So who spreads misinformation? -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Yuri Blanarovich Here we go again, Tom spreading misinformation. IT IS important where the coil is placed in the loaded antenna. _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
