|
15m Vertical Matching help
I've constructed a 1/4-wave 15m vertical from 11' of 3/4" copper tubing
(water type). It's being fed with coax. Much to my frustration, I am unable to get this thing to resonate w/o the use of a transmatch. Any tips, ideas or good plans? 73's -=Jon |
"J. Laub" wrote in message ... I've constructed a 1/4-wave 15m vertical from 11' of 3/4" copper tubing (water type). It's being fed with coax. Much to my frustration, I am unable to get this thing to resonate w/o the use of a transmatch. Any tips, ideas or good plans? 73's -=Jon How long are your radials, and where are the? If you used four 11 foot radials, and drooped them down about 45 degrees, the antenna should look like 50 Ohms somewhere around 21.2 MHz. Is the SWR better at the high or low end of the band, i.e. 21.0 or 21.4 ? Coax is 50 Ohms, right. You might want to look in some charts to see how much effect the fat 3/4 conductor is going to make, as opposed to wire. Tam/WB2TT |
I took a quick look at the ARRL antenna book. Assuming your 3/4 pipe is
actually 1" OD, resonance will be off by quite a bit. About 6 - 7 inches too long. Tam |
"J. Laub" wrote in message ... I've constructed a 1/4-wave 15m vertical from 11' of 3/4" copper tubing (water type). It's being fed with coax. Much to my frustration, I am unable to get this thing to resonate w/o the use of a transmatch. Any tips, ideas or good plans? Is it ground mounted? And what kind of radial are in use (if any). Does resonate in your terms mean that you have a low swr? Mogens |
Hi John,
You didn't say, but I assume that you are feeding it against several quarter wave radials at or near ground level. You will get a feed impedance of less than 50 ohms, so you will need some matching to get a 1:1 swr. You need to concentrate on getting resonance irrespective of swr and then match the anteena feed for minimum swr. This can be done quite simply by putting a capacitor, usually silver mica, across the coax at the feed point, or by inserting a transformer between the coax and the antenna to match something like 10 to 20 ohms to the 50 ohm feed. The capacitor is the easiest to try first, and you will probably need something between 50 and 100 pf. I hope you find this useful, and I wish you success. 73, Jack. G3PVG. "J. Laub" wrote in message ... I've constructed a 1/4-wave 15m vertical from 11' of 3/4" copper tubing (water type). It's being fed with coax. Much to my frustration, I am unable to get this thing to resonate w/o the use of a transmatch. Any tips, ideas or good plans? 73's -=Jon |
Tam/WB2TT wrote:
I took a quick look at the ARRL antenna book. Assuming your 3/4 pipe is actually 1" OD, resonance will be off by quite a bit. About 6 - 7 inches too long. Tam What page did u find that table on? This may explain why it tunes (with transmatch) so much easier on 20 than 15. |
Mogens wrote:
"J. Laub" wrote in message ... I've constructed a 1/4-wave 15m vertical from 11' of 3/4" copper tubing (water type). It's being fed with coax. Much to my frustration, I am unable to get this thing to resonate w/o the use of a transmatch. Any tips, ideas or good plans? Is it ground mounted? And what kind of radial are in use (if any). Does resonate in your terms mean that you have a low swr? Mogens Yes, ground mounted and using 4 5-1/2ft radials. Bad word choice in orig post-poor SWR is the problem. The other poster mentioned my pipe diameter may be an issue. Am looking into that now. |
J. Laub wrote:
Yes, ground mounted and using 4 5-1/2ft radials. Try making one of them 11 feet long and see what happens. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
"J. Laub" wrote in message ... Tam/WB2TT wrote: I took a quick look at the ARRL antenna book. Assuming your 3/4 pipe is actually 1" OD, resonance will be off by quite a bit. About 6 - 7 inches too long. Tam What page did u find that table on? This may explain why it tunes (with transmatch) so much easier on 20 than 15. I have the 19th edition. There is a graph on page 2 - 5. Kind of rough, but I got k=.95 for 1" conductor at 21.3 MHz, which makes the real resonance 21.3x.95=20.235. I did not read the text, but they may give an equation also. If the SWR is lower at 21.0 than 21.4, the radiator is too long. Tam |
"J. Laub" wrote in message ... Mogens wrote: "J. Laub" wrote in message ... I've constructed a 1/4-wave 15m vertical from 11' of 3/4" copper tubing (water type). It's being fed with coax. Much to my frustration, I am unable to get this thing to resonate w/o the use of a transmatch. Any tips, ideas or good plans? Is it ground mounted? And what kind of radial are in use (if any). Does resonate in your terms mean that you have a low swr? Mogens Yes, ground mounted and using 4 5-1/2ft radials. Bad word choice in orig post-poor SWR is the problem. The other poster mentioned my pipe diameter may be an issue. Am looking into that now. First change the radials to 11 feet, and then see what happens. Your SWR at resonance should be 1.5:1. Tam/WB2TT |
"J. Laub" wrote in message
... I've constructed a 1/4-wave 15m vertical from 11' of 3/4" copper tubing (water type). It's being fed with coax. Much to my frustration, I am unable to get this thing to resonate w/o the use of a transmatch. Any tips, ideas or good plans? 73's -=Jon Jon - One of the old ARRL Antenna Handbooks (Green cover - circa 1973) had a 15 meter dipole constructed form 2 piece of 1/2 inch 10' electrical conduit and a small coil wound from 1/8" copper or brass tubing (50 ohm coax fed). The impedance for a vertical will be quite low (less than 50 ohms) what are you using for matching? 15 meters / 4 = 3.75 meters (1/4 wave) ~ 12.3 Feet Greg w9gb |
I'd like to construct a 15m vert that does not require use of my MFJ
Versa Tuner II. Portability. I started over this afternoon on a new vertical using plans from a web site. WIRING: I've suspended an 11'1" #12 wire for 15 inside some pvc. (While I was at it I also suspended a 16'5" #12 wire inside the same piping for 20m.) RADIALS: I've got six underground radials, 2 @ 11' and 4 @ 5-1/2" FEEDER & CONNECT POINT: Using 52ohm RG58 (the thin stuff) to feed into a female coax chassis mount at base of system. I have a small (maybe 4") of line from the center of the chassis mount leading to the connection point bolt/wing nut for each/either wire. This wire is 4" and I suspect this 4" may cause some electrical lengthening right? If it does, I'm over on measurements for each. errr.... Other than this possible lengthening, I cannot think of what else to do. In short, I should probably borrow a dip meter and check for impedance problem? I was reading that I should attach a silver mica capacitor across the wires. Haven't tried this yet as they are still in the mail. I was thinking ahead too when I put this stinker up. I've got a 22-turn base coil sitting there as my next try but that sort of defeats my original simplicity plan. 73's- -=Jon w9gb wrote: "J. Laub" wrote in message ... I've constructed a 1/4-wave 15m vertical from 11' of 3/4" copper tubing (water type). It's being fed with coax. Much to my frustration, I am unable to get this thing to resonate w/o the use of a transmatch. Any tips, ideas or good plans? 73's -=Jon Jon - One of the old ARRL Antenna Handbooks (Green cover - circa 1973) had a 15 meter dipole constructed form 2 piece of 1/2 inch 10' electrical conduit and a small coil wound from 1/8" copper or brass tubing (50 ohm coax fed). The impedance for a vertical will be quite low (less than 50 ohms) what are you using for matching? 15 meters / 4 = 3.75 meters (1/4 wave) ~ 12.3 Feet Greg w9gb |
A simple antenna is resonant at one fundamental frequency.
Get your hands on one of the new cheap antenna analyzers and find that frequency. Improve your counterpoise and adjust the radiator's length to make your wire resonant where you want it to be resonant ("resonant" = a purely resistive load). Then match the antenna's impedance (surely 50 ohms for any 1/4 wave vertical) to your line with a tuner or transformer. BTW tuners suck. Power. 73 H., NQ5H PS I like my BiggIR on 15 as a 3/4 lambda "singer". "J. Laub" wrote in message ... I'd like to construct a 15m vert that does not require use of my MFJ Versa Tuner II. Portability. I started over this afternoon on a new vertical using plans from a web site. WIRING: I've suspended an 11'1" #12 wire for 15 inside some pvc. (While I was at it I also suspended a 16'5" #12 wire inside the same piping for 20m.) RADIALS: I've got six underground radials, 2 @ 11' and 4 @ 5-1/2" FEEDER & CONNECT POINT: Using 52ohm RG58 (the thin stuff) to feed into a female coax chassis mount at base of system. I have a small (maybe 4") of line from the center of the chassis mount leading to the connection point bolt/wing nut for each/either wire. This wire is 4" and I suspect this 4" may cause some electrical lengthening right? If it does, I'm over on measurements for each. errr.... Other than this possible lengthening, I cannot think of what else to do. In short, I should probably borrow a dip meter and check for impedance problem? I was reading that I should attach a silver mica capacitor across the wires. Haven't tried this yet as they are still in the mail. I was thinking ahead too when I put this stinker up. I've got a 22-turn base coil sitting there as my next try but that sort of defeats my original simplicity plan. 73's- -=Jon w9gb wrote: "J. Laub" wrote in message ... I've constructed a 1/4-wave 15m vertical from 11' of 3/4" copper tubing (water type). It's being fed with coax. Much to my frustration, I am unable to get this thing to resonate w/o the use of a transmatch. Any tips, ideas or good plans? 73's -=Jon Jon - One of the old ARRL Antenna Handbooks (Green cover - circa 1973) had a 15 meter dipole constructed form 2 piece of 1/2 inch 10' electrical conduit and a small coil wound from 1/8" copper or brass tubing (50 ohm coax fed). The impedance for a vertical will be quite low (less than 50 ohms) what are you using for matching? 15 meters / 4 = 3.75 meters (1/4 wave) ~ 12.3 Feet Greg w9gb |
"J. Laub" wrote in message ... I'd like to construct a 15m vert that does not require use of my MFJ Versa Tuner II. Portability. I started over this afternoon on a new vertical using plans from a web site. WIRING: I've suspended an 11'1" #12 wire for 15 inside some pvc. (While I was at it I also suspended a 16'5" #12 wire inside the same piping for 20m.) RADIALS: I've got six underground radials, 2 @ 11' and 4 @ 5-1/2" FEEDER & CONNECT POINT: Using 52ohm RG58 (the thin stuff) to feed into a female coax chassis mount at base of system. I have a small (maybe 4") of line from the center of the chassis mount leading to the connection point bolt/wing nut for each/either wire. This wire is 4" and I suspect this 4" may cause some electrical lengthening right? If it does, I'm over on measurements for each. errr.... Other than this possible lengthening, I cannot think of what else to do. In short, I should probably borrow a dip meter and check for impedance problem? I was reading that I should attach a silver mica capacitor across the wires. Haven't tried this yet as they are still in the mail. I was thinking ahead too when I put this stinker up. I've got a 22-turn base coil sitting there as my next try but that sort of defeats my original simplicity plan. 73's- -=Jon You may have to use the base coil to properly match this vertical. A 1/4 wave (with a reflected image - Marconi style) will have a 36 ohm impedance at the feedpoint. http://pages.intnet.mu/ingepru/antenna.htm gb |
w9gb wrote:
"J. Laub" wrote in message ... I'd like to construct a 15m vert that does not require use of my MFJ Versa Tuner II. Portability. I started over this afternoon on a new vertical using plans from a web site. WIRING: I've suspended an 11'1" #12 wire for 15 inside some pvc. (While I was at it I also suspended a 16'5" #12 wire inside the same piping for 20m.) RADIALS: I've got six underground radials, 2 @ 11' and 4 @ 5-1/2" FEEDER & CONNECT POINT: Using 52ohm RG58 (the thin stuff) to feed into a female coax chassis mount at base of system. I have a small (maybe 4") of line from the center of the chassis mount leading to the connection point bolt/wing nut for each/either wire. This wire is 4" and I suspect this 4" may cause some electrical lengthening right? If it does, I'm over on measurements for each. errr.... Other than this possible lengthening, I cannot think of what else to do. In short, I should probably borrow a dip meter and check for impedance problem? I was reading that I should attach a silver mica capacitor across the wires. Haven't tried this yet as they are still in the mail. I was thinking ahead too when I put this stinker up. I've got a 22-turn base coil sitting there as my next try but that sort of defeats my original simplicity plan. 73's- -=Jon You may have to use the base coil to properly match this vertical. A 1/4 wave (with a reflected image - Marconi style) will have a 36 ohm impedance at the feedpoint. http://pages.intnet.mu/ingepru/antenna.htm gb Thanks for the link. What tools would you recommend to check both resonance and impedance with? MFJ seemed awful pricey. |
Jonathan Laub wrote:
What tools would you recommend to check both resonance and impedance with? MFJ seemed awful pricey. If you think so, take a look at Tetronix and HP prices. :-) -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
w9gb wrote:
"J. Laub" wrote in message ... I'd like to construct a 15m vert that does not require use of my MFJ Versa Tuner II. Portability. I started over this afternoon on a new vertical using plans from a web site. WIRING: I've suspended an 11'1" #12 wire for 15 inside some pvc. (While I was at it I also suspended a 16'5" #12 wire inside the same piping for 20m.) RADIALS: I've got six underground radials, 2 @ 11' and 4 @ 5-1/2" FEEDER & CONNECT POINT: Using 52ohm RG58 (the thin stuff) to feed into a female coax chassis mount at base of system. I have a small (maybe 4") of line from the center of the chassis mount leading to the connection point bolt/wing nut for each/either wire. This wire is 4" and I suspect this 4" may cause some electrical lengthening right? If it does, I'm over on measurements for each. errr.... Other than this possible lengthening, I cannot think of what else to do. In short, I should probably borrow a dip meter and check for impedance problem? I was reading that I should attach a silver mica capacitor across the wires. Haven't tried this yet as they are still in the mail. I was thinking ahead too when I put this stinker up. I've got a 22-turn base coil sitting there as my next try but that sort of defeats my original simplicity plan. 73's- -=Jon You may have to use the base coil to properly match this vertical. A 1/4 wave (with a reflected image - Marconi style) will have a 36 ohm impedance at the feedpoint. http://pages.intnet.mu/ingepru/antenna.htm gb Unexpected success. On the 16'5" leg of the antenna by dumb luck of where I place the alligator jumpers found a 1.3 match on 40m! Though this is not the freq where the antenna is supposed to be operated on it does tell me that the coil is working. Once I get my hands on ant analyzer I think it'll live. |
"J. Laub" wrote in message ...
I'd like to construct a 15m vert that does not require use of my MFJ Versa Tuner II. Portability. I started over this afternoon on a new vertical using plans from a web site. WIRING: I've suspended an 11'1" #12 wire for 15 inside some pvc. (While I was at it I also suspended a 16'5" #12 wire inside the same piping for 20m.) That may be half of your problem. #1, the PVC may be effecting the overall length of the wire a bit. #2, if you have another vertical wire right next to it, they will couple and all bets are off. You are not tuning on 15 because with that extra 20m wire next to it, you are now too long I bet. RADIALS: I've got six underground radials, 2 @ 11' and 4 @ 5-1/2" Another comment...Ground mounting a 15 or 20 meter vertical is never going to be that great a performer. You would be much better off with something elevated off the ground. Of course, I realize this may not be possible in your case. FEEDER & CONNECT POINT: Using 52ohm RG58 (the thin stuff) to feed into a female coax chassis mount at base of system. I have a small (maybe 4") of line from the center of the chassis mount leading to the connection point bolt/wing nut for each/either wire. This wire is 4" and I suspect this 4" may cause some electrical lengthening right? Right... If it does, I'm over on measurements for each. errr.... errrr....Yep, that, and the 20m wire, and you are probably way too long... Other than this possible lengthening, I cannot think of what else to do. In short, I should probably borrow a dip meter and check for impedance problem? I was reading that I should attach a silver mica capacitor across the wires. Haven't tried this yet as they are still in the mail. You should not need *anything* to match a 1/4 wave vertical. I know I never have, on any band, or with any ground condition. If it doesn't tune at least under 2:1 SWR, something is wrong... Like running two verticals an inch apart... You also shouldn't need any fancy analysers...I've never owned one myself, and I don't have any trouble. I was thinking ahead too when I put this stinker up. I've got a 22-turn base coil sitting there as my next try but that sort of defeats my original simplicity plan. You shouldn't need it. Just curious...If this is going to be a portable antenna, what are you going to do about radials? Are you going to add ground radials at each location? What a pain.... For a portable 15 m vertical, I would use something like a base fed half wave. Can be mounted anywhere, no radials are needed. Can be elevated, or near the ground, although the higher the better. But, you can get what you have to work, if you ditch the 20m wire that is next to the 15 in the PVC. Or at the least, ditch it until you get the other band tuned. In the real world, if you tried to make such a dual band antenna, it would be best to tune 20 first, and then 15. But I don't really recommend you doing that as it's a PIA to tune. I'm almost sure thats most of the trouble you are having. The PVC could be effecting the overall length also. MK |
This is why I move the wires to the outside of the pvc. I have at least 2"
of separation between wires now. In addition to the ability to tune up on 40m w/o transmatch have noticed that generally speaking it tunes much easier on each band when use the ant tuner. I bet the wires, when strung on the inside, were crossing over or too close to each other. In any event, my next step is to obtain an analyzer and move the alligator clips around on the load coil. Once this beast is functioning, I am going to write up a short how-to for the web site. This pvc actually looks okay in the backyard. -=Jon "Mark Keith" wrote in message om... "J. Laub" wrote in message ... I'd like to construct a 15m vert that does not require use of my MFJ Versa Tuner II. Portability. I started over this afternoon on a new vertical using plans from a web site. WIRING: I've suspended an 11'1" #12 wire for 15 inside some pvc. (While I was at it I also suspended a 16'5" #12 wire inside the same piping for 20m.) That may be half of your problem. #1, the PVC may be effecting the overall length of the wire a bit. #2, if you have another vertical wire right next to it, they will couple and all bets are off. You are not tuning on 15 because with that extra 20m wire next to it, you are now too long I bet. RADIALS: I've got six underground radials, 2 @ 11' and 4 @ 5-1/2" Another comment...Ground mounting a 15 or 20 meter vertical is never going to be that great a performer. You would be much better off with something elevated off the ground. Of course, I realize this may not be possible in your case. FEEDER & CONNECT POINT: Using 52ohm RG58 (the thin stuff) to feed into a female coax chassis mount at base of system. I have a small (maybe 4") of line from the center of the chassis mount leading to the connection point bolt/wing nut for each/either wire. This wire is 4" and I suspect this 4" may cause some electrical lengthening right? Right... If it does, I'm over on measurements for each. errr.... errrr....Yep, that, and the 20m wire, and you are probably way too long... Other than this possible lengthening, I cannot think of what else to do. In short, I should probably borrow a dip meter and check for impedance problem? I was reading that I should attach a silver mica capacitor across the wires. Haven't tried this yet as they are still in the mail. You should not need *anything* to match a 1/4 wave vertical. I know I never have, on any band, or with any ground condition. If it doesn't tune at least under 2:1 SWR, something is wrong... Like running two verticals an inch apart... You also shouldn't need any fancy analysers...I've never owned one myself, and I don't have any trouble. I was thinking ahead too when I put this stinker up. I've got a 22-turn base coil sitting there as my next try but that sort of defeats my original simplicity plan. You shouldn't need it. Just curious...If this is going to be a portable antenna, what are you going to do about radials? Are you going to add ground radials at each location? What a pain.... For a portable 15 m vertical, I would use something like a base fed half wave. Can be mounted anywhere, no radials are needed. Can be elevated, or near the ground, although the higher the better. But, you can get what you have to work, if you ditch the 20m wire that is next to the 15 in the PVC. Or at the least, ditch it until you get the other band tuned. In the real world, if you tried to make such a dual band antenna, it would be best to tune 20 first, and then 15. But I don't really recommend you doing that as it's a PIA to tune. I'm almost sure thats most of the trouble you are having. The PVC could be effecting the overall length also. MK --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.786 / Virus Database: 532 - Release Date: 10/29/04 |
| All times are GMT +1. The time now is 12:08 AM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com