|
Johnson Matchbox on 30 Mtrs?
I am using a Johnson KW Matchbox antenna tuner with a 130 foot long, 30
foot high dipole fed with about 40 feet of ladder (window) line. It works well on all bands including the WARC bands *except* for 30 meters. (it doesn't make any difference if the band switch is on 20 or 40--it will not tune 30 in either case). The question is, does anyone have any tips/suggestions/modifications to make this also operate on 30 meters? By the way, modifying the antenna is not an option--lucky to have it up at all with city and subdivision restrictions. Maybe could add extra ladder line in the basement shack, but would have to loop it around the basement ceiling??? 73, Carter K8VT |
Carter,
Have you tried the other band selections? 'Doc |
There are several options you can take..
Install a new set of taps on the coil for 30 meters (probably the best way to go) Add additional caps across the matching cap Add a variable cap on the input link Install taps on the input link Add a variable cap across the output where the twin lead is attached Except for the input link, lift all other cap ties to ground And you can add another tap on the matching capacitor..on the other side of the random wire tap and use these two together for the twin lead. "Carter Grabarczyk" wrote in message m... I am using a Johnson KW Matchbox antenna tuner with a 130 foot long, 30 foot high dipole fed with about 40 feet of ladder (window) line. It works well on all bands including the WARC bands *except* for 30 meters. (it doesn't make any difference if the band switch is on 20 or 40--it will not tune 30 in either case). The question is, does anyone have any tips/suggestions/modifications to make this also operate on 30 meters? By the way, modifying the antenna is not an option--lucky to have it up at all with city and subdivision restrictions. Maybe could add extra ladder line in the basement shack, but would have to loop it around the basement ceiling??? 73, Carter K8VT |
Carter Grabarczyk wrote: I am using a Johnson KW Matchbox antenna tuner with a 130 foot long, 30 foot high dipole fed with about 40 feet of ladder (window) line. It works well on all bands including the WARC bands *except* for 30 meters. (it doesn't make any difference if the band switch is on 20 or 40--it will not tune 30 in either case). The question is, does anyone have any tips/suggestions/modifications to make this also operate on 30 meters? By the way, modifying the antenna is not an option--lucky to have it up at all with city and subdivision restrictions. Maybe could add extra ladder line in the basement shack, but would have to loop it around the basement ceiling??? 73, Carter K8VT Hi Carter, That's a very high impedance you are trying to match on 30m. Looks like the only options you have are modifying the Matchbox or changing the Feedline lenght. Another poster gave some good ideas on modifying your tuner. If you don't want to modify the tuner, then feed the 130' dipole with 11.3' of 450 ohm line and then go 50 ohm coax to the transmitter. Don't need a tuner. Or if you could lenghten to ladder line to 56' that would give a good 50 ohm match, no tuner needed. This is a guess but I think you would need to lenghten or shorten the ladder line 8-10' to get within range of the Matchbox. Gary N4AST |
If you put a 500pF cap in a box, with a couple of SO239 connectors so that
it's in series with the coax to the tuner, you'll probably be able to tune 30M. Adjusting feedline length is another approach. Hth. 73, Dave, N3HE Cincinnati OH "Carter Grabarczyk" wrote in message m... I am using a Johnson KW Matchbox antenna tuner with a 130 foot long, 30 foot high dipole fed with about 40 feet of ladder (window) line. It works well on all bands including the WARC bands *except* for 30 meters. |
On Thu, 17 Mar 2005 01:10:07 GMT, Carter Grabarczyk
wrote: I am using a Johnson KW Matchbox antenna tuner with a 130 foot long, 30 foot high dipole fed with about 40 feet of ladder (window) line. It works well on all bands including the WARC bands *except* for 30 meters. (it doesn't make any difference if the band switch is on 20 or 40--it will not tune 30 in either case). The question is, does anyone have any tips/suggestions/modifications to make this also operate on 30 meters? By the way, modifying the antenna is not an option--lucky to have it up at all with city and subdivision restrictions. Maybe could add extra ladder line in the basement shack, but would have to loop it around the basement ceiling??? 73, Carter K8VT I also have a 130 foot low dipole fed with ladderline. My feedline is 47 feet, going to an mfj tuner. I can tune 30 meters easily. You might try adjusting the length of your feedline. You're using a different tuner, so what you do may not match what I do, but playing with the length of your feedline may help. Then again, it may not :-( Guess that's why they call it amateur radio... bob k5qwg |
"'Doc" wrote in message om... Carter, Have you tried the other band selections? 'Doc For what it's worth department; I use my LP version of the Johnson Matchbox in conjunction with a 40 meter Delta loop feed with ladder-line. I tune it on 30 with the tap in the 20 meter position. I also tune this same loop on the AF MARS frequency, way up the band from the top of 75 ham band by 500 khz. It tunes it down to 3 to 1, using the 80 meter tap. Just for info....your results may vary depending on millions of factors. Dan/W4NTI |
Bob Miller wrote:
I also have a 130 foot low dipole fed with ladderline. My feedline is 47 feet, going to an mfj tuner. I can tune 30 meters easily. You might try adjusting the length of your feedline. You're using a different tuner, so what you do may not match what I do, but playing with the length of your feedline may help. Then again, it may not :-( Guess that's why they call it amateur radio... "Playing" with the length of feedline may not help but making it about 54 feet long will solve the problem. A little cut-and-tryin' will eliminate the need for a tuner altogether. Of course, 54 feet of window-line may put the impedance out of bounds on some other band. -- 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 =--- |
Cecil Moore wrote: wrote: If you don't want to modify the tuner, then feed the 130' dipole with 11.3' of 450 ohm line and then go 50 ohm coax to the transmitter. Don't need a tuner. Or if you could lenghten to ladder line to 56' that would give a good 50 ohm match, no tuner needed. There's a DOS BASIC program on my web page that allows one to enter frequency, dipole length, and type of ladder-line to obtain the length of feedline that will resonate the entire antenna system. Your 56' is pretty close to what my BASIC program says (54' for 10.125 MHz, 130' dipole, 450 ohm VF = 0.9). As you say, this length gives a virtually perfect SWR of 1:1 on 30m - no matchbox required. The DOS BASIC program can be downloaded from: http://www.qsl.net/w5dxp/imax.exe -- 73, Cecil, 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 =--- Hi Cecil, thanks for the info, I will take a look. BTW I used one of Reg Edwards programs to get 56'. I'd say 2' is close enough for engineering approximations. Have you bumped your program with his to see how they compare? Gary N4AST |
wrote:
Hi Cecil, thanks for the info, I will take a look. BTW I used one of Reg Edwards programs to get 56'. I'd say 2' is close enough for engineering approximations. Have you bumped your program with his to see how they compare? Reg once compared them and they were close enough for government work. I assume a VF of 0.9 for 450 ohm window- line. Reg may assume something different or allow the user to enter the VF. In any case, it won't be exactly 54' or 56'. Some adjustment will always be necessary. -- 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! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
Cecil Moore wrote: wrote: Hi Cecil, thanks for the info, I will take a look. BTW I used one of Reg Edwards programs to get 56'. I'd say 2' is close enough for engineering approximations. Have you bumped your program with his to see how they compare? Reg once compared them and they were close enough for government work. I assume a VF of 0.9 for 450 ohm window- line. Reg may assume something different or allow the user to enter the VF. In any case, it won't be exactly 54' or 56'. Some adjustment will always be necessary. -- 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! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- Good enough! Gary N4AST |
On Thu, 17 Mar 2005 01:10:07 GMT, Carter Grabarczyk
wrote: I am using a Johnson KW Matchbox antenna tuner with a 130 foot long, 30 foot high dipole fed with about 40 feet of ladder (window) line. It works well on all bands including the WARC bands *except* for 30 meters. (it doesn't make any difference if the band switch is on 20 or 40--it will not tune 30 in either case). The question is, does anyone have any tips/suggestions/modifications to make this also operate on 30 meters? By the way, modifying the antenna is not an option--lucky to have it up at all with city and subdivision restrictions. Maybe could add extra ladder line in the basement shack, but would have to loop it around the basement ceiling??? Dear Carter, As the owner of a cherry Viking Kilowatt Matchbox Tuner, I would want to avoid any modifications of the tuner itself. So, what I do is build up a modular approach for connecting feedlines to the tuner's balanced terminals. I use the General Radio design banana plug adapters as the basic building block. They are available from Radio Shack and have the advantages of having the exact spacing to match the 450 ohm ladder line and being both a jack and a plug at the same time as screwing down the ladder line. My approach is t ohave a short piece of 450 ohm ladder line from the Tuner Terminals to a GR banana connector. The antenna feed line has a similar GR banana connector at its end. When lighting is in the vicinity I disconncect the connectors and throw the feedline to the floor or to an earthing. Whenever I need a matching network for a given antenna due to extreme mismatches, I build that network between two GR banana connectors and just plug it in series with the line and tuner. The network is usually as simple as two inductors wound on PVC or it could be just a mica transmitting cap or a vacuum cap or any combination or balanced L or Pi circuit components. It helps to have a means of measuring the misbehaving antenna's impedance at the end of the feedline at the frequency in question and then design and build the necessary matching network based on the Smith Chart solution. Bob, W9DMK, Dahlgren, VA Replace "nobody" with my callsign for e-mail http://www.qsl.net/w9dmk http://zaffora/f2o.org/W9DMK/W9dmk.html |
| All times are GMT +1. The time now is 10:59 AM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com