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Coax + Ladder Line
Is it advisable to use a combination of Coax and a ladder line to feed a
simple horizontal multiband dipole antenna? In my new QTH it would be very easy for me to get a short run of coax out of my shack window but I would like to use a low loss ladder line for the main run up to the antenna feed point. Is it OK to place a 4:1 balun just outside of the window for the transition? Kash, AG4EL |
Coax + Ladder Line
"Kash J. Rangan" wrote in message ... Is it advisable to use a combination of Coax and a ladder line to feed a simple horizontal multiband dipole antenna? In my new QTH it would be very easy for me to get a short run of coax out of my shack window but I would like to use a low loss ladder line for the main run up to the antenna feed point. Is it OK to place a 4:1 balun just outside of the window for the transition? Kash, AG4EL you can, but how long of a run will it be from the shack to the antenna?? unless it is a very long distance just go with the coax... the added loss and complexity of the balun and then the mismatch of the ladder line to the dipole at the far end is probably going to be more than just going with coax all the way. |
Coax + Ladder Line
On Jun 10, 3:36�pm, "Kash J. Rangan" wrote:
Is it advisable to use a combination of Coax and a ladder line to feed a simple horizontal multiband dipole antenna? In my new QTH it would be very easy for me to get a short run of coax out of my shack window but I would like to use a low loss ladder line for the main run up to the antenna feed point. Is it OK to place a 4:1 balun just outside of the window �for the transition? Kash, AG4EL The G5RV antenna uses a combination of coax and ladder line, so this type of antenna is in use by 1000's of Hams. The 4:1 balun is a bad idea for a multiband antenna, due to the impedances involved at the various operating frequencies. Just transistion from the ladder line to the coax and use a 1:1 choke balun at the antenna input of your tuner. You did not mention an antenna tuner, but you will need one for multiband operation. In general keep the coax length as short as possible. Gary N4AST |
Coax + Ladder Line
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Coax + Ladder Line
If I remember correctly, the original design of the G5RV does NOT use coax. [If interested, check it out on Google.] -- Ian- Hide quoted text - - Show quoted text - I think you are right. Most of the commercial antennas called "G5RV" have coax supplied with them or instruct you to attach a certain length coax. One of Reg Edwards programs, Dipole3 models a twin lead-coax miltiband antenna. It also has a G5RV feature. Gary N4AST |
Coax + Ladder Line
wrote in message ... On Jun 10, 3:36?pm, "Kash J. Rangan" wrote: Is it advisable to use a combination of Coax and a ladder line to feed a simple horizontal multiband dipole antenna? In my new QTH it would be very easy for me to get a short run of coax out of my shack window but I would like to use a low loss ladder line for the main run up to the antenna feed point. Is it OK to place a 4:1 balun just outside of the window ?for the transition? Kash, AG4EL The G5RV antenna uses a combination of coax and ladder line, so this type of antenna is in use by 1000's of Hams. The 4:1 balun is a bad idea for a multiband antenna, due to the impedances involved at the various operating frequencies. Just transistion from the ladder line to the coax and use a 1:1 choke balun at the antenna input of your tuner. You did not mention an antenna tuner, but you will need one for multiband operation. In general keep the coax length as short as possible. Gary N4AST Another thing to consider is that the length of the 450/300 ohm twinlead feedline is an important factor when considering the operational bandwidth of said "dipole" antenna (it's only a dipole when operated at its resonant length). The twinlead is utilized as part of the radiating system when operated on certain bands. This unusual impedance is why the tuner is needed. Shortening the twinlead and using more coax limits this antenna's ability to operate over wide frequency ranges. My Van Gordan All Bander's twinlead enters my shack and then connects to a balun, which is then fed by coax that is connected to my MFJ-989C tuner. I can often tune down into the 160 meter band using this setup, though I wish my twinlead feedline length was a bit longer for even greater tuning flexibility. By the way, my All Bander also works great on six meters. Ed, AJ4PJ |
Coax + Ladder Line
"Kash J. Rangan" writes:
Is it advisable to use a combination of Coax and a ladder line to feed a simple horizontal multiband dipole antenna? In my new QTH it would be very easy for me to get a short run of coax out of my shack window but I would like to use a low loss ladder line for the main run up to the antenna feed point. Is it OK to place a 4:1 balun just outside of the window for the transition? I use a combination of window line and coax for my 80m antenna. I don't have enough space for a full size dipole, so I had to shorten it somewhat. From memory, about 6m of window line makes up for about 3m of missing wire on each dipole leg. Easier to do than loading coils, that's why. EZNEC claims that losses are negligible, don't know if that's really so or a transmission line model is inappropriate here. Totally by accident, the antenna also ended up with a resonance in the 30m band. Jon LA4RT, Trondheim, Norway |
Coax + Ladder Line
In Varney's original r.s.g.b. article in July 1958 he showed it both
ways, 100% open wire feeder to a tuner, or 34' of open wire feeder to any length of 72 ohm coax or twin lead to a tuner or the transmitter. bob k5qwg On Thu, 11 Jun 2009 10:43:38 +0100, Ian Jackson wrote: In message , writes On Jun 10, 3:360 Is it advisable to use a combination of Coax and a ladder line to feed a simple horizontal multiband dipole antenna? In my new QTH it would be very easy for me to get a short run of coax out of my shack window but I would like to use a low loss ladder line for the main run up to the antenna feed point. Is it OK to place a 4:1 balun just outside of the window 0 Kash, AG4EL The G5RV antenna uses a combination of coax and ladder line, so this type of antenna is in use by 1000's of Hams. The 4:1 balun is a bad idea for a multiband antenna, due to the impedances involved at the various operating frequencies. Just transistion from the ladder line to the coax and use a 1:1 choke balun at the antenna input of your tuner. You did not mention an antenna tuner, but you will need one for multiband operation. In general keep the coax length as short as possible. If I remember correctly, the original design of the G5RV does NOT use coax. [If interested, check it out on Google.] |
Coax + Ladder Line
I agree with Gary N4AST: the direct answer to your question is:
* Use the shortest length of good quality coax you can get away with. * Use a good quality 1:1 current (choke) balun at the ladderline/coax junction. * If you find the tuner can't reach a match on some bands, only then consider a 4:1 balun; even so choose a 4:1 **current** balun. On the topic of G5RVs, some (unscrupulous) antenna suppliers provide a nice long length of RG58 as part of the package to "tame" the VSWRs. Take a look at some of the losses that introduces: http://www.karinya.net/g3txq/g5rv/ 73, Steve G3TXQ |
Coax + Ladder Line
Ed Cregger wrote:
Another thing to consider is that the length of the 450/300 ohm twinlead feedline is an important factor when considering the operational bandwidth of said "dipole" antenna (it's only a dipole when operated at its resonant length). I have to chuckle when you bring this up in a discussion of that true chimera, the G5RV. I've heard so many antennas called G5RV's that the term means nothing any more - kinda of like scotch tape. So yeah, I guess we should call it a doublet. Of course, all doublets are dipoles at some point, and all dipoles are doublets....... - 73 de Mike N3LI - |
Coax + Ladder Line
Thanks for all your responses and ideas.
Yes, I do have an antenna tuner. The maximum length of the antenna I can hope for can only be about 65ft because of the placement of trees in my back yard and access to my shack. At this time I will be happy if I can tune to some bands up to 40M. I did not want to drill any additional holes for outside access if I can help it amd make use of the existing one. I also wanted the option of total disconnect from the outside. My equipment has been fried by lightning in my previous QTH. I figure it would be about a 60 ft run to the feed point. I am aware that certain feed line lengths are to be avoided to minimize transmission line radiation and tuning problems. In addition to low loss I thought ladder line would be much lighter than coax. I don't have any way to support my antenna at the center so I am trying to keep it as light as possible. Not sure of the wind loads though but I will have a modest workable antenna up soon. You all have been very helpful in sharing your thoughts. 73 AG4EL, Kash |
Coax + Ladder Line
"Michael Coslo" wrote in message ... Ed Cregger wrote: Another thing to consider is that the length of the 450/300 ohm twinlead feedline is an important factor when considering the operational bandwidth of said "dipole" antenna (it's only a dipole when operated at its resonant length). I have to chuckle when you bring this up in a discussion of that true chimera, the G5RV. I've heard so many antennas called G5RV's that the term means nothing any more - kinda of like scotch tape. So yeah, I guess we should call it a doublet. Of course, all doublets are dipoles at some point, and all dipoles are doublets....... - 73 de Mike N3LI - Well, that wasn't the point that I was trying to make. I was saying that the length of the twinlead is very important and that it shouldn't be shortened (commercial versions) any more than necessary, lest one lose some of the utility of this type of antenna. I know that folks are eager to transition to coax, but that isn't the way that leads to the best working sample of this antenna. Ed, AJ4PJ |
Coax + Ladder Line
On Jun 11, 11:17*am, "Kash J. Rangan" wrote:
Thanks for all your responses and ideas. Yes, I do have an antenna tuner. The maximum length of the antenna I can hope for can only be about 65ft because of the placement of trees in my back yard and access to my shack. At this time I will be happy if I can tune to some bands up to 40M. I did not want to drill any additional holes for outside access if I can help it amd make use of the existing one. I also wanted the option of total disconnect from the outside. My equipment has been fried by lightning in my previous QTH. I figure it would be about a 60 ft run to the feed point. I am aware that certain feed line lengths are to be avoided to minimize transmission line radiation and tuning problems. In addition to low loss I thought ladder line would be much lighter than coax. I don't have any way to support my antenna at the center so I am trying to keep it as light as possible. *Not sure of the wind loads though but I will have a modest workable antenna up soon. You all have been very helpful in sharing your thoughts. 73 AG4EL, Kash If it were me and I were using a tuner, I'd just run ladder line the whole way. I've noticed that even if you pass the line across a metal window frame, there is usually no noticeable change to speak of. If you have to do that, it's best to keep the line at right angles to the frame to keep it as balanced as possible. You could easily chunk the line outside during storms, or you could rig up a way to disconnect by using banana plugs, etc.. That way you can disconnect but not have to fiddle with unplugging from the rig. I would prefer to have those outside, so when disconnected the line is totally out of the house. It's probably quite well known on this group that I don't like mixing feed line types in a case like this. :/ Running ladder line the whole way is the least lossy vs mixing ladder line with coax, choke, etc.. Using G5RV type feeding schemes will work, but they can take a decent hunk of your RF and turn it to heat in many cases. Even with a 80/1 mismatch, ladder line has low loss. If the length of coax is short, the loss will be fairly low. But.. many add a choke, etc, and I think the choke is where a good portion of the loss is on these type of feed systems. Some of these might use fairly long coax lines, and the loss could add up vs ladder line. BTW... Tune the tuner using the least inductance needed to get a usable match whichever way you go. |
Coax + Ladder Line
Running ladder line the whole way is the least lossy
vs mixing ladder line with coax, choke, etc.. Often, but not always: * Depending on the impedances, frequencies and lengths involved, the loss in a coax section can be lower than in the equivalent length of ladderline. * Although there may be losses in a 1:1 current balun at the ladderline/coax transition, don't forget that there will also be losses in the tuner balun if ladderline is used all the way; if the ubiquitous 4:1 tuner internal voltage balun is used, those losses could be significant. Steve G3TXQ |
Coax + Ladder Line
In message
, steveeh131047 writes Running ladder line the whole way is the least lossy vs mixing ladder line with coax, choke, etc.. Often, but not always: * Depending on the impedances, frequencies and lengths involved, the loss in a coax section can be lower than in the equivalent length of ladderline. * Although there may be losses in a 1:1 current balun at the ladderline/coax transition, don't forget that there will also be losses in the tuner balun if ladderline is used all the way; if the ubiquitous 4:1 tuner internal voltage balun is used, those losses could be significant. Maybe, instead of 'ubiquitous', read 'inappropriate' (at least on certain occasions). I'm sure that, if you can't resist the urge to use coax, a current balun / longitudinal choke (often wound from the coax) could have much less loss. -- Ian |
Coax + Ladder Line
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Coax + Ladder Line
Owen Duffy wrote:
wrote in : ... Even with a 80/1 mismatch, ladder line has low loss. 30m of Wireman 551 with a load of 5+j0 has VSWR=80 at the load end, VSWR=28 at the source end, and the transmission loss is 4.6dB... 65% of the input power is converted to heat. Speaks to your meaning of "low loss". Mythical properties are ascribed to ladder line, some of attributable to ARRL publications. Or, I think more properly, to statements in ARRL publications taken with a different set of underlying assumptions.. For instance, ladder line between a tube amp output tank and a doublet is probably "reasonably" low loss in most common practical applications.. And in an inappropriate application (reactive load with weird Z to 50 ohm transmitter) it's probably lower loss than RG-58. Maybe it's that subjective term "low loss"??? Half a dB per foot is low loss at 32 GHz, but you'd be hard pressed to find a commercially available transmission line with that kind of loss at 7 MHz. (maybe that funky 1000 ohm Z delay line stuff?) Ham applications in any case are kind of an odd thing, efficiency-wise, since the limit is on RF power at the transmitter output connector. Pretty much every other user of RF power amplifiers sets the system measurement plane somewhere else.. in space (EIRP or ERP) or at the power source (power budgets). For instance, you can trade increased power consumption against lower feedline loss. |
Coax + Ladder Line
Jim Lux wrote in
: .... Mythical properties are ascribed to ladder line, some of attributable to ARRL publications. Or, I think more properly, to statements in ARRL publications taken with a different set of underlying assumptions.. The ARRL has long published characteristics of "Generic ladder line" being #18 conductors spaced 1". They publish loss figures better than theoretical loss for the same size copper conductors in a vacuum (eg at 10MHz, about 0.27dB/100m vs 0.47dB/100m). The second factor is, I think, the notion that since one-way loss is relatively low on open wire lines, that it is safe to consider it *always* insignificant (irrespective of VSWR), then exagerate the point by talking about it being essentially lossless at extreme VSWR. I think that the best characterisation we have of ladder line is that of Wes, N7WS. Similar measurements at lower frequencies might well reveal whether the stranded copper clad steel versions have inadequate cladding depth for copper-like performance at low HF. For instance, ladder line between a tube amp output tank and a doublet is probably "reasonably" low loss in most common practical applications.. Perhaps a better concept is "acceptable loss" where acceptable is influence by the application. The compromises accepted for multiband operation might well include 3dB of line loss on the lowest band. .... Ham applications in any case are kind of an odd thing, efficiency-wise, since the limit is on RF power at the transmitter output connector. Pretty much every other user of RF power amplifiers sets the system measurement plane somewhere else.. in space (EIRP or ERP) or at the power source (power budgets). For instance, you can trade increased power consumption against lower feedline loss. Actually, interesting you mention that. I recently had cause to probe the meaning of the term "transmitter" in our (VK) regulatory framework. Whilst we are limited in transmitter power output, the meaning of transmitter is relevant. From our legislation: ===quote 8 Definitions of radio emission and transmitter (1) For the purposes of this Act, a radio emission is any emission of electromagnetic energy of frequencies less than 420 terahertz without continuous artificial guide, whether or not any person intended the emission to occur. (2) For the purposes of this Act, a transmitter is: (a) anything designed or intended for radio emission; or (b) any other thing, irrespective of its use or function or the purpose of its design, that is capable of radio emission. === end quote It could be argued that an "emission" exists beyond the antenna ("without continuous artificial guide"), and that everything up to an including the antenna could be captured as part of a "transmitter" as defined. Though there is a well understood ordinary meaning to the word "transmitter", the drafters of the legislation have provided a definition that should override any ordinary meaning in the context of that law. Perhaps we (VK) are entitled to apply our limit to radiated power! Owen |
Coax + Ladder Line
It's a mistake to lump all ladder and window line together as "ladder
line" and draw conclusions about its loss characteristics. There's a vast difference between punched polyethylene window line and real 600 ohm ladder line made with large diameter conductors and low loss spacers. Even more so when the line is wet. Roy Lewallen, W7EL |
Coax + Ladder Line
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Coax + Ladder Line
On Jun 13, 12:05*am, Jim Lux wrote:
Ham applications in any case are kind of an odd thing, efficiency-wise, since the limit is on RF power at the transmitter output connector. Jim, That's not the case in the UK. The licence conditions specify ".... power supplied to the antenna by a transmitter ...." Steve G3TXQ |
Coax + Ladder Line
On Jun 13, 6:54*am, steveeh131047 wrote:
On Jun 13, 12:05*am, Jim Lux wrote: Ham applications in any case are kind of an odd thing, efficiency-wise, since the limit is on RF power at the transmitter output connector. Jim, That's not the case in the UK. The licence conditions specify ".... power supplied to the antenna by a transmitter ...." Steve G3TXQ How interesting, so in both VK and UK (mixing abbreviations).. the "reference plane" for the measurement is potentially "after" the transmission line. The 5kW Active Antenna Tuner lives! Here in the US, I'm sure the rule is interpreted the way it is because of the heritage of "1kW DC power to the final stage" rule, which in turn came from pre-ham radio rules for marine transmitters using sparkgaps, etc... It was simple change from measuring plate current/ voltage to hooking a power meter at the output connector. I wonder if anyone ever measured RF power on a non-50 ohm transmitter in an enforcement action? My father and grandfather both had stories, apocryphal perhaps, about clever hams having very large "exciters" that fed through a relatively low power "final stage"... using the final tube as a coupling capacitor, perhaps, with unity gain. |
Coax + Ladder Line
On Jun 12, 5:43*pm, Owen Duffy wrote:
wrote : ... Even with a 80/1 mismatch, ladder line has low loss. 30m of Wireman 551 with a load of 5+j0 has VSWR=80 at the load end, VSWR=28 * at the source end, and the transmission loss is 4.6dB... 65% of the input power is converted to heat. Speaks to your meaning of "low loss". Mythical properties are ascribed to ladder line, some of attributable to ARRL publications. Owen I might have been a bit carried away with the degree of mismatch and loss, but I still think running the ladder/window line the whole way to the tuner will still be the best in most cases for "all band" use. If the major portion of the feed line will still be ladder line, even with the coax lead in, he will still deal with the same line losses for the majority of the run with such a severe mismatch. It won't be that bad most of the time. With the coax and choke addition, even more loss is added to the system. And if he saw an 80:1 mismatch, just 15 feet of RG-8 should cost you half your power at 14 mhz. That's more loss than 15 extra feet of the ladder line which at 80:1, should be about 1 db loss or so. I just find the addition of the coax and choke as totally unnecessary unless there is no way at all to feed the ladder/window line through to the shack. Sure, there are losses with the balun used in most tuners, but I consider that a price to pay for a multi band antenna. Myself, I don't use many all band antennas.. Most of my dipoles are single band, and coax fed. :/ Here is one online calculator which seems to match your numbers fairly close if set for 14 mhz. They include the 551 line as one of the choices. I notice "generic" 450 line has less loss.. I don't know what the difference is between generic and 551.. Maybe 551 has more plastic, and less open window.. I notice generic 600 ohm ladder line will show about 2.2 db loss with an 80:1 mismatch. I'll agree.. Maybe not low loss, but it's quite usable considering an ugly 80:1 mismatch. http://www.qsl.net/co8tw/Coax%20Calculator.htm |
Coax + Ladder Line
Kash J. Rangan wrote:
Is it OK to place a 4:1 balun just outside of the window for the transition? Given the impedance seen by the balun, is a 4:1 transformation what you want? If the impedance seen by the balun is 10 ohms, for instance, do you think taking the impedance down to 2.5 ohms is an improvement? -- 73, Cecil, IEEE, OOTC, http://www.w5dxp.com |
Coax + Ladder Line
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Coax + Ladder Line
"Kash J. Rangan" wrote in
: Is it advisable to use a combination of Coax and a ladder line to feed a simple horizontal multiband dipole antenna? In my new QTH it would be very easy for me to get a short run of coax out of my shack window but I would like to use a low loss ladder line for the main run up to the antenna feed point. Is it OK to place a 4:1 balun just outside of the window for the transition? If your antenna is balanced, it would probably be better to simply split the ladder line onto the center conducters of two identical short coaxes and then run ladder line inside to your tuner. If you MUST ground the shields that's OK and you can use lightning arrestors on both coaxes. But remember, no lighning arrestor is as good for protecting equipment as a foot or two of air. Disconnecting during thunderstorms is solid policy! -- Dave Oldridge+ ICQ 454777283 |
Coax + Ladder Line
"Dave Oldridge" wrote in message 0... "Kash J. Rangan" wrote in : Is it advisable to use a combination of Coax and a ladder line to feed a simple horizontal multiband dipole antenna? In my new QTH it would be very easy for me to get a short run of coax out of my shack window but I would like to use a low loss ladder line for the main run up to the antenna feed point. Is it OK to place a 4:1 balun just outside of the window for the transition? If your antenna is balanced, it would probably be better to simply split the ladder line onto the center conducters of two identical short coaxes and then run ladder line inside to your tuner. If you MUST ground the shields that's OK and you can use lightning arrestors on both coaxes. But remember, no lighning arrestor is as good for protecting equipment as a foot or two of air. Disconnecting during thunderstorms is solid policy! -- Dave Oldridge+ ICQ 454777283 Sounds a little backwards. The Ladder Line should transition to coax (balanced as you pointed out) inside to hopefully reduce RF in the shack. An arrestor outside in addition to disconnecting from equipment will avoid arcing in the shack at least. You have to be there to even remember to disconnect. |
lightning protection Coax + Ladder Line
Dave Oldridge wrote:
"Kash J. Rangan" wrote in If your antenna is balanced, it would probably be better to simply split the ladder line onto the center conducters of two identical short coaxes and then run ladder line inside to your tuner. If you MUST ground the shields that's OK and you can use lightning arrestors on both coaxes. But remember, no lighning arrestor is as good for protecting equipment as a foot or two of air. Disconnecting during thunderstorms is solid policy! If you have a direct hit, a one foot air gap isn't necessarily going to do you much good, unless the antenna end of the gap is on the ground surface. (i.e. the wire going from where the coax ends to your lightning dissipation ground has some non-zero inductance/resistance) If you're worried about induced voltages from adjacent strikes, then a good transient suppressor will help, but almost all suppressors have "let through" voltage that is above the damage threshold for, say, a FET front end. Depends on what your equipment sensitivity is. Shorting the input of the radio and tying it to chassis ground.. that WILL protect the radio. |
Coax + Ladder Line
"Jim Lux" wrote in message ... Mike Coslo wrote: wrote: Sure, there are losses with the balun used in most tuners, but I consider that a price to pay for a multi band antenna. Chiming in late on this one... Mythical attributes aside, I believe the real reason that ladder line has become more popular is: 1. Almost all rigs are All HF band these days. 2. Many people have just one antenna they can put up at any given time. Whether it is space considerations, maintaining a low profile or keeping the XYL happy I remember the discussions with my wife when I wanted to put up the HF vertical. "Why do you need two antennas?" "Are you going to transmit two signals at the same time?". Twasn't easy, and a lot of Hams might lose that argument. So assuming it is a doublet, and I wanted to run 80 to 10 meters, I'd put up much wire as I could, not mess with coax, just run ladder line to a window panel, then into the house, into a tuner that can handle balanced line. And pay attention to the lengths that might make for trouble in matching. Or, put up as much wire as you can, put an autotuner at the feedpoint, and run coax back to the shack. probably a six of one, half dozen of the other, depending on what you already have, what kind of support structures you have (if you are putting up an inverted V, then supporting the weight of the tuner isn't an issue..), etc. for most people the feedline won't be that long so just put up the inverted v, wind a coax choke at the feed point (or not) and just run it back to the shack and use the tuner in the rig. |
MFJ autuner review, was Coax + Ladder Line
Jim Lux wrote:
Mike Coslo wrote: wrote: Sure, there are losses with the balun used in most tuners, but I consider that a price to pay for a multi band antenna. Chiming in late on this one... Mythical attributes aside, I believe the real reason that ladder line has become more popular is: 1. Almost all rigs are All HF band these days. 2. Many people have just one antenna they can put up at any given time. Whether it is space considerations, maintaining a low profile or keeping the XYL happy I remember the discussions with my wife when I wanted to put up the HF vertical. "Why do you need two antennas?" "Are you going to transmit two signals at the same time?". Twasn't easy, and a lot of Hams might lose that argument. So assuming it is a doublet, and I wanted to run 80 to 10 meters, I'd put up much wire as I could, not mess with coax, just run ladder line to a window panel, then into the house, into a tuner that can handle balanced line. And pay attention to the lengths that might make for trouble in matching. Or, put up as much wire as you can, put an autotuner at the feedpoint, and run coax back to the shack. probably a six of one, half dozen of the other, depending on what you already have, what kind of support structures you have (if you are putting up an inverted V, then supporting the weight of the tuner isn't an issue..), etc. Speaking of autotuners, I just got my MFJ933, and have been working with it this last week. MFJ has an interesting reputation, but I have to say they pretty much got this one right. For $224, it is one impressive piece of hardware/programming. I run my window line directly to the tuner, which was a big selling point. NOt many other auto tuners have that feature. Construction was quite acceptable, performance has been fine so far, and appearance good with only one exception. One of the front panel's letters had a little rub mark on it. No biggie, just cleaned it with an eraser. The analog meter is a little small, but the whole unit would have to be made bigger to put in a larger one, so that was a tradeoff. It also has the digital readout, so I find myself looking at the analog meter for initial reference on a frequency, then at the readout after that. It has a lot of other features that I'm still learning. I give the unit an A, at least on my experience so far. - 73 de Mike N3LI |
MFJ autuner review, was Coax + Ladder Line
Michael Coslo wrote in news:h1geb3$do4i$1
@tr22n12.aset.psu.edu: MFJ933 ??? |
MFJ autuner review, was Coax + Ladder Line
On Jun 19, 11:28�am, Michael Coslo wrote:
Jim Lux wrote: Mike Coslo wrote: wrote: Sure, there are losses with the balun used in most tuners, but I consider that a price to pay for a multi band antenna. Chiming in late on this one... Mythical attributes aside, I believe the real reason that ladder line has become more popular is: 1. Almost all rigs are All HF band these days. 2. Many people have just one antenna they can put up at any given time. Whether it is space considerations, �maintaining a low profile or keeping the XYL happy I remember the discussions with my wife when I wanted to put up the HF vertical. "Why do you need two antennas?" "Are you going to transmit two signals at the same time?". Twasn't easy, and a lot of Hams might lose that argument. So assuming it is a doublet, and I wanted to run 80 to 10 meters, I'd put up much wire as I could, not mess with coax, just run ladder line to a window panel, then into the house, into a tuner that can handle balanced line. And pay attention to the lengths that might make for trouble in matching. Or, put up as much wire as you can, put an autotuner at the feedpoint, and run coax back to the shack. probably a six of one, half dozen of the other, depending on what you already have, what kind of support structures you have (if you are putting up an inverted V, then supporting the weight of the tuner isn't an issue..), etc. Speaking of autotuners, �I just got my MFJ933, and have been working with it this last week. MFJ has an interesting reputation, but I have to say they pretty much got this one right. For $224, it is one impressive piece of hardware/programming. I run my window line directly to the tuner, which was a big selling point. NOt many other auto tuners have that feature. Construction was quite acceptable, performance has been fine so far, and appearance good with only one exception. One of the front panel's letters had a little rub mark on it. No biggie, just cleaned it with an eraser. The analog meter is a little small, but the whole unit would have to be made bigger to put in a larger one, so that was a tradeoff. It also has the digital readout, so I find myself looking at the analog meter for initial reference on a frequency, then at the readout after that. It has a lot of other features that I'm still learning. I give the unit an A, at least on my experience so far. � � � � - 73 de Mike N3LI- Hide quoted text - - Show quoted text - The MFJ-933 is a manual loop tuner according to their catalog. Which ever one you are using sounds nice, and is worth a look, but I don't think it is a MFJ-933. Gary N4AST |
MFJ autuner review, was Coax + Ladder Line
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MFJ autuner review, was Coax + Ladder Line
J. Mc Laughlin wrote:
Dear N3LI: Might the MFJ model be 993? Sorry, Germs, I typo'd. It is indeed a 993. - 73 de Mike N3LI - |
lightning protection Coax + Ladder Line
Jim Lux wrote in
: Dave Oldridge wrote: "Kash J. Rangan" wrote in If your antenna is balanced, it would probably be better to simply split the ladder line onto the center conducters of two identical short coaxes and then run ladder line inside to your tuner. If you MUST ground the shields that's OK and you can use lightning arrestors on both coaxes. But remember, no lighning arrestor is as good for protecting equipment as a foot or two of air. Disconnecting during thunderstorms is solid policy! If you have a direct hit, a one foot air gap isn't necessarily going to do you much good, unless the antenna end of the gap is on the ground surface. (i.e. the wire going from where the coax ends to your lightning dissipation ground has some non-zero inductance/resistance) If you're worried about induced voltages from adjacent strikes, then a good transient suppressor will help, but almost all suppressors have "let through" voltage that is above the damage threshold for, say, a FET front end. Depends on what your equipment sensitivity is. Shorting the input of the radio and tying it to chassis ground.. that WILL protect the radio. I have been through some VERY violent storms. I always disconnected all antenna and power leads from the radio. Outside arrestors will help keep it out of the house but you need airspace to protect receiver front ends. Also disconnect any ethernet runs. Surge protection can only do so much. I learned the hard way about disconnecting stuff. My neighbour across the street had a direct hit and it danced across the phone lines into my equipment. I lost several modems, a couple of ethernet cards and a monitor and considered myself lucky that none of the computers was totalled. But my radios were disconnected and unscathed. Now the coast station I worked for had a direct hit on our Nautel 500khz transmitter's tower. Blew out half the solid state final modules but the damn thing kept right on ticking on the others! -- Dave Oldridge+ ICQ 454777283 VA7CZ |
lightning protection Coax + Ladder Line
MUST ground the shields that's OK and you can use lightning arrestors on both coaxes. This is probably not going to work in most cases. Remember an open wire feedline can have rather high voltages on it compared to a matched coax liine. This is because they are often mismatched at the antenna. If a voltage peak should happen to occur at the place where you have the arrestor, it can fire the gas tube because of the rf voltage. For example, a gas tube arrestor made for legal limit typically has a firing voltage of about 800 volts. In a matched 50 ohm system, even with a full 1500 watts into 50 ohms the peak rf voltage is in the neighborhood of 600 volts. But even a moderate power into a high impedance open line could be enough to fire the gas tubes. Neither the transmitter nor the gas tube would be happy with this situation. Rick K2XT |
lightning protection Coax + Ladder Line
"Rick" wrote in
: MUST ground the shields that's OK and you can use lightning arrestors on both coaxes. This is probably not going to work in most cases. Remember an open wire feedline can have rather high voltages on it compared to a matched coax liine. This is because they are often mismatched at the antenna. If a voltage peak should happen to occur at the place where you have the arrestor, it can fire the gas tube because of the rf voltage. For example, a gas tube arrestor made for legal limit typically has a firing voltage of about 800 volts. In a matched 50 ohm system, even with a full 1500 watts into 50 ohms the peak rf voltage is in the neighborhood of 600 volts. But even a moderate power into a high impedance open line could be enough to fire the gas tubes. Neither the transmitter nor the gas tube would be happy with this situation. That's true. You would probably need air-gap arrestors that can be adjusted to not arc on normal transmitted voltages. Still, the only really effective way of feeding a non-trap wire system on several bands that I've encountered is to use open wire. -- Dave Oldridge+ ICQ 454777283 |
lightning protection Coax + Ladder Line
In article ,
Dave Oldridge wrote: That's true. You would probably need air-gap arrestors that can be adjusted to not arc on normal transmitted voltages. Still, the only really effective way of feeding a non-trap wire system on several bands that I've encountered is to use open wire. -- Dave Oldridge+ ICQ 454777283 One of the best "air-gap arrestors" of the home-brew variety I have seen, was made with a couple of Wide Gapped Spark-Plugs, threaded into a 1/4 Steel Plate that was bonded to a very deep Grounding System. The fellow used GTO15000 to connect the spark-plugs to the Wire-Feeders. Worked very well....... -- Bruce in alaska add path after fast to reply |
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