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Question running balanced line
Greetings
I have been using balanced line for many years and am convinced of its virtues, particularly since I use a single tuned doublet for multiband use. The question I have never been able to get a clear answer on is this; How critical is it for the balanced line to avoid metal objects? Specifically, I now use about 6 feet of LMR 400 coax from a Radio Works remote balun into my shack where I tune the antenna from either a manual tuner or the auto tuner in my FT920. In order for me to run the twinlead all the way into the shack there will be about 18 inches where the twinlead will share a portal that I constructed to get my grounds and other cables in and out of the shack. Now I always thought this was a problem area for twinlead, hence the use of the remote balun. I am considering the purchase of a new tuner and was thinking I would like a Palstar Balanced Tuner. But can I use it? Would I be better of with a T match and a short length of coax to a balun, or would a balanced tuner be better even with the 18" or so of twinlead coming in close proximity to the other conductors? I really can not bring the twinlead in without it crossing paths as I desribed. Is a balanced tuner all that better than a T match anyway in terms of antenna performance or loss? What say? Thanks |
On 6 Dec 2004 08:22:19 -0800, "
wrote: Greetings I have been using balanced line for many years and am convinced of its virtues, particularly since I use a single tuned doublet for multiband use. The question I have never been able to get a clear answer on is this; How critical is it for the balanced line to avoid metal objects? Specifically, I now use about 6 feet of LMR 400 coax from a Radio Works remote balun into my shack where I tune the antenna from either a manual tuner or the auto tuner in my FT920. In order for me to run the twinlead all the way into the shack there will be about 18 inches where the twinlead will share a portal that I constructed to get my grounds and other cables in and out of the shack. Now I always thought this was a problem area for twinlead, hence the use of the remote balun. I am considering the purchase of a new tuner and was thinking I would like a Palstar Balanced Tuner. But can I use it? Would I be better of with a T match and a short length of coax to a balun, or would a balanced tuner be better even with the 18" or so of twinlead coming in close proximity to the other conductors? I really can not bring the twinlead in without it crossing paths as I desribed. Is a balanced tuner all that better than a T match anyway in terms of antenna performance or loss? What say? Thanks I've tried it both ways: bringing the ladderline to a coiled coax balun at the window, with coax coming into the shack; and I've tried bringing the ladderline directly into the shack. I'm currently doing the latter -- the ladderline comes through the wood-frame window opening (with a towel and toilet paper plugging up the air gap), it then passes within 2 or 3 inches of a couple other cables, and finally goes to the 4:1 balun on my Tmatch tuner. That seems to work well. I think you have to just experiment and see what works with each particular antenna. bob k5qwg |
On 6 Dec 2004 08:22:19 -0800, "
wrote: Is a balanced tuner all that better than a T match anyway in terms of antenna performance or loss? Hi Jim, I've seen reports of "better tuners" equipped with fans - take warning that this would be a contradiction of claims and features. What you fail to discuss is what is motivating you to make this change? Do you perceive your tuner heating up? Does it fail to tune your antenna? Are you having problems with Common Mode currents? Are you bored with the current arrangement? 73's Richard Clark, KB7QHC |
Hello
Well, what concerns me is that I may not have things working as well as they could be. I'm not having any problems and in fact this system works out quite well. I have read that a remote balun and coax will work, and it does, but going direct to a balanced tuner is better. But how much better? Is it worth the effort and expense? I'm satisfied that the LMR400 and Radio Works balun are as low loss as I can get for this kind of system, but I can never leave well enough alone if I think there is room for improvement. Thanks |
Hello
Well, what concerns me is that I may not have things working as well as they could be. I'm not having any problems and in fact this system works out quite well. I have read that a remote balun and coax will work, and it does, but going direct to a balanced tuner is better. But how much better? Is it worth the effort and expense? I'm satisfied that the LMR400 and Radio Works balun are as low loss as I can get for this kind of system, but I can never leave well enough alone if I think there is room for improvement. Thanks |
Jim,
The differences between the two 'ways' can be fairly large. But, on the whole, I honestly doubt if you would 'see' any difference in performance. Running balanced lines near 'stuff' isn't as big a 'problem' as most people think. If you can stay away from things, fine. If not, then try to stay as far away as possible, and keep the proximity of the balanced line to other things 'symetrical' (if that makes sence), both conductors an equal distance from the other stuff. 'Doc PS - If the idea is to try something different or new, have at it! |
Jim,
Well, let me say this... I've run window line for years, and will be switching to open wire line, in part, next year. In a test that I did about 7 years ago, I ran a 1 ft section of window line across a metal flourescent light fixture, laying right on it. I could measure no change in SWR and no change in signal strengths using a 40 m horizontal loop on 40 m. I'd recommend running a test if possible and see if it makes a difference. Right now, I run an 80 m loop and run window line all the way to the tuner in the shack. Only metal is about a foot away, water pipes and heating ducts that parallel the feedline for about 25 feet. It works so if there is a problem, it might not be severe and I'm willing to live with it, hi. 73s, Evan |
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On 6 Dec 2004 09:53:00 -0800, "
wrote: But how much better? Hi Jim, Probably not enough for you to notice. Is it worth the effort and expense? Worth is subjective, even if you feel good about, but discern no evidence of improvement in performance, that may be sufficient. I'm satisfied that the LMR400 and Radio Works balun are as low loss as I can get for this kind of system, but I can never leave well enough alone if I think there is room for improvement. As Doc suggests, goferit. Bob's advice is not uncommon either, although absorbent material could get damp and affect local line performance. The question then becomes one of our academic knot twisters in that would it matter. Myself, I see a potential short across the line and tender nearby to support combustion or smoldering. To solve my 15X15 inch basement window problem, I replaced the plate glass with Plexiglas and drilled holes with abandon. This replacement was not without taking so long a time that my buddy lost his patience: "Just bust that $5 worth of glass out!" Instead, I had to do this by carefully removing the petrified putty all around - and cracked the pane in the last nip. Care and precision is not always worth the effort. 73's Richard Clark, KB7QHC |
I considered a remote tuner and did in fact use the RT-11 for a couple
of years. It worked, but it was a bit troublesome. What I am doing now is far better. One of the things I have learned about autotuners is that they all seem to have a higher insertion loss than a good manual tuner. Probably due to the toroids, fixed caps, and relays they use. Good airwound coils and variable caps are less lossy. So using an autotuner may be convenient, but I have seen insertion loss figures as high as 65% under some mismatch conditions!.. I can live with my current system, and it works just great. But since I am in the market for a new tuner, I just wanted to know if I should go T match or balanced, as I originally stated. Thanks for all the feedback! Jim |
wrote:
One of the things I have learned about autotuners is that they all seem to have a higher insertion loss than a good manual tuner. The lowest loss is no tuner at all! Let the transmission line do the tuning. How to accomplish that is covered on my web page under, "No- Tuner All-HF-Band Antenna". -- 73, Cecil http://www.qsl.net/w5dxp |
Cecil, what tests, measurements or calculations have you made to satisfy
yourself that loss in the feedline is no greater than in the tuner the feedline replaces? ---- Reg. ======================================== "Cecil Moore" wrote How to accomplish that is covered on my web page under, "No- Tuner All-HF-Band Antenna". |
Jim,
with respect to keeping the system all balanced and running the balanced line through portals along with metal objects, you can simply make a length of shielded balanced line using two pieces of coax with the braids connected at each end and connected to shack ground on the inside end. It becomes a shielded balanced line of twice the coax Zo and can be directly inserted into the transmission path with no problems. Check out "Some Aspects of Series and Parallel Coaxial Cable Assemblies" at Cebik's site, in particular the "Series-Connected Coax" section http://www.cebik.com/spcoax.html 73, John wrote in message oups.com... Greetings I have been using balanced line for many years and am convinced of its virtues, particularly since I use a single tuned doublet for multiband use. The question I have never been able to get a clear answer on is this; How critical is it for the balanced line to avoid metal objects? Specifically, I now use about 6 feet of LMR 400 coax from a Radio Works remote balun into my shack where I tune the antenna from either a manual tuner or the auto tuner in my FT920. In order for me to run the twinlead all the way into the shack there will be about 18 inches where the twinlead will share a portal that I constructed to get my grounds and other cables in and out of the shack. Now I always thought this was a problem area for twinlead, hence the use of the remote balun. I am considering the purchase of a new tuner and was thinking I would like a Palstar Balanced Tuner. But can I use it? Would I be better of with a T match and a short length of coax to a balun, or would a balanced tuner be better even with the 18" or so of twinlead coming in close proximity to the other conductors? I really can not bring the twinlead in without it crossing paths as I desribed. Is a balanced tuner all that better than a T match anyway in terms of antenna performance or loss? What say? Thanks |
John
I read that link with great interest. Some years back I saw an article where twinlead was constructed out of coaxial cable for the purpose of running it through environments that would be bad news for normal twinlead. I thought it was rather stupid because the loss on such a line would defeat the whole purpose of using twinlead. However, for my purposes where I just need a couple of feet or less to be in close contact with other cableing, this might work. The question is, why then are remote baluns promoted as the solution to this common problem? And, is the coax twinlead and a balnaced tuner a better choice than a short lenght of very low loss coax, a good current balun, and a T match? I am not trying to be difficult, I just want to set this up as efficinetly as possible. This might actually be the key! I just need to know if I should go with a short section of coaxial twinlead and a balanced tuner...or leave well enough alone. |
John
I read that link with great interest. Some years back I saw an article where twinlead was constructed out of coaxial cable for the purpose of running it through environments that would be bad news for normal twinlead. I thought it was rather stupid because the loss on such a line would defeat the whole purpose of using twinlead. However, for my purposes where I just need a couple of feet or less to be in close contact with other cableing, this might work. The question is, why then are remote baluns promoted as the solution to this common problem? And, is the coax twinlead and a balnaced tuner a better choice than a short lenght of very low loss coax, a good current balun, and a T match? I am not trying to be difficult, I just want to set this up as efficinetly as possible. This might actually be the key! I just need to know if I should go with a short section of coaxial twinlead and a balanced tuner...or leave well enough alone. Great info! Thanks! |
I am not trying to be difficult,
=========================== There's no need to try - you don't appear to have any problems. Where did you receive your training? |
Now that was helpful !
Maybe you should sign up with the local radio club as an Elmer? No one is forceing you to read my posts or help me. Thanks anyway. |
On 7 Dec 2004 09:56:10 -0800, "
wrote: Now that was helpful ! Maybe you should sign up with the local radio club as an Elmer? No one is forceing you to read my posts or help me. Thanks anyway. Jim, I believe you mentioned you were considering the Palstar balanced tuner -- I looked at the "inside" picture of it, and the variable inductors look suspiciously exactly alike the variable inductor in my mfj-989c unit. I'm not saying that's good or bad -- just thought I'd mention it... Bob k5qwg |
Thanks for that info..I would consider that as "bad"..Hi.
But the Palstar reviews that I have read all seem to be quite favorable. I am now using an old Daiwa tuner that does a real nice job, but it is old and uses small 365 mmf broadcast type variables, a dainty looking coil, and cheap push switches for antenna selection. The cross needle metering seems to be OK. I just want to upgrade to something built a bit better, and I am not fond of Mighty Fine Junk ( no offense intended ), even if they are the most popular in the world. I probably will go for a Palstar, but I can't decide on a T match model or the balanced tuner. Thanks for the reply. Jim |
wrote in message oups.com... The question is, why then are remote baluns promoted as the solution to this common problem? Well, there's more than one way to skin a cat, a remote balun wouldn't be bad if it fed the balanced feedline of a resonant antenna which is used at its resonant frequency. But if you want to operate the antenna everywhere then you don't want a balun feeding the open wire, weather it be at the antenna or on the antenna side of a shack side antenna tuner. Go to Cebiks index section, in particular the Transmission Lines, Impedance Coupling, and Construction section, - there's lots of reading there on antenna tuner matching issues including a great tutorial :^) http://www.cebik.com/radio.html And, is the coax twinlead and a balnaced tuner a better choice than a short lenght of very low loss coax, a good current balun, and a T match? Oh Yes. If you keep everthing balanced and then use a GOOD balanced antenna tuner things will work out fine. Avoid any balanced tuner design that has a matching network followed by a ferrite core balun on the *antenna feedline* end. These types of baluns are meant to be used close to their design inpedances, not when connected to a multiband antenna which is going to have wild variations in Z. 73, John |
Good info! I think Palstar has a tuner that places a 1:1 balun on the
input or transmitter side of a T match tuner. I think I will look into that one and use a short length of coax twinlead instead of the remote balun. Thanks for the help! Jim |
Good info! I think Palstar has a tuner that places a 1:1 balun on the
input or transmitter side of a T match tuner. I think I will look into that one and use a short length of coax twinlead instead of the remote balun. Thanks for the help! Jim |
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