This has been very useful Tim, thanks. I shall be building a doublet this Spring and will bear these points in mind. I'll let you know how it works out. 😃
Your calculation matches my real world experience. I have a 108' doublet into a DG0SA 1:1 balun into 12' of LMR-400 into my tuner. My antenna system works very well. 73 de w8tam
A bit of feed-line terminology: Though some hams call pretty much everything that isn't coax, 'ladder-line', ladder-line is actually composed of 2 wires held apart by separators. The large plastic 450 Ohm 'twin-lead' is 'window-line'.
Good summary, Tim. I would add that if one is running a short run of thin coax from the tuner to the balun, the heat generated should be a consideration as well. Those lost dBs have to go somewhere, and that is likely to be in heating up the coax. As others have suggested, that could indeed cause its dielectric to melt. If I were doing that with my doublet, I would feel the coax link to the balun from time-to-time to see if it were getting warm --- which is something it might do on one band but not on another.
Good video, off point, I have some 75-ohm cable hardline at least as large as lm r600, using it would be much better than smaller coax even if the 75/50 mismatch is there for longer runs. thanks !!
Some of the RSGB and ARRL antenna handbooks contain charts that show the combinations of doublet top plus balanced feeder lengths to avoid. This helps to avoid extremely reactive loads at the feedpoint, making living with a doublet much easier. The ZS6BKW optimised G5RV is a good approach to the problem making matching easier on most bands. I was taught that using magnetic cored baluns at points of extreme mismatch is bad engineering practice. This can lead to heating of the balun core ( = wasted power) and crossmodulation distortion on TX as the core becomes saturated. A 500 Watt 4:1 balun is rated for its' designed purpose, matching a 50 Ohm coax to a flat 200 Ohm balanced line or a 75 Ohm coax to a 300 Ohm balanced line. Away from these impedances the performance of the balun will be an unknown quantity, so go for the most heavily rated balun you can afford. Better still use balanced line all the way through to a fully balanced tuner, not a T match or L match with a built in balun. As regards the routing of balanced lines, keep any solid objects spaced away from the feeder by at least the distance between the conductors of the feeder and you won't go wrong. Also don't be shy about mixing balanced feeders, for example using 450 Ohm outdoors and running 300 Ohm indoors because it is physically smaller and easier to route. The loss transitioning from 450 to 300 is minute, a fraction of a dB. Indoors it is perfectly acceptabe to use the really cheap 300 Ohm feeder with a solid translucent insulation. This stuff is a problem when used outdoors but is fine indoors because will be kept dry. Its' visual impact is much reduced too when compared to slotted feeder or window line. Keep the videos coming, you are doing a great job. 73 Gareth GW4JPC.
Tim, how about turning a video over to the particular problems of 80m in a modern (ludicrously small) UK garden size? I have never had insurmountable RF in the shack problem with 40 and upwards. But at 80, the tables turn horribly. About 6 antennas into the problem and it remains a lesser, but detectable problem. I am now considering shares in ferrite beads and in line common mode filters.
Hi Tim, Many thanks for another great & educational video. However I have a 😅for you. What is that program with the Smith Chart in the lower centre called please Tim. It looks looks very useful, but it does not look like a section of "MMANA-GAL" unless I've missed something when I've been using MMANA-GAL when I'm looking at antenna designs? Many Thanks, Kind Regards, Ray, M0RAY.
Interesting stuff Mike, I’ve been looking at this for a while not sure weather to run open wire feeder round to the front of the house! the next question is should you really use a balun? Seems S match tuners don’t…. keep up the good work I’ll learn mmana one day. M0UDB
There is another one you should look at... the convenience of Co-ax but the lower loss of higher characteristic impedance balanced line.... using both cores of "shotgun" 75 ohm sat tv co-ax (connecting/earthing both braids) gives you 150 ohm balanced line that you don't need to worry about the routing of.
Im confused, i just watched another guys video, and he was saying you would need a 9 to 1 balun, or maybe even a 12 to 1. Tim says a 1 to 1. Who is right? Who is wrong?
For a doublet, if you use a range of bands then the impedance at the balun end of the ladderline will vary massively. A 1:1 is less likely to reduce the impedance to the extent that a tuner may have trouble matching that band. A 9:1 and even a 4:1 may have more trouble in doing so. Some think that because the ladderline is 450 ohm that a 9:1 would change the impedance to 50 ohms - not so!
G5RV or ZS6BKW antennas are not Doublet antenna systems. A true Doublet from any old ARRL antenna handbook is achieved by using a 300ohm, 450ohm ladder line or preferably 600ohm balance line directly terminated to the back of an L or T network type balanced tuner/matchbox, then cutting the antenna legs length to the lowest band of operation. No COAX at all for minimum losses which gives maximum efficiency. A G5RV or ZS6BKW must have at least 50-plus feet of coax to counterbalance the antenna, tuner, and radio.
This has been very useful Tim, thanks. I shall be building a doublet this Spring and will bear these points in mind. I'll let you know how it works out. 😃
Please do! 👍👍
Great information...thanks for your content.
Thank you!
Your calculation matches my real world experience. I have a 108' doublet into a DG0SA 1:1 balun into 12' of LMR-400 into my tuner. My antenna system works very well. 73 de w8tam
Glad it works well for you Thomas 73
Interesting information Tim. Congrats on the 6k subs!
Thanks mate
Thanks for this informative video. Cheers wz2j 🎉
Excellent! I’m going to try it. I’ll only have a run of 3ft of coax
Worth a try 👍👍
A bit of feed-line terminology: Though some hams call pretty much everything that isn't coax, 'ladder-line', ladder-line is actually composed of 2 wires held apart by separators. The large plastic 450 Ohm 'twin-lead' is 'window-line'.
Good summary, Tim. I would add that if one is running a short run of thin coax from the tuner to the balun, the heat generated should be a consideration as well. Those lost dBs have to go somewhere, and that is likely to be in heating up the coax. As others have suggested, that could indeed cause its dielectric to melt. If I were doing that with my doublet, I would feel the coax link to the balun from time-to-time to see if it were getting warm --- which is something it might do on one band but not on another.
Totally agree. Thank you 73
A better question would be, which is less expensive! Some ladder lines are a dollar a foot.
Good video, off point, I have some 75-ohm cable hardline at least as large as lm r600, using it would be much better than smaller coax even if the 75/50 mismatch is there for longer runs. thanks !!
Nice one!
300 Ohm for very long Doublet or 9:1 UNUN with low loss RG-8X for very long Random Wire . I use a MFJ 941E tuner with both with very good results ...
Some of the RSGB and ARRL antenna handbooks contain charts that show the combinations of doublet top plus balanced feeder lengths to avoid. This helps to avoid extremely reactive loads at the feedpoint, making living with a doublet much easier. The ZS6BKW optimised G5RV is a good approach to the problem making matching easier on most bands. I was taught that using magnetic cored baluns at points of extreme mismatch is bad engineering practice. This can lead to heating of the balun core ( = wasted power) and crossmodulation distortion on TX as the core becomes saturated. A 500 Watt 4:1 balun is rated for its' designed purpose, matching a 50 Ohm coax to a flat 200 Ohm balanced line or a 75 Ohm coax to a 300 Ohm balanced line. Away from these impedances the performance of the balun will be an unknown quantity, so go for the most heavily rated balun you can afford. Better still use balanced line all the way through to a fully balanced tuner, not a T match or L match with a built in balun. As regards the routing of balanced lines, keep any solid objects spaced away from the feeder by at least the distance between the conductors of the feeder and you won't go wrong. Also don't be shy about mixing balanced feeders, for example using 450 Ohm outdoors and running 300 Ohm indoors because it is physically smaller and easier to route. The loss transitioning from 450 to 300 is minute, a fraction of a dB. Indoors it is perfectly acceptabe to use the really cheap 300 Ohm feeder with a solid translucent insulation. This stuff is a problem when used outdoors but is fine indoors because will be kept dry. Its' visual impact is much reduced too when compared to slotted feeder or window line. Keep the videos coming, you are doing a great job. 73 Gareth GW4JPC.
Great info thank you Gareth 73
Tim, how about turning a video over to the particular problems of 80m in a modern (ludicrously small) UK garden size?
I have never had insurmountable RF in the shack problem with 40 and upwards. But at 80, the tables turn horribly.
About 6 antennas into the problem and it remains a lesser, but detectable problem. I am now considering shares in ferrite beads and in line common mode filters.
I have done some 80m stuff in my small garden .. have a look at my 80m doublet ..
I run ladderline to the laundry window then a 1to 1 balun and 6 meters of coax to the radio room I can tune it ok with an mfj travel tuner.
Nice job!
Always use at least 7/8 hard line for any run over 30 meters.
Unless you have a nice 1500 watt cloud warmer. Then 1/2 Heliax is fine.
Would I be correct that you passed some threaded bar through the wall for your ladder line connection, if so how would that affect things?
Now that is a very good question
Very well explained, thank you
Glad it was helpful!
Hi Tim,
Many thanks for another great & educational video.
However I have a 😅for you.
What is that program with the Smith Chart in the lower centre called please Tim. It looks looks very useful, but it does not look like a section of "MMANA-GAL" unless I've missed something when I've been using MMANA-GAL when I'm looking at antenna designs?
Many Thanks,
Kind Regards,
Ray, M0RAY.
I’ll need to watch the vid again!
Thanks Tim,
I await your reply in earnest 🙂
Interesting stuff Mike, I’ve been looking at this for a while not sure weather to run open wire feeder round to the front of the house! the next question is should you really use a balun? Seems S match tuners don’t…. keep up the good work I’ll learn mmana one day. M0UDB
Its all about experimenting Dave!
There is another one you should look at... the convenience of Co-ax but the lower loss of higher characteristic impedance balanced line.... using both cores of "shotgun" 75 ohm sat tv co-ax (connecting/earthing both braids) gives you 150 ohm balanced line that you don't need to worry about the routing of.
Interesting info thanks
Tim when would you use 300ohm twin feedline rather than 450ohm...or 600ohm for that matter.
Mostly if weight was a consideration
Im confused, i just watched another guys video, and he was saying you would need a 9 to 1 balun, or maybe even a 12 to 1. Tim says a 1 to 1. Who is right? Who is wrong?
For a doublet, if you use a range of bands then the impedance at the balun end of the ladderline will vary massively. A 1:1 is less likely to reduce the impedance to the extent that a tuner may have trouble matching that band. A 9:1 and even a 4:1 may have more trouble in doing so. Some think that because the ladderline is 450 ohm that a 9:1 would change the impedance to 50 ohms - not so!
Nice video tim, however the lower you go in the band the less loss, as compared to the higher frequencies
Good point!
👍👏👏
Cheers Mark
G5RV or ZS6BKW antennas are not Doublet antenna systems. A true Doublet from any old ARRL antenna handbook is achieved by using a 300ohm, 450ohm ladder line or preferably 600ohm balance line directly terminated to the back of an L or T network type balanced tuner/matchbox, then cutting the antenna legs length to the lowest band of operation. No COAX at all for minimum losses which gives maximum efficiency. A G5RV or ZS6BKW must have at least 50-plus feet of coax to counterbalance the antenna, tuner, and radio.
Also spend a lot of money on coax connectors buy the best quality connecters that you can find.
Very wise