Help Please. I have a Maco 5/8 GroundPlane. Using 65 FEET OF LMR400 Coax. I recently made a 1:1 Choke Balun out of 6 inch Diameter Pvc piping. I used 25 feet of extra LMR400 And only wound 21 feet 10 turns of it on this pvc piping. single Layered only Leaving 2 feet of coax coming out on either end. Tested this Balun before putting her up with my 1500 watt MFJ dummyload and got a Flat Match on my Astatic 600 Meters.I plugged one end to my Maco and the other End I used a coupler to join them together. The wound coax is not in any way touching my mast because of the 3 inch legs on both ends of the pvc that hold it away. I noticed My match is higher and I'm now causing Ripples on my TV set which is satellite Controlled. Match with my box on is now close to about 2 where before it was Flat. I took her off and thing went back to normal. Is there a reason Why this Happened. Please any Advise on this Matter would be greatly appreciated. Cant Upload a pic.Too big. I can Email pic if needed. Thanks.
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1:1coax balun Help Please
- Thread starter LightFoot
- Start date
You don't really need it for this antenna, and besides, it does not seem like you had a need for it before. The v58 is a nice grounded antenna that hooks up quite well directly to coax.
Although, installing a coaxial choke should not give you a problem either. I run one, only 8 turns on a 6-inch form, but the leader is only about two inches to the antenna and I wound it at the end of the main coax run, so no barrel connector issues to worry about...
Although, installing a coaxial choke should not give you a problem either. I run one, only 8 turns on a 6-inch form, but the leader is only about two inches to the antenna and I wound it at the end of the main coax run, so no barrel connector issues to worry about...
LMR400 has a solid center conductor, making it a bad choice for bending around forms or constant movement like when using a rotor and a beam.
if you really feel the need to run a coax balun, buy some LMR240 UF (ultra flex)
it is the size of RG-8mini but with much better characteristics and power handling ability.
use the LMR240 UF to make your choke balun.
my guess is that you bent the LMR400 around too tight of a radius and the center conductor migrated towards the shield of the coax, thereby changing its inherent impedance.
remember that 50 ohm coax is only 50 ohms because of the distance relationship between the center conductor and the shield.
change that distance, and change the impedance of the coax.
sounds like you didnt need one in the first place anyway,
good luck,
LC
if you really feel the need to run a coax balun, buy some LMR240 UF (ultra flex)
it is the size of RG-8mini but with much better characteristics and power handling ability.
use the LMR240 UF to make your choke balun.
my guess is that you bent the LMR400 around too tight of a radius and the center conductor migrated towards the shield of the coax, thereby changing its inherent impedance.
remember that 50 ohm coax is only 50 ohms because of the distance relationship between the center conductor and the shield.
change that distance, and change the impedance of the coax.
sounds like you didnt need one in the first place anyway,
good luck,
LC
I just want to thank C2 And LooseCannon for Participating in my question. I was just wondering what might of happened because it was reading flat match in the shack with my Dummy load prior to the install so I didn't think it should of changed up by the feed point. I just don't want to keep going up and down my roof since i don't have an MFJ Analyzer. So Its staying off for know. Thanks againg guys.........................John with the wave from Sunny San Francisco.
B
BOOTY MONSTER
Guest
so if it was too tight for the coax he has and the center migrated and changed the impedance does that section or coax need to be replaced ?
i would think so ....... but that doesnt always work right . LOL
i would think so ....... but that doesnt always work right . LOL
booty,
i guess i would say "probably" on that one, but lucky for thundir, he used a separate section of coax to make his balun and used a barrel connector to connect it to his coax run.
LC
i guess i would say "probably" on that one, but lucky for thundir, he used a separate section of coax to make his balun and used a barrel connector to connect it to his coax run.
LC
B
BOOTY MONSTER
Guest
ive herd folks say the barrel connecters can cause problems . i use one on my home made wire starduster copy . 50 foot of 8x (smaller than what Thundir is using) to a 12 foot peice (8x again) with one connector cut off for connecting shield and center to grounds and radiator and whats left of the 12 foot section is wrapped neatly around a 3 or 4 inch diameter (i forget which) PVC connector . my vswr is 1.3 to 1.1 .
Last edited by a moderator:
Hello Booty Monster: You don't want that type of Balun feding a "Unbalanced Antenna"
The Colied up coax is trying to feed the antenna with equal currents, not how its designed.
Try a 9 foot length of 7/8" OD Aluminum Tubing fitted over the PL-259 connector on the antenna, and allow it to be supported down the mast, but insulated. Use cut slots in the tubing and a hose clamp to hold the tubing onto the PL-259 connector.
I have a few female bullet connectors with a coax run. But I usually have new coax to replace it if I am going use it with any power. Its just a dime holding up a dollar using cheap coax and spliced in several places.
Jay in the Mojave
The Colied up coax is trying to feed the antenna with equal currents, not how its designed.
Try a 9 foot length of 7/8" OD Aluminum Tubing fitted over the PL-259 connector on the antenna, and allow it to be supported down the mast, but insulated. Use cut slots in the tubing and a hose clamp to hold the tubing onto the PL-259 connector.
I have a few female bullet connectors with a coax run. But I usually have new coax to replace it if I am going use it with any power. Its just a dime holding up a dollar using cheap coax and spliced in several places.
Jay in the Mojave
B
BOOTY MONSTER
Guest
thanks jay . it is up in the air now but i do plan on either doing upgrades taking the main radiator to 1 inch aluminium or upgrading to a maco 5/8 and im still considering a 1/4wgp from some guy in a desert that makes the finest 5/8 cb antenna in the world (hehehe) if it becomes available and more importantly .... IF i can afford it . 
. i was of the impression that i would need the choke/coils to help/prevent CMC's , my antenna has 4 108 inch ground radials angled down and is on PVC pipe for the mast so its not grounded . ill probally go to metal mast if i get another antenna . your idea would eliminate the barrel connector (good thing) and would also apparently also give me a 5th ground radial .
now when/if i go to a 5/8 with typical horozontal ground radials do you think a regular coax bauln would be appropate or stick with the pipe idea you just mentioned or just a straight coax run to the 239 on the antenna ? would you recomended that type of antenna be grounded or insulated from earth ground (no ground wire) and insulated from a metal mast if metal is used ? or ground it as effectively as i can ?
thanks jay
. i was of the impression that i would need the choke/coils to help/prevent CMC's , my antenna has 4 108 inch ground radials angled down and is on PVC pipe for the mast so its not grounded . ill probally go to metal mast if i get another antenna . your idea would eliminate the barrel connector (good thing) and would also apparently also give me a 5th ground radial . now when/if i go to a 5/8 with typical horozontal ground radials do you think a regular coax bauln would be appropate or stick with the pipe idea you just mentioned or just a straight coax run to the 239 on the antenna ? would you recomended that type of antenna be grounded or insulated from earth ground (no ground wire) and insulated from a metal mast if metal is used ? or ground it as effectively as i can ?
thanks jay
There are a couple of things you might keep in mind. The first is that this coiled up coax is not a balun. Most people call it a bauln, but it isn't one, it does nothing that will convert from a balanced to unbalanced condition.
It is a 'choke'. It can/does affect the currents on the outside of the coax. It doesn't affect anything on the inside of the coax, other than change the total length of the feed line.
So why the change in the 'match'? Beats me, about all I can honestly think of is that it has to do with the length of the feed line. That ought to give you a hint of two anyway.
Not being sure of what the diameter of that coil is, can you really bend LMR-400 that much? My experience with LMR-400 is very limited and coiling it wasn't part of that experience. There's several different 'kinds' of '400, but anything as small as a foot or so, seems like it would be sort of tight, you know? That tightness of the coil depends entirely on the coax being used, there's no set, or 'standard' diameter for a choke, and until it gets really huge, the diameter really doesn't make a lot of difference. What's used as the coiol form is usually decided by weight more than anything else. If it's ferrous just would mean the choke could have less coils and the same inductance. Depending on how/where you do that, it might be a better solution, wrapped around a mast, for instance. (Beside the point, but I have a choke wound on the mount of a mobile antenna, big mount, little too much feed line, just worked out as a handy place to 'save' it, sort of. Haven't had any problems yet. Uh, no, isn't LMR-400.)
And just to make everyone's day...
All those PL-259's, SO-239's, double-female, double-male, connectors are not 50 ohm devices. Isn't that thrilling to know!? What their actual impedance ends up being is always a matter of how well they are assembled and the particular coax they are used on. There will almost always be an impedance 'bump' (very small one!) at any UHF connector put in the feed line. I'm not sure, but I think an 'N' connector, and maybe(?) a 'BNC' connector are supposed to be 50 ohms, but not a UHF connector (PL-259, etc.).
Does that mean I think you should run right out, buy 2 or 3 hundred 'N' connectors and change everything around you? ONLY if I get to sell you those 'N' connectors! Or in other words, no, I don't. It just won't make that much practical difference at HF, especially on 11 meters. (You don't wanna know what happened the last time I tried putting an 'N' or 'BNC' connector on a feed line, and I'm too embarrassed to volunteer it!)
- 'Doc
Having 'made your day', I'm going to the lie-berry and find a good book... and having made several 'edits' to correct spelling, I give up. If you find a few it just means I didn't.
It is a 'choke'. It can/does affect the currents on the outside of the coax. It doesn't affect anything on the inside of the coax, other than change the total length of the feed line.
So why the change in the 'match'? Beats me, about all I can honestly think of is that it has to do with the length of the feed line. That ought to give you a hint of two anyway.
Not being sure of what the diameter of that coil is, can you really bend LMR-400 that much? My experience with LMR-400 is very limited and coiling it wasn't part of that experience. There's several different 'kinds' of '400, but anything as small as a foot or so, seems like it would be sort of tight, you know? That tightness of the coil depends entirely on the coax being used, there's no set, or 'standard' diameter for a choke, and until it gets really huge, the diameter really doesn't make a lot of difference. What's used as the coiol form is usually decided by weight more than anything else. If it's ferrous just would mean the choke could have less coils and the same inductance. Depending on how/where you do that, it might be a better solution, wrapped around a mast, for instance. (Beside the point, but I have a choke wound on the mount of a mobile antenna, big mount, little too much feed line, just worked out as a handy place to 'save' it, sort of. Haven't had any problems yet. Uh, no, isn't LMR-400.)
And just to make everyone's day...
All those PL-259's, SO-239's, double-female, double-male, connectors are not 50 ohm devices. Isn't that thrilling to know!? What their actual impedance ends up being is always a matter of how well they are assembled and the particular coax they are used on. There will almost always be an impedance 'bump' (very small one!) at any UHF connector put in the feed line. I'm not sure, but I think an 'N' connector, and maybe(?) a 'BNC' connector are supposed to be 50 ohms, but not a UHF connector (PL-259, etc.).
Does that mean I think you should run right out, buy 2 or 3 hundred 'N' connectors and change everything around you? ONLY if I get to sell you those 'N' connectors! Or in other words, no, I don't. It just won't make that much practical difference at HF, especially on 11 meters. (You don't wanna know what happened the last time I tried putting an 'N' or 'BNC' connector on a feed line, and I'm too embarrassed to volunteer it!)
- 'Doc
Having 'made your day', I'm going to the lie-berry and find a good book... and having made several 'edits' to correct spelling, I give up. If you find a few it just means I didn't.