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Ladder Line to Coax




 
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Author Topic: Ladder Line to Coax  (Read 16540 times)
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WA1GFZ
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« Reply #25 on: December 20, 2009, 08:48:15 PM »

Dave, I think your problem is you have too much common sense and not enough common mode.
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W2VW
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« Reply #26 on: December 20, 2009, 09:27:44 PM »

Dave, I think your problem is you have too much common sense and not enough common mode.
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K3ZS
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« Reply #27 on: December 21, 2009, 12:06:51 PM »

The DX Engineering web site recommends using a 1:1 current balun as an add-on to an unbalanced tuner.  The reason is that by chance the impedance could just as much be much lower that 50 ohms at the end of the feedline than higher.   In that case the 4:1 makes it even lower.   If you know that your impedances are always going to be higher then the 4:1 is the better choice.    Seems to me if you have to make a choice it would be better to calculate or measure your actual impedance at all the bands you want to use.   The same would go for link coupled tuners, whether to use series or parallel tuning.
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Steve - WB3HUZ
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« Reply #28 on: December 21, 2009, 12:42:23 PM »

You would have to imagine this because that's not what exists with balanced line.



It solely depends on the length of your feedline and the length of your ground system because the feedline is going to act like a single wire Marconi and both transmission lines are at the end open circuited.

In most cases the Z at the input to the feedline with common mode will be very low, but you still only have a single wire Marconi with an insufficient ground in most cases. Imagine tuning a single ľ wavelength wire without the other ľ wave mirror half/ground connected.

Anyway, I’m done with this topic for now so you guys can take it from here. You can believe what you want, that’s your choice.
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W2VW
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« Reply #29 on: December 21, 2009, 01:10:50 PM »


If you look at those 4:1 toroid baluns used inside of all modern tuners and ready-made remote baluns the center of the windings are grounded. Depending on the length of the feedline and the length of the ground system the common mode Z can be really low. It just depends on where that feedline length is resonate. The 4:1 baulns will usually get pretty warn on 75 and 160, but itís better than overheating and burning up the components inside of the tuner. I posted earlier that the main issue was the balunís power rating.



Soooo you think the common mode current on a balanced feedline depends on resonance somewhere??
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WA1GFZ
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« Reply #30 on: December 21, 2009, 02:40:37 PM »

WOW
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K3ZS
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« Reply #31 on: December 21, 2009, 04:40:08 PM »

My last post I assumed this was with balanced ladder or window line.    I found out the hard way that the balun built into my MFJ just was not providing a very good balance on 40 and 80 meters.   On 160 it might as well not been there at all.    I salvaged the situation by getting an external high power balun.    I plan on building something like the K1JJ tuner for 160-40.   Will be curious to compare that with what I have now.
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WA1GFZ
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« Reply #32 on: December 21, 2009, 04:51:34 PM »

You will have a real tuner if you build one then you can sell the toy on epay
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Ed/KB1HYS
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« Reply #33 on: December 21, 2009, 06:09:04 PM »

The MFJ baluns are tiny, barely adequate for 100w SSB. Well atleast mine was.  It got baked when i was running my Valiant.

A good link-coupled tuner is easy to build, costs a lot less per watt of power handling (compared to commercial products) and will be able to tune just about anything from the gutter & Down spout to a Multiband OW fed Dipole - no balun required.
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73 de Ed/KB1HYS
Happiness is Hot Tubes, Cold 807's, and warm room filling AM Sound.
 "I've spent three quarters of my life trying to figure out how to do a $50 job for $.50, the rest I spent trying to come up with the $0.50" - D. Gingery
W2VW
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« Reply #34 on: December 21, 2009, 08:45:02 PM »

The MFJ baluns are tiny, barely adequate for 100w SSB. Well atleast mine was.  It got baked when i was running my Valiant.

A good link-coupled tuner is easy to build, costs a lot less per watt of power handling (compared to commercial products) and will be able to tune just about anything from the gutter & Down spout to a Multiband OW fed Dipole - no balun required.


A link coupled tuner used this way IS a balun.
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WA1GFZ
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« Reply #35 on: December 21, 2009, 09:05:46 PM »

yes very true Dave. And a T tuner is an UN-UN
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Ed/KB1HYS
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« Reply #36 on: December 21, 2009, 10:47:54 PM »

The MFJ baluns are tiny, barely adequate for 100w SSB. Well atleast mine was.  It got baked when i was running my Valiant.

A good link-coupled tuner is easy to build, costs a lot less per watt of power handling (compared to commercial products) and will be able to tune just about anything from the gutter & Down spout to a Multiband OW fed Dipole - no balun required.


A link coupled tuner used this way IS a balun.

Funny, but I guess that's right.  I never looked at it that way, I only looked at it as an impedance transformer, not as an unbalance to balanced transformer as well, which it is...

Well I'll be...
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73 de Ed/KB1HYS
Happiness is Hot Tubes, Cold 807's, and warm room filling AM Sound.
 "I've spent three quarters of my life trying to figure out how to do a $50 job for $.50, the rest I spent trying to come up with the $0.50" - D. Gingery
W1GFH
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« Reply #37 on: December 22, 2009, 03:38:27 PM »

As a result of this (rather long and interesting) discussion I have taken a sledge hammer to any 4:1 baluns in my possession, pummeled them to dust, and scattered the remains among unmarked graves. Cheesy
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"A perfect 1:1 SWR is for sissies" - Joe W1GFH
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« Reply #38 on: December 22, 2009, 04:41:59 PM »

Actually, I confess, I operated a 4:1 balun and a T-tuner with a multiband nonresonant dipole for years. I enjoyed lots of terrific QSO's with stations all over the world and didn't even know I was doing the wrong thing...
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"A perfect 1:1 SWR is for sissies" - Joe W1GFH
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« Reply #39 on: December 22, 2009, 05:03:47 PM »

Actually, I confess, I operated a 4:1 balun and a T-tuner with a multiband nonresonant dipole for years. I enjoyed lots of terrific QSO's with stations all over the world and didn't even know I was doing the wrong thing...

Chances are you were only doing the wrong thing 1/3rd of the time.
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The Slab Bacon
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« Reply #40 on: December 23, 2009, 10:29:18 AM »

This 4:1 balun has served me very well for many years! ! !


* balun!.jpg (55.93 KB, 480x710 - viewed 221 times.)
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flintstone mop
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« Reply #41 on: December 23, 2009, 10:39:54 AM »

This 4:1 balun has served me very well for many years! ! !

OK Frank ....wecome back home.
That was the balun you made? Very nice and big ball#.
Could you pls PM me and give a list of material....the mixture for the Ferrite and the number of turns. I can hopefully make out from the pic what goes where. I gotta make a copy of that for future uses.
Phred
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Fred KC4MOP
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« Reply #42 on: December 23, 2009, 11:49:37 AM »

What led me to find out the lousy balance of the MFJ tuner balun was the noise pickup from all the noise and crap generators in my house.   At one time, being a cheapskate, I was using and end-fed wire with an L tuner.    I set up a temporary 40M coax fed dipole about 50 feet from the house.   The noise from the house was greatly reduced.     I then set up a 130 ft doublet about 150 feet from the house, fed with #14 window line.    I got an MFJ T-tuner to use with it.    I found out that the noise was about as bad as with the end fed wire.     I tried an external, but low power voltage balun and found the noise pickup went away on all bands.   I confirmed the crappy inbalance with a scope and a pair of matched 100 ohm resistors to ground.  I then purchased a high power rated 4:1 current balun from DX Engineering rated for use with tuners with HV rated insulation.    I have been perfectly happy with using it with the MFJ.    The balun stays cold when running with the linear amp on 80-10M.   I can only run barefoot on 160.    With the shortened antenna on 160, and everything tuned, I can run 100W carrier into the balun and don't notice any heating.    However, maybe I don't know what I have been missing so I will try a link coupled tuner and do some honest comparisons between the two systems to see if I see a difference.
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W2VW
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« Reply #43 on: December 23, 2009, 03:05:04 PM »

http://www.hnsa.org/doc/radio/chap9.htm
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K3ZS
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« Reply #44 on: December 23, 2009, 04:56:05 PM »



Because most 4:1 baluns use toroids it reduces common mode interference coming back down the coax to your equipment so the received noise decreases or will often just go away. But, since the center of the balun's windings are usually grounded it induces common mode on the feedline during transmit.

Build a real link coupled tuner and don't tie the series caps (if used) to ground in the middle. Thatís how you eliminate it.

I see your point about common mode voltage, but that's why you use a balanced line and a balanced input device, to cancel out common mode signals.    The isolation of link coupling presumably has other benefits as you have described.

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WA1GFZ
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« Reply #45 on: December 24, 2009, 09:55:31 AM »

Bull Pucky
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