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rollers, babbling abut roller inductors




 
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Author Topic: rollers, babbling abut roller inductors  (Read 3739 times)
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Opcom
Patrick J. / KD5OEI
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« on: August 29, 2014, 06:54:25 PM »

OK so a little topic for rollers and how badly they do in tough situations. The OT was about the challenges of matching up a particular antenna: http://amfone.net/Amforum/index.php?topic=36883

So, here's the deal, after the replies on the rollers, it looks like they "considerable amounts of heat at QRO" according to W2VW. - although giant ones might be acceptable. Most folks don't find those.

From a little experience collecting them, the heavier duty they are, the less likely they are to be like a 'ham/consumer' roller in the inductance rating. YMMV.

For a wide range balanced tuner, a large inductance might be preferred such as the main coils from two BC-939 tuners. (one in each leg).
But we can't go burning up BC-939 main coils and costly store bought MFJ-tuner-sized parts.

 I'm lucky to have four 'large' ones, but their total L is not really enough for 160M, and around here 160M is a thing the funky dipole antenna is going to have to be 'forced' to do. Bad idea but I do bad ideas. It's called experiments.

This all leads to the question for this topic:

What if I put the large ones in series with the smaller ones (BC-939 ones), and bring the L of the large ones fully into the circuit -before- starting to use the L of the weaker, higher L ones?

My guess is that the more the L used in an impedance step-up, the less the current output and higher the voltage?

What I mean, referring to the schematic, is that suppose there is  1KW/50 Ohms and 4.47A at the input (223V), and the output is 2000 Ohms?
Would there then be 0.707A at the output (1400V)? Good for the roller.
At 8000 Ohms (0.35A), the voltage of 2800V might start to be an issue but my question is about current.

But if only a little of the total L, like a random 4uH were used, and the output was more like 300 Ohms, 1.8A would flow (547V). It would be better to have this through the big-wire roller, not the small-wire one.

I guess this is a strange way to arrange two rollers to try to make the massive but low-L one take more of the current but that's what experiments are for. I just wonder if the idea is sound and worth a try to make some real measurements. It would be a considerable amount of work and time to do this.

as far as what to do when the antenna is a low-Z one, and the current is high, not sure. turn the tuner around maybe.

If this is a stupid idea just say so but also say why if possible.

* balanced-tuner.pdf (6.94 KB - downloaded 412 times.)
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Radio Candelstein - Flagship Station of the NRK Radio Network.
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« Reply #1 on: August 29, 2014, 07:19:59 PM »

Let's qualify the quote a little. Rollers don't do well at QRO when run at high current and or with small inductance used.

High SWR amateur QRO applications especially on 160 meters can require the same inductor capability as a 10kw AM radio station.

Another one way trip to Palookaville is being lazy calculating amplifier plate tank values. Some folks use a roller coaster hoping to Edison the final into operation. Not a good solution.

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W7TFO
WTF-OVER in 7 land Dennis
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« Reply #2 on: August 29, 2014, 07:59:55 PM »

I've seen Broadcast phasing units with two coils on the same circuit, sort of a coarse & fine arrangement.

The coarse unit has two taps (or several with a ganged switch setup), each going to the ends of a roller coil.  The tap on the roller is the output.

One sets the coarse for a general value, then fine tunes it with the roller.

They are usually mounted parallel adjacent to each other, so a bit of mutual coupling is expected. 

That will handle more IE than a single adjustable.

I like the "Edison" analogy, try a million combinations until something actually works...LOL

Tesla & math won out, no?

73DG
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« Reply #3 on: August 29, 2014, 10:50:43 PM »

Nice as rollers may seem I like tapped coil and a very HD switch. I can arrive to close L quickly and trim with my variable caps. With a roller and I had a viewstar one once in what seems like now another life, I never knew where I was and it took forever to get where I wanted to be. In my HD homebrew tuner my  L is 15 turns of 3/8 copper tubing. Thirteen taps installed by drilling the tubing inserting some stiff #12 solid copper wire and soldering using a benzene torch. Main 15 position switch was a junk box find the looks like it came from a small welder. I keep a log of common settings on the rack so if I want for example 40m (7290kc)I switch to #7 tap, 50% in(tune) C and 75% out (load)C. then on the dummy trim for best which is often not even required. Quick durable and easy. Having had both  I have no interest in returning to  roller.
don
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Don VE3LYX<br />Eng, DE & petite Francais
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