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Author Topic: Will this coil work for a balanced tuner?  (Read 17508 times)
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ke7trp
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« Reply #25 on: November 21, 2010, 11:17:00 PM »

Thank you!  Someone wrote 43 UH on it and that is probably where it is tapped for with the single tap that was on the coil. This will work if in fact, I have enough space to tap for the bands.

C


Looked up the Johnson coil in the old "Radio-Electronic Master" catalog. It lists the 200-206 as 50uh.
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K5UJ
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« Reply #26 on: November 21, 2010, 11:27:21 PM »

could you use the GDO in the procedure above but find band tap points by shorting the ends to some pair inner points, one on each end, and putting the cap across the unshorted part of the coil?   

Rob,

If I correctly understood what you were asking this was probably the most typical use in the old days. 

Okay right; thanks--what I was searching for is an easy way to get in the ballpark finding places to tap a coil for a balanced tuner with a link in the middle.  I was wondering if you could take a coil of decent size, and set the GDO in the middle of 80 m. say, (to cover the band with one pair of taps) then start shorting the coil coming in from each end equally, until you have shorted enough turns on each end to achieve a dip on the meter.  Then repeat coming in farther shorting more turns for 40 m. etc.  I wondered if this might be a way to mess around with just the coil, marking the points on it so that once the whole thing is built it would make it faster to find the actual tap points.  John (or someone) wrote that finding the tap points the first time is a pain.  I can believe it.
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Steve - WB3HUZ
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« Reply #27 on: November 22, 2010, 07:58:11 AM »

If you are not dipping it when it's connected to the antenna, it probably won't be close. Remember, with the tuner, you are resonating the entire antenna system - tuner, wires and feedline.
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K5UJ
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« Reply #28 on: November 22, 2010, 08:17:52 AM »

If you are not dipping it when it's connected to the antenna, it probably won't be close. Remember, with the tuner, you are resonating the entire antenna system - tuner, wires and feedline.

Okay thanks Steve; oh well, you win some you loose some  Cheesy  I guess there's no easy way here.
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flintstone mop
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« Reply #29 on: November 24, 2010, 05:33:24 AM »

I need some more books.  My handbooks have a very small section on tuners and how to build one. So not much to learn with the books I have.  I probably wont have time until after the Tday holliday but I am going to mock this up on a plywood board and start playing around with it.

C
Hi Clark I think if you tackle the famous K1JJ tuner you will be impressed with the ease of tuning and simplicity.
I wrestled with 3/8 copper tubing and wound it on a 6 inch PVC pipe. I found a ceramic coil form 3 inches dia and wound 6 turns on that. That's the input coil. I carefully grabbed the coax connected to the input coil while transmitting and found a better match by moving it around within the bigger coil. First I made sure that my antenna taps and cap were equal distances and then played with the input coil,,,,THEN I used clear RTV sealant to permanently fix the input coil in its spot.

Tom or Steve posted mods to enable 160-10 use .
FRED
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Fred KC4MOP
w3jn
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« Reply #30 on: November 24, 2010, 11:11:19 AM »



 I guess there's no easy way here.

The easy way is to beg borrow or steal a HP 3577A, or a service monitor with a tracking generator and a directional coupler.
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W2VW
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« Reply #31 on: November 24, 2010, 12:59:06 PM »

You forgot rent.



 I guess there's no easy way here.

The easy way is to beg borrow or steal a HP 3577A, or a service monitor with a tracking generator and a directional coupler.
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k4kyv
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Don
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« Reply #32 on: November 24, 2010, 01:20:29 PM »

I haven't bothered to calculate μHs in a coil for decades.  Years of working with transmitters gives me a ball-park idea of the tuning range of a coil just by eyeballing it.  I figure out the amount of capacitance I need, then find a bread slicer within that range, attach the coil with clip leads, and search for resonance.  I then add or subtract turns by moving the clip around on the coil until it resonates with the appropriate amount of capacitance. Then I trim the coil to the required number of turns and fabricate some kind of physical mounting.

I have several GDOs, but usually I just tune my transmitter to frequency and run the variac way down to only a few watts output, and couple to the coil with a JS link, maybe a couple of turns of clip lead or hookup wire, and hold a neon lamp near the  coil, using minimum coupling to the transmitter that allows the lamp to light up at resonance.

I have tried the mathematical method of calculating the inductance needed, then calculating the dimensions of the coil, but find the trial-and-error method as described above much faster, and the results usually come out right the first time.  When doing it by calculations and then constructing the coil, on the first try I would be lucky to get it within +/- 40% anyway, so I still ended up doing trial-and-error, regardless.

I don't even think about μHs; I just go by whatever resonates with the appropriate capacitance.
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flintstone mop
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« Reply #33 on: November 26, 2010, 10:21:00 AM »

Clark
Tuning my K1JJ tuner on its virgin voyage took about an hour to find the happy spots for 160-40M using the famous MFJ 259 analyzer.
I have an A3S for the "upperbands"

Fred
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« Reply #34 on: November 27, 2010, 12:51:03 AM »

Some of those old Agilent CDMA analyzers have an analog service monitor included, with a 400 KHz- 1 GHZ tracking genny/spec an.  I use the 8935 and it can be had for about a grand.

A hamfest coughed up a couple of MiniCircuits directional couplers for ten bux.
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