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Author Topic: Balanced Tuner on Inverted L  (Read 888 times)
AD4J
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Posts: 3




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« on: March 31, 2010, 08:01:09 PM »

I have a 67 foot doublet (40 meter dipole) with homebrew open wire feeders. Currently, I use an unbalanced tuner (MFJ-949E) and an external balun (DX Engineering BAL050-H10-AT) for 40 - 10 meters. On 160 and 80 meters, I use one side of the feedline and doublet as an inverted L with a quarter wave raised radial for each band. On those two bands, the unbalanced tuner is used directly without a balun.

I have ordered a balanced L tuner (Palstar BT1500A) for use on 40 - 10. My thinking is that it will have lower loss in both the tuner and balun, as well as the simplicity of a single matching solution on a given frequency (L network vs. T network).

My question is: How should I tune the inverted L on 160 and 80 meters? Here are the options I have considered:
1. Continue to use the MFJ-949E unbalanced tuner for 160 and 80 only.
2. Use a coil in series with L on 160 and a capacitor on 80 to resonate it, in which case the rig (K3) tuner will handle QSY across each band. I could also use the balanced tuner after the coil or capacitor.
3. Tune the inverted L directly with the balanced tuner.

I'm particularly interested in how the third option is likely to work.

73,
Jim AD4J
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WB7TDG
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« Reply #1 on: March 31, 2010, 11:00:56 PM »

I had a Palstar BT1500A that I used with my 235 ft horintal loop that I used for 80 thru 10 meters and fed one leg only of the balanced line for use on 160.

While I could obtain a match on 160 that way, anything above about 50 watts the swr would start to climb.

I don't think the balun in the input end of the 1500A liked me doing that!

Stick with your current tuner for 80 and 160 and switch to the new tuner for the other bands.
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WX7G
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« Reply #2 on: April 01, 2010, 05:29:38 AM »

Option 3 is what I would use.
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AD4J
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« Reply #3 on: April 01, 2010, 05:30:35 AM »

Thanks for the good info on your experience with this. When you used just one side of the feedline to your loop on 160, what did you connect to the other tuner terminal?
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VE3WMB
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« Reply #4 on: April 01, 2010, 07:08:16 AM »

Sorry this isn't a direct answer to your question, but have you ever considered connecting both sides of the ladder-line together at the tuner and working that against your raised radials on the lower bands?

It might be worth a try to see how that compares with the inverted-L configuration for performance.  This would be a T configuration, where the feed-line itself becomes the radiator (vertical) and the doublet acts as a Top loading mechanism.  It may actually be easier to match on the lower bands.

Michael VE3WMB
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AD4J
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« Reply #5 on: April 01, 2010, 07:41:22 AM »

Michael: Thanks for your suggestion to work this as a T instead of an L. I did try that a couple of months ago on both bands. With the quarter wave 160 radial, the T resonates at a higher frequency than the L, so I went with the L. With the 80 meter radial, the resonant frequency is pretty much the same in either configuration (and lower than the 80 meter band).
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WB7TDG
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« Reply #6 on: April 01, 2010, 08:30:07 AM »

I grounded the terminal that goes to ground through the balun.
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KL7AJ
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« Reply #7 on: April 01, 2010, 09:48:06 AM »

You can certainly get by with your balanced tuner, but it wouldn't be my preference.  On 160 especially, the SWR can rise PRECIPITOUSLY (hmmm....I guess something can only FALL precipitously, to be grammatically correct) as you move off frequency.  If you really are using a full sized L, with no loading coil, it won't be QUITE so extreme...but....any significantly shortened and loaded antenna will have a pretty high Q.

I learned a while back that 160 isn't the band you want to "get by" with....you have to "mean it" to do anything worthwhile on 160.   Or, to rephrase:

"Life's too short for a lousy 160 antenna."

Smiley

Eric
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KL7AJ
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« Reply #8 on: April 01, 2010, 09:52:40 AM »

p.s.

   This in no way implies that an inverted L is a lousy antenna.  It's what I use, and is an excellent choice.  You just want to eliminate any unnecessary losses in the FEED system, and I don't think method 3 is the best.  I always consider any good 160 antenna pretty much as a "single frequency" antenna.

Eric
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