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Author Topic: 160 and Small Antennas  (Read 113998 times)
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WU2D
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CW is just a narrower version of AM


« Reply #75 on: October 11, 2006, 06:01:44 PM »

Frank,
I'll throw it into my simulation some day next week and see what happens.
Egg plant was pretty FBOM and my buddy Gary gave me 2 jars to bring home.

2 JARS!! AND YOU DIDNT EVEN SEND ANY DOWN THIS WAY!!

with 2 jars aorund, you better be careful that you dont throw the eggplant into the simulator Grin Grin


MMM Good and it keeps you and the XYL warm under the covers.

Mike
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These are the good old days of AM
WA1GFZ
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« Reply #76 on: October 11, 2006, 09:41:15 PM »

I simulated the balanced/balanced tuner with series tuned caps into 10 ohms. It worked pretty well. Then I added another cap across the input 1500 pf variable.
this really raised the Q of the tuner. A higher Q may reduce noise so need to look at it some more.
Every configuration I have tried so far seems to work about the same as long as the correct LC ratio is hit. The Hi pass T network will not help harmonic rejection. A T with 2 inductors and 1 cap seems to do a better job as a low pass filter.
I've only worked with resistive loads so things may change with reactance but suspect it may only modify the L/C ratios
A low Q network has the advantage of wide bandwidth but a high Q might help under poor conditions.
I will try to put the link coupled tuner in and see how it plays.
The Balanced/balanced with a dual differential cap has some interesting results.
I have one from a KW match box and might consider making a custom with 350 pf per section just to see what it will do.
Glad to share switcher cad files if anyone wants to play. You will also have to download switcher cad (freeware)
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Steve - WB3HUZ
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« Reply #77 on: October 11, 2006, 10:07:05 PM »

Interesting. Need to check out Switcher CAD.

Quote
A low Q network has the advantage of wide bandwidth but a high Q might help under poor conditions.

Although you don't want to have the Q go too high. The circulating currents get up there and loss is incurred.
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WA1GFZ
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« Reply #78 on: October 12, 2006, 08:22:12 AM »

http://www.linear.com/index.jsp

go here and down load it Steve. Pretty easy to use.
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Steve - WB3HUZ
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« Reply #79 on: October 22, 2006, 06:44:59 PM »

Frank:

If your seaside antenna was 180 feet long and about 60 feet high, the Z at the feedpoint at 1.9 MHz would be 31 -J586 Ohms. At the end of about 75 feet of 600 Ohm open wire made with #14 wire, the Z would be 19 +J96 Ohms. Not too bad. If you go with about 74 feet of 450 Ohm open wire line (same #14 wire),  you would get 14 +J0, no reactance! A Z step up of 4 gets you 56 Ohms. Might not even need a tuner.
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WA1GFZ
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« Reply #80 on: October 22, 2006, 08:31:18 PM »

Steve,
We had some high winds Friday night that pulled a lot of leaves off the trees. I  have my eyes on a tree branch that is close to the top of the shorter tree almost 70 feet up. Now if I can get a clean shot at it from the street under the  primary power run. The high side is all low voltage so it will be an easy shot up higher plus the 30 or so foot increase in elevation. I'm planning on #10 spaced 4 inches which is around 400 ohms. Also have some old glazed 6 inch spreaders so could press them into service. The feeder length should be 60 to 70 feet. I've run a number of simulations at 10 ohms on 160 meters and find I don't need a lot of L. This is good because I have a matched pair of strapping 12 uh variable inductors. The lot is 60 by 175 feet so not sure if I can get 180 feet without some hanging vertical. The end of the house is near the middle of the lot so it will depend on the branch I
 hit. TNX for the information higher Z. gfz
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flintstone mop
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« Reply #81 on: October 23, 2006, 02:23:47 PM »

OK Fine  Huh
Thanks for planting a thought in my shorted out mind......GFZ
Now that the leaves have come down, it might be time to smoke over the situation in the back yard. There are some nice tall pines back there..........approx 500 feet from the house.

Fred
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Fred KC4MOP
Steve - WB3HUZ
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« Reply #82 on: October 25, 2006, 10:53:28 AM »

Another modeloing program shows the feedpoint impedance to be around 18 Ohms resisitive, with 500-600 Ohms of capacitive reactance. Adjust feedline length and Z accordingly.


Steve,
We had some high winds Friday night that pulled a lot of leaves off the trees. I have my eyes on a tree branch that is close to the top of the shorter tree almost 70 feet up. Now if I can get a clean shot at it from the street under the primary power run. The high side is all low voltage so it will be an easy shot up higher plus the 30 or so foot increase in elevation. I'm planning on #10 spaced 4 inches which is around 400 ohms. Also have some old glazed 6 inch spreaders so could press them into service. The feeder length should be 60 to 70 feet. I've run a number of simulations at 10 ohms on 160 meters and find I don't need a lot of L. This is good because I have a matched pair of strapping 12 uh variable inductors. The lot is 60 by 175 feet so not sure if I can get 180 feet without some hanging vertical. The end of the house is near the middle of the lot so it will depend on the branch I
 hit. TNX for the information higher Z. gfz
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WA1GFZ
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« Reply #83 on: October 25, 2006, 11:40:13 AM »

Steve,
How would you simulate that load across the output of the tuner? A 18 ohm resistor with a 600 ohm Xc in parallel?
I was trying to determine the load on the home qth antenna and seems to be an inductor across the load. It is a 125 foot on a leg Vee with about 70 feet of feed line.
Adding this reactive component required a lot more C in the tuner to get a match.
This is exactly what happened. When the dipole broke I lost about 50 feet of feedline and the tuner wanted more C. Also went from a dipole to a vee.
Dave Ape Man shared some tuner ideas at hostraders.  The nice thing is I won't need a lot of L so I can build another strapping tuner and use heavy wire to reduce losses.
fc
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Steve - WB3HUZ
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« Reply #84 on: October 25, 2006, 12:09:14 PM »

That's the impedance at the antenna feedpoint, not the output of the tuner. The resistive component will be lower at the end of 60-100 feet of open wire. The reactive component will be changed in value and may be even be inductive, depending on the line length and Z. Use the feedline calculator posted today  in another thread to determine the load at the end of your feedline/output of the tuner.

Yes, you can simulate the impedance as an 18 Ohm resistor in parallel with a capacitor of 500 Ohms reactance at the frequency of interest (I used 1.9 MHz).
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WA1GFZ
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« Reply #85 on: October 25, 2006, 12:14:28 PM »

TNX will do
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W2VW
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« Reply #86 on: October 25, 2006, 12:22:56 PM »

Check this out. What are realistic Q values for tuner inductor and capacitors though?
http://fermi.la.asu.edu/w9cf/tuner/tuner.html
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Steve - WB3HUZ
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« Reply #87 on: October 25, 2006, 12:25:57 PM »

Z at the end of 70 feet of 600 Ohm ladder line calculates at 11.86 + J80.65.

A good coil would have a Q above 100, maybe more like 200.

That tuner simulator is for a unbalanced T.
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W2VW
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« Reply #88 on: October 25, 2006, 12:52:05 PM »

Yup on the unbalanced T. Most hamateurs use those into a BalUn. Watch the loss with reactance... yikes.
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WA1GFZ
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« Reply #89 on: October 27, 2006, 09:48:04 AM »

Anybody ever try a 1/2 wave delta loop on 160 with the center of the top open with an insulator in the middle. This would alow me to put up a full 250 feet of wire.
I would be on a 30 degree tilt all up about 70 feet. 60 feet across the top with an insulator in the middle sides would be 95 feet and fed at the bottom with open wire line.   
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K1JJ
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« Reply #90 on: October 27, 2006, 11:41:12 AM »

Anybody ever try a 1/2 wave delta loop on 160 with the center of the top open with an insulator in the middle. This would alow me to put up a full 250 feet of wire.
I would be on a 30 degree tilt all up about 70 feet. 60 feet across the top with an insulator in the middle sides would be 95 feet and fed at the bottom with open wire line.

Frank,

What it sounds like you would have is a 160M dipole with the ends configured in a "rhombus" and kinda laying on it's side.  The antenna take-off angle would be the average height of the array.  No a good scenario pattern-wise.

I would definately opt for your original plan of putting up a flat top fed with #8 or #10 open wire (I would instead use coax due to the ~50 ohm match - keep it simple)  and the ends dropped down for whatever you needed to fill it out to 1/2 wave.  Can't beat a flat dipole.  Any other config close to the ground in terms of wavelength is a compromise, OM.

T
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Steve - WB3HUZ
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« Reply #91 on: October 27, 2006, 03:49:28 PM »

Quote
Anybody ever try a 1/2 wave delta loop on 160 with the center of the top open with an insulator in the middle.


Sounds more or less like a 160 meter halo. Don't see how it would be much, if any better than a dipole.
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WA1GFZ
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« Reply #92 on: October 27, 2006, 04:14:35 PM »

only that it would have 1/2 wave length of wire in the air and tilted 30 degrees on the side of a hill facing west.
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K1JJ
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« Reply #93 on: October 27, 2006, 04:33:07 PM »

The quad or delta or even rhombus to some degree works FB when used as a full wave, but as a 1/2 wave broken at the opposite junction you are into the leg cancellation zone. Picture it like a severly angled 1/2 wave inverted vee.

Try to get that flat 160M dipole using dropped loading ends into the same place on the hillside for better performance, OM.

T
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

Wise Words : "I'm as old as I've ever been... and I'm as young as I'll ever be."

There's nothing like an old dog.
WA1GFZ
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« Reply #94 on: October 27, 2006, 11:32:35 PM »

OK just putting too much thought into it.
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W2VW
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« Reply #95 on: November 02, 2006, 02:56:02 PM »

That's the impedance at the antenna feedpoint, not the output of the tuner. The resistive component will be lower at the end of 60-100 feet of open wire. The reactive component will be changed in value and may be even be inductive, depending on the line length and Z. Use the feedline calculator posted today  in another thread to determine the load at the end of your feedline/output of the tuner.

Yes, you can simulate the impedance as an 18 Ohm resistor in parallel with a capacitor of 500 Ohms reactance at the frequency of interest (I used 1.9 MHz).

I've been thinking about this and can't grasp the concept. I know that the circuit impedance can be converted from series to parallel but I keep picturing what a change in the J portion does. No J and all that is left is radiation resistance and a little (in practical terms) resistance from copper loss. Lots of J and the power will not transfer unless the J is overcome. That looks like a series circuit to me. I did find one online reference which agrees with this for a model of less than a resonant half wave ant. The reactance model then changes with the J in parallel up to a full wave where it flips to series again. Calling all professors.
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Steve - WB3HUZ
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« Reply #96 on: November 02, 2006, 04:59:07 PM »

I think I was smoking dope when I wrote that. It should be R in series with the cap. It can be converted to the parallel equivalent by


Rpar = Rs2 + Xs2/Rs

Xpar = Rs2 + Xs2/Xs
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W2VW
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« Reply #97 on: November 02, 2006, 06:05:25 PM »

OK. I feel better now.
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kf6pqt
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« Reply #98 on: April 18, 2007, 07:31:59 PM »

Hey, for the tuner design in the amwindow tech page... Do I really, really need to run 3/8" tubing for the main coil? Sad that its the most painfully expensive part these days! I have a 4kv ef johnson varable cap as big as my thigh that I picked up at a swap for cheap, but the thought of shelling out for all that copper makes me cringe.

I'm not going to be running a "New England Kilowatt," just a pair of 811a's.  Wink

Thanks,
Jason kf6pqt
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W6IEE, formerly KF6PQT
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« Reply #99 on: April 18, 2007, 10:11:27 PM »

Hey, for the tuner design in the amwindow tech page... Do I really, really need to run 3/8" tubing for the main coil?

This tuner?
http://amfone.net/ECSound/K1JJ13.htm

As the power handling capability is defined by the diameter of the tubing/wire used in the main coil, I think you could get away with some #4 ga. solid copper coated steel.  Bet Apex would have a hunk.
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