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Author Topic: 160 and Small Antennas  (Read 114022 times)
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WA3VJB
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« Reply #50 on: October 04, 2006, 10:48:46 AM »

Where's the full size graphic of that?  Found it.
I need typeface for the hard-of-seeing.
Center support is possible yes, but yow, 60 feet is a lot of lumber. 
Remember this has to be or at least look temporary.
Tnx

Any thoughts on this one?

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WA1GFZ
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« Reply #51 on: October 04, 2006, 11:08:42 AM »

Steve,
Look close the fold back to the load is the center of the three and all three tied at the ends. So the high current section is two conductors in parallel on the outside.
The feed line is terminated to the outside 2. Look at the configuration with the balun at the ground using open wire line.  fc
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Steve - WB3HUZ
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« Reply #52 on: October 04, 2006, 11:20:51 AM »

The one you posted is a receive antenna. A push-up, guyed mast is temporary.

Where's the full size graphic of that? Found it.
I need typeface for the hard-of-seeing.
Center support is possible yes, but yow, 60 feet is a lot of lumber.
Remember this has to be or at least look temporary.
Tnx

Any thoughts on this one?


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W2VW
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« Reply #53 on: October 04, 2006, 10:32:12 PM »

snip  the antenna length will be about 150 to 160 feet depending on which branch I catch on the trees.

Frank, that is plenty. Should not be too hard to feed on 160 at all. Run the model. Just has plenty of SWR on the feeder. No big deal. More copper = more signal.
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The Slab Bacon
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« Reply #54 on: October 05, 2006, 07:51:13 AM »

snip  the antenna length will be about 150 to 160 feet depending on which branch I catch on the trees.

Frank, that is plenty. Should not be too hard to feed on 160 at all. Run the model. Just has plenty of SWR on the feeder. No big deal. More copper = more signal.


Yea, what he said!!
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WA1GFZ
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« Reply #55 on: October 05, 2006, 08:59:08 PM »

I ran some simulations on tuners driving low Z loads and it is interesting how one could have a nice match but 4 to 6 dB of loss. Frank You said you had a tee but what is it 2 Caps and one inductor? how are the caps connected. I would like to dump your values in and see how it compares to others I have tried. We know your's works so I could find the antenna Z that sets the loss lowest then use that load to try other configurations. I found the balanced/balanced tuner didn't need much L to convert 50 ohms to 25 ohms. Reconfigurating it turned it into a high pass network.
The only way I could use l valuse greater than 2 uh each was to step 50 ohms up to 450 then use the network to get back down. Not pratical.This makes me think the transformer on the output side works when the antenna Z is low. Then what happens when you go to higher bands?? 


A dual differential cap in the output like the johnson match box gave it a very wide tuning range. But the value has to be much higher than used in the matchbox.
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The Slab Bacon
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« Reply #56 on: October 06, 2006, 08:06:34 AM »

Frank,
         It is 2 caps and 1 inductor. the 2 caps are in series from the inpoot to the outpoot, with the inductor from the junction point of the 2 caps to ground. Your basic simple as it comes "T" tuna.

I have used it on 80, 40, and 20. I have never found a situation that it would not give a good matchup, and have never needed to add any parallel capacitance across the outpoot.
 
                                                  The Slab Bacon
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WU2D
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CW is just a narrower version of AM


« Reply #57 on: October 06, 2006, 09:07:04 AM »

Hi Frank,

This is what I would suggest for a small 160M antenna. It is modeled on the antenna that I used to used on my 1750 M Beacon in the early 1990's - It really got out with a 1 Watt input power transmitter. That antenna was 30 Feet high and had a 40 FT diameter Top Hat which was made of a loop of hardline suspended by several large Pine Trees. It looked wierd but worked very well. I call it WLW. This is a mini version.

See you at Hosstraders!

Mike WU2D


* WLWU2D.jpg (52.4 KB, 571x673 - viewed 912 times.)
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WA1GFZ
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« Reply #58 on: October 07, 2006, 12:01:54 AM »

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.
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The Slab Bacon
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« Reply #59 on: October 09, 2006, 09:03:02 AM »

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
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WA1GFZ
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« Reply #60 on: October 09, 2006, 09:17:18 AM »

Frank,
I would have if I knew a way to get it delivered. I had to bug out at 7:30 Friday night.
I think most of the gang was out eating.
Bought some antenna rope and a pair of fixed vac caps 75 pf lots a volts.
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WA1GFZ
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« Reply #61 on: October 09, 2006, 11:29:01 AM »

Frank,
I simulated your tuner and found a good match at a number of combinations but only a tight range put maximum power / current into the feed line. The more I look at tuners the more I'm convinced of the need to monitor tuner output current at the feed line. I don't see any other way of knowing if the tuner is in the best position to transfer power to the antenna.
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The Slab Bacon
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« Reply #62 on: October 10, 2006, 07:58:46 AM »

Frank,
        I have said that for years. An swr meter between the tuna and the transmitter doesnt tell the whole story. It only tells you if ur keeping the transmitter happy or not.

With a roller inductor tuna you have too many possible choices, and not all of them work in your favor. An RF ammeter in the feedline WILL tell the whole story. Many times a setting that shows some rize in the swr to the transmitter gives a lot more current into the feeders. Unfortunately, I smoked my last one playing with my short antenna on 160 with the 4X1 transmitter.

Many times the old way is still the best way. Ah, yes, what's old is new again!

                                                                The Slab Bacon
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W1VD
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« Reply #63 on: October 10, 2006, 09:50:13 AM »

2 cents...

The best method I've found to adjust the adjust C - L - C tuners is to start with the capacitors at full mesh and look for a vswr dip with the  inductor. Only reduce C values enough to get a match. This normally yields max antenna current.

Jay 

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K3ZS
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« Reply #64 on: October 10, 2006, 10:18:59 AM »

I read online an article about tuning a T tuner for maximum efficiency (don't remember the website).   The main point was to have both caps fully meshed and tune for minimum SWR with the inductor first.  Then go back and forth with the inductor and the input capacitor for the best SWR, leaving the output cap fully meshed if possible.   I managed to tune my 135 ft doublet and about 160 feet of ladder line on all bands except 80M with the output cap fully meshed to 1:1 SWR.  I am using an external DX Engineering balun on the output.   I suppose the lower impedance of the antenna matched with an almost 1/4 length of the feedline on 80M is the reason for not being able to do it on 80M.
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WA1GFZ
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« Reply #65 on: October 10, 2006, 10:22:42 AM »

Jay,
that makes sense. My balanced antenna tuner has a pair of variable inductors in l networks with a wide range of adjustment. I need to connect the rf amp meters back into the line. I find the caps will flash if I run the series L too low.
 I'm thinking of building a pair of high voltage current transformers. This way the output could be rectified and monitored at the operating position.
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W1VD
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« Reply #66 on: October 10, 2006, 10:54:43 AM »

Roger the current transformers. At LF I use a single wire primary through the ferrite torroid core with 50 or 100 turns as the secondary and terminate that in 50 ohms so the reflected resistance into the pass through single turn wire is low. If you had one of these on each leg of the open wire you could run the two outputs to a dual trace scope and have a real look at things. Once happy with the tuner adjustments replace the scope with a couple diodes, resistors and meters.

Jay   
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WA1GFZ
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« Reply #67 on: October 10, 2006, 11:01:12 AM »

Yup,
I figure a 1 inch ID core with a plastic spacer inside to hold the feed line in the center of the core. Also a couple layers of teflon tubing on the feed line. 50 ohm load would also be a good interface to a monitor scope or spectrum analyzer. 50 ohm attenuator pads if required. Also 50 ohm coax could work.  A center tapped winding would also work as a SWR monitor if you wanted to be crazy about measuring things. This would work cool in Frank's set up since the balun is outside.
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kf6pqt
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« Reply #68 on: October 10, 2006, 11:04:06 AM »

Hey, if somebody has a chance, could they draw a quick diagram of the link-coupled tuner? I dont know if its just a matter of not enough caffeine in the blood yet, but I'm having difficulty visualizing it!

Thanks,
Jason kf6pqt
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WA1GFZ
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« Reply #69 on: October 10, 2006, 11:26:23 AM »

I think the tom vu tuner is on this site somewhere ansl check out rick measures turer. frank is using a t tuner 2- 500 pf variable caps in series with a variable inductor to ground connected at the junction between the two caps.
The T tuner has a heck of an adjustment range but it is a hipass network so does not help much in reducing harmonics. The t might be easier to use with a low Z load.
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Steve - WB3HUZ
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« Reply #70 on: October 10, 2006, 08:36:10 PM »

Quote
Hey, if somebody has a chance, could they draw a quick diagram of the link-coupled tuner? I dont know if its just a matter of not enough caffeine in the blood yet, but I'm having difficulty visualizing it!


A schematic is found in the article below.

http://www.amwindow.org/tech/htm/160smallants.htm
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kf6pqt
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« Reply #71 on: October 10, 2006, 08:38:22 PM »

Awesome, thanks! Something tells me there was a direct link that I missed.  Tongue

Caffeine's a hell of a drug!

-Jason kf6pqt
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Steve - WB3HUZ
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« Reply #72 on: October 10, 2006, 08:50:37 PM »

If that tuner config won't work (may not for some very low-Z loads), try this config.


http://www.amwindow.org/misc/gif/SeriesTuner.gif
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WA1GFZ
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« Reply #73 on: October 11, 2006, 08:50:24 AM »

This is a configuration I need to throw into the simulator..
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Steve - WB3HUZ
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« Reply #74 on: October 11, 2006, 03:31:58 PM »

I posted previously...

Quote

I've looked at those BushComm antennas before. Interesting stuff. What I can't quite tell is if the three wires in the flattop are all tied together, just making it a "fat" dipole, or if some sort of folding back or snaking of the wires are done to increase length. Some company in the NE area (IIRC) makes such an antenna. It was discussed here on the forum a while back.


Found the link. Called the Cobra, caw mawn!

http://www.k1jek.com/
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