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Author Topic: Sloper for 80/160m  (Read 8310 times)
PU2LYC
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Posts: 6




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« on: August 11, 2010, 10:59:29 AM »

Dear ham friends,

I'm looking for to work on the lower bands and I intent to build a Sloper antenna.
Is that possible to build a sloper antena that works in 80m(75m)/160m. Maybe I'll need to use some coil/inductor and coaxial balun.
Does anybody know any scheme, website or literature that has information about Sloper Antena for 80/160m, with draw, schematics of the coils (if needed), choke bakun and the others stuffs?

Thanks for the help,

Yuri - PU2LYC
« Last Edit: August 11, 2010, 05:00:27 PM by Yuri Jivago De Maman » Logged
WB2WIK
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« Reply #1 on: August 11, 2010, 06:01:34 PM »

Yuri, how tall is the tower you'll be hanging the sloper antenna from?

If it's tall enough, I have some great plans for a dual-band sloper, but the tower needs to be pretty tall or it won't work.
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PU2LYC
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« Reply #2 on: August 12, 2010, 03:46:06 AM »

WB2WIK,

Unfortunatelly my tower is about 50' heigh. That's why I tought in a coil sloper antenna.

73's

PU2LYC
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K4SAV
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Posts: 1851




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« Reply #3 on: August 12, 2010, 09:05:32 AM »

Getting a sloper (1/4 wave wire) to operate efficiently is difficult because your tower is part of the antenna and that tower must be of the proper configuration for that to happen.  For best efficiency the current should be confined mainly to the sloping wire and the top section of the tower above the attachment point, with minimal amount of current in the bottom section of the tower below the attachment point.  Most people don't modify their tower just to get a sloper to work.

Here is an example of something that should work well on 80 meters.  A 110 ft tower with a 3 element 40 meter Yagi on top, a quarter wave sloping wire attached at the 80 ft point on the tower and sloping to 50 ft above ground.  For 160 the best configuration would require a tower over 200 ft tall.

That should produce a good antenna for 80 meters, but other configurations will "work".  They just won't be as good, and some configurations may have very poor performance.  Invariably a short tower will produce large currents in the bottom section of the tower, and that current goes into the dirt and produces losses.  That loss can be reduced a little by adding a radial system to the tower.  A short tower with only a small amount of Yagi loading on the top will produce a configuration that looks a lot like an inverted vee with a very acute included angle and with one end of the wire connected to ground.  Most people would never implement something like that knowingly, but that's what you will have with a sloper on a short tower.

A short tower with some significant amount of loading on the top will cause the sloper system to look like a three leg antenna.  That can produce some interesting resonance points, at frequencies where you never expect a resonance.

Of course it is pretty easy to get a good SWR on a short tower because the loss in the dirt lowers the SWR and widens the bandwidth.  The gain just drops.  If a short tower is used, guy wires should be insulated, all cables should exit the tower at the bottom and have their shields connected to ground at the bottom of the tower, and a radial system should be added to the tower.  Other antennas being held up by the tower, such as inverted vees, should have a very good choke (that works well on the sloper frequency) added at the feedpoint of the vee to keep that antenna from loading the tower.  (A wire which loads the tower might be a good thing if that wire was attached at the top of the tower, but that will interfere with the Yagi.)

Most antennas are a lot easier to make work correctly, compared to getting a sloper to work correctly.

Jerry, K4SAV
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PU2LYC
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« Reply #4 on: August 14, 2010, 05:42:00 AM »

Jerry - K4SAV,

TKS a lot for your explanation about low-bands antennas, mainly the sloper issue. For sure I'll looking for some solutions to my tower. For now I'll study and for sure give a try to the Reduced-Size Half Sloper described at WD8DSB, Don Kirk, on ARRL's Wire Antenna Classics. What do you think? For 80m I did a research and found some kind of antennas, even sloper that requires a 50/60 feet tall tower. I intent to try another style of wire antennas, such trap dipole for 40/80m and full dipole.

TKS again and hugh 73,

Yuri - PU2LYC
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K4SAV
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« Reply #5 on: August 14, 2010, 03:35:06 PM »

I have the article by WD8DSB.  Notice that he doesn't say anything about the Yagis on top of the tower for loading, and he also says that you can build this without ANY top loading, stringing it from a tree for example.  That's the configuration that I said didn't work well.  So I decided to put this antenna on EZNEC to get an idea of its gain.

There appears to be some discrepancy in his coil data.  You can't wind 90 turns of enabled wire within a coil length of 4.5 inches.  That requires at least 5.0 inches.  Also that many turns makes the antenna resonate much too low.  I think this should have been 80 turns in 4.5 inches (which can be done if close wound).  That gives a coil of 41.3 uH, 4 pf of distributed capacitance and 2.9 ohms of loss resistance.  That also makes the simulation reproduce his SWR curve.

His tower is 40 ft high and he used a ground rod at the base of the tower with no radials.  EZNEC says the gain of this antenna is -11 dBi on 1.8 MHz in its best direction, and -12.2 dBi in the opposite direction.  Dissipation in the coil is low, mainly because of all the ground loss.   Radiation resistance of this antenna is close to 3.2 ohms and the feedpoint resistance is close to 54 ohms.  That gives you an idea of where all the power is going.  Antenna efficiency is about 7.3%.

Also his feedline choke doesn't do anything if the feedline is taped to a tower or metal mast.   The coupling between the two just puts the currents right back on the feedline.

Jerry, K4SAV
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WD8DSB
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« Reply #6 on: January 11, 2011, 09:04:19 AM »

Jerry and gang,

There was an error in the original article regarding the length of the coil, and it should have said 4 7/8".  The sloping wire needs to be shortened to bring the antenna to resonance in the desired section of the band (as Jerry mentioned). 

Yes, efficiency is low, but still one of the easiest ways to get on the topband.  I'm at a new QTH using a 53 foot tall vertical (radiation resistance = 5.0 ohms per EZNEC) with 48 short ground radials (average 60 feet in length), and I sure can't say it operates heads over heels (based on contest results, etc) to the reduced size half sloper as I described it in QST in which I just used a single ground rod (but yes I did have a TA33 which would have provided some top loading when using my half sloper).  I just modeled the reduced size half sloper (no top loading), and I actually come up with a radiation resistance around 6.7 ohms (using EZNEC) which is more than my 53 foot vertical, and the reduced size half sloper gain is higher in one direction and equal in the other direction compared with the vertical when both are just fed against a ground rod (using equivalent ground conductivity).  Looks like the gain of the vertical is about 2.5 dB better when using a perfect ground.

Choke at the feedpoint does do something (it does provide a high impedance on the shield at the feedpoint which forces the current into the tower) but yes the proximity of the coax to the tower can induce current back onto the outside of the shield and therefore a choke placed down near ground level would be a good addition.

Bottom line is that the reduced size half sloper is a very easy way to get on the topband which was the goal.

I did do extensive real world testing of feedpoint impedance vs. mounting height of half slopers which shed a lot of light into why folks often have difficulty with half slopers and their feedpoint impedance at resonance.  The 160 meter half sloper is easy to duplicate as long as the mounting height is approximately 40 feet or less (based on my tests).

Just FYI,
Don (wd8dsb)
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K2DC
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« Reply #7 on: January 11, 2011, 10:55:58 AM »

Yuri,

   If you're not opposed to commercially built antennas, the Alpha Delta DX-A has worked extrmely well for me.  It is two half-slopers, one simple wire for 80M, and a second with trap/center loading coil for 40/160M.  Both wires are 66' or less in length, and need to be installed 90 degrees or more apart to prevent interaction.

   Mine has the feed point at 58' on my tower, and about 5' below my tribander with a dedicated wire to ground, rather than bonded to the tower.  On 40M and 80M I see no difference between it and the parallel 40/80M inverted vees that it replaced.  On 160M I had enough confirmed for 160M DXCC in less than 9 months.  About US$100 plus shipping from stateside.

GL & 73,

Don, K2DC

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WD8DSB
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« Reply #8 on: January 12, 2011, 04:33:34 AM »

K2DC,

Great results from your half sloper.  I also tested my half sloper with it bonded to the tower versus a single wire from the feedpoint shield to ground and saw very little difference in the results (very little change in resonant frequency, etc.) which indicated my top loading was not a significant part of the picture in my installation.

As a side note, the half sloper up in the tree in my article was actually the idea of the ARRL.  I have since tested my reduced size half sloper not tower mounted (used a fiberglass popup mast to simulate a tree installation) in which I did not use a choke at the feedpoint, and I made the coax coming straight down to ground from the feedpoint just long enough to reach the ground.  At this point I installed a BNC connector on the end of the coax which was at ground level (call this coax 1), then I used a BNC barrel connector to attach coax number 1 to another piece of coax (coax number 2) to get back into the shack and wrapped the beginning section of this second piece of coax (coax 2) into a coil to make a choke (force the current on the outside of the coax into the ground rod and not allow it to travel back to the shack on the outside of the coax).  Then I grounded the barrel connector between coax number 1 and coax number 2 (connected the outside of the barrel connector to my ground rod).  This method worked just great, and this method uses the outside of the coax shield as the wire connection back down to ground which eliminates the separate wire required for ground for the tree mount approach (very clean installation).

Just FYI,
Don
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NZ0T
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« Reply #9 on: January 12, 2011, 12:43:40 PM »

I used the DX-A at our old QTH on a 40' tower with a 3 element tribander and 2 meter vertical.  It worked very well for me but be aware that a sloper needs to have a beam type hf antenna at the top of the tower acting as a capacity hat and a good ground system at the bottom to work well.  I have a friend that home brewed a 160 sloper with a loading coil and it worked very well for him.
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K5TEN
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WWW

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« Reply #10 on: January 16, 2011, 11:50:10 AM »

I did the Alpha-Delta DX-A back in the late 80's.  No tower (I was renting) but I did have a 75' tree in the back yard.

No beam for the capacitance hat...just a very large wire lead down to a 9" ground rod and 10-15 radials in the grass.

Yes, I know--absolutely, positively, NOT the ideal situation.

That thing ROCKED!  Has WAS on 40m in just a couple of months, barefoot and all on SSB (about 50w).

Worked down into the South Pacific on a nightly basis, usually 5/5, 5/7 reports.  Picked up about 25 pretty rare islands down there too.  It was sweet.  Also did VERY well on 80m.  I never did much 160m and now regret I didn't spend more time there while I had the antenna to do it with.

I wrote the Alpha-Delta company manager a letter and he turned it into a full page ad in CQ shortly after.

I MISS that antenna.   :  (
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W3HKK
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« Reply #11 on: February 28, 2011, 12:11:37 PM »

A 50 ft tower will give you an effective qtr wave sloper for both 80 and 160.  Simply run  52 ohm coax to the top and ground the outer braid to the tower.  Then connect the  center conductor to TWO qtr wave slopers. one for 80 and one for 160.  Pull them out as steeply as possible.  Then begin to trim or lengthen them one at a time.  It will take  much trial and error but it will load.  My  80m sloper on a 56 ft tower busted pile ups during contests. It was terrific.  The 160 sloper will work a lot better than a low dipole, and get you some dx.  Use full size qtr wave wires but with the  interaction  you may be 10-15% longer than expected.  Run them as far apart as you can. 

I do this single feed approach all the time  even with inverted L's, and work the world.  But a tower is far better. 

Boa sorte. Ate logo.  Bom DX rapaz de Bob
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K7GLM
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« Reply #12 on: February 28, 2011, 12:53:24 PM »

I am intrigued by your quarter-wave sloper description. By "as steeply as possible" do you mean to make the end of the sloper as close to the tower base as possible (steepness relative to the ground, nearly vertical, but close to the tower leg) or leaving the tower as steeply as possible, and tied down away from the tower leg as far as possible?

I can sort of do either, as I have a 100 tower to work with, but an 80m quarter-wave will hang straight down, right next to the tower if I take the first option. Please elaborate.
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W4VR
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« Reply #13 on: February 28, 2011, 01:12:56 PM »

Yuri - if you have the room you would be better off installing a trap 160/80 inverted vee on that tower.  Unless you have a taller tower a sloper would not work very well.
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W3HKK
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« Reply #14 on: February 28, 2011, 06:16:03 PM »

K7GLM:  steep means as vertical as possible for  greater  vertical polarization/dx.  But I didnt have the tower you do.  Try  45 to 60 degrees  down from horizontal .  I  had a 56 ft tower  which was terrific for 80 and ok on 160.  With a 48 ft tower  my 40m sloper worked gangbusters into Europe just  3-4 dBs below a 2 el yagi, but on the 56 ft tower it was less effective for DX when connected at the top.   The 80m sloper seemed to work well on both towers but best on the 56 footer. It literally broke pile ups routinely.

Another option is to connect the  sloper at a point up the tower where the bottom is  about 10 ft off the ground for safety sakes and the wire slopes down 45-60 degrees from horizontal. 

With a 100 ft tower you could go with  two delta loops on 80 for an even bigger signal.
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