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Author Topic: 20M Struggle  (Read 62614 times)
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K5UJ
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« Reply #75 on: July 07, 2009, 11:03:05 PM »

Rob. You are talking about the antenna I use and I even posted the EZnec of it..   Open wire fed, Flat top and ends turned down.

Clark

Hi Clark thanks;
looks like a higher t/o angle than I expected on 75, probably what I'm currently getting with the horizontal loop i.e. straight up Smiley   

Hi Tom; well, on top of all that, there's the metal pushup pole supports and a garage and house with aluminum siding on them.  I just have one tree here Smiley so something else has to hold up this wire and it has to be steel.  I have real doubts about a low in wavelength compromised dipole on 160.    I'm seeing an inefficient antenna there with a lot of loss to ground.  I like the idea of feeding the high band dipole against ground on 40 though.   but there is no way you're going to get a setup here that's has these clean patterns.  That's just not gg to happen.  To much metal from the house, garage, supports....I'm back to considering keeping the loop since it seems to have a good pattern on 40, continuing to run the inverted L inside the loop, and going ahead with the plan to take down the gap titan and put up the higher supports for the loop and the 50 foot mast in place of the titan and stringing up the 22 foot dipole but forgetting about the 40 and 80 vertical hanging down from the 50 footer.  I can experiment with the drooping dipole idea like what you have there Clark too.

Rob
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Steve - WB3HUZ
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« Reply #76 on: July 07, 2009, 11:33:14 PM »

Here is the info on your potential center-fed system at a height of 40 feet over average ground (Rel. dielectric constant 13.000, conductivity: 0.00500 mhos/meter) for 80 and 40 meters.  Length is 88' + 10' ends (total length is 108 feet)

3.8 MHz

Feedpoint Z: 38.961 - j251.740   about 14:1 SWR on ladder line (around 400 Ohms Z)
Efficiency:  96.47%
Max gain: 5.98 dBi
TO angle: 87 degrees
Loss in 100 feet of ladder line: 0.91 dB
Z at the end of 100 feet of ladder line: 171 - j853.26
Loss in 50 feet of ladder line: 0.79 dB
Z at the end of 100 feet of ladder line: 67.9 + j427.16

For comparison, here is the data on a full-sized, half-wave dipole at the same height.

Feedpoint Z:  61.247 + i 0.017, about 6.5:1 SWR on ladder line
Efficiency:  97.75%
Max gain: 6.33 dBi
TO angle: 87 degrees
Loss in 100 feet of ladder line: 0.39 dB
Z at the end of 100 feet of ladder line: 95 - j289.25
Loss in 50 feet of ladder line: 0.29 dB
Z at the end of 100 feet of ladder line: 640.74 + j1189.39

Not accounting for the tuner loss (which could differ some between the two antennas since the impedances at the end of the feedline are not the same), your short dipole is down about 0.87 dB with 100 feet of feedline and 0.85 dB with 50 feet of feedline. The short dipole may also suffer some increased loss not shown in the modeling due to near field coupling, since it is close to the ground. But since it is not extremely short, it's likely these losses are minimal.

So, on the air, not often that less than 1 dB going to be noticed. This setup is essentially as good as a full-sized half-wave dipole.


7.2 MHz

Feedpoint Z:   657.33 + i 1372   about 9.3:1 SWR on ladder line
Efficiency:  99.79%
Max gain: 6.47 dBi
TO angle: 49 degrees
Loss in 100 feet of ladder line: 0.68 dB
Z at the end of 100 feet of ladder line: 63.5 - j60.58
Loss in 50 feet of ladder line: 0.41 dB
Z at the end of 50 feet of ladder line: 83.96 + j290.63

See the radiation patterns for each band below. The green line on the azimuth pattern is taken at the take-off (TO) angle and the red line is at 60 degrees elevation, just to show some of the pattern at a mid/high angle.


* uj88plus10on80m.gif (36.58 KB, 602x302 - viewed 819 times.)

* uj88plus10on40m.gif (36.93 KB, 602x303 - viewed 814 times.)
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K5UJ
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« Reply #77 on: July 08, 2009, 12:09:02 AM »

wow that's great Steve thanks.  Lots to think about.  I also like Tom's suggestion to think about a clean sheet of paper, i.e. take everything down and start over.  That has occurred to me before since the antenna farm is a collection of three antennas put up piecemeal and this might be a good time to start over with everything I've learned.  I need to let things simmer for a few days.

73

rob
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« Reply #78 on: July 09, 2009, 09:27:53 AM »

Hello Everyone
I thought I could GOOGLE or look in the ARRL archives for an article I read about a Ham using vacuum (small) relays to switch in or out lengths of a dipole antenna. I did not have very good luck on the ARRL website and Google is not cooperating.
In my case, I would want to switch out the excessive length of my 160M dipole to become more friendly towards the 20M band.
Anybody remember seeing this article or could verify that it would work?

Thanks 

Fred
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Fred KC4MOP
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« Reply #79 on: July 12, 2009, 08:52:29 AM »

How do the OCF antennas model on the higher frequencies? A lot of guys rave about them, and I've been curious as to their performance. I'm also looking to string a "one dipole, all band" antenna between two tall oaks...

Pete k1zjh
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« Reply #80 on: July 12, 2009, 02:17:16 PM »

How do the OCF antennas model on the higher frequencies? A lot of guys rave about them, and I've been curious as to their performance. I'm also looking to string a "one dipole, all band" antenna between two tall oaks...

Pete k1zjh

Hi Pete,

The OCF dipoles (asymmetric dipoles) I have heard about are the ones that are coax fed and have some kind of common mode choke and/or balun at the feedpoint.  I have never used one so perhaps I should not comment.  I have not used one because I have not been interested in them for the following reasons:

1.  They seem to be one of these attempts at finding a design (point on the half wave wire and balun in this case) where if you break the line into two sides and feed at that point, you'll have some sort of impedance on several bands that can sort of be transformed to 25 to 100 ohms maybe 120, with a vswr <= 2:1 to make it a multiband antenna.  I don't like that because it seems to be just another attempt at giving a lot of coverage for the-price-of-one, type of deals.  These things always flash red lights and sound bells for me. 

2.  I don't like baluns in general where they're going to be used in a wide variety of voltages and impedances out side.  I've heard too many stories of heating frying baluns or at best, lost power in them. 

3.  I don't like using coax for the same conditions in number 2.

I know these antennas get the same positive comments, you know, the usual "I work everything I hear" type stuff but I always suspect the users of these antennas have nothing to compare them to and are running < 500 w. SSB or CW.   And to be sure, they aren't dummy loads and may be satisfying for some purposes but I would not want to use one for QRO AM.

I am from the school that says a dipole should be balanced and fed with balanced line that's tuned with a balanced tuner. 

73

Rob K5UJ
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Steve - WB3HUZ
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« Reply #81 on: July 13, 2009, 09:11:58 AM »

OCFs may yield easier to match impedances on multiple bands, but their radiation patterns will be little different from a dipole of similar length and the same height.

The except would be the OCFs that have part of the feeder (vertical portion) radiate. This arrangement will tend to fill in the nulls on the higher bands and create a more omni pattern.
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« Reply #82 on: July 14, 2009, 10:35:05 AM »

Hello Everyone
I thought I could GOOGLE or look in the ARRL archives for an article I read about a Ham using vacuum (small) relays to switch in or out lengths of a dipole antenna. I did not have very good luck on the ARRL website and Google is not cooperating.
In my case, I would want to switch out the excessive length of my 160M dipole to become more friendly towards the 20M band.
Anybody remember seeing this article or could verify that it would work?

Thanks 

Fred

Hi Fred ....Qst had that article a year or so ago .... used relays activated pneumaticaly to change radiator lengths ,,, as i recall it was 100 W level stuff, don't think it would handle your bc rig ... 73 ...John

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Beefus

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« Reply #83 on: July 14, 2009, 04:40:22 PM »

THanks John,
Now I know that I wasn't dreaming. Pneumatically operated(good work-around to avoid wires to key the relays), and low power. NOPE it won't handle the legal limit radio.
Thanks
There is an article in JULY QST for an HGSW (high gain single wire),wire antenna that is like a non-rotatable beam antenna. The author claims that he ran EZNEC on this design and there is 11dBi gain. Consists of various lengths of antenna wire with two each 13 foot lengths of ladderline hanging down, can be used for other bands with less directivity and gain, depending on feedline length. There are options to use it as a single band 20M antenna with coax or multiband with ladder line for 80-10M. The author claims that certain lengths of feedline would prevent tuning on 40 or 30 and 12M.
It would be interesting if one of our famous aerial gurus could prove this article out.
I don't want to take a chance of scanning it and posting on AMFONE.


Fred
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« Reply #84 on: July 15, 2009, 09:02:19 AM »

The best way to use EZNEC to determine gain is to compare the dBi of the antenna in question with a resonant dipole at the same height.

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Steve - WB3HUZ
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« Reply #85 on: July 17, 2009, 08:59:24 PM »

Exactly! 11 dBi is pretty meaningless unless comparing two antenna in free space. 11 dBi at what angle? How high was the antenna? Over what sort of ground.

The QST thing sounds like some sort of collinear array (some number of half-waves in-phase). No magic but it will give some gain in two directions over a dipole. Of course, you have less gain in other directions, so properly consider the trade-offs.


The best way to use EZNEC to determine gain is to compare the dBi of the antenna in question with a resonant dipole at the same height.


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flintstone mop
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« Reply #86 on: July 19, 2009, 10:40:43 AM »

I think Steve is on track with the QST article. Beings that I don't have schematic drawing software try to imagine the following:  5 egg insulators, and imagination used for the feedpoint described below.
There are two coils wound on a 1" dia PVC 3" long 19T 10 Gauge solid copper. The center and ground from the coax connect to these coils. The other end of the coils connect to 17.5 feet of wire to an egg insulator.
At these insulators hang a shorted piece of ladder line 13 feet long.
From this point connect 45 feet of wire to an end insulator.
Remember that this is a dipole, I'm just describing one side of the total dipole  Roll Eyes
The author recommends a slightly longer wire length to allow for connecting all of the elements together. But the above mentioned lengths must be accurate for the antenna to give you the performance calculated by EZNEC.

Maybe with the dimensions given here from the QST article and the description how they are connected together, someone could run EZNEC and prove out the article.
1/2 wave above ground it's supposed to have a 29 degree takeoff angle and 28 degree beamwidth.

I'm building this today (SUN) and I'll see what happens here at MOP radio


Fred


BTW What is wrong with AMFONE when I post a message??? sometimes as I get to the bottom of a message or edit the bottom line of typing keeps jumping up and down as I type?? This happens on several computers at home and one at work.
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« Reply #87 on: July 21, 2009, 01:08:27 AM »

     sorry to bust a few balloons here guys, but in my real world situation with no antenna bridge or computer amtemma modeling I am actually foolish enough to  operate a 180 foot long dipole at 60 feet fed with 4 inch spaced #12 open wire line. it's good on 160, excellent on 75, and outstanding on 40 and 20. yes, it's showing very low antenna current on some bands and the voltage at the tuner terminals is very high, but it just works. I use a 275 watt matchbox with it, and all is well. a few nights ago on 40 SSB I was told by a DL4 I worked (that's Germany for you DX challenged AMer's) that I was the strongest station he was hearing from 'stateside. this was at 7PM with all of 150 watts SSB. the "garbage" radiation pattern has served me very well with long open wire fed dipoles for years on the higher bands. So, mr. Flintstone Mop- don't sweat the details. just run it and on a good day with decent conditions you will strap. remember we still have no real sunspot activity...yet.

"just slam the hood and drive it"
Junior Johnson
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Steve - WB3HUZ
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« Reply #88 on: July 21, 2009, 01:32:46 PM »

LOL. Any antenna will work when the band is open. I've worked several VK stations running a mere 10 watts and low dipole in recent months on 40 meters. That said, I'm not taking down my delta loops or giving away my amp.  Wink
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flintstone mop
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« Reply #89 on: July 21, 2009, 08:56:24 PM »

Well,
Junior Johnson, didn't bust any balloons. It was a reality check, though. I guess we have been sanitized by the computer modelling software and want to get all we can out of our station with an effecient design.
If my A3S Yagi wasn't out of service, I wouldn't have bothered getting the grey matter working as a work-around. I'm still proceeding with the QST antenna and the Yagi will be dismantled and resurrected to a more suitable mast that can be easily maintained instead of hiring a crane truck for the utility pole.
WE had two bad wind storms and the last one musta been over 80mph and killed my Yagi.
Fred
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« Reply #90 on: August 10, 2009, 09:47:56 AM »

LATEST UPDATE FROM MOPRADIO   Shocked

The HGSW that was in last month's QST is a reality and it does work 20M. I had some flaky solder joints. Anyway it was built to the specs from the article and the modification that a group of Hams did building this thing was to use a 4:1 balun for a better match.
It brings back memories when my Yagi was working. Nice strong RX sigs. I will be trying for some A.M. on 20M in the days ahead

Fred
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« Reply #91 on: August 10, 2009, 10:54:38 AM »

Hey, cool. Glad you got it working.
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« Reply #92 on: August 12, 2009, 11:14:31 AM »

Congratulations Fred, that's great.  My own antenna projs are progressing.   I plan to post a full report maybe with pics once everything is finished and I've had time to check it all out.

73

Rob K5UJ
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« Reply #93 on: August 12, 2009, 03:47:46 PM »

Right on Rob!!

I'm RE-locating my 160M vertical a little closer to the house with the addition of a motorized tuner to use the ant anywhere on 160M.
Got to clear the hornet's nest from the base of the mast.

I have a tilt-over ability to get at the "stinger" to change freq and it was a scary surprise to see these things "crawling around" where I was standing to lay the mast down. The signal slowly came to my brain that these things were a hornet or wasp nest inside the mast. I didn't think they would have a nest so close to the ground........geesh that was close!!
Fred
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