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Author Topic: Flat top w/ 50ft. Vert and about 90ft Horiz. to work with.  (Read 39393 times)
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The Slab Bacon
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« Reply #25 on: May 27, 2010, 12:43:52 PM »

Also.. Alot of AMers I know recently switched to the Cobra ultra lite.   This is shortened dipole that has three wires.  Some actualy gained signal here.  Everyone loves them
C


What the hell is that ? ? ? ? ? ? ? ? ?  Huh  Huh  Huh
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ke7trp
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« Reply #26 on: May 27, 2010, 12:47:05 PM »

http://www.k1jek.com/

Its a Open wire line fed antenna with multiple horizontal wires so its shorter.   10 to 18 is only 73 ft long.  160 up is 140 ft.  Lots of guys switched to this to gain a band on the low end and not have to string up all that wire.  They really work well. 

C
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Superhet66
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« Reply #27 on: May 27, 2010, 01:23:49 PM »

It Looks interesting.....
I'm going to keep my A.D.D. from kicking in and stick with the 90 ft. diaper pole/ ladder.
I'm curious how that models pattern wise though.
                                                 Thanks,
                                                              DJ
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KB2WIG
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« Reply #28 on: May 27, 2010, 01:59:24 PM »

I'd venture a guess that a 73' 'crapp brown stuff' folded dipole would work well also....... and be a lot cheeper than $130 Ultra lite (shipping included).

FWIW, the cobra needs a tuna, and they suggest a balune  ($30)

.... ..and rat shack sells 3 conductor tv rotator control cable..   Ya could probably us that stuff, and that crappy brown stuff with 3 insultors fer ~$50.  and have the bragging rights to a  genuine home brew dipole antenner....


klc
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K1JJ
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« Reply #29 on: May 27, 2010, 02:12:57 PM »

When using a shortened dipole fed with openwire on several bands, probability dictates that you will have low impedance points in many spots along the line and on the flat top. Stick with #10 wire throughout and not worry about these losses.

In additional, using a balun for a dipole on all bands is guesswork. It will match on some freqs and be off on others. No balun needed. Use your link coupled Matchbox and see a 1:1 match with low losses (#10 wire) everywhere. Cheap, simple and most effective, caw mawn.

DJ, your proposed #10 wire, 90' long, flat and high dipole fed with openwire/tuner will run rings around any "snakes" out there.. Wink  (I mean Cobra snakes)


T
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KF1Z
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Are FETs supposed to glow like that?


« Reply #30 on: May 27, 2010, 02:52:29 PM »

yes, the snake antenna....

Another one of those projects from the old ARRL books, made commercially now.

Each leg is ONE piece of wire, folded back on itself twice... (looks like 3 wires in the pictures)



But alas... it only is rated for 1kw... so it isn't of any interest to most AMers....

 Wink
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The Slab Bacon
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« Reply #31 on: May 27, 2010, 03:11:01 PM »

It is kind of amazing how people will fall victim to folklore and legend when it comes to antenners!!  Where's ol P.T.Barnum when you need him??
                      
                                        'Nuff said.......................................
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Superhet66
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« Reply #32 on: May 27, 2010, 03:11:13 PM »

I like the look and sound of this product, It's not as nostalgic as the ol' ceramic but it's light, rea$onable and neat. I searched for reference to it on on the board but found none. Any opinions before I mail off my Greenbacks?

* Warning:
The narrator in the demo video for says "uuhhh" over 90 times ! Really!

http://www.73cnc.com/73cnc/laddersnap.html

                                                                         DJ


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k4kyv
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Don
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« Reply #33 on: May 27, 2010, 03:38:20 PM »

yes, the snake antenna....

Another one of those projects from the old ARRL books, made commercially now.

Each leg is ONE piece of wire, folded back on itself twice... (looks like 3 wires in the pictures)



But alas... it only is rated for 1kw... so it isn't of any interest to most AMers....

The "snake" antenna is basically a Beverage-on-the-ground receiving antenna, using a piece of coax. It has been debated whether it is any better than a plain piece of insulated wire stretched across the ground, but some folks swear by them.

It has nothing to do with transmitting or power levels.


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Don, K4KYV                                       AMI#5
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K1JJ
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« Reply #34 on: May 27, 2010, 04:19:18 PM »

Actually I was referring to the "Cobra" snake... Wink

DJ - Stay away from the cheap clip-on plasdick spacers. A few ice storms and wind and...  Plus at higher freqs, who knows how well they will perform.

You sound like a guy who works with and builds strapping stuff there.  Look on the web and find a local plastics house and stop by. They often have scrap strips of Delron? Teflon,and even Plexiglas that can be used. Just cut to length, drill holes in the ends and slide them onto the open wire - tie them using #14 solid insulated copper wire from Home Depot. Use #10 stranded for the actual openwire and flat top.

Stretch the two openwire lengths out between a pair of trees about 4' high once the spacers are on. Then pull the two wires tight. Then move the spacers  to their positions (about 2.5'-3' apart max) and tie them on with the #14. I've knocked out 200' of openwire in an hour... quick and easy once you know how.

You need #10 wire for the "hot spots" that will show up on the feedline and flat top when tuning a shortened antenna - or when using it on the various higher bands.

To do it right, don't take short cuts like the masses. A db here, a db there - after a while they add up. The average ham takes the fast and easy way out and pays the price by being PW... Grin  The OT's on this BB will set you straight since they've been there before and have already tried all the Gotham verticals of the whirl.

T
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k4kyv
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Don
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« Reply #35 on: May 28, 2010, 01:23:57 AM »

I have had better results with solid conductor wire than stranded.  The latter always eventually broke with me from metal fatigue from swaying in the wind, one strand at a time, until the whole thing failed.

I have gobs of #8 copperweld on hand and that's about all I use for antenna projects now.  Yes, it's a PITA to handle, but once up I know it's going to stay up. My open wire line is made of #10 copperweld, of which I had an abundance when I put my present antenna up in the early 80's.

The ham who gave me the big spool of the #8 copperweld had three 100' towers guyed with the stuff.
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Don, K4KYV                                       AMI#5
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N3DRB The Derb
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« Reply #36 on: May 28, 2010, 05:31:19 AM »

why Don is a AM badass:

just above the top set of guys you can see his 75 dipole feedpoint.

any more work on th dawg house?



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K5UJ
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« Reply #37 on: May 28, 2010, 08:02:07 AM »

Well, I admit I run about 90' of the hammy hambone OWL, the stuff with no. 16 stranded but have never had a problem.  I'm interested in the resistance loss between no. 16 and no. 10 though.  The dipoles are both no. 12.   It just seemed like anything thicker than no. 12 would be so darn heavy.  I think I have not had any breaking on the line because the no. 16 stranded is that stuff with about 22 strands per side, I support it so much it doesn't move around a lot, and at the feedpoint, the I solder the hell out of the connections.  The dipole wire bare spirals at the center insulator have the OWL wire spiraled between them then I saturate the whole thing with gobs of silver solder and a 150 watt iron so the no. 16 wicks up the solder partly down its length and the whole transfer point is kind of stiff.  I've heard guys complain that their feedline breaks off at the feedpoint after a while.  I've never had that happen.
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k4kyv
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Don
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« Reply #38 on: May 28, 2010, 01:04:54 PM »

The dipole wire bare spirals at the center insulator have the OWL wire spiraled between them then I saturate the whole thing with gobs of silver solder and a 150 watt iron so the no. 16 wicks up the solder partly down its length and the whole transfer point is kind of stiff.  I've heard guys complain that their feedline breaks off at the feedpoint after a while.  I've never had that happen.

That's the problem with stranded wire.  The strands tend to break right at the junction between where the solder blob is bonded and the rest of the wire.  I think the problem is that the solder holds the wire too rigidly, and even slight movement of the wire in the wind flexes the wire right at the junction and eventually causes metal fatigue.

I connect the downlead to my beverage using split copper bolts, those things designed just for the purpose of making heavy duty electrical splices.  When I partially disassemble the beverage in the spring, I notice that the copper that was under pressure in the bolt clamp is still shiny and bright even after a winter in the elements, so oxidation shouldn't be a problem, and I would think the mechanical clamping action of the split bolt allows a little more wiggle room that would solder.

For my dipole, I use the same run of wire for the OWL as for the antenna itself.  I just looped it through the insulator and twisted several turns, so there is no splice between feedline and antenna wire.  The only problem with that is that I am SOL if the insulator ever breaks and I need to replace it.
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K1JJ
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« Reply #39 on: May 28, 2010, 01:22:18 PM »

The key is to never leave a soldered joint exposed to ANY type of pull or stress.  Tie the wire off with strain relief insulators or a mechanical hold of some kind. The soldered joint should float freely, be taped and sealed to the weather.

I have used #10 Home Depot stranded for about 25 years. I have 2el 75M quads at 190'. They have never broken. The key is to support any wire antenna in the middle.  Even solid wire will stretch if unsupported and wind/trees have their way.

INSULATED stranded is the key. It will stay shiny and strong for years under the PVC.

The problem with copperweld (besides hard to work with) is I once used it and the end ceramic insulators rubbed through the thin copper plating. The steel core rusted and it broke after two years. Make sure the wire does not rub the ceramic in the wind. I taped it off to limit motion and that solved the problem, but stayed with insulated stranded after that..  I feel single strand copper is more prone to fatigue and break compared to multi strand. Don, maybe we shud try a test with two samples and see which breaks first from repeated bending by hand... Grin


Beware of that "Flex" wire. The tiny strands will rot.  A big, single strand will last for decades.
And try to resolder Flex strands once they have turned brown in the wx. No way to clean it that I've found.

T
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There's nothing like an old dog.
k4kyv
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« Reply #40 on: May 28, 2010, 01:42:27 PM »

The secret to using copperweld (first use quality stuff with a substantial sheath of copper, not that cheap-ass copper plated steel wire often sold as "copperweld"), is to carefully pre-form the wire to match the contour of the insulator and make sure it is tightly clamped round the insulator, then there will be no significant motion. Also use glazed ceramic.  Unglazed ceramic insulators have about the same abrasive characteristic as an emery wheel or sharpening stone. My #10 copperweld has been up for 29 years, and so far, no problem.
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Don, K4KYV                                       AMI#5
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ke7trp
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« Reply #41 on: May 28, 2010, 01:54:36 PM »

Ke7trp  Blows Coach whistle and thows white flag!!!!!!!!!!!!!!!!!!



The Cobra works Damn well into a balanced tuner. BIG signals from those antennas. Most run a HB or a Matchbox.  There are guys running BC rigs into them with no trouble.  Some HB there own cobras. 

Remember. Its not about having the ultimate antenna. we all know you can get something better performing. Its about having a multi band antenna that fits on a standard city lot and does not atract alot of attention.  10 to 80 with a big signal on 73 ft antenna, Is a good thing for ALOT of hams out there that do not have the room! Alot of these guys could not have been on 75 with us until they found this option!

C
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Superhet66
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« Reply #42 on: May 28, 2010, 08:10:38 PM »

All good things here, thanks.
 
I'll at least begin the 90' flat top & ladder tommorow.
I think I'll go with the continous run of #10 as Don mentioned.
Minimal vulnerable joints. 
I like the copper split nut idea, I have them in stock.

                                         DJ
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K5UJ
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« Reply #43 on: May 29, 2010, 07:04:01 AM »

Clark,

I admit I have never heard of a Cobra until now so obviously I have never tried one, therefore it can be argued I am not qualified to address this.  But, (always a but hi hi) a few general antenna maxims and principles:

1.  If you jam enough power into anything you'll get out. 
2.  Have these Cobra users done any A/B testing with a known good design?
3.  There are some observeables that give me pause:  1 KW spec'd maximum power:  It is actually as important or more important for a QRP op to have an antenna system that can at least handle the legal limit.  QRP and power restricted antennas are often power limited because they use lower limit components, and these in turn can be extra lossy.   Ironically this should be of greater concern to the 50 or 100 w. guy who should want every watt to make it to the antenna if  possible.

4.  Personally, I don't like the window line used (the term ladder line is a misnomer in this case) however that can always be tossed out and be replaced with good ladder line. 

5.  I especially don't like the use of a balun in the feedline.  A balun might be okay if its transformation function is perfectly matched to its primary and secondary components, say 50 j0 to 600 j0 but if that can be achieved, it will be on only one frequency.  Outside of that, (which is almost always) baluns start to fail IOW they at least start to heat up and get lossy.   What is needed is a "variable balun" namely a link coupled tuner. 

Get rid of the window line and balun by using ladder line and a link coupled tuner and what's left is that center fed dipole folded over on itself.    I am not sure what the electromagnetic principle is behind that idea but with that left, why not put up a regular 130 foot dipole and let the ends hang down so it is 90 feet long.   One answer is that it won't cover 160.  True, but any horizontal antenna on 160, unless it is pretty high up will work poorly anyway.  "Pretty high up" means at least 100 feet.  Now we're into the multiband antenna trap:  Hams really can't decently cover all bands with one antenna, and when I see a claim that one antenna does that, it raises another suspicion with me about performance.   I don't know what this thing does on the high bands but I'd love to see someone model it on say, 15 meters. 

I just want to make one last general point before I shut up, only because I have forgotten to mention this in other topics:  Antenna manufacturers have to some degree, gotten away with making and selling bad antennas, because slopbucket can compensate for a lot of deficiencies.   Slopbucket has low duty cycle.  It has a narrow passband.  It spreads its energy across a narrower bandwidth (usually).  This doesn't have anything to do with your friends who are all AMers, but the general ham population of casual SSB ragchewers can put up crap antennas and think they work okay, but such an antenna on AM might burn up or turn an AM guy running a Valiant into a pissweaker.  The demands of AM are why there is so much fanaticism on the subject of antennas that really work.  But anyway, like I said before, I have not tried that Cobra antenna and maybe I should.

rob
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« Reply #44 on: May 29, 2010, 06:50:17 PM »

On pages 6-19, 20 and 21 of The 18th edition of the ARRrrhL Antenna Book there is  a section on 'linear loaded short wire antennas'.   The antenna with the 3 leg-folded-back onto itself occupies about 1/3 less space than a resonant antenna......


klc
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Superhet66
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« Reply #45 on: May 31, 2010, 02:10:43 AM »

Question:
I'll eventually have room for a 130' flat top here.
I would like to leave the 20' difference at each end to hang down, for now, as I've seen done by others.
When I have the room and move the Ant., I would have the 130' with no splices in the full run, including the ladder feed.  Pros, cons, noise, weird resonance?
I made good progress this weekend.

The YAZOO 101 needs some attention. It's got a soft, 30 to 40Hz +-,  hum that comes in w/ zero vol. and fades as the vol. is increased. No other function effects it. I'm thinking cap but It does vary. A good cleaning and check for critters may help.   Wink  
      I'll work it  out.            Thanks,     DJ
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k4kyv
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Don
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« Reply #46 on: May 31, 2010, 11:58:55 AM »


The YAZOO 101 needs some attention. It's got a soft, 30 to 40Hz +-,  hum that comes in w/ zero vol. and fades as the vol. is increased. No other function effects it. I'm thinking cap but It does vary. A good cleaning and check for critters may help.

You might be able to find some helpful information here.

Quote
Question:
I'll eventually have room for a 130' flat top here.
I would like to leave the 20' difference at each end to hang down, for now, as I've seen done by others.
When I have the room and move the Ant., I would have the 130' with no splices in the full run, including the ladder feed.  Pros, cons, noise, weird resonance?
I made good progress this weekend.

That should work.  I have heard them called "inverted U"s.  You might get some directional effect from the vertical ends. Just make sure no-one walks into them while you are transmitting.  An rf burn to the eye might be hazardous to the vision.

Or you could just fold back the extra wire over the horizontal legs of the dipole.  Copper split bolts would work for holding the folded wire in place (don't use anything galvanised), and don't solder.
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Don, K4KYV                                       AMI#5
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K1JJ
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« Reply #47 on: May 31, 2010, 12:09:30 PM »

DJ,

By lengthing it to 130' (when it is eventually pulled straight out to a dipole) from 90', you will be raising the radiation resistance on 75M, which is a good thang.  90' on 75M was on the low side, but still OK.

The downside is 20M - you said you wanted to use this band too. Instead of a sharp figure 8 with gain, you will now have a 4-cloverleaf that has sharp nulls broadside. I wud suggest a second antenna to cover 10-20M, like a center fed openwire dipole that is 22' total flat top. That will give a nice dipole figure-8 on 10-20M.

Using that 130' dipole on 10M, etc will produce a useless octopus horizonal pattern. No control - pot luck.



T
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There's nothing like an old dog.
Superhet66
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« Reply #48 on: May 31, 2010, 12:51:58 PM »

Once again, thanks. I do my reading before posting to spare an endless thread but some times you just have to ask for a distilled answer. i think I'll cut it for the full length with the 90deg drops. If I get any strange / unwanted effects I'll zip tie it up tight against it self as Don said.  ( I found UV resistant zip ties FWIW. )
Even w/ the drop the HV / RF end will be about 25' in the air safety wise.

I can create a seperate 20m/10m friendly antenna from the G5RV pieces parts.

I'll report back on the FT101 hum.
                                                            All good stuff  Smiley

Have a good Memorial Day.

 



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K1JJ
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« Reply #49 on: May 31, 2010, 12:56:27 PM »

"I can create a seperate 20m/10m friendly antenna from the G5RV pieces parts."

DJ - Because of skin effect, 10-20M is even MORE critical than the lower bands for needing heavier conductors/ losses. Use the #10 wire for the entire 10-20M ant too.

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.
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