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Author Topic: HF Antenna recommendation  (Read 439 times)
KA3NXN
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« on: April 15, 2006, 07:16:04 PM »

After tearing what little hair I have left out, I finally figured out that the cause of 99.9% of my RFI issues was the Radio Works Carolina Windom itself. I hooked up my Hustler 5BTV today and fired it up with the same amp and radio that I use on my windom. The RFI is non-existent. With the windom, I get ripped appart by RFI especially on 20-15 meters. I have spent quite a bit if time messing with RF grounds, line isolators, coax chokes... with no success. After speaking with the folks at Radio Works, the fellow was not surprised about the RFI. All he could recommend is that I place the antenna as far away from my house as possible. Well the Hustler vertical is no further away from the house than the windom, and the problem is not present with the Hustler, even when I pump 1200 watts into the Hustler. Forget putting anymore than 200 Watts into the windom. I am looking for something that covers 40-10 meters including the WARC bands. I do have a good tuner that can handle balanced & unbalanced feed lines. I like to have 2 different types of antennas for HF at the same time. That's why I put up the vertical after I having put up the windom. Oh yea, did I mention  that I have an amp that is capable of 2kw? I would like to use this amp too. I find that most commercially made wire antennas cannot handle 2KW. I am am also very limitted in space so I have about 70' to put up a wire antenna. That is why I had chosen the Carolina Windom 40, which is only 66' long.
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N6AJR
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« Reply #1 on: April 15, 2006, 07:21:42 PM »

check out the gap voyager, for 40/80/160  good for those bands.. and a push up pole and an ma5b will do 10/12/ 15/18/20
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K4SAV
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« Reply #2 on: April 15, 2006, 08:29:13 PM »

Congratulations, you have learned a valuable lesson. It seems that a very high percentage of people having RFI problems is because of end-fed or off-center-fed antennas and not have proper filtering to remove the common mode currents from the feedline. This is not an easy task, and that becomes obvious when you try to run high power into it.

How do you think the guy, who posted a question recently about planning to feed a long wire with a KW from the 10th floor of a condo will fair?  I think he is likely to be very popular with the other tenants.

Jerry, K4SAV
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W8JI
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« Reply #3 on: April 16, 2006, 02:07:19 AM »

You have just learned a lesson about common mode currents.

If you change to a Gap it is likely you will have similar problems plus a huge loss of signal on 80 meters and lower and ten meters. The Gap has extraordinarily poor feedline decoupling.

A simple fan dipole with balun, or a ladderline fed dipole with a good balun on the tuner, are good choices for multiband antennas.

The vertical you already have or a trap vertical like a Butternut with a good ground system will be very good also and not have such severe common mode issues. If you try a no-radial vertical like an R8 or anything else, or use a marginal ground system vertical of any type, you will be right back into the soup.

73 Tom
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W3LK
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« Reply #4 on: April 16, 2006, 06:44:18 AM »

Just a comment ...

<< Oh yea, did I mention that I have an amp that is capable of 2kw? I would like to use this amp too. I find that most commercially made wire antennas cannot handle 2KW.>>

And you shouldn't be running 2kw anyway. The legal limit is 1.5kw.

73,

Lon - W3LK
Baltimore, Maryland
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A smoking section in a restaurant makes as much sense as a peeing section in a swimming pool.
KX8N
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« Reply #5 on: April 16, 2006, 08:38:04 AM »

"How do you think the guy, who posted a question recently about planning to feed a long wire with a KW from the 10th floor of a condo will fair?"

Wow, I missed that one.  Yeah, he's going to be on everyone's list.

And yeah, don't be complaining about not finding an antenna to handle 2KW.  You've got no business doing that anyway.  In fact, if you are even CONSIDERING running 1.5KW to a wire antenna, you need to sell that amp and buy a good antenna with the money you get from it.
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K0RFD
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« Reply #6 on: April 16, 2006, 10:37:29 AM »

Put up the fan dipole and be done with it.
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K0RFD
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« Reply #7 on: April 16, 2006, 10:42:08 AM »

A little addendum.

Since 40 is the lowest band you care to operate on, and since a 40 meter dipole will probably fit into 66 feet (especially if you hang it as an inverted vee) you will have no problems doing what you want to do with a fan dipole.
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N6AJR
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« Reply #8 on: April 16, 2006, 11:16:50 AM »

speaking of fan dipoles...  put up with or with ot a balun , flat top, inverted v or sloper, one under the other or in a star ( umbrella?) style.. good antennas, sheep and they work.

http://www.ku4ay.net/dipole.html
http://www.qsl.net/kd7rem/antdipole.htm
http://www.hamuniverse.com/multidipole.html
http://www.angelfire.com/nb/ni4l/ni4ldipole.html
http://www.arrl.org/tis/info/pdf/9611073.pdf
http://www.geocities.com/n2uhc/2banddipole.html
http://www.qsl.net/na4it/fandipole.html
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KA3NXN
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« Reply #9 on: April 16, 2006, 01:35:21 PM »

How would I benifet better if I used a balun or balanced feed line, or just forget the balun all together and just use straight coax to the elements?  I do have a really good Palstar tuner with a built in balun for open feed line. I could use this if I needed to. What would be the best configuration? Remember I want to eliminate that pesky RFI that is currently ripping me apart, and get more of my radiated signal out into the atmosphere, and not my TV, or microphone, or telephone...
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K0RFD
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« Reply #10 on: April 16, 2006, 07:16:28 PM »

Well, you're going from an unbalanced feedline to a balanced antenna.  W2DU refers to that system as a "tripole" with the third leg of the antenna being the shield on the feedline.  While Maxwell's paper might not be the be-all and end-all on the subject (you'll get other opinions), it's certainly a good read.  You can find it here: http://w2du.com/r2ch21.pdf

In the fan dipole case, the tuner has nothing to do with it.  If you put up a fan dipole, you'll presumably tune each doublet to resonance near where you operate.  Mine needs nothing much except a touch-up from the autotuner, and only on 80.  That's not the issue.  You need to make the unbalanced-to-balanced transition somehow.  You're not using the balun to make an impedance transformation.

If you put up a single all-band doublet fed with twinlead of some sort, then the tuner comes into play.  If you feed such an antenna with coax instead you might have significant losses in the feedline.  Not to mention the fact that you still have a tripole.

Use the balun when you build the antenna.  At least use a coax choke at the feedpoint.  It's easier to do it right the first time than to redo it later.
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RobertKoernerExAE7G
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« Reply #11 on: April 17, 2006, 06:01:30 AM »

At this time of year, and this portion of the sun spot cycle, consider getting up an antenna that covers 30-17.

At one time, I had a 40 meter wire ground plane, supported by a pine tree, with the radials 6 feet high, tied to other trees.  Seemed to work FB for DX.

While it might be nice to have one antenna cover many bands, you might have more fun with a few high efficiency, inexpensive wire antennas covering bands that are open when you have time to play radio.

73
Bob
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N3UMH
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Posts: 153




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« Reply #12 on: April 17, 2006, 08:37:49 AM »

If you put up an open-wire fed dipole, and its up in the clear, it will help matters if the leg lengths are equal or nearly so.  

Its a balanced antenna fed with balanced line, and the common mode currents will be fairly minimal.  It's rare to get perfect balance without a current balun to enforce it, but you'd be better with that than a Carolina Windom, which is, as has been mentioned anyway, basically a top loaded vertical.

I used to run a single wire fed against my balcony railing (apartment).  My RF problems were greatly lessened (practically eliminated) by putting up another length of wire and feeding the two as a doublet from the "balanced" output of my tuner.  

I think the ultimate no-RFI wire antenna is going to be a single band resonant half wave dipole up high away from the house fed with coaxial cable with a choke balun at the feedpoint.  (coil of coax works fine, look up the proper number of turns for the band of interest)

Similarly, a fan or trap dipole that is resonant on each band of intersest would work well.  The trick is to make sure the feedline doesn't become part of the antenna.

Incidentally, it's not the WIRE that is the problem in a wire antenna with 1500W.  1500W into a 50 ohm load is only about 5.5A.  I don't know a lot of wires that can't take five and a half amps when installed in free air.  A halfwave dipole fed with the right coax will not complain at full legal limit, unless you make it out of 28 gauge nichrome.

Traps, baluns, the voltage produced when you feed a 40m dipole in the middle on 20m with 1500W, these are what are limiting the commercial antennas' power ratings.  Additionally, unless the limit is set by the breakdown of the dielectric of some capacitor at high voltage, low power handling probably is concurrent with somewhat substantial losses in the system, as losses=heat generated in the antenna.

73,
Dan
N3OX
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