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Author Topic: HF antennas  (Read 13260 times)
KK4CRY
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Posts: 35




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« on: May 17, 2013, 10:47:37 AM »

Now that i know were im going with the V/Uhf antenna situation lets talk HF antennas.
Hf equipment: Kenwood TS-480, and Palstar AT4K tuner

I currently have a Alpha Delta DX-80 in a inverted V, legs are point East to West (only trees i can run lines to). I also use a Palstar AT4K antenna tuner where i want to go. Recently i havent been to satisfied for TX/RX of this antenna, im limited to 50watt max (TS-480), anything above that will tripp the house alarm system (i have 21ft of coax rolled into a choke below the feed point). Ive thought about adding wires to the DX-80, but cant seem to make time to cut wire and tune them for the fan dipole.

Ive been doing research into verticals, but needed ground radials busted that idea.

Ive been looking at the end fed antennas lately,

The only grounding i could do for antennas is a ground rod into the ground, but doubt that would work for anything other then lighting arrestor.

I need some Direction
Please

Tkx
Ben
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K5LXP
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« Reply #1 on: May 17, 2013, 11:16:29 AM »

How is the DX-80 fed?  Force feeding a coax fed 80M dipole on some bands may not be the most optimum solution.

Since you specifically didn't discount them, how about a vertical?   Or a beam on the roof or a tower?


Mark K5LXP
Albuquerque, NM
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W0FM
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Posts: 2055




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« Reply #2 on: May 17, 2013, 11:28:00 AM »

Ben,

Being unhappy with the TX/RX of the DX-80 (actual model is DX-CC) is less likely to be a factor of the antenna than other issues.  How high is the center of the inverted V?  What is the height of each end?  Why are you looking at adding wire to the DX-CC?  is it resonant too high and you want to bring the resonant point lower?

A balanced, resonant dipole like the DX-CC will generally be a better performer than an end fed.  I have the DX-EE version in my attic with over 275 countries confirmed using 100W.

Here is the direction you are requesting:  Forget the end fed.  Get the DX-CC as high as possible.  Prune each segment to the portion of that band that you want to use with the aid of a (borrowed?) antenna analyzer.  (There is no ground plane counterpoise required with this balanced antenna so your lightning arrestor ground will be all you should need).  Add wire if necessary to bring the antenna into resonance.

Your tuner can "fool" the transmitter into thinking the antenna is resonant, but nothing beats a good old "naked" resonant dipole.

Grab a copy of the ARRL Antenna Handbook (even an old one) and become more familiar with how each type of HF antenna works. 

Good luck.

73,

Terry, WØFM
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WB2JNA
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Posts: 92




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« Reply #3 on: May 18, 2013, 10:49:52 AM »

I agree with the last few posts. If you're feeding the antenna with coax, I'd check the SWR without the tuner. If it's very high (say over 5:1) then you're probably losing power and the tuner makes the radio see a good match but the antenna system is still inefficient. If you can trim the antenna so you don't need a tuner, so much the better.
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W1AJO
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« Reply #4 on: May 19, 2013, 05:43:28 AM »

I'd add a 1:1 BALUN at the feedpoint. If it's the RF that's trippinjg the alarm the BALUN will help keep the RF out at the antenna and away from the house.
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W6RMK
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« Reply #5 on: May 19, 2013, 10:00:24 AM »

A couple suggestions..

1) Put the tuner at the antenna feedpoint.. then you don't have to worry about "pruning" to exactly the right length, choosing another operating frequency, and not being properly resonant. Or the trees moving in the wind, etc.  There's a variety of tuners suitable for this, and if you do it, then all those comments about worrying about coax loss from mismatch just go away.

2) Get yourself a bunch of 31 Mix toroid cores or beads and use those as your RF choke at the feedpoint, rather than your coil o'coax. The air core coax is fairly narrow band, and it's unlikely that it provides a good choking impedance at all frequencies. A nice lossy core with high Z over a wide band really knocks back the current on the outside of the coax.

http://www.audiosystemsgroup.com/RFI-Ham.pdf by Jim K9YC is an excellent description of how to do all this


Ultimately, though, getting a horizontal or inverted V up a bit higher is probably the easiest bang for the buck.
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KF7CG
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« Reply #6 on: May 20, 2013, 10:48:36 AM »

Also remember. the RFI problem might be in the home alarm system. Some of them have little to no rfi rejections and just the normal radiated signal from your antenna might be too much. If that is the case it is better solved at the alarm system.

KF7CG
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KK4CRY
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Posts: 35




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« Reply #7 on: May 21, 2013, 09:14:51 PM »

Well alot of the RFI has been deduced to the proximity of the antenna to the house. So im going to make provisions to move the dipole farther and higher away from the house. One of the local hams said he had some wire left over from when he last made some dipoles. So looks like im going to make a fan dipole, IMHO would be the cheapest and easiest, at my current situation.

What do yall think?
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W0FM
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« Reply #8 on: May 23, 2013, 01:20:43 PM »

A "fan" or parallel dipole will give you a lot of inexpensive bang for the buck, Ben.  I have two:  The Alpha-Delta DX-EE for 10, 15, 20 & 40M and a homebrew fan for 10, 12 and 30M running perpendicular to it.  You will enjoy the benefit of fewer support points and (if properly tuned or used in conjunction with a good tuner at the center point) some pretty quick band changes.

Note:  My experiments proved that the 40-10M DX-EE and the homebrew WARC fan did not play well on the same feed point, which is why I ended up with two separate fan dipoles.  The other good news is that you will have access to (at least) seven HF bands with just two coax feed lines.  And if you're lucky and can run the WARC elements perpendicular to the 40-10M elements you might be able to get away with sharing a single feed line.  I didn't attempt that as I had burned enough time trying to get some of the WARC band elements to join the feedpoint of the DX-EE and gave up.

(I have a 1:1 balun at the feed point of both antennas and agree with the other poster's recommendation)

Good luck.  I had a ball experimenting with my dipoles.  Sometimes getting there is MOST of the fun.

73,

Terry, WØFM
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KT4EP
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Posts: 15




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« Reply #9 on: May 29, 2013, 08:37:03 PM »

Looking at your QRZ page, I spy three very good books;  I have them too.   October of last year I built a 20 to 10 meter vertical with 72 radials.   I'd never used one of these and it turns out to be very good on 10 meters when I have the vertical element raised for 15 meters.  I just raise and lower the vertical to what ever band I am using and go for it.    Why not a vertical?   

I also have a 15 meter delta loop, a 100 ft inverted vee w/apex at 52 feet fed with 450 line, and a big loop over my house for 160 meters.   They all work very very well.    Again, why not a vertical for your station?
KT4EP
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KK4CRY
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Posts: 35




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« Reply #10 on: May 29, 2013, 10:29:58 PM »

Im not opposed to running vertical, just cant run the Gnd radials, too many ant limits at my current living conditions.   lovely run on sentence haha
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K5KNE
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Posts: 65




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« Reply #11 on: July 17, 2013, 08:39:13 PM »

A radio man told me long ago that "a vertical antenna radiates poorly in all directions".  I have had several and not been as happy with them as simple dipoles.
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K5LXP
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« Reply #12 on: July 18, 2013, 06:36:05 AM »

A radio man told me long ago that "a vertical antenna radiates poorly in all directions". 

So why do broadcasters use them?  You'd think after a hundred years or so they would've moved on to something better.


Mark K5LXP
Albuquerque, NM
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AA4PB
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« Reply #13 on: July 18, 2013, 07:10:08 AM »

A radio man told me long ago that "a vertical antenna radiates poorly in all directions".

That's often true of amateur radio installations because they are often installed in residential areas with houses and trees all around and without an adequate ground radial system. Install one in the clear with 30 buried radials and you'll find it a pretty darn good DX antenna.

By comparison, how does a 20M, 3 element Yagi perform when installed 5-feet off the ground and surrounded by houses and trees?

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