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Author Topic: Confused About Random Wires, Long Wires, Baluns, Ununs, Grounds, Etc.  (Read 16145 times)
G3TXQ
Member

Posts: 1790




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« Reply #15 on: May 19, 2013, 05:40:32 AM »

Chris,

I have some information about UnUns on my web site that may be of interest to you:

http://www.karinya.net/g3txq/unun/

73,
Steve G3TXQ
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KR4TH
Member

Posts: 93




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« Reply #16 on: May 19, 2013, 07:55:11 AM »

K0zn:
How did you make a good rf ground for your random wire? 
Would a 1/4 wave "radial" for each band used, attached to the ground lug of the tuner be effective ?
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KD2CJJ
Member

Posts: 369




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« Reply #17 on: May 19, 2013, 09:53:09 AM »

K0ZN:
The only point I was making was to not dissuade any ham, recent or veteran on asking questions, no matter how redundant it may be, no matter how available the sources are outside of the forum.  I stress upon self education through reading but that can never replace others knowledge through experience.  I may not have the posted longevity of experience but having the book knowledge of the theory and depth of experimentation within a short time period, being in the same situations makes me an appropriate authority for this situation.. All recent experience...     The "old troll" metaphor was inappropriate but unfortunately I have been the victim of "old trolls" and am very sensitive to those who seek to just pontificate rather than help.  I apologize and see your intentions were otherwise.   I am a life long student of technology being a professional in the space.  I never proclaim to be an expert at anything, even though I am paid to do such in many areas of technology.  I truly seek further enlightenment through education and provided assistance of others.  With that said, if I was incorrect with anything I have said, I applaud the correction of my misgivings.

KR4TH - A good RF ground is relative to the Antenna system and the shacks location.  Depending on your situation a good RF ground will differ.  As an example, if your on or above the 2nd floor, a good RF ground will differ than if your on ground level close to your electrical panel.  If you want a pointed answer rather than theory then you will need to explain what your goals are (you have done this mostly), where your shack is located, what your budget is.  Only then can anyone provide you the answer your looking for.  Budget is a major consideration since external/remote, etc. automatic couplers (tuners) are far more expensive over using other impedance matching systems like a UNUN/BALUN. If budget is not a consideration then this is by far the best approach and is an excellent option for a long wire antenna.



KD2CJJ:

Since when is guiding someone to a good reference book and suggesting someone take advantage of the information therein being a "troll"?  Especially for such a lengthy and complex subject as balun design and antenna matching?  I apologize for not submitting my post to the IEEE and yourself for editing prior to posting it. By your definition I would have been even more of an "old troll" if I had additionally recommended Dr.Jerry Sevic's (W2FMI) book on baluns.

Make no mistake, there are technical errors in your post too, however, I learned a long time ago never to get into a technical debate with some self appointed "expert" who degenerates to derogatory personal attacks on others whos post he disagrees with. Just because something in a post doesn't meet your definition doesn't mean you are correct.

Your call shows you are newly licensed. Just curious, how many years of amateur and professional experience do you have in HF communications systems?

-- K0ZN
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73

Mike
KD2CJJ
AK4SK
Member

Posts: 206




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« Reply #18 on: May 20, 2013, 05:58:06 AM »

I appreciated all of the replies. For the record I have a copy of the ARRL antenna book and I reference it often. In this case I had just moved so it was in a box somewhere. I always do try to do my own research before asking questions, that way my questions are as pointed and intelligent as possible and so that I can better understand any answers I receive. Anyhow, as I mentioned there is a lot of conflicting, or at the least incomplete, information on random wire antennas out there. I think that I now better understand some of it.

It sounds like an ideal instillation would be no balun or unun and a very good RF ground and/or counterpoise. I don't think my RF ground will be great and a counterpoise isn't going to happen. So in that case it sounds like a 1:1 current balun right at the antenna feed point would be a good choice. My understanding is that I should have two RF grounds: my regular station RF ground and a separate RF ground for the ground wire coming off of the balun and that these two grounds should ot be connected. Is that correct?

By the way, to get the ~200' length I'm looking for my antenna will have to be "L" shaped, one ~140' leg and one ~60' leg. Is that a big deal?
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KD2CJJ
Member

Posts: 369




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« Reply #19 on: May 20, 2013, 08:32:23 AM »

Your best options are:

9:1 UNUN at the antenna
Tuner at the antenna

Both options require a ground plane (counterpoise) at the base of the antenna and a good RF ground in the shack. Only resonant lengths of the radiator can a tuner at the control position can tune an end fed without impedance help BUT may preclude you from tuning on other bands - thus the needed for some matching network at the antenna w/ a non resonant length radiator.  The Tuner at the antenna will provide proper matching with significantly greater efficiencies over using UNUN.  But also is the most expensive.  I highly recommend the tuner at the antenna option if you can afford it. - Neither approach does not preclude the need of a ground plane and RF ground in the shack - BOTH are needed for any solution.

You can use a balun at the feed point but my suggestion is that an UNUN is a better approach.   I would suggest you use a 9:1 UNUN  since your going from an unbalanced feedline to unbalanced antenna. Having transformation at the antenna will be more efficient than without.  Using a 1:1 balun will force you to purely use a tuner at the operating position (with no transformation at the antenna) you will have much higher losses due to significant SWR on the coax for non resonant frequencies (if you can tune them).     If you have issues with common mode current coming back into the shack and your RF ground is not sufficient then you can put a balun inline closest to the shack and will function as a choke; this will take some experimenting as each persons situation is different.  Ideally you should focus on your RF ground in the shack if you have a sufficient ground plane at the antenna.  If you can not have a sufficient ground plane at the antenna then you will for sure have common mode current on the shield of the coax and/or coupling to anything else around the antenna.  Even then end feds/long wire antennas easily couple to their surroundings.  This is a major fault of this type of antenna.  Issues will manifest into noise on receive and RF in the shack during transmit.

If you absolutely have no way to get common mode current off the shield of the shack then you can ground the counterpoise to a ground stake at the base of the antenna  Your performance will be significantly impacted so I dont recommend this approach.  Your next best approach is to use the shield of the coax and your best approach is using a counterpoise... You can try any length of counterpoises and many of them until you are satisfied with your results.

My setup is a 9:1 UNUN with NO counterpoise.  It is defaulting using the shield of the coax.  I have a balun on feedline just outside the wall of my shack but far away from the UNUN.  I have the LDG tuner, and rig grounded to a RF ground which is my water pipe since my rig is on the second floor of my house.   I had major RF in the shack and RF on transmitting (my voice was very distorted) before I grounded my tuner/rig and added the balun.   My radiator is roughly 64 feet... I can tune it from 10 - 160 with no issues but poor performance 10 - 17m, 160m, good performance 20 - 40m, OK performance 80m.  It is 1-2S points higher in noise on 20 meter than my dipole and/or mini beam.  On 40 meter it beats my shortened dipole by 2S points!  On 20 meter my dipole and minibeam match some times but canr beat it by 2S or less.  For get it on 17M - 10M - it works but not all that well.. Its 1S-2S or more lower than the dipole.


If you can put up end fends with at least 10 feet apart then I would suggest using more appropriate length end feds for 10 - 17, 20 - 40, 80 -160.  This is an idea but have never experimented with.. It may help performance for those bands since too long radiators can cause deep nulls in the patterns which I believe is happening on 10 - 17 thus the poor performance.




I appreciated all of the replies. For the record I have a copy of the ARRL antenna book and I reference it often. In this case I had just moved so it was in a box somewhere. I always do try to do my own research before asking questions, that way my questions are as pointed and intelligent as possible and so that I can better understand any answers I receive. Anyhow, as I mentioned there is a lot of conflicting, or at the least incomplete, information on random wire antennas out there. I think that I now better understand some of it.

It sounds like an ideal instillation would be no balun or unun and a very good RF ground and/or counterpoise. I don't think my RF ground will be great and a counterpoise isn't going to happen. So in that case it sounds like a 1:1 current balun right at the antenna feed point would be a good choice. My understanding is that I should have two RF grounds: my regular station RF ground and a separate RF ground for the ground wire coming off of the balun and that these two grounds should ot be connected. Is that correct?

By the way, to get the ~200' length I'm looking for my antenna will have to be "L" shaped, one ~140' leg and one ~60' leg. Is that a big deal?
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73

Mike
KD2CJJ
AK4SK
Member

Posts: 206




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« Reply #20 on: May 23, 2013, 12:40:59 PM »

I finally got a hold of my ARRL antenna book, I'm afraid that there isn't much info on random wire antennas in there, I was a bit disappointed.

I have a question about grounding related to lightning protection. It is recommended that the shield side of the coax should be grounded to the tower/mast near the feed point and then again at the base of the mast. That is a general statement I have found regarding feed lines and lightning protection. Is that true for wire antennas such as the random wire being discussed here and others such as dipoles? So in this particular installtion following that recommendation the shield side of the coax would be grounded to the mast via a grounding block immediately before the coax goes into a balun/unun that feeds the antenna. Is that correct?

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W5WSS
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Posts: 2272




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« Reply #21 on: May 23, 2013, 03:40:26 PM »

I needed to build an antenna from a summer cottage so Ive built a wire antenna where at the station end of the wire antenna I crimped and soldered a banana plug onto it.

The wire was insulated#14 copper stranded thhn.

The Tuner was located indoors on the wood frame window sill. I routed the wire underneath the wood frame window then I plugged the antenna wire directly into the tuner S0-239 centered hole located on the back.

From the ground lug of the tuner I then attached a 3ft short length an exacting size #14 Thhn wire to a complete tuned and elevated 1/4 wave radial system of pairs per band where the radials traveled away in opposite direction to non conductive stakes as anchors.The wire exiting the shack was spaced about 3/4 of an inch and held parallel to the antenna wire forming a balanced feed line of roughly 300-400 ohms. Or I could have simply used a 3ft length of 300 ohm flatline from tuner to junction box which I also tried and was fine.

The radial system Instead of  using a radial ring the wires were brought to a single point, twisted together crimped and soldered to a large terminal and when connected to the 3ft wire exiting the shack from the tuner lug junction ed outside with the radial system after which a strain relief was utilized and located forming a junction which was simply located just outside and at the window sill height.about 4ft high above the ground.

The strain relief consisted of a 5 gallon bucket filled with concrete and a short non conductive pipe.and some guy rope and stakes to hold it in place.

The strain relief junction allowed for single point entry box to be fastened to the top of the short non conductive pipe and a wander lead to be included for connection to a dc earthing rod driven into the ground and was utilized when away or preceding poor weather and also providing a weather proofed interior for the connections.

When viewed from outside the radials simply sloped downwardsfrom the box and were held taught where they met the anchors and looked like cat whiskers or a sloped peace sign relative to the wire traveling upwards to a rope and hoist over a tree.

The antenna wire was held practically vertical.

The system was defined by the center feed point since the radials were tuned 1/4 wave pairs.
I varied the antenna wire length held to range of lengths but did not exceed 5/8 wave length.
The 1/4 wave antenna wire length would have allowed the use of a short length of coaxial cable along with using the 1/4 wave radial pairs but I wanted to try varying antenna wire lengths and settled with the balanced line feed.

The tuner handled 10m to 40 meter and high efficiency power manifest radiation ensued.

The radials completed and satisfied Kirchhoff's Law.
 The box and rod served as a single point pre entry bonding panel for all the antenna connections and the wander lead was applied to switch the antenna wire to ground.

A bonding wire was attached from the station entry rod to the ac mains entry rod.

The sway of the tree limbs could have but never broke the wire up at the hoist rope and dogbone insulator.

All that sounds complicated but not so.

The total cost was less than $50.
The performance was very good.

A word of caution when installing any antenna out the second floor window.
Research and understand single point entry bonding for lightning.

73

 

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WB6BYU
Member

Posts: 17070




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« Reply #22 on: May 24, 2013, 07:49:45 AM »

Grounding the coax shield to the tower at the feedpoint will allow the tower
to serve as the ground/radial portion of the antenna.  How well it performs
this task will depend on the height of the tower, how well it is grounded at
the base, how the guy wires are attached, etc.  It is quite possible for the
tower to be well grounded, but of such a length that it presents a high
impedance to RF at the feedpoint.  (Performance depends on the electrical
height of the tower in wavelengths, so it will vary from one band to the next.)

For lightning protection, the most important places to ground the coax
shield are at the base of the tower, and again before it enters the house.


With regards to your previous question about bending the wire, that will change
the radiation patterns, but the antenna will still work.
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AK4SK
Member

Posts: 206




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« Reply #23 on: June 03, 2013, 12:56:58 PM »

I got a random wire put up a week ago Saturday. I'm not sure of the length, 200'+ and the height varies from a little over 20' at the feed point to maybe 30' in some places back down to 15' or so at the far end. It's also in a "L" shape horizontally. I have a 4:1 current balun at the feed point with one side going directly to a dedicated ground. So far I'm pretty happy with it. I can tune it anywhere I want from 1.8 to 54 MHz. No issues with RF in the shack so far but I haven't tested in it on all bands at high power (100W).
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AC2EU
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Posts: 1208


WWW

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« Reply #24 on: June 03, 2013, 02:14:58 PM »

I got a random wire put up a week ago Saturday. I'm not sure of the length, 200'+ and the height varies from a little over 20' at the feed point to maybe 30' in some places back down to 15' or so at the far end. It's also in a "L" shape horizontally. I have a 4:1 current balun at the feed point with one side going directly to a dedicated ground. So far I'm pretty happy with it. I can tune it anywhere I want from 1.8 to 54 MHz. No issues with RF in the shack so far but I haven't tested in it on all bands at high power (100W).

That setup is indeed random on many levels. That's why you didn't find much about "random wires" in the ARRl antenna book. They attempt to define the design process to obtain more or less predictable  results. However, if it works to all of your expectations, then it's a good antenna.
Good luck !
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