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[Articles Home]  [Add Article]  

A 'Balanced' Remote Autotuner

Bill Savage (K3AN) on July 16, 2006
View comments about this article!


A “Balanced” Remote Autotuner

I have used SGC-230 remote automatic antenna tuners to match inverted L's and other long wire antenna configurations for over a decade now. At my current QTH, one is installed at the base of a tree, where it's connected to a 130 foot inverted L (55 feet vertical, 75 feet horizontal). The SGC can find a match on all bands 80-10 except for a 60 kHz or so segment (about 3660 to 3720 kHz) of the 80/75 Meter band. I suspect the wire is exactly a half wave somewhere in that range, which results in a very high feed point impedance.

The inverted L works quite well on the lower bands. But modeling shows that much of the radiation on 20 Meters and up is at high angles, so I investigated simple designs that would give me more low-angle radiation on those bands.

The antenna I came up with was a single diamond quad loop, fed with ladder line. After reading up on loop antennas on the excellent W4RNL web site, I learned that a loop radiates broadside to its plane only if the overall length of the loop wire is greater than about 0.75 wavelengths and less than about 1.7 wavelengths. Doing some basic math, I determined that a loop with a circumference of about 56 feet would provide the desired broadside pattern from 14 to 29 MHz. Its radiation at high angles is suitably low, meaning it doesn't hear high angle signals well either. This could enhance my signal (DX stations) to noise (local stations) ratio.

SGC tuners are inherently unbalanced, and are designed to connect to a mobile whip or other single-wire antenna, working that antenna against a good ground. I noted an ad for a balanced remote autotuner in a recent issue of QST, but the price of almost $700 was higher than I wanted to pay. Therefore I decided to see if I could adapt one of my two SGCs to more-or-less balanced operation.

One way to “balance” this kind of tuner is to raise the entire device above RF ground potential. That means using a common mode choke or current balun, not just on the coaxial feedline, but on the power and control lines as well. Through their QST ads, I learned that two new choke balun kits have recently been added to the Palomar Engineering product line. One is for quarter-inch cables (RG-8X, RG-58) and the other is for half-inch cables (RG-8, RG-213). Each kit consists of five relatively long ferrite cores, some lengths of different size heat-shrink tubing for insulation and weather proofing, and a very brief but adequate instruction sheet.

Since they were less expensive, I purchased a couple of the kits for the quarter-inch cable. That meant I had to remove much of the SGC's common outer jacket over the coax and control wires. In retrospect, it would have been easier to install the kit for the half-inch cable, as it would avoid having to remove that outer jacket. In either case, you'll still need to cut off the factory coaxial connector, install the balun kit over the coax and the power and control wires, then install a new PL-259. To keep radiation from the coax and other wires to a minimum, there should no more than a short section of the cable (less than 10 inches) between the case of the SGC and the closest balun core. Also, if I intended to use the SGC with a balanced antenna on the lower HF bands (80, 40 and 30) I would have installed two kits in series on the cable instead of just the one.

Here's a photo of the final installation. The ladder line connects to the SGC's antenna and ground terminals. The choke balun is the fatter, dull gray part of the cable that drops down from the bottom of the SGC enclosure. Sorry for the poor quality of the photo. Those of you who own one of these tuners will note that I cut off a significant portion of the factory-supplied cable. There's no real need to do this, however. Just make sure the choke balun is near the enclosure.

0x08 graphic

I used a weatherproof trailer light connector for the 12 Volt and ground connection. I did not extend the SGC's other two (control) wires, as I have never used them. That's vinyl electrical tape over the coax connectors (bottom center, against the tree trunk). After I snapped this photo I found my roll of Coax Seal, so that connection is now more weather proof.

The loop is in the midst of a dense canopy of pine and hardwood trees. As installed, the top corner is at about 55 feet, the same height as the flat top portion of my inverted L. The bottom corner is at 35 feet. The plane of the wires is north/south, to enhance signals to and from east and west. About 32 feet of ladder line is attached at the bottom corner, allowing the SGC to be mounted near ground level.

How well does this configuration work? First of all, the SGC is able to find a match on all bands 20 through 10. On 20 Meters, domestic signal levels are about the same on the loop as on the inverted L. The DX is definitely stronger however, and I can often copy a weak one on the loop that's just too far down on the L. On 17 Meters and higher the difference is more pronounced. Most signals are a good two S-units higher on the loop, except for those stations located off the edges (north and south of my QTH). On 15, I can easily hear stations in the Pacific that are completely inaudible on the inverted L. However, I still can't break most phone pileups on the rare ones there with my hundred watts and South Carolina QTH. I'm much more successful with stations in Africa and the Middle East, getting through a small pileup to S9SS on the first call one recent afternoon. I haven't been able to do a lot testing on 12 or 10 yet, but the small sample of received signals on 10 so far have been consistently stronger on the loop, sometimes by as much as 4 S-units. Finally, just as you've always heard, the loop is pretty darn quiet on receive.

Is this arrangement as good as a 3-element SteppIR? Of course not. What it really shows is how poor the inverted L is on the higher bands.

I'd love to know how well the ladder line's conductor currents are balanced with this setup. I know the balance is not as good as it would be using a truly balanced tuner, so there's undoubtedly some radiation from the ladder line. However, I'm not worrying about it much, as I'm too busy enjoying all the solid QSOs on 17 Meters and higher. It's going to be really tough waiting for the next sunspot maximum.

If you'd like to try your hand with a multi-band balanced antenna and ladder line feed, and want the convenience and band changing speed of an automatic antenna tuner, this is one possible way to do it. G5RV dipole, horizontal loop, traditional delta loop, this arrangement should work with most if not all of them. It's especially suitable when you can't (or don't want to), bring the ladder line into the shack. And with the SWR on the coax always 1.5:1 or less, signal loss there is minimized. By the way, I see no reason why this solution can't be applied to the Icom AH-4 and other similar autotuners.

K3AN

Member Comments:
This article has expired. No more comments may be added.
 
A 'Balanced' Remote Autotuner  
by NS6Y_ on July 16, 2006 Mail this to a friend!
Sigh. Oh I wish. In my neighborhood, the tuner and wire etc would be stolen by the local crackheads during the first night.

Oh give me a home, where the meth-heads don't roam, and motion-sensitive lights and fields of fire interplayyyyyy.........
 
RE: A 'Balanced' Remote Autotuner  
by W6TH on July 16, 2006 Mail this to a friend!
.

I noticed where the ladder line is separated where it connects, forms a sort of delta conection, yes this will make the ladder line radiate some power. Any separation of the ladder will cause the radiation of rf.

Seventy five feet plus fifty feet of "L" equals onehundred thirty feet of wire. That 130 feet is an excellent half wave for the 80 and 75 meter band and no matter where you go on the 80/75 meter band the antenna will always be at a high impedance point, being fed at the end.

You accomplished something and you are pleased with your work and what you tried, that is the most important part.

.:
 
RE: A 'Balanced' Remote Autotuner  
by K0BG on July 16, 2006 Mail this to a friend!
Bill, I have a similar arrangement using an SG235 auto coupler mounted under an eave. However, I did not choke either the feed line or the control line.

The ladder line is connected just like yours, runs up about 25 feet to the apex of the doublet. The coax is grounded at the entrance to the house, and the control cable is bypassed by .01 caps at the same location. With 50 feet on each leg, the coupler will match the doublet's impedance from 80 through 10 easily, and will even do the top part of 160 (with less efficiency obviously).

I have never noticed any phenomenon that I could associate with not "choking off" the coax and control lines. I know of at least 5 others who are doing the same with both SGC and Icom couplers. To my knowledge none of them are choked off either. It begs the question why you did, other than it is good practice?

Alan, KBG
www.k0bg.com
 
RE: A 'Balanced' Remote Autotuner  
by K3AN on July 16, 2006 Mail this to a friend!
If you look at the SGC schematic, you'll see that the shield of the coax going into the SGC is at the same RF potential as the ground terminal of the SGC. They are normally connected to earth or other RF ground via a short, low-inductance conductor.

But if the SGC ground terminal is instead connected to one of the antenna elements (directly or via a balanced feedline), then the coax shield is also effectively connected to that side of the antenna or feedline, and it upsets the balance. The choke balun should reduce that imbalance, which in turn should reduce feedline radiation.
 
A 'Balanced' Remote Autotuner  
by WW5AA on July 16, 2006 Mail this to a friend!
Bill,

I would be interested in how many radials you have for the inverted "L". If I understand this correctly, you are end feeding the antenna at the base of the tree.

73, de Lindy
 
RE: A 'Balanced' Remote Autotuner  
by WY3X on July 16, 2006 Mail this to a friend!
QUOTE: NS6Y Sigh. Oh I wish. In my neighborhood, the tuner and wire etc would be stolen by the local crackheads during the first night.

KR4WM says (most assuredly tongue-in-cheek and with no intention of you doing this!!!) That's what plate transformers are for. One side of secondary to ground, the other side to the item you want to protect against theft. If the voltage is high enough, you'll find the perpetrator there the next morning. <GRIN> Of course, don't accidentally hook the coax to your rig or touch it while high voltage is present!!! I know someone who did this to their car which was being vandalized. It was vandalized no more.

It helps to have displays of sparks and what-not in your yard from time to time to discourage thievery too. You have to be a good actor though, and make sure the thieves see you getting "shocked" by the item you want left alone. You could also set up a neon transformer on top of the item you want protected, and make a small jacob's ladder with a good show of sparks and fire. Make SURE the crackheads see the arcing and sparking! Then hook the wires up and walk away. Use a long extension cord so you can unplug it from a distance (indoors) without being seen. I once scared the pants off a fellow firefighter with a coat hanger, two AA batteries, and a lawnmower engine condenser held together with a rubber band. (Firefighters do this sort of thing all the time....) I hung it on his bunk, and got some other firefighters to point it out to him and make a big deal of seeing me get shocked by it when I put it there. The guy slept in the day room in a chair all night long!!! The power of suggestion worked! The device didn't do a darned thing, it was all just a scare tactic! The next morning I let him see me pick it up with some insulated needle nose pliers and put it in my locker for safe keeping. It helps to have a reputation as a mad scientist... and officers who had a great sense of humor as accomplices! -KR4WM
 
A 'Balanced' Remote Autotuner  
by WF7A on July 16, 2006 Mail this to a friend!
Bill, I may have missed it in reading your article, but I'm curious: did you position your quad loop vertically or horizontally?

Nice place you have there: you have trees! Here on the Idaho prairie there isn't a single tree and nothing but lossy, dry dirt and river rock. Talk about RF slurpus maximus. *sigh*

Ciao,
Rich
 
RE: A 'Balanced' Remote Autotuner  
by K3AN on July 16, 2006 Mail this to a friend!
Lindy (WW5AA),

The Cebik (W4RNL) web site has a lot of info about inverted L antennas. The following comes from one of his articles.

"NEC-4 modeling strongly suggests that the addition of a ground plane adds virtually nothing to antenna performance for the inverted-L and the T, both of which we have described as complete antennas. In contrast, the vertical is dependent upon the most extensive (up to 60-100 radials) that a builder can install."

By vertical, he means a quarter-wave monopole.

My ground system consists of a single ground rod just below the tuner. At a prior QTH, I demonstrated W4RNL's conclusion to my own satisfaction (this was before I had found his web site). That QTH's 130 foot inverted L also had just a single ground rod. I laid down eight 35 foot insulated wire radials and ran tests with a number of hams on 40M. Neither they nor I could ever see a difference on our respective S-meters when the radials were connected to or removed from the tuner's ground lug.

160M is an entirely different situation. On this band the L is just a quarter wave, and the SGC constantly hunts for, and fails to find, a match. When the weather cools, I will be installing at least eight radials, and more if that's what it takes to get me on 160 this winter.
 
RE: A 'Balanced' Remote Autotuner  
by W6TH on July 16, 2006 Mail this to a friend!
.

This doesn't make sense.

The SGC can find a match on all bands 80-10 except for a 60 kHz or so segment (about 3660 to 3720 kHz) of the 80/75 Meter band. I suspect the wire is exactly a half wave somewhere in that range, which results in a very high feed point impedance.
--------------------------------
Answer:
The 130 feet is a half wave and a high impedance feed point if fed at the end.
--------------------------------


The antenna I came up with was a single diamond quad loop, fed with ladder line
---------------------------------
Answer:
This indicates the antenna was vertically polorized if fed at the bottom.

.:
 
RE: A 'Balanced' Remote Autotuner  
by W6TH on July 16, 2006 Mail this to a friend!
.
Sorry, typing error, should read: "polarized".
.:
 
RE: A 'Balanced' Remote Autotuner  
by K3AN on July 16, 2006 Mail this to a friend!
A 130 foot wire is an EXACT half wave at just one frequency. Above and below that frequency, the impedance is most definitely high but it's not infinite. It is within the matching range of the SGC. Given the frequencies at which the SGC cannot find a match, I suspect I must have cut the wire a bit shorter than 130 feet. Or maybe the so-called "end effect" is not the same reduction factor as it is for a dipole antenna.

A diamond configuration vertical loop fed at the bottom corner will have the same polarization as a square configuration vertical loop that's fed at the midpoint of the bottom wire. Horizontal. Check the old "All About Cubical Quad Antennas" book by Bill Orr, W6SAI.
 
RE: A 'Balanced' Remote Autotuner  
by WR8D on July 16, 2006 Mail this to a friend!
I use a jw miller at-2500 with a centaur 4-1. I tried these two jewels together on differant antenna types. I ended up with about 275 feet of number 12 in a triangle loop configuration, fed with a little over a hundred feet of homemade open wire number 12 feeder. Mine is spaced at 6 inches apart and the number 12 stranded holds up to the wind and ice here good in the winter. After years of putting other wire antennas up and trying them against this loop i just gave up and took them all down. The horizontal loop at 40 feet smokes any wire antenna i ever tried. I used to use the 450 ohm commercial made stuff and as we all know when it rains or snows you get the skin effect and have to retune all the time. Homemade stuff spaced 6inches is the only way to go. Only way you know its raining is to hear it hitting the window, i just change bands and tune it one time and thats it. Maybe retouch at the band edges only. Snow and rain once tuned don't have any effect at all. The loop works just fine mounted lower at just 20-25 feet too. Very nice thread on antennas and tuners, thanks to the author. --... ...-- WR8D
 
RE: A 'Balanced' Remote Autotuner  
by W4VR on July 16, 2006 Mail this to a friend!
I don't understand why you don't simply use a remote balun at the output of the tuner to prevent the transmission line from radiating. The way you're feeding the antenna you would be just as well off feeding the antenna with a single wire and keep the other end of the loop open...this way the tuner would handle the variety of impedances it encounters and improve your SWR from the current feed method.
 
RE: A 'Balanced' Remote Autotuner  
by W6TH on July 16, 2006 Mail this to a friend!
.

Never mentioned as to the feed point of your Diamond Loop.

It should be noted that horizontal loops can only transmit in the horizontal plane. Vertical loops can be fed in such a way as to either effect horizontal polarization or vertical polarization depending on how and where they are fed. If a vertically oriented antenna is fed at either the bottom or the top, the polarization will be horizontal; should it be fed on the side or bottom corner, it will be vertical. If you are going to the trouble of putting up a large vertical loop, be sure to feed it to take advantage of the low angle of radiation mentioned above. If a delta, then feed it at one of the bottom corners. If a diamond, then feed it a mid "corner." If a square, then at the center of one of the vertical sides.

.:
 
RE: A 'Balanced' Remote Autotuner  
by NS6Y_ on July 16, 2006 Mail this to a friend!
KR4WM I appreciate the suggestions, but I'd have to be at least a millionaire to own enough forest like that to put the antenna in, in the first place.
 
A 'Balanced' Remote Autotuner  
by N0AH on July 16, 2006 Mail this to a friend!
Excellent-
 
'Balanced' Remote Autotuner Postscript  
by K3AN on July 16, 2006 Mail this to a friend!
In response to questions and comments posted here, let me add the following postscript.

To the readers who weren't sure of the antenna's orientation, it's a vertical loop. Each of the four sides is about 14 feet in length. Dacron tensioning lines at the side corners pull it to an approximately square shape (90 degrees at each of the 4 corners). It's fed at the bottom corner.

I recently found an article on the web about losses in commercial window-type ladder line when it's wet. Yikes, six plus dB per hundred feet at 50 MHz! That's a matched loss. Imagine what it is with a high SWR. As a result, I'll be making or buying old-style line with plastic spreaders in the near future.

I avoid bifilar-wound, core-type baluns when the load can have a high reactive component, such as in a multi-band wire antenna. Sevick and others all caution that the losses can be significant. What I installed isn't really a "balun" at all. I think the term "line isolator" used by one ham supplier to describe this kind of device on coaxial cable is a better description than "choke balun."

My "forest" is a 100' by 180' lot. There are really too many trees, and it was difficult to get even this small loop up in the air. The horizontal portion of my inverted L crosses an open space in the front yard just in front of the house, but well above it of course. 26 gauge "stealth" black insulated wire makes it invisible to all but other hams. I'd love to put up a large horizontal loop, but I'd have to relocate the inverted L. I haven't yet figured out how to have both antennas. When I do, I'll use the same feed system described here for the big loop (but not with window-type ladder line!).

Finally, if you have any interest at all in antennas, there's a few hours of very informative reading awaiting you at the L. B. Cebik web site, www.cebik.com. I don't care how long you've been a ham, you're bound to learn something by reading his articles. You'll also probably discover that at least one antenna-related "fact" you've long known is actually a myth.

Thanks to all for your interest and your posts.
 
RE: 'Balanced' Remote Autotuner Postscript  
by DD3LY on July 17, 2006 Mail this to a friend!
I know that Rohde & Schwarz has built such a "by force" balanced autotuner from a common mode choke and an unbalanced autotuner. They wrote an article in their R&S company journal why they think it works. Generally most hams suppose that the voltages at the transceiver side are modest. But if you try to raise the impedance level of the grond line simply by adding a 1:1 current balun as it is done here on the antenna side with the tuning elements, this only works in a relatively small range of antenna impedances and in a limited range of wavelengths. At high impedances the limited impedance of the 1:1 current balun working as a common mode choke will cause loss due to imbalance and feedline radiation.
It seems strange to me that the industry does obstinately refuse to build and offer a balanced autotuner. I have asked SGC, LDG and MFJ with aout the same result. I think there is NO risk to redesign an existing autotuner and simply add one binary switched inductivity-stack as it is already existing in the unbalanced tuner. OK, they need to add a 1:1 current balun, but that's all. Such a tuner even could be used as an unbalanced tuner, simply by deactivating the additional binary switched inductivity-stack. SO WHERE IS THE RISK WHEN ALL COMPONENTS HAVE BEEN INVENTED???
I hope that there is somewhen a ham who is inventing a universal controller-board for an autotuner, which you can equip as you like: QRP or QRO, balanced or/and unbalanced, switchable input transformers, artificial ground tuning for radom wire antennas and such gadgets. Sometimes I regret that I am not a software-programming-freak...
 
A 'Balanced' Remote Autotuner  
by K5UJ on July 17, 2006 Mail this to a friend!
<<<"NEC-4 modeling strongly suggests that the addition of a ground plane adds virtually nothing to antenna performance for the inverted-L and the T, both of which we have described as complete antennas. In contrast, the vertical is dependent upon the most extensive (up to 60-100 radials) that a builder can install."

By vertical, he means a quarter-wave monopole.

My ground system consists of a single ground rod just below the tuner. At a prior QTH, I demonstrated W4RNL's conclusion to my own satisfaction (this was before I had found his web site). That QTH's 130 foot inverted L also had just a single ground rod. I laid down eight 35 foot insulated wire radials and ran tests with a number of hams on 40M. Neither they nor I could ever see a difference on our respective S-meters when the radials were connected to or removed from the tuner's ground lug.

160M is an entirely different situation. On this band the L is just a quarter wave, and the SGC constantly hunts for, and fails to find, a match. When the weather cools, I will be installing at least eight radials, and more if that's what it takes to get me on 160 this winter. >>>

I am going to have to dispute some of this. The quote from the W4RNL website, taken out of context, isn't clear, but in any event, there are too many hams already who fool themselves into thinking they don't need radials. I know of hams who rx S9 signal reports running 1.5 kw and think that means they don't need radials, not knowing that if they had 60 to 100 radials they'd be 20 to 40 over S9.

An inverted L works against ground period. When it is 1 lambda at operating freq. there may be all sorts of lobes coming off at high angles, but you can be sure there is some component of the field that is lost in ground R. Your experiment comparing no radials to 8 radials was flawed because it did not involve enough of them to make a noticable difference overcoming variables such as propagation, and rx station locations. I guarantee that if you did an A/B test with no radials and 70 or 80 of them you would see a difference. A better test would be to have a station give you a signal report where the station is located not far from you, say 5 miles away. You tx a 20 w. carrier so they can get a steady field strength reading. they will be close enough to get a direct spacewave or groundwave signal, eleminating the skywave variable. you do your a/b test--i promise they will report an indication of much better ant. efficiency with radials. Only possible exception to this is if you are located in a salt water marsh ,hi. I agree that ladder line would be better than window line and thank you for sharing an innovative use of the sgc tuner, 73
 
RE: A 'Balanced' Remote Autotuner  
by AA4PB on July 17, 2006 Mail this to a friend!
An inverted L works against ground period
----------------------------------------------
This is a fact that seems to slip by many. A current article on the ARRL site makes the incomplete statement that a 1/2 wave antenna is a complete antenna and requires no ground plane or counterpoise. Yes, a 1/2 wave antenna is a high impedance load and therefore has much less current in the ground path than say a 1/4 wave antenna. The fact remains that if there really is *NO* ground connection then *NO* current can flow into the antenna and it doesn't work. We may think that our 1/2 wave end-fed wire has no counterpoise because we didn't lay out a bunch of radial wires. In fact, it does have a counterpoise. The coax shield (ala the PAR antenna) or the capacitance between the radio chassis and ground may be sufficient to make it work. It also often results in the radio, mike, etc. being "hot" with RF and all of the associated problems. For every amp of current flowing into an end-fed antenna there must be an amp of current flowing into a counterpoise somewhere. You can't make current flow into a light bulb with only one connection to a battery.
 
RE: A 'Balanced' Remote Autotuner  
by AA4PB on July 17, 2006 Mail this to a friend!
By the way, the W4RNL modeling data I saw was a comparison of an inverted-L with 4 radials to one with 20 radials. There is a major difference between 4 radials and 0 radials. I didn't see any data with *no* connection to one side of the source.
 
A 'Balanced' Remote Autotuner  
by W2XS on July 17, 2006 Mail this to a friend!
I could not agree more with DD3LY. I have also asked LDG and Elecraft for balanced versions of their tuners. It would need another row of inductors and associated relays and a balun at the input. The software should not need to change. Although I appreciate the German balanced tuner being offered in a small ad in QST, it is too expensive to consider at this time.
 
RE: A 'Balanced' Remote Autotuner  
by AA4PB on July 17, 2006 Mail this to a friend!
The firmware is a minor issue in terms of the cost. An extra set of relays, inductors, and capacitors probably doubles the cost of the unit.
 
A 'Balanced' Remote Autotuner  
by N9XY on July 17, 2006 Mail this to a friend!
Great article Bill, and good timing too. I just finished a similar project over this past weekend. I now have a horizontal loop (basically a delta, but am working to make it more like the theoretically ideal circular shape).

The loop is full wave on 80m, about 264 feet long and it is hung at about 60 feet in the pine trees here on Lake Hartwell (yes we are almost neighbors!)

I tune mine with the Kenwood KAT-1 autotuner. However, instead of splitting the window line as in your project, I instead modified my autotuner. I added another ceramic stand-off on the top of the box, and connected that internally to "ground". That way, I can connect the 450-ohm window line directly to two connections on the top without splitting the line for a long distance and possibly disturbing the balanced nature of the feed line.

I did not use any choke baluns on the RG-213 feeding the tuner. However after reading all of the comments here, I am still not sure if that is needed our not?

I haven't used the setup much yet, but considering that the tuner tunes on all HF bands, and the signals on most bands are stronger than my dipole, I am closer to my ideal of only one antenna for all HF bands....

Here is another reference that might be of interest
http://www.g3ynh.info/atu/sgc230.html



73
Michael
N9XY
 
RE: A 'Balanced' Remote Autotuner  
by KG5JJ on July 17, 2006 Mail this to a friend!
I also use an SG-230 (mobile) and SG-235 with 500 watt smartcube. I asked an SGC engineer if it would be good operating practice to choke the coax and control lines at the coupler, with a twin-lead fed loop, some years ago. He said absolutely unnecessary. He was right.

I wouldn't worry about it, unless you have some RF in the shack problems, but this shouldn't be unless the loop is almost in the shack with you!

73 KG5JJ (Mike)
 
RE: A 'Balanced' Remote Autotuner  
by KG5JJ on July 17, 2006 Mail this to a friend!
Awright! Who may come-up with an elegant solution to maintaining ladder-line integrity, right-up to the feed points of the SGC-235? ;-}

73 KG5JJ (Mike)
 
RE: A 'Balanced' Remote Autotuner  
by K3AN on July 17, 2006 Mail this to a friend!
Separating the wires of the ladder line for that short a distance isn't going to cause much radiation. Feedline radiation is caused primarily by an imbalance in the currents in the two feedline conductors.

The SGC's antenna terminal has one feedline conductor connected to it, nothing else. The SGC's ground terminal has TWO conductors connected- the other feedline conductor AND the outer surface of the coaxial cable shield. Current coming out of the ground terminal is split, with part of it going onto the coax shield and part going onto the feedline conductor. Therefore the currents in the feedline are not balanced.

By putting a "current balun" or "line isolator" on the coax, you raise the impedance of the shield's outer surface, forcing most of the current to go onto the feedline conductor. The result is less imbalance, which also means less feedline radiation.

A line isolator/choke balun can't achieve an infinite impedance on the shield's outer surface, so there will always be some imbalance. A truly balanced antenna tuner is still the best way to go. Let's hope it's not too long before we see some weatherproof, remote, balanced autotuners that are reasonably priced.

NOTE: If you check for continuity between the SGC's ground terminal and the coax connector shell, you'll see there's none. But don't be misled. A look at the SGC schematic shows a .01 uf capacitor between the coax shield and the ground terminal. That's pretty close to a dead short at HF.
 
RE: A 'Balanced' Remote Autotuner  
by DD3LY on July 18, 2006 Mail this to a friend!
Dear hams, dear W2XS,

I already had explained in my reply that one additional row of coils and a 1:1 balun is neccessary to build such a balanced tuner. This surely will raise the price, but does NOT neccessarily double the cost for a professional company. And surely this is NOT the real reason WHY the mentioned companies do not offer such a type of balanced tuner. I asked the companies in an e-mail conversation. "engineering risk" was stated, "sales risk" was another argument they have mentioned. WE are the customers, WE have to express what we would like to buy.
I agree that the balanced tuner from Germany, mentioned by W2XS, is relatively expencive, but in an exceptional position on the market, a manufacturer can ask ANY price... as long as there is no competitor.

During some kind of brain storming (hi) we had here, we discussed that a processor taken from such a relatively cheap tuner like LDG Z-11, a balun, an additional relay driver for big relays, two rows of coils and one row of capacitors with relays would do the job. A professional Z/Phi-bridgeagree from a military surplus tuner would do keep the effort low, from a point of few as homebrewers...
 
RE: A 'Balanced' Remote Autotuner  
by K5UJ on July 18, 2006 Mail this to a friend!

If you want to see another excellent (but expensive) remote balanced matching network option, click on the link below:


<a href="http://airwaterkinginc.purification.com/bzmmremotemotor.html">Bliss Matchmaster</a>
 
RE: A 'Balanced' Remote Autotuner  
by AA4PB on July 18, 2006 Mail this to a friend!
Okay, maybe not double the cost but certainly a major increase. The relays and coils are fairly expensive items and there are a lot of them. If you double the number of those components I expect it will result in a significant increase in cost. The "sales risk" is whether there are a significant number of customers who are willing to pay the extra cost to get a truely balanced tuner. You are correct that those who want such a tuner should contact companies like SGC and make their interest known. That reduces the "sales risk" for them.
 
RE: A 'Balanced' Remote Autotuner  
by KT8K on July 18, 2006 Mail this to a friend!
I looked at the link - and for $1800 and up I think I can take an existing automatic tuner for $250 or so and "remote" it. Also, the unbalanced tuners seem to be doing pretty well in a balanced configuration, so why do I need to spend twice as much (let alone $1800+) for that auto-tuned horizontal loop I plan to put up in the trees?

I think the high priced units are ridiculously expensive. If one of these companies wanted to, they could engineer a 150 watt one-box remote tuner that would be so inexpensive it would sell quite well.

Isn't one of the LDG or SGC models that just came out capable of running in a fully automatic mode, and doesn't it run for a couple of years on a few double-A batteries? I am going to weatherproof one of those puppies and hang it at the feed point of a doublet or horizontal loop, then just drop it to replace the batteries every couple of years. Why mess around??

Keep asking for what you want, folks. If you don't ask, you're not likely to get ...
73 de kt8k - Tim
 
A 'Balanced' Remote Autotuner  
by WW5AA on July 18, 2006 Mail this to a friend!
I see now that a lot of the confusion about the inverted "L" has to do mustly with configuration. The center fed inverted "L" which is really an inverted "V" on it's side does not need a ground plane(radial field). An end fed (from the bottom of coarse) inverted "L", just as any 1/4 wave monopole, requires an extensive radial field if fed with in a couple of feet from the ground. If the feed point is elevated to at least 5-10' above ground, tuned radials for each band, at least 2-4 will work fine. When Cebik writes about the "L" not being inhanced by the use of radials he is writing about the center fed "L".

73, de Lindy
 
RE: A 'Balanced' Remote Autotuner  
by K3AN on July 18, 2006 Mail this to a friend!
There's a long discussion of the end-fed L on Cebik's site. Go to "Tales and Technicals," then click on the "Straightening Out The Inverted-L" link, which is in the "Practical Antenna Notes, Lower HF" group of documents. It opens as a PDF file, so it's not possible to copy and paste his text. The discussion on the end-fed antenna starts on page 11 of the document. It's very worth reading.

Here's a quote.

"Because the base fed inverted L is fed at its end, it requires a good RF ground when its length is at least 1/2 wavelength. If used as a 1/4 wavelength monopole at its lowest frequency of operation, then it ALSO (my emphasis) requires radials to complete the antenna."

The author modeled a 69 foot L on 7 MHz (1/2 wavelength) with one 15 foot radial and again with 32 of them. The NEC model predicted just a 0.2 dB improvement with the 32 radials. He also ran the model using longer radials.

Maybe my single ground rod is insufficient, but my testing with 8 radials vs just the ground rod showed no obvious difference.

If NEC-4 is wrong, and Cebik is inadvertently misleading us by using it, then prove it. Do some actual tests and publish the results, or demonstrate where the formulas and the physics associated with the NEC model are in error.
 
RE: A 'Balanced' Remote Autotuner  
by WB5HZE on July 18, 2006 Mail this to a friend!
That is indeed what Cebik's 1/2 wl (40M) model indicates- however, I think it's important to note that when the same antenna is used as a 1/4 wl vertical (80M) then his models show that a radial system IS required (w/ 16 radials providing the most "bang for the buck," BTW). Given that many ops prefer to use their antennas on as many bands as possible, it would seem to make sense to lay a radial system regardless.

Nice article.

73 . . . Ron W5HZE
 
RE: A 'Balanced' Remote Autotuner  
by AA4PB on July 18, 2006 Mail this to a friend!
An end-fed 1/2 wavelength antenna does require a counterpoise of some type (not necessarily a bunch of radials). You can't possibly get any current to flow into the antenna if you don't have a counterpoise to feed it against. Because the impedance is high (high voltage, low current), the IR loss is low and you don't need an extensive radial system as would be required for a 1/4 wave end fed antenna. You do need something however. A single ground rod may be enough in some cases. The coax shield may be enough. The capacitance between the radio and the ground may be enough - but somewhere there must be an RF ground or the antenna doesn't work. You can't get current into an antenna with only one side of the circuit connected any more than you can light a flashlight bulb by connecting only one wire to a battery.
 
RE: A 'Balanced' Remote Autotuner  
by KQ6XA on July 18, 2006 Mail this to a friend!
The Autotuner Inverted-V-Fan-Dipole
and
Autotuner V-Fan-Dipole

Design and Installation Notes
by Bonnie Crystal KQ6XA

Click here:
http://hflink.com/antenna/


Common Mode Chokes
I've set up 3 different SGC autotuner systems at base stations using the common mode chokes (1:1 balun a misnomer) in the control/DC cables/feedlines, combined with a grounding strap to earth. These techniques keep some of the noise from computers and equipment in the station from being conducted into the autotuner's antenna system on receive, and they help choke off RF currents on transmit from going down the cables into the station. In the first two of those installations, severe RFI was eliminated that was present before the "chokes" were installed. In the third, I installed the chokes during the initial installation, and have not removed them to see how much difference they make.

73---Bonnie KQ6XA



.
 
RE: A 'Balanced' Remote Autotuner  
by W6EM on July 18, 2006 Mail this to a friend!
NS6Y Says:
"KR4WM I appreciate the suggestions, but I'd have to be at least a millionaire to own enough forest like that to put the antenna in, in the first place."

As another displaced former Californian, you can buy several acres and a nice house in the southeastern US including the Appalacians, decorated by mother nature at about half what you'd spend for a Los Angeles condominium, including 3000-4000 square feet of living space in the forest. And, most states won't tax you out of it.

Just curious. What are you using for insulators and suspension of the antenna(s)? Also, how do you compensate for swaying trees varying tensions?

I'm going to be hanging some wires up soon in some similar looking territory.

Lee
W6EM/4
East of Birmingham





 
RE: A 'Balanced' Remote Autotuner  
by KC0PET on July 18, 2006 Mail this to a friend!
I have not tried this particular configuration, but have used the SG230 for all sorts of "temporary" setups including long wires, inverted L's, dipoles and ladderline fed dipole. This is an extremely robust tuner and seems to work with about anything.

I have not tried the balun, but sounds like a good idea. I have discovered that the tuner does like to be above ground (the higher the better).

The most successful configuration I have found is a "crosssed dipole" configuration directly fed from the tuner with the tuner about 20 feet above ground. A fan dipole seems to work well also. A crossed dipole (two dipoles or 4 wires) cut for 40m and 60m (5 mhz) seems to tune anywhere including 80m just fine (I suspect with reduced efficiency at 80m).

With some setups, I have also found some "notches" that won't tune. usually with minor changes, this can be overcome.

de KC0PET
 
A 'Balanced' Remote Autotuner  
by KN4LF on July 20, 2006 Mail this to a friend!
In defense of W4RNL's comment on his antenna's website, that a 1/2 wave inverted Lantenna is self contained and needs no radial system, I have experimented with voltage fed 1/2 wl to 7/16 wl inverted L's for many years and have found that statement to be true.

I've conducted extensive experimentation over the years using these long inverted L antennas with one 1/4 wave radial and 64 1/4 wave radials. Far field measurements as well as 160 meter daytime groundwave signal reports were the same whether I used 1 or 64 1/4 wave radials on the ground surface. I always got excellent signal reports on DX too.

I have a website on the 7/16 wl inverted L at http://www.kn4lf.com/kn4lf52.htm.

--... ...--,
Thomas F. Giella, KN4LF
Lakeland, FL, USA
Grid Square EL97AW
kn4lf@arrl.net

KN4LF Amateur & SWL Radio History: http://www.kn4lf.com
Radiowave Propagation Yahoo eGroup: http://groups.yahoo.com/group/radiowavepropagation
 
RE: A 'Balanced' Remote Autotuner  
by W6EM on July 21, 2006 Mail this to a friend!
KQ6XA, Bonnie says:

"common mode chokes (1:1 balun a misnomer)"

Actually, more like an unbalanced-to-balanced current transformer. And, if the common mode series reactance is high enough at the frequency of interest, then, its a common mode choke.

Remember filament chokes in series with the filament supplies to grounded grid diectly-heated-filament triode amps? Same thing. Lets the 60Hz current through, but stops common-mode cathode RF current.

The concept is also useful for antenna lightning protection. A few turns of the coax, (or stacked cores about the coax) toward the shack from an antenna bonding and grounding point can create a common mode choke/CT that will help impede lightning current flow back to the QTH. (A direct strike of 40,000 Amps for 10 microseconds through even a 0.5 Ohm ground isn't exactly low voltage, so making the path back to the shack appear as a high impedance to common mode current/voltage rise is very desirable.)

Lee
W6EM/4
 
RE: A 'Balanced' Remote Autotuner  
by K3AN on July 24, 2006 Mail this to a friend!
Lee (W6EM),

The loop is made from the intermediate sized "stealth" insulated wire, #18 I believe. The top corner is supported by 3/16 inch Dacron line that's a continuous loop so I can lower as well as raise the antenna. The two sides are held open by 3/32 inch Dacron lines, tensioned to establish the desired square configuration. At each of those corners is a UV-stabilized tie-wrap "insulator." The side lines come almost all the way down to ground level before being tied off, so there's only one swaying treetop to worry about. As the top sways, the square loop is momentarily distorted first in one direction and then the other, but there's no need to provide any real strain relief.

K3AN
 
RE: 'Balanced' Remote Autotuner Postscript  
by W3PH on July 28, 2006 Mail this to a friend!
Re: I recently found an article on the web about losses in commercial window-type ladder line when it's wet. Yikes, six plus dB per hundred feet at 50 MHz! That's a matched loss. Imagine what it is with a high SWR.

--

I live on a lake, where it's wet a lot of the time, and at my location the window-type ladder line is almost useless. Tuning changes when it's even a little damp, and if it's really wet it seems as if most of the RF is consumed heating the water on the way up the line.

The good stuff is the open-wire line made by W7FG: http://www.w7fg.net/ - I've bought several big spools from him over the past few years and performance is excellent - I'm sure there's *some* loss when it's wet, but I really don't notice it, and tuning doesn't change at all.
 
RE: A 'Balanced' Remote Autotuner  
by WA2JJH on July 28, 2006 Mail this to a friend!
Nice work!
 
A 'Balanced' Remote Autotuner  
by WB1AEX on July 31, 2006 Mail this to a friend!
Nice project Bill! I went in another direction with my SGC remotely tuned balanced feedline antenna project, but the end result has been very effective over the past year from 160 meters through 10 meters. The largest factor in operating satisfaction involved the simple installation of an Elecraft BL2 1:1 balun on the output end of the SGC-239. I could not ask for a better behaved wideband HF antenna!

Details on what I ended up doing are at:

http://members.cox.net/wb1aex/sgctuner.html
 
RE: A 'Balanced' Remote Autotuner  
by 9V1VV on August 1, 2006 Mail this to a friend!
Hi,

I have the 500 watt SG-235 coupler feeding a 270 foot doublet, with 35 feet of 450 ohm open feeder. Previously I was using the Icom AH-4 coupler in the same configuration, but wanted more power.
The SG-235 comes with 25 feet of RG58 and a separate multicore cable for power and control. I did find some RF in the shack at 500 watts when dropping this cable straight down to the shack, so I cut off all but 2 feet and built a choke balun on an 8-inch plastic former, winding 30 feet of RG213 and 6-core shielded cable round this, then down to the shack by the same cable. I find there is no noticeable RF in the shack now on any frequency.
SGC do say that they don't recommend a balun, but it certainly does work. The coupler can be floated above ground no problems.
Unabalanced couplers can be made balanced in this way.
73
John
 
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