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[Articles Home]  [Add Article]  

Auto Antenna Tuner Notes

Alan Applegate (K0BG) on January 14, 2003
View comments about this article!

In a recent post on the Mobile Forum was a admonition against using an automatic antenna tuner in conjunction with a mobile antenna. It was stated that this would burn up the antenna in question. I don't think burn is the correct description, and I'd like to dispel the rumor(s).

Auto antenna tuners (AATs) like Icom's AH-4, SGC's various models, and several others, have become quite popular of recent and for good reason. They're easy to install, will match just about any antenna they are attached to within their limits, and offer the ability to QSY in seconds. But their use in mobile installations still remains mysterious and evil. And this shouldn't be the case, so let's take another look at them.

The most popular tuners in current use utilize a "T" matching circuit. That is to say, a shunt, variable inductance with input and output series capacitors. Within limits their efficiency is typically over 90%, but at their limits this can drop to just a few percent. AATs on the other hand can handle just as wide of ranges as the "T" match and yet maintain efficiencies of over 90% in most cases. This is because they are switched LC circuits.

These LC circuited AATs use a computer-controlled, binary-stepped series of inductors, and a binary-stepped series of shunt capacitors which can be switched between the input or output to match loads below or above line Z (impedance) respectfully. In the case of the Icom AH-4, the values are 24 uh and 2,200 pf and its impedance matching range is nominally 5 to 5,000 ohms. This is enough range to match an 8.2-foot antenna from 7 to 54 MHz. If the antenna is twice this length it will cover most of 75 meters as well.

What we have then is a versatile AAT which works on 12 VDC (ideal for mobile operation), offers a wide range of matching, has a quick QSY capability, so why not for mobile? Indeed, it is an elegant solution to many old problems, but it does have a limitation which needs to be understood.

A typical mobile HF antenna (<25 MHz) is 7 to 9 feet in length and requires some sort of loading coil to cancel the capacitive reactance, a result of the less than full 1/4 wave physical length. If the coil is fixed in value, it is necessary to remove and replace coils when changing bands. On 40 and 80 meters, any large QSY also requires retuning of the coil and/or whip to maintain a low VSWR.

Of late, there seems to be a proliferation of small, short, helically wound mobile antennas. They become popular because they tend to be less expensive than other antennas, they're light and easy to mount on a variety of cheap mounts, and they match well because their inherent losses are so high. But they still have the shortcomings listed in the last paragraph.

Obviously, it would be convenient to find a simple way to QSY without having to stop. There are many ways to do this, and one of the more popular ways is the screwdriver antenna. Remotely controlled from the drivers seat, it offers large excursions of frequencies albeit slowly. One benefit of their design is they maintain a relatively high Q because the coil is not short tapped like on some bug catcher designs. In some cases, it still requires changing a tap on an impedance matching device when band changes are made. So, the AAT is looking better all the time, except for those few shortcomings I mentioned previously.

Every mobile antenna has losses and the formula Rt=Rr+Rc+Rg describes those losses. Rt=total or input resistance (more correctly input impedance), Rr the Radiation resistance, Rc the coil resistance, and Rg the ground loss resistance. To maintain efficiency, we can raise the Rr, or lower the other losses Rc and Rg. We have some control over the radiation resistance since it is a factor of the electrical length of the antenna (loading coil position is also a factor). And to a lesser extend we can control the other losses too. Just for fun, let's look at an average 8-foot, bumper mounted, center loaded 20-meter antenna. It has a radiation resistance of 11 ohms, a coil resistance (loss, not reactance) of 5 ohms, and a ground loss of 8 ohms for a total of 24 ohms. The efficiency is 45%. A similar antenna for 40 meters will measure, 3, 14, and 10 respectfully for an input of 27 ohms. The efficiency is 11%. But what if we took the 20-meter antenna and matched it to 40 with our AAT? The respective calculated figures would be 3, 5, and 10 for a total of 18. Adding in the approximate losses in the tuner and we have an efficiency of 12%. In other words, this would be slightly better than our resonant 40-meter antenna. A lot of operators would (will) dispute this, but it just means they haven't done the math.

In my personal case, I use a rather long 20-meter antenna (13.5 feet) mounted on the left quarter panel with a heavy-duty GE mobile ball-mount. The coil is 4" in diameter, 2.5 inches long, and has a Q approaching 900. With the AH-4, I have full coverage from 75 meters through all of 6 meters. Subjective and empirical testing favors this combination from 40 through 6 meters, and equal to most on 80.

Let's get back to our poster and his admonition and that one limitation. If you were to use one of the aforementioned short, small, helically wound antennas, this trick wouldn't work. The reason is that these types of antennas have a lot of coil turn to coil turn capacitance, or what is referred to as distributed capacitance. They wouldn't burn up per s, but an arc could occur between adjacent windings and might render the antenna useless.

Alan Applegate, KBG

Member Comments:
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Auto Antenna Tuner Notes  
by NE2I on January 14, 2003 Mail this to a friend!
What is a good auto tuner to use with an icom 735.
It will be used mobile.
 
RE: Auto Antenna Tuner Notes  
by K5DVW on January 14, 2003 Mail this to a friend!
Autotuners are one of the best antenna innovations around these days!

I use an SGC auto tuner and a 9' CB style whip. Works great from 75m up, as you might expect. Anyone using a single band helical antenna with an autotuner just doesnt understand physics.

In my situation, the autotuner is likely to "burn up" before the antenna.

K5DVW
 
RE: Auto Antenna Tuner Notes  
by N8IK on January 14, 2003 Mail this to a friend!
Autotuners and single-band helical antennas work great together as long as you stay within band. I do it all the time from a 5th floor balcony. Having said that I did work JT1CO on 17m with a 15m hamstick.
 
Auto Antenna Tuner Notes  
by K1MKF on January 14, 2003 Mail this to a friend!
Nicely written and well said. The microprocessor controlled ATU with either a whip or a wire worked against ground radials is probably the best all band antenna available. No mismatch losses in the coax, no losses in traps or loading coils. It's essentially doing what the big manual tuners located at huge Shortwave antenna farms do. Just a lot quicker.

That said Alinco, Icom, SGC and formerly Yaesu made these units. Anybody have first hand bad luck with any?
 
RE: Auto Antenna Tuner Notes  
by K0BG on January 14, 2003 Mail this to a friend!
George, NE2I, the 735 mates well with the AT500, but lacks the control circuitry to control the AH-4. You could use an after market adapter (look here http://www.hamoperator.com/ah4/ ) or one of the SGC models which use RF keying. Just beware of some of the AATs which advertize "up to 10:1" as they might not have enough range for full QSY mobile use.

Alan, KBG
 
Auto Antenna Tuner Notes  
by N7NHS on January 14, 2003 Mail this to a friend!
Good Day all. I have a 706MKIIG with a AM-COM ASAC-100 controller running a Yeasu ATAS 100 screwdriver antenna mounted on a MFJ-345 lip mount on the 3rd door of my s-10 truck. AND BOY AM I HAPPY. Am-Com makes a FANTASTIC controller. I work 440-40 meters with it and even have good luck on 6 meter. It is real nice to drive to work or home and hit the tune button and within seconds the radio is tuned and ready to use, so you can jump into that pileup using "mobile" usually with great results. And from what I understand these automatic controllers work with all different kinds of radios and screwdriver antenna's. So I guess what I am trying to get to is, I dont think I will have any trouble burning up my mobile antenna using this automatic controller.
 
Auto Antenna Tuner Notes  
by AD7DB on January 14, 2003 Mail this to a friend!
Alan,

Thanks for a very informative and (for me) timely article. I have an IC-706MkIIg and am considering going the route of using an AH-4 and a whip. My brother is installing a screwdriver antenna for his own installation.

Dave AD7DB
 
RE: Auto Antenna Tuner Notes  
by K3WVU on January 14, 2003 Mail this to a friend!
I haven't used my IC-706MKIIG mobile with my AH-4, but I can tell you that I've had excellent results using them both in a fixed installation (about a 65' wire and an equal length counterpoise). I would imagine that the AH-4 with the Icom whip element, or a cheap Radio Shack quarter wave CB whip and a good ground to the car frame would be an excellent mobile setup.

I'm now getting ready to install a Yaesu FT-100D and ATS-100 combo in the car.
 
RE: Auto Antenna Tuner Notes  
by KE1MB on January 14, 2003 Mail this to a friend!
There are two types of these closely wound ant. i can think of. For 20m for example, one is 4ft long, not sure who makes it, then there is the hamstick that is 8ft. Now I don't think anyone would argue with me about the fact that the 4ft helic wound ant. is a dummyload on a stick. Is this the ones that are reffered to in the article?
 
Auto Antenna Tuner Notes  
by KL7XL on January 14, 2003 Mail this to a friend!
NE2I - The AH-2 Tuner (ancestor of the AH-4) will work well with the IC-735. Since the 735 lacks the internal circuitry to control the AH-2, Icom made an AH-2 control box which mounts on the side of the 735. Loosen a couple of case screws, slide the control box on, tighten the screws, hook up the cables, and ready to plug in the AH-2. Nice simple setup, and all Icom.

The AH-2 is physically a few inches larger than the AH-4 and the specs do not include 6 meters. Both AH-2 and AH-4 are weather resistant and can (should) be mounted physically close to the antenna.

The AT-500 will certainly work well with the 735, but the AT-150 is the "correct" tuner. Correct as in matching the size and styling of the 735. The AT-100 and AT-500 are styled to match the IC-751, so are just a bit different in color and size from the AT-150. These will work mobile, but are intended more for home QTH use.

I don't know if the AH-2 controller will work with the AH-4 tuner. I picked up my AH-2 Tuner for $150 and the control box (new in the box) for $25. If you decide to get the AH-2, a good place to look is on the Icom reflector.

My 735 manual is not at hand, but I believe all the above details are covered in the manual.

Ron
KL7XL
 
RE: Auto Antenna Tuner Notes  
by K0BG on January 14, 2003 Mail this to a friend!
Thanks for the comments Ron. I owned a 730 once upon a time, but not the 735. I suspect the AH-2 would work with any Icom with the 24 pin molex control port, but just for fun, I'll look it up on the Icom site.

The dummyload on a stick was coined by Don Johnson, W6AAQ, as a description for any helically wound HF mobile antenna. And compared to some of the better mobile antennas around, it's basically true. Fact is, the efficiency difference between a hamstick (even an 7 foot one) and a properly mounted screwdriver or bug catcher is in the order of 20 db or more.

And the ATAS isn't any better than a hamstick as far as losses are concerned. Remember this; the longer it is, the higher it is mounted (properly), and the higher the Q, the better the signal.

The fact that you can make contacts with the antenna efficiency under 2% or 3% is a testament to just how little power it really takes.

If you use an AH-4 and any antenna to band QSY, remember the tuner must be as close to the antenna base as possible to minimize ground losses.

Alan, KBG
 
Auto Antenna Tuner Notes  
by N8EMR on January 14, 2003 Mail this to a friend!
I use an AH4 on my tahoe with a 12ft whip while mobile. I can goto 16ft for portable operation if needed with screw in mast. Due to mounting requirements I have about 1ft of feeder line from the ah4 and the antenna base.
This arrangement works well for most bands. 80m of course is a bit tricky but I can use the 12ft whip and get a "good enough" match to work the local traffic net on the way home. With the 16ft whip 80m is fine. I also carry a spool of copper and can run a longwire off the body mount for extended stationary work.
 
Auto Antenna Tuner Notes  
by N0RU on January 14, 2003 Mail this to a friend!
IC-706MkIIG, AH-4, and RS 9ft fiberglass whip is tough to beat for a good, all around HF system. Sure, it may not be as efficient as a screwdriver or bug catcher, but for my purposes it is perfect. Working DX like OD5 and VQ9 along with numerous domestic stations proves it works. I have never used it to transmit on 75, but it will tune. Worked a KL7 on 6 SSB last fall. Did have to employ some cures to get it to settle down on 17 due to the lenght of feeder and antenna. I like the low profile of the system, too.
Robb N0RU/4
 
RE: Auto Antenna Tuner Notes  
by K0BG on January 14, 2003 Mail this to a friend!
Robb, you might be surprised just how good your setup is compared to the average screwdriver. Contrary to what the manufacturers of screwdrivers tell you, their Q on 80 and 40 isn't much better than 80 or so, and in some cases less than 50! This makes the AH-4 and an 8 to 11 foot whip superior in efficiency overall, if the tuner is mounted close to the antenna base.

Alan, KBG
 
RE: Auto Antenna Tuner Notes  
by KZ9G on January 14, 2003 Mail this to a friend!
Hi Alan,

Thanks for another good article.

I can live with the hamsticks if their 3 dB down, or less, on 20m thru 10m. I've found their relatively high mounting positions on my Bravada most important for effective operation (lower ground losses). If and when I begin to operate on 40m or 75m mobile again, I'll upgrade to a screwdriver mounted high on a vehicle. Just have to save those pennies...

BTW, has anyone done ground loss comparisons between various mounting locations on vehicles? I remember reading something to this effect in the early nineties, but cannot remember where.

73 de Steven, KZ9G
 
RE: Auto Antenna Tuner Notes  
by KZ9G on January 14, 2003 Mail this to a friend!
Hi again Alan,

I've always wondered what the throughput losses of these mobile tuners really are on the lower bands, especially when they have to match such diverse impedances. I also wonder if a valid test of efficiency would be to measure tuner input versus output voltages while an RF carrier is applied. One could use a VTVM, such as a HP 410B to do this. My only reservation is not knowing the feed point impedance of the attached whip on the output. But, I believe that impedance could be measured with test equipment available to amateurs. Obviously, this impedance could affect the output power determination (P=E2/R), and the resulting loss determination. I'll have to reread the methodologies employed in those great QST articles a few years ago on base station antenna tuner efficiency.

As youve stated, if these tuners couple with a relatively small amount of loss, a modest whip coupled by one may prove to be more efficient. I'd sure like to see some scientific investigation into this subject. It could prove to be illuminating.

73.
 
Auto Antenna Tuner Notes  
by N0GZ on January 15, 2003 Mail this to a friend!
Thank you for a very informative and well presented article. With a 13.5 foot antenna and a big coil in the middle, I can imagine that your system works extremely well. I hate to rain on the parade, but it's apples-to-oranges comparing this setup to Hamstick-type antennas. Autotuner systems don't scale down well to something the average ham can more likely live with, i.e., a 9' or less fiberglas antenna.

I have run fiberglas whips with and without an Alinco EDX-2 autotuner (very similar to the Icom AH-4) and have done A/B testing and come to the conclusion that the autotuner performs significantly worse in this configuration. The Hamsticks were mounted on a Lakeview license plate mount (wonderful!). A lighter antenna up higher raises the top of the antenna (high voltage point) and reduces ground loss enough to make a significant difference. In every case, running the autotuner to a 9' unloaded and a 9' 15M resonant fiberglas whip. Using the autotuner produced significantly lower field strength readings and worse on-the air reports.

A significant factor is internal tuner loss. In my experience this loss can be very high, certainly worse than the 90% efficiency quoted, particularly on the lower bands where it matters most. In general the less antenna you have the more internal inductance gets switched in, and the losses soar. You also have to run a high voltage line through the car body, which up north here where it rains, snows, and roads get salted, can lead to arcing problems.

In the end I decided to stick with the "handful of hamsticks" with quick disconnects and the license plate mount. It is not as convenient to QSY bands, but I can get the car in the garage in a flash.

Autotuners are very convenient and can work well, especially on 20 meters up. Its a law of physics that the more metal you have in the air the better any mobile antenna will work. However, in my humble opinion if you can live with a big, permanently mounted antenna, get a long screwdriver-type antenna so every inch radiates outside the vehicle. Otherwise, forget the autotuner, save your $$$, and go with basic Hamsticks mounted as high as possible.

73 de Ken / NGZ
 
RE: Auto Antenna Tuner Notes  
by K0BG on January 15, 2003 Mail this to a friend!
To answer Steve's, KZ9G, question about ground loss. Some years back, QST published several articles dealing with ground loss, and it is still accepted today. If you look in the ARRL Antenna book at the impedance table, you can figure out the ground loss with simple substraction. But as I stated in my article, the lower the antenna is mounted, the higher the losses. On 80 meters, a bumper mounted setup exhibits a ground loss of approximately 10 to 12 ohms depending on the vehicle and the ground it is over. On 10 meters, a roof mounted unit will have a loss of about 1 to 2 ohms. I use 6 as an average.

As for the input impedance, that is a function of length, and the Antenna book and the Handbook both have formulas for figuring it.

And Ken, NGZ makes some interesting points. The loss through the tuner can be calculated, and even measured with the correct equipment. Fact is, if you know the unloaded Q of the network components, and you know the approximate in and out impedances, again calculatable, you can figure the loaded Q and hence the loss.

The CD-ROM which comes with the Antenna book has a program called AAT.EXE which prints out the loss percentages based on the network configuration (LC, T, etc.) and load impedance, Qs, etc. and does the calculations. Although this is a good indication, it is not an absolute.

One thing to keep in mind is the actual capacitive reactance of the antenna. The addition of just a couple of feet of coax (about 2 pf or so) can reduce the efficiency as much as 50%, perhaps more. In my personal case, the ouput of the AH-4 is just a couple of inches from the antenna input. So you are right, you have to be careful not to "apple and orange" the configurations differences.

Incidentally, you should read the mobile section of the latest Handbook. Makes interesting reading in light of my article.

Alan, KBG
 
RE: Auto Antenna Tuner Notes  
by K8YOY on January 15, 2003 Mail this to a friend!
Alan, is the AH tuner mounted inside the vehicle or outside? Thanks
 
RE: Auto Antenna Tuner Notes  
by W3ETC on January 15, 2003 Mail this to a friend!
I just received the Icom 706 and would like to take it mobile on HF. It appears that the AH-4 and the whip make for an effective if somwhat cost effective combination. My question in reading that the tuner should be as close to the antenna as possible what type of wire do you use to connect from the tuner to the whip ? I am trying to figure out how I can place everything in the car.

Thanks for a great forum.
 
RE: Auto Antenna Tuner Notes  
by K0BG on January 15, 2003 Mail this to a friend!
To Ed and Mike both, the tuner is mounted in the truck behind the trim panel of my 1998 Mercury Mystique. The link to the inside of the ballmount is about 3 inches long or so, and IS NOT coax. The tuner is grounded to the unibody just below the tuner. The mount is a heavy-duty GE unit (no longer available unfortunately) which has a provision to ground the mount's inter ring to the body through the rubber gasket.

As I have stated previously, it is imperative that the tuner be mounted as close to the antenna base as possible. The use of even a 2 foot chunk of coax will greatly degrade the overall performance. Read that as efficiency.

Alan, KBG
 
RE: Auto Antenna Tuner Notes  
by NO9E on January 15, 2003 Mail this to a friend!
I would not agree with the universal statement that ATU have lower losses than manual tuners. Most manual tuners have air coil with high Q. Most ATU have toroid cores with lower Q. The L network has higher efficiency matching low Z but not high Z loads.

Feeding unbalanced antennas, the efficiency of ATU may drop drastically if baluns are used in the output esepcially with wrong cores. With manual tuners, almost any toroid will provide good isolation between the radio and the tuner.

Once I made a small 4:1 balun. It did not even get warm with 100W to a 50 Ohm load. It got hot on output of K2 with 10W. On the other hand, K2 ATU tuned all antennas with the toroid while being unable to do so without. A dummy load added to the output would do the same.

Summarizing, a manual T tuner would mostly tune any antenna on any band with mostly acceptable performance. An automatic tuner would tune many antennas, but in some matches most of the power may indeed stay in inductors or the output balun.

Ignacy, NO9E
 
Auto Antenna Tuner Notes  
by N6VUJ on January 15, 2003 Mail this to a friend!
Does any one know where I can find an auto tuner that can handle 1.5 kw?

 
RE: Auto Antenna Tuner Notes  
by K0BG on January 15, 2003 Mail this to a friend!
Ignacy, NO9E, you are correct about SOME AAT like the LGC units; they use toroids for the inductors. The AH-4, and several others made by Icom use air wound inductors. But it isn't the inductor type you have to be worry about. It's Q. In this case, both unloaded and loaded Q.

The unloaded Q of the inductors are important, and in the case of the Icoms, it's about 100 to 200 depending upon how much inductance is used to tune the load. The Q of the capacitors is at least 1,000 and maybe a little more.

But the real measure is the LOADED Q. If you do not understand the difference, the best source is to read the ARRL Handbook's Networks section which gives a much better explanation than I can.

The average loss through the AH-4, or the Z11 LGC unit, is about 2% but maybe as high as 15% at the edges of its matching ability.

But there are other things to consider too, and after I have digested all of the information, questions, and comments, it is my plan to publish another article to address as many as I can. Stay tuned (excuse the pun).

Alan, KBG
 
RE: Auto Antenna Tuner Notes  
by W1VON on January 16, 2003 Mail this to a friend!
Thanks for a very informative posting regarding automatic antenna tuners.. I learned something today!

A while ago, I purchased an Icom AT-120E, new in the box, but without docs of any type. I did a search with Google, but came up with no references. I believe it is a marine model but am not sure.

Can anyone enlighten me as to what this ATU is capable of and how I can interface it to my Icom 746?

It appears to be very similar to the AH-4 with a heavy pigtail for the control interface. This is such a nice piece of kit I'd like to put it into operation..

Thanks,

Ron
 
Auto Antenna Tuner Notes  
by WA4PTZ on January 16, 2003 Mail this to a friend!
I have been using an SGC autotuner with both my
screwdriver antenna and my hustler 40 and 80 meter
coils for about 2 years with no problems or damage.
My rig is 100 watts PEP and I have no plans to
increase the power level. I can talk to Australia
on that, so I don't need any more.
Thanks for the article and 73 -
Tim
 
RE: Auto Antenna Tuner Notes  
by KZ9G on January 16, 2003 Mail this to a friend!
Alan,

Let's see a mobile whip/AAT product review article employing the scientific method. The theory is great, but I'd like to read about real-world coupler efficiencies that are measured using notable test equipment. Included would be theory, initial expectations, equipment facts, explanation of the methodologies used, a conclusion, and bibliography. An article presented in similar ARRL "Antenna Anthology" format would be nice, too. 73.
 
RE: Auto Antenna Tuner Notes  
by VE6XX on January 17, 2003 Mail this to a friend!
Greetings from the Great White North:

Alan....once again you have delivered a first class tutorial, subjective & free from the technical drivel
that is all too prevalent in some articles. In one of your replies, you mention keeping the coax from the AAT to the antenna base as short as possible. I am certain that you meant to say "feedwire" or some such name. To your readers who may be unaware, coax must NOT be used between the output terminal on the AAT & the input terminal of the mobile antenna because of the shunt "C" of the coax. Ditto for running the feedwire paralell to a conductive surface. I own several SGC tuners & an Icom AH-2 with which I ran mobile with a 735 for more than 10 years without problems. The die hards all scream against tuners,but fail to recognise that convenience may be more important than the last dB ! Alan, It has been my experience running home made "bug catchers" & 1/4 wave antennas mobile (full 1/4 wave, not loaded) that occasionally a load/tune situation arises where the circulating RF currents in the tuner become high & burn ground leads &/or boards in the tuner. I burned two SGC tuners over the years, but SGC has or had a board replacement deal that was very reasonable price wise. SGC told me that I had an intermittent ant or ground, but that simply wasn't the case. I lament the unavailability of the old style GE or Motorola ball mounts. The pot metal crap that is made today is a joke, as are the plastic base insulators. I make my own base insulators from 5/8 " HDPE(high density polyethylene) or Teflon(r) stock. I make my own ball mounts from 2 1/4 " trailer Ball hitches. I drill the ball & tap it & then saw the ball at an appropriate angle & VOILA! A local machine shop will do the job for $70 Canadian, which is steep for most hams, but they are BULLETPROOF!! Grounds grounds grounds! Wide braid or strap. Please! No wire grounds! RF flows along the surface of a conductor, so you want all the surface area possible...thin & WIDE please, & paralell grounds are best. Remember, the antenna ground is at the AAT , NOT at the antenna. Therefore, everything from the output post on the tuner forward is antenna & radiates! Grounds MUST be cleaned regularly & often.
Bigger antennas are better, all other factors being equal. The gentleman who was having difficulties with his tuner & was claiming it was lossy was using that "license plate" mount. What do folks have against either drilling a bloody hole, or if its a leased car or whatever, having a mount welded to the frame, & bolting an extension on it? Assuming the "license plate" mount is on the trunk lid, most likely a capacitor exists because no RF ground exists between the trunk lid & vehicle ground. Most of the "no holes" mounts are a nightmare as regards RF grounding, & are suitable only for lightweight antennas. Thanks again Alan for your treatise, always a pleasure to read your well presented & factual missives.

CHEERS! Brian, VE6XX
 
RE: Auto Antenna Tuner Notes  
by K0BG on January 17, 2003 Mail this to a friend!
Brian, VE6XX, thanks for the kudos. Several of the items you bring up I plan to address in a follow up article. The lead between the base of the antenna and the AAT in my installation is less than an inch. And I did mention coax in my article which was a mistake on my part. You are aware (most hams are not) that most commercial HF amateur antennas exhibit a capacitance between 20 to 40 pf or so depending upon band and physical length. Some, like the 75 M Hamsticks measure less than 15. Obviously ANY extra or stray shunt capacitance will greatly affect the performance.

A couple of folks mentioned redoing the article replete with formulas, test data, calculated data, and real world comparisons. I'd like to do that, but then most hams wouldn't read it. And besides, most of the data is out there in the form of ARRL publications and university white papers.

Thanks again, Brian.

Alan, KBG
 
RE: Auto Antenna Tuner Notes  
by KC0JBJ on January 17, 2003 Mail this to a friend!
How do you use the AH-4 tuner with a mag-mount mobile antenna that has a 50 ohm coax feed? Do you need a balun?

I have a Wilson 1000 (11-meter) antenna that works great on the lower end of the SSB portion of 10 meters without cutting down and without a tuner (not so good SWR on the FM portion). Although the loading coil is at the base rather than at the center, I understand it has a pretty hi Q, as the coil is pretty beefy (rated for 1000 watts).

I would love to be able to use a AH-4 with my IC-706 MKIIG and this antenna. Center of roof location is ideal with no hole cutting, plus easy to remove. With its 60-inch whip on top of my wagon, the top is as high as many 102-inch whips mounted on bumpers and trailer hitches.

Please tell me how make this set-up workable!
 
RE: Auto Antenna Tuner Notes  
by K0BG on January 17, 2003 Mail this to a friend!
Don, K11 and similar CB/10 meter antennas have a loading coil in the base to make the 60" whip appear electrically longer 108" in this case. I don't know how much distributed capacity it has, but I suspect you couldn't match it very well even on 12 meters. A 60" whip is way too short to make it effective even with a lossless tuner much below 15 meters. And to tune it with any tuner through a few feet of coax is nearly impossible. This is true for two reasons.

First, even if you could match it, the VSWR on the coax would be so high, your effective radiated power would be nearly zinch.

Secondly, ANY, even a few picofarads of shunt reactance, especially with an antenna so short, would again make the antenna usless.

And Don, it isn't the height of the antenna that makes the difference, it is the length of the antenna. And when you use any tuner to match the impedance or an unloaded (or loaded) antenna on a band it was not designed to resonant on, the tuner must be as close to the base of the antenna as possible, due again, to shunt reactances.

Alan, KBG
 
Auto Antenna Tuner Notes  
by W0LPQ on January 18, 2003 Mail this to a friend!
Alan, thank you for your very informative article. I have a 706IIg, RT-11 and Hamsticks. The run from the RT-11 to the antenna base is about 24". From the digest of information presented, I think I need to shorten this a bunch...somehow. I think that I can get rid of maybe 12" approximately. This should improve the efficiency of the system. The system is patterned from the QST article of a couple months ago. It have had "good results" during an Arkansas trip over the holidays, but from reading, I think it can be better. This, in retirement days, is a neat project.

Having worked aircraft HF systems for the last many years, I can attest to the short lead from the tuner to the antenna, but never really thought of it in an auto environment...but your message has made me think again.

Thanks and keep us in the loop on other pieces of info that you can post here for our edification.

73

Bill, W0LPQ

 
RE: Auto Antenna Tuner Notes  
by W0LPQ on January 18, 2003 Mail this to a friend!
Alan, another question. I use RG-58C for the feedline from the RT-11 to the antenna. Could I improve even more switching to RG-213..!

Bill, W0LPQ
 
RE: Auto Antenna Tuner Notes  
by K0BG on January 19, 2003 Mail this to a friend!
Bill, if you're using the RT11 to match the antenna impedance to 50 ohms, and not trying to band QSY, then it really doesn't make much difference about the coax. The VSWR nominally with even the best of mobile antennas will be under 3:1, and the additional loss through even RG8 is enough to worry about.

Incidentally, the run from the tuner to the antenna in my vehicle is maybe an inch.

Alan, KBG
 
RE: Auto Antenna Tuner Notes  
by KC0JBJ on January 20, 2003 Mail this to a friend!
OK, AH-4 (or similar) auto-tuner with base-loaded coax-fed 11 meter whip, baaaaaad. Tuner with 8-11 foot whip and short single wire lead, goooooood.

For a 100-watt mobile HF (ICOM 706), what gage and type of lead wire and insulation is needed for optimum performance? Also, how important is it to mount the tuner outside the vehicle? I have a mid-size wagon with good mounting locations under the cargo deck (spare tire well), or in a storage compartment to the side near the lift-gate (hatch-back). This would require a little longer leadwire than external mounting but would be a whole lot easier and cleaner, besides protecting the tuner from road-hazards and theft. Keep in mind the lead wire diameter should be small enough lay across the lift-gate weather seal without damage during repeated openings and closings.

And how do you place a bumper mount on a late-model (1997) vehicle with plastic bumpers?
 
RE: Auto Antenna Tuner Notes  
by K0BG on January 20, 2003 Mail this to a friend!
Don, I don't think it is important to mount the tuner inside the vehicle. In my case, I mounted the antenna on a heavy-duty GE ballmount, and the output of the tuner is just about an inch from the antenna input terminal.

In nuber seven of the ARRL's Antenna Compendiums, they show an amateur who used the ladder on his RV for an antenna. The tuner was mounted just a couple of inches from the bottom of this ladder. I'm sure it worked as good as he said it did.

The main reason for mounting the tuner as close as you can to the antenna is stray capacitance. The average mobile antenna is about 20 to 45 pf or so, so it is easy to see why even a few pf of shunt capacitance can greatly affect the efficiency.

I prefer to mount antennas with ballmounts, or other permanate mounts. If you can, place it in such a position that the cubby hole is but a few inches from the mount base. And don't use coax to feed the antenna. Use solid copper wire.

Hope this helps.

Alan, KBG
 
Auto Antenna Tuner Notes  
Anonymous post on January 23, 2003 Mail this to a friend!
The explaination concerning efficiency of T tuners and automatic tuners in this article is total nonsense. A T tuner is nothing more than 2 back to back L networks in hi-pass configuration and the typical auto tuner is usually a switchable hi-z or lo-z L network or Pi network in lo-pass configuration. Either tuner will perform matches either as Pi (or T)or L in hi or lo pass configuration. The fact that autotuners use 1,2,4,8,... sequenced switched caps or inductors is irrelavent.

In order to use a T or Pi network as an L network, just put one of the caps at minimum (Pi network) or one of the caps at maximum (T network hipass config.)

Factors that influence losses and efficiency is the Q of the circuit components which need to be very high for very low or very high impedance matches because circuit Q is high which dictates that component Q must be much higher.
 
RE: Auto Antenna Tuner Notes  
by K0BG on January 23, 2003 Mail this to a friend!
Richard, what you say is basically correct, however, the "T" match is not as efficient as an LC circuit. Typical losses thru a "T" match hover around 10%, while an LC under the same conditions will be about 2%.

While unloaded component Q is very important, so is loaded Q. A quick play of the AAT.EXE and the TLW.EXE programs which come with the ARRL Antenna book will prove the point.

Also, a recent series of articles is QST about the EZmatch (now also in the 2003 ARRL Handbook) explains the situation better than I.

Alan, KBG
 
Auto Antenna Tuner Notes  
Anonymous post on January 23, 2003 Mail this to a friend!
Where do you people get these crazy ideas? A T isn't an LC network???? Alan, you have no idea what you are talking about. I don't use ARRL calculators or QST articles. I use long accepted network theory used for at least the last 100 years by anybody doing network design.

If you really wanted to make a point you would show how losses are related to load impedance, LC transformation ratio , resulting Q for various reactive loads and network configurations. Instead you babble generalized BS from magazines and web sites.

Different networks work better with certain kinds of loads but then loose some other way, its always a compromise.

Alan, your arrogant demeaner will not cover your total lack of knowledge.

The internet is full of people talking about something they don't really understand and then dump it on those who may not know better and pass more nonsense on the the next guy.

And you also don't seem to know what's inside those automatic tuners, like close wound coils with small gauge wire with cheap relays and cheezy fixed caps, result is relatively high loss. I know because I have an AH-4. Its works well but not like a continuous variable tuner.
 
RE: Auto Antenna Tuner Notes  
by K0BG on January 23, 2003 Mail this to a friend!
Your previous comment about making an LC tuner out of a "T" network by setting one or the other capacitor to full mesh, speaks for itself.

As I said, UNLOADED Q is important, but so is LOADED Q. The problem with "T"tuners is there are several setting for any given load that will provide a match. Most of them have a VERY high LOADED Q, thus the losses are great (> 30% to 40%). In fact, it is possible to load the tuner without any load attached.

If you think, Richard, that I'm telling fibs, or that I am arrogant, I suggest you get a copy of the latest QST and look at the review of the 5 antenna tuners they tested.

As for the AH-4, the worse case scenario is 15.49% loss. Average loss is under 2%. Theoretically, and by actual measurement.

Alan, KBG
 
Auto Antenna Tuner Notes  
Anonymous post on January 23, 2003 Mail this to a friend!
Alan,

I give up, you can't read plain English and you don't have any understanding of what is being illustrated. Have a nice day.
 
To WA8KJP and K0BG  
by KF6KHH on January 25, 2003 Mail this to a friend!
WA8KJP: Is being personally insulting to K0BG really necessary because he has different opinions than you do? Why don't you try being helpful instead of being insulting?



K0BG: Thanks for the articles and followups. I'm trying to come up with the best mobile antenna I can within XYL limitations and appreciate your attempts at assistance.
 
RE: Auto Antenna Tuner Notes  
by AK4DD on January 25, 2003 Mail this to a friend!
hi from nc
i use a wilson 1000 -alinco dx70 and an ldg tuner
the wilson is cut to 28.3 mhz and the ldg does a fine job on all of 10,12 and 17m-i5 is a little tougher-
tuner is mounted on the left rear glass and works w/ the 706 wonderfully.i also use an a/b switch
b= diamond series 400 mount on the top left hatch on my explorer-a 15m hamstick or ironhorse covers 10-12-15-17 meters w/ alittle compromise-20 ,40 and 75m antenna's round out the mobile station-
check on the ldg unless u have already invested in the icom.
mobile safety is a must and the automatic systems afford some degree of same
73
david
 
Auto Antenna Tuner Notes  
by KI8JD on January 26, 2003 Mail this to a friend!
I have a pickup truck with a fiberglass cap. Could I run a wire around the inside of the cap, and load it up with an Icom AH-4? I believe there would be lots of capacitance, as the wire would only be about 2 feet above the sheet metal. Running towards the rear on one side, across the back, and back forward on the other side would give me 20 feet of wire. I also thought I could install a coil 12 feet from the AH-4, (in the rear corner) to increase the current on the first side, and on the rear 4 feet.
The top of the truck is already 6 feet high, and the 10 foot railroad bridge up the road has already got one antenna, when I forgot to slow down to a crawl. I don't have any experience with HF mobile, other than 11 meters. With the upcoming solar decline, a low angle of radiation is not a concern. I would probably be more interested in 40 meters.
Anyway, I wonder if anyone has played with wire inside a fiberglass cap? Dipoles, loops, or whatever.
Thanks, Jim ki8jd
 
Auto Antenna Tuner Notes  
by N1KHB on January 27, 2003 Mail this to a friend!
Great article. I have used an SGC auto tuner and before that, an MFJ manual random wire tuner (about $40 back then) with a 8.5' stainless whip. Great setup with either. The manual tuner was nice because it was so cheap! Imagine a complete HF mobile antenna system for a total of $60 or so. I eventually graduated to the auto tune unit for convenience. I eliminated the problem of grounding outside with all of the associated bumper grounding nonsense by grounding the tuner inside the trunk, then snuck a high voltage wire thru the trunk lid gasket to the radiating element base. This insured not only a good clean reliable ground not subject to the elements, but also added a little length to the radiator by using the lead wire from tuner to antenna.

Joe N1KHB
 
RE: Auto Antenna Tuner Notes  
by AC6DN on April 16, 2003 Mail this to a friend!
I HAD a SCG antenna tuner (1-54 MHz) and a 102 in whip (Now, I have a Don Johnson screwdriver antenna (DK-3). It was located on my 4x4 trucks upper finder of the bed, near the taillight. The tuner was located inside the bead opposite the antenna, with a 12 in. long HV lead). Everything was, vary well, grounded with rf brads. I found that this, set up, did not work well. It worked ok on 10-20M, poorly on 40M, and sucked on 80M (it would actually tune on 160M). After numerous calls to there tech support, without any improvement, I eventually got a refund. I wanted this setup because of the perceived hands-off tuning, and because, I lost my DK-3, somewhere??? I found my screwdriver antenna, installed it in the same location, and it worked radically better everywhere, 80-6M!!! Later I experimented with a 9ft whip, a High Sierra capacity hat, vs. a 66 inch whip on the DK-3. I found that with the HS cap hat, I got at least a 10db improvement on 80M, and almost that, on 40M. Although, I cant use 12-10M with it (w/ cap. hat).
My conclusion: By a HI-Q (4 or 6 in coil), a N7LYY, or a DK-3(if low cost is most important) or dont waist your time.

Bruce
AC6DN
1.8-1300 MHz mobile, all mode, w/ 14 antennas
 
Auto Antenna Tuner Notes  
by V1ERDJ on April 18, 2003 Mail this to a friend!
I am installing an Icom 802 with An At140 Atenna tunner. I have 44 feet of usable backstay after I allow for the insulators and I am wondering what is the best lenght.
 
RE: Auto Antenna Tuner Notes  
by G2JL on November 23, 2003 Mail this to a friend!
Greetings from England (That's near Europe, by the way !)

I've been struggling with the highly confusin Internet to try to locate information about the Icom AT-120E.

I came across your note of January this year. Did you ever find any information ? I don't want to bother to re-invent the wheel when others have already done a Grand Job !

73 & good DX de Mort, G2JL
 
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