Introduction

The most important choice, any mobile operator will ever make, is his/her antenna. It pays to be very picky!

High frequency mobile antennas come in every imaginable configuration. Their efficiency, overall length, quality, design, sturdiness, ease of mounting, and selling price all vary. Choosing any one of these specific attributes is no guarantee you're getting another needed attribute included. The unfortunate truth is, far to many mobile antennas are selected based on their cuteness factor, spousal acceptance, and/or no holes mounting.

Toward the goal of helping the neophyte mobile operator to make a wise selection, I have applied an ABCD & F ratings systems. What the ratings are based on (in part) is not well known, and those are covered in the next section. However, you need to keep a few important ratings factors in mind as you read forward.

The number one factor with respect to efficiency is ground loss (Rg). Minimizing ground loss is priority one! This fact cannot be over emphasized, as even a one ohms reduction can have a large effect on efficiency.

The number two factor is length. An antenna's radiation resistance (Rr) is a factor of the square of the overall length. Shorter lengths also require more inductance in the loading coil. Think of it this way; half the length, less than one fourth the efficiency.

The number three factor is loading coil Q. Once coil Q surpasses about 350, there is little advantage to increasing it. If the Q is under 150 (as most commercial antennas are), doubling it can more than double efficiency in some cases, and at least 30% in most cases. In equations, Q losses are referred to as Rc (resistance, coil).

The number four factor is matching. The fact is, if your antenna doesn't require matching, you either need a better antenna, better mounting, or both!

The number five factor is construction. Some commercial antennas are so poorly made and/or designed, a blind man would rate them an F! So, if you're favorite antenna is listed here as an F, you'll know why.

If you need some antenna buying advice, read this article. Once you make your purchase, if you haven't already, and you just can't get it to work, read the Antenna Problems article.

Lastly, the inclusion, or exclusion, of any one particular brand or model, should have no weight in selecting an HF antenna. There are, after all, over 75 manufacturers of HF mobile antennas, and there may indeed be twice this number. Nonetheless, they are all subject to the exact same limitations listed herein.

Basics

One very important point needs to be made here. A vehicle is not a ground plane, but rather a capacitor between the antenna and the surface under the vehicle which acts as the ground plane. Since the surface in question is a poor conductor of RF, ground losses occur. The term ground plane in the following text is therefore a bit of a misnomer, but is used to differentiate it from DC and RF grounds.

The most important aspects of installing mobile antennas is having a good understanding of what is, and what isn't, ground. Ground, in this context includes ground plane, DC ground, RF ground, and the ground surface under the vehicle the antenna is mounted on. Because of the importance of this subject, I have dedicated a separate article to it. Before you plan, or complete, any antenna installation, do yourself a favor, and read the Grounds, RF & DC article.

Ground plane losses are the single largest factor in determining efficiency. If you don't understand the importance of a good ground plane, then the Ground Plane Notes article is for you. Remember this; Excessive ground plane losses will render the best of antennas nearly worthless.

Proper bonding is also important. Bonding aids in the performance of any antenna system by maximizing what little ground plane a vehicle represents. Bonding also minimizes the chances of of RFI ingress and egress. If you still have RFI issues, and you don't know what they are, read the Noise ID article. You might also want to read the Static Control article.

There are many reasons to permanently install your HF mobile antenna. Aside from minimizing ground and shunt capacitance losses, there is also a safety issue, and an insurance issue. As noted above, an otherwise decent antenna can be made nearly useless by poor mounting schemes and/or location. If you're not into drilling holes in sheet metal, at least pay attention to the ramifications temporary mounting schemes have on efficiency. Temporary mounting schemes include mag mounts, lip mounts, and clamps. Each one of these increases ground losses which are already too high in the best of installations.

Very few amateurs realize how important overall length is. Radiation resistance is based on (electrical) length, and to a lessor degree of how the current flows over that length. A full-sized 1/4 wave antenna has a radiation resistance (Rr) of ≈36 ohms. If we halve the length (1/8 wave), the radiation resistance drops to 9 ohms! Halve it again (1/16 wave), and the radiation resistance is just over 2 ohms! If the resistive losses were fixed at 10 ohms, simple math will tell you the efficiency rating. If you haven't read the efficiency article yet, the calculated efficiencies would be; 22%, 2%, and just over 1% respectively, assuming there are no other losses present. There will be, of course, because the shorter the overall length, the larger the loading coil inductance has to be, hence the greater the Q losses will be.

Contrary to popular belief, it is very difficult to design a loading coil with a Q over 500, and once it becomes part of the antenna, maintaining a Q over 350 is just as difficult, especially over a wide frequency range (i.e.: remotely-tuned antenna). This said, even if you could double the Q (to 1,000), the increase in efficiency would be barely measurable in the real world. Again, this is because ground loss (Rg) is the dominant factor in calculating efficiency.

This begs the question; what is the coil Q of an average HF mobile antenna? That is a hard to define parameter, difficult to measure, and one that varies a lot over an antenna's bandwidth. However, if you go through the requisite iterations, you'll discover loading coil Q factors are considerably less than those assumed, or advertised, to be! Fact is, the average coil Q for a spirally wound antenna is less than 50, and may be as low as 10 (!) for a 75 meter model. Screwdriver type antennas are all over the board Q wise, but the average is typically less than 150. There are a few that surpass the 300 mark, and the amount you pay isn't always an indication.

There is one more point which needs to be made. Purchasing an antenna with a high Q loading coil, dictates that you take the necessary steps to properly mount the antenna, or any advantage is might give you over one with a lessor coil Q, will be masked by the dominance of ground losses.

Some HF mobile antennas are so poorly designed, it doesn't take much knowledge to know they're nearly worthless. This also applies to junk science claims some antenna manufacturers tout in their literature, especially imported ones. On the other hand, some antennas are so superior in form and function that even an untrained eye can spot the difference. Again, the selling price isn't always an indicator of quality, longevity, or efficiency.

One more point about design. There are a lot of copycat antenna manufactures, primarily copying one another's screwdriver designs. In far too many cases, these manufacturers are clever machinists, but poor antenna designers. Here's a question which will separate the men from the boys. Ask them if their antenna requires a matching coil to obtain a low SWR. If they say no, don't buy it! If you don't get the pun, keep reading.

Dummy Loads

There are actually antennas sold which are nothing more than a 50 ohm resistor with a radiating element (?) attached to one end. Obviously, they rate an F. One of these is the Maxx-Com. At $400 it is as costly as some screwdriver antennas.

The Comet HA-750BL is similar, but uses a very lossy, 6:1 impedance transformer, It's even worse than a dummy load if that's possible. It appears Comet has come to their senses, as the antenna is no longer listed on their web site.

Comet's UHF 6, shown at right, isn't any better. At less than five feet overall (72 inches with 80 meter coil), coils wound with #26 wire, it is the epitome of a dummy load on a stick.

The Diamond HV7A isn't a dummy load per sé, but it might as well be. Besides UHF and VHF, it covers 6 and 10 meters, plus one other HF band (40 and above). It's overall length is just 50 inches, and the coils are not just small, they're miniscule. The optional 40 meter coil is wound with what appears to be size #26 wire.

The Opek^®, shown at left, shouldn't be called an antenna. With just 100 watts of power, the coil gets very warm after just a minute or two of operation.

If you buy one of these F rated antennas, you're throwing your money away.

Short, Stubby Antennas

Short, stubby, remotely controlled, HF mobile antennas have seemingly become the rage, lead by the Yaesu ATAS-120 shown at right. They're popularity is in part due to their diminutive size (less than 7 feet overall), light weight, and apparent ease of mounting. They're not necessarily less expensive than their stable mates. For example, the list price of the ATAS-120 is 0ver $460, with the street price hovering around $375, not including the mount. Incidentally, it uses an SO239 type mount which is one of its major drawbacks.

Owners typically resort to trunk lip mounts (K400, click on left photo to enlarge), luggage rack clamp mounts, and even mag mounts. All of these add to the overall losses, including the mini-sized coax most of these mounts utilize. These losses are seldom noticed because owners have nothing to compare them to. If they can make contacts, especially DX ones, that's all they seem to care about. Nonetheless, they all rate a D at best, except for the ATAS, which rates a solid F.

Yaesu's ATAS antenna is the least efficient, remotely controllable, HF mobile antenna, money can buy. It's mechanical and electrical aspects are also questionable, as are its operating methodology. The driving transceiver sends a DC voltage (<8.3 or >9.7) causing the antenna to move to a lower or higher frequency respectively. The SWR detection has two levels; over 2:1, and under 2:1. There is no choke in the control lead (coax) which makes common mode current a given problem exacerbated by the type of mounting usually employed. These facts, coupled with its high cost of ownership, makes the ATAS a very poor choice indeed. Yet, it is the highest selling single model mobile antenna in the world! An unexplainable conundrum save for its ease of installation.

No matter the brand, all short, stubby antennas have an excessive level of RF flowing on their control leads, and coax cables too (common mode currents). Thus choking off common mode current is especially important if you're using (or plan to use) an automatic controller. The requisite chokes need to be mounted outside the vehicle, and as close to the base of the antenna as possible. This requirement is very difficult to accomplish when using a clip mount; a fact which should be considered before purchase.

None of the current batch of these antennas requires any impedance matching (save one, see below), because their inherent resistive losses bring their input impedance close to 50 ohms. This means, the antennas are not DC grounded, and therefore tend to be noisier than their big brother counterparts, especially in rain and dusty conditions.

If you're intent on using one, keep the aforementioned inherent problems (and shortcomings) in mind. You'll need to purchase additional split beads (RF chokes) to tame the common mode currents, and other maladies which will occur.

Digressing for just a moment. I'm often asked how much difference there is, between a short, stubby antenna, and a full-sized one, all else being equal. In almost every case, the difference is at least 15 dB, and can be as much as 25 dB. You typically don't notice the difference if the band is wide open. However, when conditions are marginal, even a 3 dB difference in signal strength can make a huge difference in the S+N/N ratio generated in the front of a transceiver. Remember, you have to have enough signal strength on the opposite end of the propagation path, or you won't be heard. It is this latter aspect where minimal antennas suffer the most. Unfortunately, the situation is often justified by citing band conditions rather than blame the antenna, which is the true cause.

There is one antenna, advertised by its manufacturer as short, and that's the Scorpion 680SA. Calling it short, or stubby, is a bit of a misnomer. It's 28 to 36 inches long (less the whip) depending on the frequency, and weighs 13 pounds! Rated a solid C+, this shortened version of the Scorpion 680 is almost as big as the competitors full-sized models, and outclasses most of them with its 3 inch diameter coil (#14, 10 tpi). It does require proper matching (included), and a heavy-duty mounting scheme.

Standard Sized Antennas

There really isn't a standard-sized HF mobile antenna, so calling them that is a bit of a misnomer. On average, they're about 9 to 11 feet in overall length (including the whip), with some of them extending to 13 feet. With a couple of noted exceptions, they rate a C.

Remotely controlled (motorized) antennas are commonly referred to as screwdriver antennas. They're called that because the first examples utilized a stripped down Black & Decker rechargeable screwdriver assembly to adjust the resonant frequency of the antenna. The motor turned a threaded rod in and out of a nut attached to the bottom of the coil. This in turn moves the coil in and out of the mast. Contacts at the top of the mast slide on the outside of the coil, thus adjusting the resonant point. Nowadays, calling them screwdrivers is a bit of a misnomer as the infamous B&D motor have been replaced with much more reliable gear motors (with two known exceptions).

Don Johnson, W6AAQ, is credited by many as the father of the screwdriver antenna. His was, in fact, not the first motorized antenna, nor was it the first to hide the unused portion of the loading coil inside of a sleeve (mast). He certainly popularize it, and perhaps that's all that counts.

The last time I did a Google search, there were 79 different manufacturers of screwdriver antennas. Some are copies, some improve on the basic idea, some are marketed better, some try to be something they're not, and some aren't worth the effort. Although there are exceptions, most on-line reviews need to be taken with a grain of salt, especially if they mention working lots of DX. Remember, a log sheet might be a measurement of bragging rights, but it sure isn't a comprehensive measurement of antenna efficiency or performance.

Quality wise, remotely controlled antennas run the gamut from poor to excellent, and as I stated above, price isn't always an indicator. Some of the better brands are GS (at lower right), Scorpion (at left), and Tarheel (right). Further, they all come in several different overall lengths, power ratings, color finishes, and mounting configurations.

A lot of the commercial antennas use beryllium copper as a contact material. It wears very well, and provides a secure connection when properly implemented. Some manufacturers would have you believe this is a dangerous practice. They cite the sluffing off of beryllium particles during normal operation. The facts are, the amount of beryllium sluffed off is almost nil, and so is the danger. Want to know the real reason they don't use beryllium finger stock? Cost!

Let me clarify a point or two. With few exceptions (the GS is one), every commercially available, remotely tuned HF antenna, changes length as the resonant frequency changes. This is because the coil slides in and out of the base section (mast if you will) as the resonant frequency is adjusted. This makes weather sealing a top priority if you use your HF antenna year-around.

While the weather sealing of some models are admittedly better than average, dirt and moisture can eventually take their toll. This fact exacerbates the wear on the finger stock that contacts the coil, and the other various rotating and sliding parts. If you operate on the lower bands (80 or 160 meters as the case may be), the coil is extended nearly its full length. This not only lessens the strength of the antenna, it exacerbates the weather sealing problem.

The one item to keep in mind when buying any HF mobile antenna, is the warranty. Do yourself a favor, and read very carefully, even if it takes reading between lines.

Scorpion is one of the newer screwdriver antenna manufacturers. I have to admit, the machining is first rate, the build quality is excellent, so it garners a solid B+. Weather sealing is above average, and with 3 inch coils (#10, 6 tpi), efficiency is about as good as it gets. Several different models are available, so visit their web site for more details. When you do, you'll also find they're very competitive, price wise. Their 680 model is shown upper left. It sells for $600, and is worth every penny of it. If you order one, make sure you ask about lead times, as it's becoming a very popular choice.

I've been using a Scorpion 680 since June 2009, and it has lived up to my expectations, and then some. I recently snagged my cap hat (left photo) on a very low limb. The whip ferrule was broken off, and one of the three loops severely bent out of shape. There was no damage to the 680.

Incidentally, the Scorpion 680, with its 3 inch coil, wound with #10 silver-plated wire, and 6 turns per inch, has one of the the highest average Qs of any commercially available, HF mobile antennas. It achieves this by using a liberal amount of Delrin^® and Lexan^®, and a minimal amount of metal, in close proximity of the coil. For those who think Q isn't important, you need to review the efficiency article.

They have another unique feature, and that's the built-in, base quick disconnect at the base of the antenna. The bottom of this page explains the construction. It has other unique features which make it a standout among all of the other screwdrivers.

This is a good point to mention current draw. The average motor run current for the majority of remotely tuned HF antennas is between 250 and 350 mils, depending on the model. Stall currents average from 4 to 5 times running current. This fact negates powering them from the accessory sockets of most mobile transceivers! I cover this in more detail in my controller article. The article also covers the requisite chokes as mentioned above. While some manufacturers supply motor lead chokes with their antennas, some are the wrong mix and/or the wrong size. It's always best to follow the controller manufacturer's recommendations.

There are two screwdriver models which incorporate a heavy-duty drill motor which draws several amps. As a result, care must to be taken in feeding them power, and setting up most automatic controllers.

A few antenna manufacturers supply a factory-wound matching coil. All too often, the coil is mounted inside, and very close to the mounting hardware. This fact make impedance matching very difficult. If you follow the directions in my Antenna Matching article, you'll have much better luck.

In case you didn't notice, there isn't an HF mobile antenna which rates an A! The reason is, there is always ground losses to contend with, and for no other reason, the best money can buy will never exceed a full-length, quarter wave, antenna with lots of radials.

Digressing for a moment. Some remotely controlled HF mobile antennas, are available with 160 meter coverage. The inductance required to resonant a 160 meter, 8 foot long mobile antenna, is nearly 5 times greater than that required to resonant an 8 foot, 80 meter antenna. On average, this more than quadruples the coil losses, which brings the input impedance very close to 50 ohms, and sometimes over it. This adds a level of complexity to proper input matching, and reduces efficiency to sub 1%! Further, due to coil design requirements, antennas with 160 meter through 10 meter coverage, will always be less efficient on the upper bands (80> meters) when compared to an 80 through 10 meter one. Unless you're dead set on having 160 coverage along with its special needs, you're much better off with a 80 through 10 model.

Spirally Wound Antennas

There are a bunch of spirally wound antennas on the market. They rate a D at best. One manufacturer who markets both spirally wound and bug catcher style antennas, openly states on their web site that their bug catcher design (a 2 inch coil isn't what I would call a bug catcher) is 2 S units stronger than their spirally wound antenna. That's 12 dB of difference, and a lot of food for thought!

The popular ones tend to be the Hamstick^®, the Outbacker^®, and the various copycats. All are very low in efficiency, as their Qs are about 50 or less. A few of the 80 meter models have Qs less than 10! If you want a really lossy antenna, use one of the stubby 3 foot long versions.

Their only attributes are, light weight, low wind loading (some models), and low cost (≈$20USD, less mount). This means they can be attached by just about any type of mount, some of which add to their overall losses (i.e.: license plate mount). Efficiencies range in the .3% to 20% (80 through 10 meters), and they typically don't need matching as the system losses bring the input impedance to near 50 ohms.

Adding insult, almost all spirally wound antennas are hollow which allows the whip to slide inside the mast far enough to affect the inductance of the loading coil. This fact makes them nearly impossible to tune (especially on 80 meters) without an antenna analyzer like the MFJ 259B. Secondly, even if you get a good match, the proximity of the tail of the whip to the coil further reduces their already poor Q factor. Some of the cheaper imports are made with an inferior grade of fiberglass which weathers badly. After just a few months use they get very stiff and brittle, and often snap off.

Most spirally wound antennas are monoband, even though some of them have taps for the various HF bands. There is one made in Germany that has the coil wound in clumps along the length, and uses a 1:9 unun and/or auto coupler. Aside from the DX contacts bragged about on their web site, it is a very lossy antenna, and perhaps (?) marginally better than the aforementioned dummy loads.

Mono Band Antennas

Monoband antennas are limiting in so many ways, they're not a wise first-purchase choice. Aside from the various hamsticks mentioned above, there isn't much choice in the market place nowadays with the exception of the Hustler^® series. You can occasionally find older monoband coils made by Master Mobile, HyGain, and Mosley, but you're on your own for masts mounts, and whips.

The Hustler^® (made by New-Tronics Antenna Corporation) is one of the oldest suppliers of mobile HF antennas in the world (the left photo depicts their standard RM-75 meter coil). You can even make them multi banded by using their "spider" mount to hold additional coils. They have a lot of drawbacks, so they rate a C- to a D-, depending on the band, coil size, and mast length.

They promote their super coils as being the ultimate. They're not. The first-addition addendum in Dr. Jerry Sevick's (W2FMI-sk)) booklet Building and Using BALUNs and UNUNs (now out of print) contained charts and loss tables on both the standard and super coils. In short, it is the large metal end caps on the super coil which makes them lossier than the standard ones. In other words, don't spend your money on the larger coils hoping for more efficiency. Besides the extra wind loading, their power handling capability isn't any better than the smaller ones, advertising hype notwithstanding.

Hustler^® antennas have at least two additional drawbacks. One is moisture ingress. Water tends to get under the vinyl heat-shrink tubing covering the coil assemblies. This will detune the antenna and possibly cause arcing between the coil turns. This is the reason some authors suggest removing the vinyl sleeve which allows quicker drying. This is not a good idea as it allows road grime to build up on the coil windings which causes more problems than it solves.

If water ingress happens to you, here is a solution. Remove the whip assembly and place the coil in an oven at about 120° for 20 minutes or so. Don't leave them in too long, or use any higher temperature as you'll melt the heat-shrink. Once they cool down they'll be usable again. You can use a hair dryer for this operation, but be careful not to over heat the vinyl.

The another drawback is their masts. You often see examples of their fold over ones with a braided copper jumper across the hinge assembly to maintain a good connection. Unless you just have to use one, you're better off with their solid mast. In either case, you should use a base spring to minimize stress on the mast. If you notice any looseness (on this or any other mobile antenna), replace or tighten the part(s) before they come off while you're driving down the freeway!

Here is something to be very cognizant of. Hustler coils are secured to the mast by about five threads. Further, the 3/8x24 stud is pressed into the mast. The coil's 3/8x24 ferrule the mast screws into is also a press fit. It makes little difference if the coil unscrews, or the mast fails, or the ferrule fails, the coil will fly off! Over tightening them isn't the answer either, as this just hastens the connection's failure mode. If you use a cap hat, it behooves you to tether (guy) the antenna, as the extra wind load will hasten the loosening problem.

Recent manufactured models no longer have the compression type fitting to secure the whip; it's been replaced with a set screw. Whether this is a step backwards is perhaps moot.

Bug Catcher Antennas

Big ugly antennas have fallen out of favor, perhaps for obvious reasons. Besides being big, they're ugly, cumbersome, costly, and a nuisance to retune. They can also be the most efficient if they're mounting correctly, and most are rated B+ as a result. Some of the better ones are made by GLA Systems as is the coil shown in the photo. Overall lengths vary, but masts are available up to 8 feet in length, and whips to 102 inches (standard CB style). Coil diameters vary from 3 inch to 8 inch.

Some caution should be exercised here, as larger coils do not necessarily have higher Qs, regardless of advertising hype. Further, their low self-resonant points may negate their use on the higher bands. I cover Q factors in depth here. On the lower frequencies, additional performance can be garnered by adding a cap hat which raises the radiation resistance while bringing added drag and complexity to the formula.

One thing is for sure. If you're not into drilling holes, you can forget about bug catcher antennas. The 640 TBC coil shown at left weighs just over 2 pounds. Mounted at the end of a 5 foot mast, the wind loading at 65 mph, is almost 30 pounds!

GLA Systems has ceased production effective December 1st, 2009, thus ending 30+ years of Texas Bug Catcher products. Henry Allen and his crew will be missed.

Cap Hats

Cap hats, sometimes referred to a top hats, are a mixed bag of tricks. As their name implies, cap hats add capacitance to the top portion of the antenna (the whip), which has the same effect as increasing its electrical length. There is so much to say about them, and this article, Antenna Cap Hats, covers the details. There's also a Antenna Cap Hat How To article for the home brew folks.

The left photo depicts a cap hat incorrectly installed. So installed, the input impedance and bandwidth increase, however, the changes are due to increased coil losses, and not by the increase in radiation resistance (Rr).

There is one attribute about cap hats which needs to be mentioned here as well, and that is where they are placed in relation to the loading coil. In order to be effective, cap hats must be mounted away from the coil; not under it, not on top of it, but way over it. A good rule of thumb is at least twice the length of the coil, and for best performance, at the very top of the whip!

Cap hats have a drawback which might not be apparent, and that is the requisite mounting methodology. For example, the cloverleaf-shaped cap hat shown below right, has a solid 4 foot extension below it, and a solid one foot extension above it with a one inch corona ball on top. No matter how well an antenna is built, it can be destroyed if you smack it hard enough, and it doesn't take a big limb in most cases. This is especially true if the mast holding the cap hat is solid (not flexible like a whip). It's your basic, high school physics, lever law. Overcoming this problem isn't always simple.

Correctly applied, cap hats will increase efficiency by raising the radiation resistance, at the expense of wind loading and complexity. It's a tradeoff which may or may not be beneficial. Read the Antenna Cap Hats for more details.

End Caps

Any metal structure placed within the field of a loading coil, will have a detrimental effect on coil Q. Several current designs incorporate a large aluminum or stainless steel end cap which supports the whip and/or cap hat assembly. In at least two cases, there is also a metal shorting plunger which slides up and down. This motor-driven plunger shorts out the unused portion of the coil (short tapping-see next section) thus reducing its inductance. These metal masses can cause the coil to operate above close to its self resonant point which also increases coil losses (reduces Q).

At some point, these Q reducing factors add up, and the Q effectively becomes zero. At that point, the coil starts acting more like a rather lossy capacitor (operating above self resonance) than an inductor. At which point this occurs in any given antenna design, depends on a lot of factors, and ones which aren't easy to measure or calculate. They aren't easy to comprehend either, unless you have a fair understanding of how loading coils behave.

Short Tapping

The term short tapping isn't well known, and requires a little explanation. Assuming the loading coil in our antenna has too large of an inductance, and we wish to reduce it, we have two choices. We can remove turns, or we can short out the unused (unneeded) portion of the coil. If we remove turns, it's very difficult to add them back later if required. If we just short some of the turns on one end or the other with a small jumper, we can always relocate the jumper if required. However, there's a hidden problem if we do.

Shorting out unused turns reduces the Q of the coil. The occurs because eddy currents flow in the shorted portion. Some might argue that the reduction is slight. However, when approximately 60% of the coil is shorted out, Q drops almost precipitously. Any remaining coil operates very near self resonant frequency, further increasing losses. In some antenna designs, the upper bands (20 and up), become less efficient than the lower bands, resulting in near-dummy load efficiency.

By the way, you just can't let the unused end of the coil hang loose. If you do, the RF voltage at that point will be high enough to arc over to the mast or whip as the case may be, destroying the coil in the process.

Odds & Ends

Antenna weight can be a major purchasing factor. This is why most full-sized remotely controlled antennas end up being mounted on a trailer hitch type mount. As I alluded to above, spending your hard-earned cash on a quality antenna, and then mounting it poorly, is counter productive. Remember, it is the mass under the antenna that counts, not what's along side.

There are some drawbacks to large diameter loading coils besides the extra wind loading. First, the ratio between coil diameter and length are major factors in determining coil Q. Other factors include the dielectric material the coil is made out of; the size, pitch, and coating (if any) of the wire; and the resulting inter and intra capacitance between all of the parts making up the coil. As a general rule, the large diameter coils are preferred on the lower bands, and smaller ones on the upper bands. However, the rule can't be applied without knowing a lot more about the construction than mentioned here. In other words, don't justify your antenna purchase by the size of the coil.

I've stated many times that the most important point you need to establish is your personal level of satisfaction. The old proverb, one man's treasure is another man's trash, says it all. If your HF mobile setup is a treasure to you, then don't let someone tell you it isn't. If it is trash, then hopefully some of what you've read here will aid you in your quest for a better mobile station. Whatever you do, don't tell me you like it because you were able to work some rare DX. All that proves is your gullibility.