Short, unloaded whips such as the stainless steel 102-inch whip present some special installation requirements when operated at frequencies well below their 1/4-wave resonance point. Such whips are often fed at the base by an automatic antenna tuner of one type or another. Most of the reports of poor performance of these whips result from a failure to understand and follow their special installation requirements rather than any inherent problem in the whip or tuner. A good tuner/whip installation will not only perform reasonably well, it will offer a great deal of convenience in moving around the bands. Notice that I said "reasonably well". It will likely not fair well against a Texas Bug Catcher in a 75M shootout. It will however perform as well as a Hamstick type antenna on 75M and it'll get you plenty of contacts. On 20M and above it will likely perform as well as any other mobile antenna and will be a good deal more convenient and a whole lot less obtrusive than most.
First we should address the tuner itself. The ability of the tuner to load a short whip on various frequencies depends primarily on the range of impedances that the tuner is able to match. Many automatic tuners (especially those built into the radio) are designed with a very limited impedance range. They are designed to match an antenna that is being operated just a little off its resonance point. For example, a 40M Hamstick tuned for the center of the band will present a high SWR when operated near the band edges. A limited range tuner can handle this situation quite well. Coax cable can be used between the tuner and the antenna because the base impedance of the antenna is not too far off from 50-ohms.
A limited range tuner is not designed to match an antenna that is being operated far off its resonance point. A 102-inch whip is resonant around 10M and presents a higher and higher impedance as you move lower in frequency. On 75M the impedance will be on the order of 1000 ohms or more. A limited range tuner is simply not capable of matching such a high impedance. Some tuners are designed to match a 102-inch whip down to 40M while others can match it down to 75M. Don't be fooled by the type of connector used on the tuner. It is true that wider range tuners tend to use large feed-thru insulators in order to handle the higher voltages present at high impedances and limited range tuners tend to use SO-239 type coax connectors. The use of a coax connector however does not mean that the tuner has some special circuit designed only to feed coax or that the tuner with a feed-thru can only feed a single open-wire line. The proper choice of coax or open-wire is determined primarily by the impedance at the base of the whip.
A 102-inch whip should never be fed by coax cable (not even a very short length) when operated below 10M. It is not the loss in the coax created by high SWR that is the problem. It is the capacitance of the cable; the capacitance between the center conductor and the shield. The higher the impedance of the antenna, the more power will be "shunted" around the antenna by the capacitive reactance. You can see this affect with a quick test. Load up a 102-inch whip on 75M. While receiving a signal, place your hand near the base of the whip. The signal level drops significantly. Now try the same thing with a 75M Hamstick. The signal drops very little because the capacitance of your hand does not have as much impact on a low impedance Hamstick as it does on a high impedance whip.
Coax cable is not the only thing that can present a shunt capacitance to the base of a whip. If you run a single wire feed near the body of the vehicle or pass it thru a hole or opening somewhere in the body, you have created capacitance that can shunt the signal around the antenna. If you mount the whip on the bumper and let it pass close to the body for a few feet you have created shunt capacitance. Even the typical CB type ball mount attached to a fender can produce a shunt capacitance to the body. Have you ever noticed that SGC and Icom sell antennas with big, ugly, expensive insulators? These insulators minimize shunt capacitance in addition to having the ability to handle the high voltages present at the base of a short, unloaded whip antenna. You'll also notice that military mobile HF whips use some rather massive insulators at their base.
So the key to the successful installation of a short, unloaded whip is to minimize the shunt capacitance. Mount the antenna high on the vehicle, well away from the metal body. Use a large insulator at the base. Use a well insulated but unshielded feed wire between the tuner and the base of the whip. Keep the feed wire as short as possible and keep it away from the metal body of the vehicle. If you have to pass the wire thru the body, use a large feed-thru insulator to keep it centered in the hole and away from the metal. Remember that the feed wire is actually a part of the antenna. The RF doesn't know where the feed wire ends and the antenna begins so the feed wire will radiate the same as the antenna. If you have a 9-foot whip and a 1-foot feed wire then the feed wire represents 1/10th the total length of the antenna. You don't want the lower 1/10th of your antenna radiating inside the vehicle where it does you no good and may create a lot of RFI problems.
The higher the feed impedance, the higher the RF voltage developed for a given power output. The base of a 102-inch whip can develop on the order of 1000 volts with 100 watts applied; even more when you increase the feed wire length. Be sure to take this into consideration when selecting a feed wire, insulator and mounting position. Fortunately the same wider spacing that reduces shunt capacitance also provides better insulation for the high voltage.
The other important part of any mobile antenna installation is a good RF ground. This applies whether you have a short, unloaded whip or a resonant antenna like a Hamstick. In the case of a tuner/whip combination the RF ground needs to be at the tuner. Make sure it is well bonded to the body and frame of the vehicle, Use heavy bonding strap to make the connections. Use strap or braid to bond as many pieces of the vehicle together as possible. Bond the fenders, doors, hood, trunk cover, tail pipe, etc. together and to the frame of the vehicle. The more you can make the various pieces of the vehicle look like on big chunk of metal to the RF, the better.