The MP-1 from Superantennas was the first antenna I bought for portable operation. Originally, I bought it for use with my Elecraft K2, after reading some recommendations of it on the K2 reflector. When I got my Yaesu FT-817, I hoped to use it with that.
The MP-1 is very well made, and uses a similar design to all the best-performing mobile HF antennas. It has a standard 3/8in. mounting. There's a short (8in.) vertical section, above which is a large diameter high-Q loading coil, tuned by moving a sleeve up and down. A 4 foot whip section screws into the top of the sleeve. This whip breaks down into six lengths of rod which can be stored inside the coil for ease of transportation. As supplied, the antenna tunes 10m through 40m. An extra coil is available as an accessory to allow 80m to be covered, as is a tripod stand for the antenna.
The loading coil of the MP-1 is quite a large diameter - much larger than those found in other portable whips such as the Mizuho ATX. This gives it a high Q, which should result in good efficiency. However, as noted, this is essentially a mobile whip. Anyone who has tried to work HF mobile will know that to get good results a mobile whip needs an excellent ground, with as low impedance as possible to the car body. The MP-1 is marketed as a portable antenna and comes with a "ground plane" consisting of a 10 foot length of ribbon cable split into four lengths. This isn't even an approximation of a good ground. Using this, I obtained results no better than when using other, allegedly less efficient antennas, with the added problem that the best SWR achieved on some bands was well over 2 to 1, and varied wildly as I moved toward or away from the radio, indicating that it was "RF hot". These are the classic symptoms of an inadequate ground. So my main complaint about the MP-1 is that it doesn't work as advertised, out of the box.
Some MP-1 users advised me to try using longer radials. I tried this, but although it had an effect on the noted problem, it didn't solve it.
Users of the MP-1 who seemed to have most success appeared to be using a resonant counterpoise cut for each band. Although this is markedly less convenient when you want to change bands, I tried this, too. It certainly did give better results, allowing a good match to be achieved and ending the "RF hot" problem. However, finding the optimum length of counterpoise for each band is tricky. There is a wide range of counterpoise lengths for which a low SWR can be achieved for each band. With two variables - counterpoise length and coil setting - how do you know which is optimum? It is clear that a willdly wrong counterpoise length results in broader tuning of the antenna, and obviously lower efficiency. Some users confessed to using an MFJ antenna analyser to tune this antenna, which obviously makes band changing even more of a hassle, quite apart from adding substantially to the cost (if you don't already have an analyser) and the bulk of equipment you have to carry around.
Like other portable whips that need a counterpoise, I found the MP-1 to be very sensitive to how the counterpoise is deployed. A counterpoise that allowed a good match to be found when pruning it in comfort indoors, may give a poor SWR when used in the field. Trying to bundle counterpoises for different bands together, for greater band changing convenience, was a nightmare as they seemed to interact with one another.
Seasoned MP-1 users advised tuning the antenna for maximum received signals or noise, not lowest SWR. The noise peak would indicate best efficiency. However, this may mean an ATU is needed to give a satisfactory match to the radio. Again, this isn't too surprising, as theory shows that the impedance of a resonant high-Q mobile whip is usually much lower than 50 ohms. However, the FT-817 doesn't have an ATU, and adding one to the package detracts considerably from the benefits this radio offers in terms of portability. It's no problem for K2 users, though.
Other advice I received when trying to get the best results from the MP-1 was that the counterpoise should be elevated above ground as much as possible. Otherwise ground losses will reduce the efficiency. In this configuration, the MP-1 is effectively working as half a dipole, with the counterpoise providing the other half. Whilst this may be sound technical advice, my objection to it is that it often isn't possible to raise the counterpoise or the antenna above the ground (e.g. operation from a bare hillside, or a beach.) In situations where it is possible, it is probably no more difficult to deploy another, equal length of wire, in the opposite direction, in place of the MP-1, and raise the center up a bit, forming a more effective (and much less expensive) dipole. This isn't the convenient, portable operation that I was looking for.
Eventually, I sold my MP-1. Technically, it may be a sound design, but it is far from being an ideal portable antenna. It's high-Q design means that it needs a really good ground to work effectively as a ground plane, and this is almost impossible to provide in a portable situation. The workaround is to use a resonant quarter wave counterpoise instead, but this isn't always convenient, makes band changing more of a hassle, and tuning up is still fiddly. The tuning point of best efficiency with the MP-1 rarely corresponds to minimum SWR into 50 ohms, which means an ATU or other matching device is really needed to get the best from this antenna.
The MP-1 is a lot of money for a radiator that, relative to a dipole, is still not all that efficient. It's unclear to me how much of the effectiveness claimed for this antenna by its enthusiasts comes from radiation from the counterpoise that provides "the other half of the dipole." If I can lay out a counterpoise, I'd be inclined to put up the whole dipole, and forget the MP-1 altogether.
The MP-1 isn't a bad antenna, in my opinion, just a flawed portable antenna. Its critical dependence on resonant counterpoises means that it isn't as convenient to use or as portable as its small size implies. It will reward those who are prepared to tolerate its fussy nature with performance which outshines its competitors, but the difference in practice is not as great as some published test results suggest. For me, the MP-1 was simply too much hassle.