Some final speculation. Although the MP-1 ought theoretically to
outperform
the ATX by virtue of its bigger loading coil, you will only get the
benefit
of that if you have a very good ground system to go with it. In our
portable application with short wire ground planes or conterpoises,
it is
the ground resistance or the counterpoise, not the coil resistance
that is
determining performance. Therefore the ATX will probably work as
well as
any antenna of similar size used in that situation.
Anyone want to buy a used MP-1? :-)
--
Julian, G4ILO. (RSGB, ARRL)
Home page:
Julian - I did some computer modeling of the MP1 a while back, and
found a BIG difference in making the lower mast about 3' long instead
of the 10" stock length - like over 6 db on 7 mhz and decreasing to
about 3 db on 28 mHz (in fact, the performance should be sililar to
what you nboted on the Pro-am, as they would then be about the same
physical size). I have not found the MP1 to be as fussy about the
ground plane as the ATX, and the it certianly is more efficent, even
with the short lower section, on 10, 18 & 24 mHz. I use 4 radials 18'
long of 18 guage wire.
I've tried different counterpoise solutions, but the best seems to be
a "roll-up" counterpoise made from a Radio Shack short wave antenna -
no problem getting it to work on the MP1, but the ATX is EXTREEMLY
fussy - actually, the only way I can get the SWR anything close to
low on 14 mHz is by adjusting the length and then bring the end back
to near the rig..... putting it out in a straight line doesn't work
at all unless the whip on the ATX is made about 6" longer with a clip
lead - similar problem on 21 mHz. On 7 mHz, it is not fussy about the
groundplane and presents a reasonalble match across the whole band -
so does a dummy load!!! The MP-1 has a definite bandwidth that is
MUCH narrower, which means the coil is higher Q, and therefore should
be more efficent.
Yes - a dipole would be better - just as long as you have a place to
put it up. But also not as easy to change bands. And I shudder at the
thought of adding gear to the package in the form of an ATU. I am
very happy with the MP1 and the clamp mount or tripod - lets me get
the antenna outside in the clear, tunes easily, performs well.
I'll trade you my ATX for your MP-1 anyday
Don
W6ZO
