Hi Barry et al
Another point that should be made is that when tuning the MP-1 or the
AP-10A (or like antennas), the operator should make an adjustment and
then get back (away) from the antenna (and counterpoise) at least a
meter or so before checking the tuning. I have noticed that some
folks have tried "real-time" adjustment of the coil by watching the
tuning as they move the coil. Their body loads the system. When
they move away from the antenna to operate, the tuning is all wrong.
Thats absolutely essential! When I compared some of this small antennas for
a test review last weekend I found that especially the ATX Walkabout is
extrem sensitive against loading by man.
I would like to point out an other aspect about the MP-1. The functionality
of the PM-2 IMO is another than that of a standard base or center loaded
monopol.
Think of the MP-1 as a Top loaded Vertical. Why? The Tube you use to shorten
the coil is actualy a big Capacitor. It is derivated from a vertical with a
big capacitive hat. A capacitiv hat shortens the vertical significant. (like
in a series tuned circuit) If you make the hat big enough, the vertical part
will be shortened to zero. Thats what the PM-1 is.
I tried the MP-1 without the Whip. I had to give a little more inductivity
for compensation, but it works as fine as with the whip.
The theory of this antenna type you will find at
What DL7PE describes there are
monoband monopoles, but if you look close, they are very similar to the MP-1
If you use the PM-1 with a coax cable between it an the Transceiver, this
coax will act as an active counterpoise. You will have extreme
unreproducible results from band to band until you introduce a current choke
1/4 wavelength (x factor) in the coax line.
72/73 de Peter, DL2FI
German QRP Group DL-QRP-AG
QRPproject QRP and homebrew international
