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Hi All
Sorry to hear of the odd problem with some MP-1's. For what it's
worth I have had nothing but great results with mine. Running the
817 both portable and mobile into this antenna I have worked most of
Europe and both coast of Canada with excellent signal reports. When
I first put the 817 in my car I was running off the internal
batteries at 2.5w and put the MP-1 on the trailer hitch with the c
clamp...by the time I walked back to the front seat there was a loud
F6 on the air calling CQ (10m). I picked up the mic thinking "fat
chance" and he came back with a 5x7 report. I drove for about 2
hours and worked a dozen or more European DX. I arrived at my
parents and took the radio and antenna in to show off the world of
minature communications. Again, with batteries and the MP1 on its
tripod with the counterpoise thrown out on the floor, my first
contact on 20m was the Azores...all this from Toronto.
It works well for me. Thanks Verne!
73 Lynn Hilborn VE3CSS

Lynn VE3CSS wrote:

Sorry to hear of the odd problem with some MP-1's.
...I have had nothing but great results with mine.

Same here, Lynn. I have tried at least 30 different types of
commercial and homebrew HF portable and whip antennas. My antenna of
choice is now the MP-1.

Successful portable whip operation is more dependent upon the
operator than other types of antennas. It's all in how you use them
that counts. Getting the feedpoint and counterpoise up above ground
level adds 6~10dB or more.

No manufacturer is selling a better performing or more versatile
portable whip for the FT-817 at this time, as far as I know. Anyone
tried a better one?

Bonnie KQ6XA

No manufacturer is selling a better performing or more versatile
portable whip for the FT-817 at this time, as far as I know. Anyone
tried a better one?

Bonnie KQ6XA

Hi Bonnie,

Yes, I find the B&W AP-10A works somewhat better than the MP-1. The
B&W antenna is more efficient than the MP-1 (Q of B&W coil (length to
diameter ratio = 2) is higher than for the MP-1 (length to diameter
ratio = 7)) by perhaps 40% depending upon ground loss resistance and
various other parameters. I am comparing apples to apples by getting
rid of the supplied MP-1 radials and using a tuned counterpoise for
bands below 12 m. I note that both antennas are essentially the same
size when in their operational configuration.

Either antenna will give reasonable results when the bands are open.
Seems to me significant factors are weight, packed size, and cost.
With the brackets and such of the B&W, its weight is a bit more than
the MP-1. The packed size of the MP-1 can not be beat and is a
factor for real consideration by those that travel a lot and have
serious limitations on luggage. On the other hand, the B&W AP-10A
only costs about 1/2 of the MP-1 and still packs well. Is the slight
improvement in efficiency important? I suggest that a faction of a S-
unit is well within the signal fluctuations typically observed during
a QSO. Consequently, no.

As a final note to those using the FT-817 SWR meter, beware. It is
not that good. Get a good SWR meter or an antenna analyzer such as
the MFJ 259B if you have room or the Autek RF-1 if size (and cost)
are a factor. If you need to find a good starting place when
adjusting the coil on either antenna, listen for maximum noise. The
atmospheric noise is (almost) always a lot higher than the receiver
noise. Also, just moving the radials about to get a low SWR doesn't
mean you are radiating. A dummy load has low SWR as has been pointed
out many times before. The importance of a proper counterpoise and
being sure the antenna and the counterpoise are not heating up the
Earth or some other object can not be over stressed.

72 de Barry - W4WB

I think this is a good starting point. After trying with radials of
different lengths, I tried the MP-1 with the steel tape measure
counterpoise I used with the ATX. I managed to get good SWR on all
bands 10 thru 20 and no RF on the feeder. Haven't come up with a
solution for the lower bands yet. though.

I echo your warning about the risks of adjusting for low SWR, though.
On any band, you can move either the coil or adjust the counterpoise
to get the best SWR. However, I found that you can be moving the coil
away from the point at which signals are loudest, in order to get the
lowest SWR. You need to keep an ear on the signal level as well as
the SWR, and try to pick a coil setting/counterpoise length combo
that gives the best results for both. The MP-1 is not an easy antenna
to tune, for that reason.

To be honest, I don't think the MP-1 is an ideal antenna for use with
the FT-817. It is better suited to the K2, which has a built in
tuner, so you can peak for maximum noise and then just hit the Tune
button. Trying to adjust the MP-1 to get a 1:1 into 50 ohms seems to
be the root cause of all the problems. Which is understandable when
you read the antenna books which state that a base loaded whip is
anything but 50 ohms...

Julian, G4ILO

Julian,

Good points. However, I have found that the impedance is about 50
ohms when properly tuned (reading the MFJ antenna analyzer). The
design of the MP-1 has residual inductive reactance when the coil is
properly tuned. The radials can be left in a wad and moved about to
provide the needed capacitive reactance. Gets the SWR down, but
radiation efficiency is not so good this way. By getting the antenna
up off the ground, and likewise for a tuned counterpoise, the antenna
radiation efficiency improves.

Improved performance can often be realized by tilting the antenna
from the nadir. The AP-10A is normally used at 45 degs; however, the
radiation pattern is not uniform (which is often a great advantage).

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.

72 de Barry - W4WB

g4ilo@... wrote:

However, I found that you can be moving the coil
away from the point at which signals are loudest, in order to get the
lowest SWR.

Anyone have a theory why this happens?


Nick
WB4SQI

Mine is that at the frequency where the Q is highest (hence strongest
signals) the impedance is not 50 ohms. As I de-tune the antenna, the
impedance changes and appears to give a better match. That's why I
think the MP-1 ideally needs some kind of matching unit at the base,
as indeed do many base loaded mobile whips.

Julian, G4ILO

--- In FT817@y..., Nick Marsh <nmar@e...> wrote:

g4ilo@q... wrote:

However, I found that you can be moving the coil
away from the point at which signals are loudest, in order to get

the

lowest SWR.

Anyone have a theory why this happens?


Nick
WB4SQI

How about an MFJ 910? I believe this is a small box with fixed caps that
can be switched to aid in finding a good match. Usually mounts at or
near the base.

I haven't seen anyone discussing this old trick in any of the MP-1/ATX
or other vertical threads. Swan, Master Mobile and others had these many
years ago for their particular types of mobile verticals.

Nick
WB4SQI

g4ilo@... wrote: