"Richard Clark" wrote in message
...
On Mon, 3 Jan 2011 23:39:10 -0800, "Ron Hinds"
wrote:

Hi - I'm an amateur radio newbie - don't even have a license yet (taking
the
Technician exam 1/15). I have a Kenwood TH-F6A and I'm looking for an
antenna for use from home. This looks like a good one - and it's in my
price
range ;-) I'm wondering what you experts think of it for a beginner?

http://www.diamondantenna.net/d130j.html

Hi Ron,

Welcome to the possibly the last vestige of Amateur Radio hardware
experimentation.

Insofar as your antenna goes, it presents you with a learning
opportunity that far exceeds the material you will be tested for.
However, it does embody the significant first principles.

1. The correlation between physical size and wavelength.
2. The discussion of match.
3. Unfortunately it says nothing of the radiation pattern which has
very serious implications for use.

Let's return to item 1 and examine the antenna. The overall height
can be rounded to 2 meters for simplicity's sake (there is no reason
to be exact and this is sufficiently accurate enough for the moment).
Your coax connection goes somewhere near the middle of the structure
to make it a dipole - a vertical dipole of unusual shape, but still
within the terms of first principles, a dipole.

This makes it suitable for use on the 4M band by simple correlation
between size and wavelength. However, there is no 4M amateur band,
and the vendor claims down to 10M and below.

The paragraph above marks our transition in the discussion towards
match. By virtue of its shape (its unusual shape), it benefits from
being a match at frequencies that are outside of its 4M native band.
This is true for the frequencies on BOTH sides of this band. The long
and short of it is that YES, the antenna is a suitable load over the
entire range of frequencies, and this is of high interest to any Ham.

However, being a suitable load to your transmitter (the antenna
matching the transmitter's requirement for a particular size value,
often 50 Ohms resistive with little or no reactance) is only half of
what interests any Ham. The other half is how well does it radiate
towards my intended listener?

This brings us to item 3 listed above. At the lower frequencies
(below 2M band), you can well allow that you will obtain a lack-luster
performance. This antenna design is suited for multiband operation
which sacrifices gain opportunity to achieve it. This is the see-saw
of antenna design - and you choose what is most important at the cost
to the other issues.

Further to item 3 is the fact that above the 2M band this antenna
might well seriously disappoint. This is a first-pass observation,
but on close examination, you have selected an antenna that is
actually two in one. Look closely at the two distinct sets of spoking
elements. The lower flaring down are chosen for the lower band, the
upper, more horizontal are chosen for higher bands - such as 2M and
440. The antenna has been optimized to recover from the see-saw of
conflicting choice (we ALL want an antenna with universal coverage and
maximum gain knowing we can not have both, and worse, we can barely
expect half than less).

Still, even with this hail Mary pass, above 440 the antenna is going
to be a very poor performer in getting signal out towards the horizon
(where your listener might be), and instead put it up into the air
(where no one is, except satellites, model rockets, and airplanes).

So, this being a brief discussion (some might argue otherwise), more
is left to be said in response to all the questions it might provoke.

Hi Richard,

Thanks for the detailed response. The Kenwood TH-F6A radio I intend to use
this antenna with is a handheld with 5W max output power. It is a 2m, 1.25m
and 70cm transceiver, with a separate wideband, all mode receiver built in
that has a capability from 0.1 - ~1300 MHz.

http://www.kenwoodusa.com/Communicat...rtables/TH-F6A

With that in mind, what is your opinion of the adequacy of this antenna?

Also, I thought this might make a good mobile antenna. But the
instructions
say don't use a magnetic mount. I'm really not interested in any kind of
permanent mount. Why do they say not to use a magnetic mount?

http://www.diamondantenna.net/d220.html

Wind force and moment arm. It is a LOT of wire in the air for highway
speeds. Trust the instructions.

Thanks, I thought that might be the case. Again, keeping in mind the radio I
intend to use, would this antenna be a good fit?


Ron Hinds

73's
Richard Clark, KB7QHC