A view of the as-received "440 Yagi
Beam Antenna"
sold by "Electronicsales425" on Ebay. Click on image for a larger version.
Note: It was noted that this
particular
user ID is no longer to be found on Ebay, so this means that
products
of this quality will have to be obtained from other sources. (It
is possible that the user simply created another ID, however.)
Several years ago a friend of mine bought four of
these "440
Yagi
Beam Antenna" as sold on Ebay by "Electronicsales425"
for
approximately
$22
each
and
upon receipt of these antennas, he could
not say enough good things about them. He also inferred that no
price
would be too high for an antenna of this quality!
Being impressed by them in this manner, he asked me
to
take a look at them - and I must say that they are like no antenna that
I have seen before.
This antenna has a number of interesting
features
as
noted below:
Rugged PVC boom construction! In
an
outdoor
environment,
PVC can withstand months of UV exposure. If replacement of this
material
is required, there is almost nothing that is less expensive.
Reduced weight! The avoidance of a
boom clamp reduces the
weight of
this
antenna.
Matching network! All antennas can
have losses associated with
their
matching
networks. In this antenna, this aspect is well taken care of with
its unique "J-shaped" driven element.
Soft-drawn copper tubing elements!
With
these
elements,
you need not worry about their breaking or bending due to wind or
ice-loading!
Avoidance of lossy coax on the antenna!
Many
antennas use lossy
coax between the connector and the matching network - but not
antenna! It's "J-shaped" driven element has
no lossy coax connected to it, but rather it uses open-wire line:
Two separate strands relatively heavy PVC-covered hookup wire connect
from
the driven element to the connector, minimizing DC losses.
This antenna is shipped disassembled!
It
is
extremely
easy
for the elements to come out of the boom.
A boom-mounted coaxial connector!
As you
can
see from
the picture (at the bottom) the UHF antenna connector is cleverly
mounted
to the PVC end cap on the antenna.
Reduced chance of connector galling!
How
many times have you had a coax connector "gall" and
were
unable
to unscrew it from the coax connector? Well, if you have had this
problem in the past, it may not happen
with
this antenna: Being mounted as it is on the PVC, you won't be
able
to bottom out the threads on the UHF connector and thus, there is less
likelihood of the threads seizing! In addition to this, routing
cable is easier since even tightened as far as it will go, you'll be
able to rotate the PL-259's barrel to prevent tangling of the coax - a
common problem as I'm sure you'll agree!
Low return loss! If you were worried
about high return loss, you need not do so with this antenna!
Over the
intended
"440 band"
this antenna does not exhibit a high return-loss
factor!
In fact, the return loss did not, anywhere on the "440 band," exceed 5
db! No doubt, this is a result of the combination of the unique
"J-shaped"
feed design and the use of the open-wire feedline going to the UHF
connector.
As you can see from the return-loss plot, the only place that the
return
loss was high was in the range of 370 MHz and around 500 MHz - well
away
from the intended operating frequencies!
Lower chance of intermod! With the low
return loss in and near the "440" band, signals that might reach the
receiver to cause intermod and overload are reduced!
Good SWR! If an antenna like this
is fed with 200 feet
of
a good
quality RG-58 or just 50 feet of RG-174 coaxial cable you can
reasonably expect a
good SWR over the entire design frequency range!
The unique "J-shaped" driven element. Note how the two wires comprising the "open-wire" feedline
attach
to the driven element. Click on image for larger version.
The unique "J-shaped" driven element and the open-wire
feedline. Observe how the two strands comprising the open-wire feedline
are
cleverly routed into the boom. Click on image for larger version.
The end-mounted UHF connector. The open-wire feed connects to this single-hole UHF
connector.
As you can see, the use of this style of UHF connector and the
relatively
thick wall of the ABS cap takes up most of the threads of the UHF
connector
- as evidenced by the the connector to the left showing the
comparison. As I'm sure that you'll agree, this lesser amount of exposed
threads
prevents one from "bottoming out" the connector and thus it may reduce
the likelihood of the threads galling and being unable to remove the
antenna. Click on image for larger version.
This shows the return loss from 350 MHz to 550 MHz with no
more
than 5 db of return loss at 450 MHz! As you can see, excessive
return
loss is no problem over the "440 Band" range for which this antenna was
designed! When the 3 foot coaxial cable jumper was removed and the
antenna
was connected with a barrel to the directional coupler, the return loss
was less than 2db! (Major horizontal divisions are 20 MHz and major vertical
divisions
are 10 db, with the "zero" line being the major division below the
frequency
readout.)
As you can see from the quality of the construction and design of this
specimen,
it is likely that no antenna will perform as well as
this one does and that this antenna cannot be
recommended too
highly!
It need not be said how lucky you would be to get an antenna such as
this
to work well for you!
P.S. I have no pecuniary interest in this antenna or its
seller.
I have offerred what I believed to be a fair opinion based on
the evaluation of one of four identically-constructed units from the
seller's
production.