W6RVB%20%20%20End%20Fed%20Antennas%20======================== - PowerPoint PPT Presentation

About This Presentation
Title:

W6RVB%20%20%20End%20Fed%20Antennas%20========================

Description:

W6RVB End Fed Antennas ===== Introduction A big problem with an end fed half wave antenna is that the antenna presents very high impedance, creating ... – PowerPoint PPT presentation

Number of Views:104
Avg rating:3.0/5.0
Slides: 24
Provided by: W6R
Category:

less

Transcript and Presenter's Notes

Title: W6RVB%20%20%20End%20Fed%20Antennas%20========================


1
W6RVB End Fed Antennas

Introduction A big problem with an end fed half
wave antenna is that the antenna presents very
high impedance, creating a significant miss-match
with the usual transceiver impedance of 50 ohms.
The magnitude of the miss-match is significantly
greater than typical tuners can accommodate
without a matching transformer. This
construction project produces a trifilar wound,
91 UNUN (unbalance to unbalance) toroid matching
transformer that will match the high input
impedance of a 33 or longer end fed antenna into
the range where most antenna tuners can produce
good performance. This project requires a tuner
to achieve satisfactory SWR. The matchbox
project uses readily available common hardware
and materials. For your convenience, the
Emergency Amateur Radio Club of Honolulu has
volunteers who produce fully assembled matchboxes
for those who dont want to construct one.
Proceeds support the club and amateur radio.
Order information is included on the last page.
2
W6RVB End Fed Antennas

This construction project produces a trifilar
wound, 91 UNUN (unbalance to unbalance) toroid
matching transformer that will match the high
input impedance of a 33 or longer end fed
antenna into the range where most antenna tuners
can produce good performance. The finished
product looks like this
?Long Wire Ant
91 UNUN ---?
Coax to rig --?
3
W6RVB End Fed Antennas

4
W6RVB End Fed Antennas

5
W6RVB End Fed Antennas

6
W6RVB End Fed Antennas

7
W6RVB End Fed Antennas

Schematic of a 91 UNUN (NOT a BALUN!)
8
W6RVB End Fed Antennas

What is the impedance ratio?
9
W6RVB End Fed Antennas

Matchbox Parts List 1 small plastic enclosure
and cover 1 powdered iron toroid T106 -2 or
larger 3 24 pieces of 22 gauge solid insulated
copper wire in red, green, and black 2 6/32 x
½ machine screws and nuts 2 6 lock washers 1
10-24 x ¾ machine screw and nut 2 10 flat
washers 1 10 lock washer 1 10 wing nut 2 10
wire lugs 1 6 wire lug 1 SO-239 panel mount
connector 1 33 20 gauge insulated stranded wire
antenna
Preparing the MATCHBOX Plastic Enclosure Start
the project by drilling one 5/8 hole and two
6/32 holes for mounting the SO-239 coax
connector on the lower side of the enclosure. Use
the connector as a guide to mark for accurate
drilling of smaller holes. Next, drill a 3/16
hole in the upper right side of the box for
mounting the antenna connector.
10
W6RVB End Fed Antennas

Matchboxes come in many sizes/shapes
11
W6RVB End Fed Antennas

Matchboxes come in many sizes/shapes
12
W6RVB End Fed Antennas

Matchboxes come in many sizes/shapes
13
W6RVB End Fed Antennas

Original Schematic of the Johnson Viking KW
Matchbox Tuner
14
W6RVB End Fed Antennas

Matchbox Parts List 1 small plastic enclosure
and cover 1 powdered iron toroid T106 -2 or
larger 3 24 pieces of 22 gauge solid insulated
copper wire in red, green, and black 2 6/32 x
½ machine screws and nuts 2 6 lock washers 1
10-24 x ¾ machine screw and nut 2 10 flat
washers 1 10 lock washer 1 10 wing nut 2 10
wire lugs 1 6 wire lug 1 SO-239 panel mount
connector 1 33 20 gauge insulated stranded wire
antenna
Website http//www.earchi.org/
15
W6RVB End Fed Antennas

Matchbox performance will be determined by two
factors The length of the antenna wire, and the
capability of the tuner. The length of the wire
should generally be between 22 and 60 feet for
best performance. Longer wires may have excessive
impedance for tuners to properly match. Wires
shorter may not radiate effectively. A 30 foot
insulated 18 gauge stranded wire antenna and
connecting lug should meet most requirements.
Experience has shown that most external tuners
and many internal tuners will tune 806 meters
with an antenna length of 22 to 30. If a longer
antenna is desired, the provided antenna can be
lengthened. Some tuners, in particular internal
tuners, may not tune the full 80-6 meter range.
You may need to try different wire lengths to
optimize your antenna configuration. If you are
having difficulty getting your rig to tune, start
with a 26 wire. This should produce good results
on at least 40-6 meters using the narrowest
performance range of internal tuners. Best
performance is achieved with a coax of 16 or
longer. Additional counterpoise is not required
in this design. The system works well in
horizontal, sloper, and vertical configurations.
Observe established safety practices working
with antennas avoid proximity to power or
utility wires. Permanent installations should be
equipped with appropriate static and lighting
protection. Keep amateur radio safe and fun! If
you would like to share your experiences with
this project, email the club at
http//www.earchi.org.
16
W6RVB End Fed Antennas

The "Best" Random Wire Antenna Lengths Random
wire lengths you should and should not use! The
random wire antenna is probably one of the least
expensive, easiest and cheapest HF antennas to
use if you have a tuner and you want to get the
"most out of a length of "random" wire without
having to pull out that calculator, doing the
math, getting the center insulator built or
bought, running the feed line, and all the rest
that goes with putting up a more elaborate
antenna. All you need for a random wire antenna
is some wire, your tuner, one or more supports up
as high as you can get them to string the wire
from the supports to the tuner, at least one or
two insulators and a little time.
17
W6RVB End Fed Antennas

One single wire, no solder connections, very
simple.... all the way from the tuner to the end
support. That's it in a nutshell.....or is
it? Many hams have tried till they are blue in
the face to install the random wire antenna that
works on most if not all of the HF bands with
terrible results. SWR is usually is all over the
place and the tuner will just not do it's job.
You can get good loading and low SWR on sometimes
2 or 3 bands, but one or more of the bands that
you want, just will not cooperate with an SWR
that can be adjusted with the "tuner". So after
much frustration. down it comes and you go on to
a totally different type of antenna....all that
time just wasted in your opinion.....until now!
18
W6RVB End Fed Antennas

We recently found some good information about
random wire lengths that you should and should
not use. Jack, VE3EED, hopefully has solved a
major headache we all have when we attempt to go
thru the trial and error and frustration with
getting the random wire to work where WE want it
to work. He knew that in order for the tuner to
"see" a fairly low SWR to work within it's range,
that the antenna had to be NOT A HALF WAVE ON
ANY FREQUENCY that we wanted to us, because a
half wave will give us a very high impedance and
the resulting SWR into a 50 ohm transmitter! So
Jack took most of one day, did the math with the
aid of his trusty calculator, several cups of
coffee and came up with...........................
....
19
W6RVB End Fed Antennas

The table below represents half wave lengths and
multiples that you DO NOT WANT TO USE! You have
to stay away from a half wavelength on any
frequency. Therefore, we came up with the
following numbers to avoid (IN FEET) These
lengths in the table below are the culprits that
cause all of the trouble when using random
lengths.
20
W6RVB End Fed Antennas

Here are the final numbers (in my opinion) in
green below that would be good for a long-wire
antenna (You may want to make a note of them)
Antenna lengths in FEET REVISED 29 35.5 41 58
71 84 107 119 148 203 347 407 423 REVISION NOTE
We had a note from James, KB5YN, pointing out
that one of the so-called GOOD numbers was 220
feet. That is the 10th multiple of a half wave on
15 meters. Well, I didn't think it would make any
difference at that many multiples. However, the
radio didn't tune up very well on 15 meters. So,
having nothing better to do one day, I re-did the
calculations going out to 500 feet. That meant
calculating all the way to 32 multiples of a half
wave on 10 meters. I won't bore you with all that
so the first portion of this still only shows up
to the 4th multiple. There are so many new
frequencies to stay away from, that it gets
pretty tricky for the longer wires. However, the
list has been revised and is good for wires as
long as 500 feet.
21
W6RVB End Fed Antennas

Wire, Connectors, etc
22
W6RVB End Fed Antennas

23
W6RVB End Fed Antennas
  • "To invent, you need a good imagination and a
    pile of junk."
  • - Thomas A. Edison

I remember attaching a wire clothing hanger to
the antenna of my radio in my bedroom, so I could
get the frequency and get that station and listen
to the top 10 every night.
- Steve Higbee, AJ6LN
Write a Comment
User Comments (0)
About PowerShow.com