What about the dipole? I have a 1:1 balun and both ladder line and coax.
Which is prefered?

If you want to work a wide range of bands with a single center-fed
doublet, I think you'll have more success using ladder-line, and
feeding directly from the balanced output of your tuner. If your
tuner has only a non-balanced (coaxial) output, I'd suggest using a
1:1 choke (current balun") as close as is practical to the tuner
output, and then transitioning over to ladder line.

If you're using coax, and a balun at the top, you may find yourself
suffering from significant losses in the coax at high SWRs. Using
ladder or open-wire line, with its higher characteristic impedance,
can reduce these excess losses quite a bit (although not entirely
eliminate them).

Are you firm about using a center-fed doublet/dipole? A number of
people I know are very positive about their "off-center-fed"
dipoles... these can work as coax-fed antennas (using a 4:1 or 6:1
balun at the feedpoint) on a set of harmonically-related bands (e.g.
80/40/20/10). Another option here is to use an off-center-fed wire,
but feed it with ladder line (no balun at the feedpoint)... gives even
more band coverage.

These OCF antennas are typically fed at a point around 2/3 of the way
along the length (e.g. one arm is around twice the length of the
other) and are cut to a length which is halfwave-resonant on the
lowest band being used.

An example is the Alpha Delta DC-OCF - 135 feet long (legs are 45 and
90 feet), 6:1 balun at the feedpoint, coax-fed, covers 80/40/20/
17/12/10 meters "No tuner required". It covers the lower end of 6
meters pretty well, and the higher frequencies with an increased SWR
("use with caution", presumably to avoid overstressing the balun and
transmitter).

Most of these doublet/dipole antennas can also be treated as a
top-loaded vertical, and fed Marconi-style (short the two sides of the
feedline together, connect to the "hot" side of the tuner, and feed
the ground side of the tuner to a good bed of radials). This can let
you work lower-frequency bands (e.g. 160) on an antenna that by itself
is too short to load up properly at such a low frequency.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Nice explaination,,

I understand it a lot better now, I like your idea of the off centre
advantages especially when the tree distances are off,
should work out ok, unless I cut one of my neighbor's tree,,,, might look
too planned.

Any good ideas for a homebrew omni on the top of the 50ft tower?

I also have a couple hd antennas I must get higher, the dish is on there but
lower.

I would like to put a whip on the top mast, half way down the masting put
the two hd antennas for tv ( I figure one aiming north, one south (my
local's station most direction)) then tee that up then there at the top of
tower tie in a OCF dipole towards two trees.

The chap at the electronic store who sold me the hd antennas said it is
better to do it this way or to have the router. Any body confirm or deny
that? only a hundred bucks worth of parts there so not much but great signal
and high def.

thanks again for your experteeze on the topic, my plan is to minimize the
climbing.





"Dave Platt" wrote in message
...
What about the dipole? I have a 1:1 balun and both ladder line and coax.
Which is prefered?

If you want to work a wide range of bands with a single center-fed
doublet, I think you'll have more success using ladder-line, and
feeding directly from the balanced output of your tuner. If your
tuner has only a non-balanced (coaxial) output, I'd suggest using a
1:1 choke (current balun") as close as is practical to the tuner
output, and then transitioning over to ladder line.

If you're using coax, and a balun at the top, you may find yourself
suffering from significant losses in the coax at high SWRs. Using
ladder or open-wire line, with its higher characteristic impedance,
can reduce these excess losses quite a bit (although not entirely
eliminate them).

Are you firm about using a center-fed doublet/dipole? A number of
people I know are very positive about their "off-center-fed"
dipoles... these can work as coax-fed antennas (using a 4:1 or 6:1
balun at the feedpoint) on a set of harmonically-related bands (e.g.
80/40/20/10). Another option here is to use an off-center-fed wire,
but feed it with ladder line (no balun at the feedpoint)... gives even
more band coverage.

These OCF antennas are typically fed at a point around 2/3 of the way
along the length (e.g. one arm is around twice the length of the
other) and are cut to a length which is halfwave-resonant on the
lowest band being used.

An example is the Alpha Delta DC-OCF - 135 feet long (legs are 45 and
90 feet), 6:1 balun at the feedpoint, coax-fed, covers 80/40/20/
17/12/10 meters "No tuner required". It covers the lower end of 6
meters pretty well, and the higher frequencies with an increased SWR
("use with caution", presumably to avoid overstressing the balun and
transmitter).

Most of these doublet/dipole antennas can also be treated as a
top-loaded vertical, and fed Marconi-style (short the two sides of the
feedline together, connect to the "hot" side of the tuner, and feed
the ground side of the tuner to a good bed of radials). This can let
you work lower-frequency bands (e.g. 160) on an antenna that by itself
is too short to load up properly at such a low frequency.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Nice explaination,,

I understand it a lot better now, I like your idea of the off centre
advantages especially when the tree distances are off,
should work out ok, unless I cut one of my neighbor's tree,,,, might look
too planned.

Any good ideas for a homebrew omni on the top of the 50ft tower?

For which band or bands? 2 meters? If so, you could install a
homebrew J-pole (these are easily made from copper pipe), or a simple
quarter-wave whip with a few ground radials bent down at a 45-degree
angle (two radials is enough for a very functional ground plane).

There are fancier omni antennas available, depending on what
frequencies you want to work, how much gain you need, and how much you
want to spend. A 1.25-wavelength "extended double zepp" made out of
copper pipe, side-mounted at the top of the tower, would give you a
few dB of gain compared to a J-pole or ground-plane.

I also have a couple hd antennas I must get higher, the dish is on there but
lower.

I would like to put a whip on the top mast, half way down the masting put
the two hd antennas for tv ( I figure one aiming north, one south (my
local's station most direction)) then tee that up then there at the top of
tower tie in a OCF dipole towards two trees.

The chap at the electronic store who sold me the hd antennas said it is
better to do it this way or to have the router. Any body confirm or deny
that? only a hundred bucks worth of parts there so not much but great signal
and high def.

Well, let's see. "HD" antennas aren't fundamentally any different
than decent analog-TV antennas - the RF has no idea whether it's
carrying analog or digital modulations. What you want or need, in an
ATSC (US digital TV) antenna, depends to a significant extent on which
RF frequencies your local stations are using. In many areas, they're
all up in the UHF band these days, and you can get away with a
relatively small antenna... multi-bay bowtie-and-reflector antennas
are popular.

In some areas (mostly urban) there are still stations transmitting
digitally on the VHF bands - quite a few in the VHF "high band" (old
channels 7-13) and a few still down in the VHF low-band (old channels
2-6). In these areas you'll need an antenna which is big enough to do
a decent job on VHF... and the old UHF/VHF log-periodic rooftop
antennas work just fine for this.

In general, you will get the best results with an antenna pointed
fairly much towards the transmitter... you'll get some gain, and the
antenna will be more likely to reject multipath reflections from
nearby buildings and trees. If your local stations are split between
mostly-north and mostly-south, then either using a bidirectional
antenna, or a single antenna with a rotator, or a pair of fixed
antennas with a selector switch, would make sense.

I wouldn't hook up two antennas (north and south) and just wire them
in parallel... the signals will interfere and you could end up with
worse results than you'd have gotten from a simple dipole.

A few HDTVs and set-top boxes now support a "smart antenna" control
system. They can send a control signal (and some DC power) back up
the coax to the antenna, allowing a multi-element antenna to switch a
phasing network and thus "aim" itself electronically... no moving
parts, just some phased beam-shaping. The DTV decoder / TV will
"switch" the antenna around when channel-tuning, to figure out which
beam pattern gives the cleanest signal.

Unfortunately, the control protocol and specs for this system aren't
freely available, so I don't think it's possible to home-brew one.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Thanks for comming back,,,,

not for 2m but for hf.
Something that doesn't have to be too long and tunable with the mfj
adjustable tuner.
I would like to use it also for 156 megs as I talk to the boats a lot and I
know that is higher freq but would prefer to have the lower frequencies and
if the tuner will keep it safe.

I have one with the three traps in the middle, it is rather long and believe
it is meant to be on the ground.
I have a couple of those rings with 8 dimple male 1" insert stubs that allow
8 aluminum ground planes to be clamped on and if I keep them short enough
the winds wont blow them down. So I have the parts, just need to know what
the measurements or heights to be useful on as many busy bands, I don't
think 160m would be practical.







"Dave Platt" wrote in message
...
Nice explaination,,

I understand it a lot better now, I like your idea of the off centre
advantages especially when the tree distances are off,
should work out ok, unless I cut one of my neighbor's tree,,,, might look
too planned.

Any good ideas for a homebrew omni on the top of the 50ft tower?

For which band or bands? 2 meters? If so, you could install a
homebrew J-pole (these are easily made from copper pipe), or a simple
quarter-wave whip with a few ground radials bent down at a 45-degree
angle (two radials is enough for a very functional ground plane).

There are fancier omni antennas available, depending on what
frequencies you want to work, how much gain you need, and how much you
want to spend. A 1.25-wavelength "extended double zepp" made out of
copper pipe, side-mounted at the top of the tower, would give you a
few dB of gain compared to a J-pole or ground-plane.

I also have a couple hd antennas I must get higher, the dish is on there
but
lower.

I would like to put a whip on the top mast, half way down the masting put
the two hd antennas for tv ( I figure one aiming north, one south (my
local's station most direction)) then tee that up then there at the top of
tower tie in a OCF dipole towards two trees.

The chap at the electronic store who sold me the hd antennas said it is
better to do it this way or to have the router. Any body confirm or deny
that? only a hundred bucks worth of parts there so not much but great
signal
and high def.

Well, let's see. "HD" antennas aren't fundamentally any different
than decent analog-TV antennas - the RF has no idea whether it's
carrying analog or digital modulations. What you want or need, in an
ATSC (US digital TV) antenna, depends to a significant extent on which
RF frequencies your local stations are using. In many areas, they're
all up in the UHF band these days, and you can get away with a
relatively small antenna... multi-bay bowtie-and-reflector antennas
are popular.

In some areas (mostly urban) there are still stations transmitting
digitally on the VHF bands - quite a few in the VHF "high band" (old
channels 7-13) and a few still down in the VHF low-band (old channels
2-6). In these areas you'll need an antenna which is big enough to do
a decent job on VHF... and the old UHF/VHF log-periodic rooftop
antennas work just fine for this.

In general, you will get the best results with an antenna pointed
fairly much towards the transmitter... you'll get some gain, and the
antenna will be more likely to reject multipath reflections from
nearby buildings and trees. If your local stations are split between
mostly-north and mostly-south, then either using a bidirectional
antenna, or a single antenna with a rotator, or a pair of fixed
antennas with a selector switch, would make sense.

I wouldn't hook up two antennas (north and south) and just wire them
in parallel... the signals will interfere and you could end up with
worse results than you'd have gotten from a simple dipole.

A few HDTVs and set-top boxes now support a "smart antenna" control
system. They can send a control signal (and some DC power) back up
the coax to the antenna, allowing a multi-element antenna to switch a
phasing network and thus "aim" itself electronically... no moving
parts, just some phased beam-shaping. The DTV decoder / TV will
"switch" the antenna around when channel-tuning, to figure out which
beam pattern gives the cleanest signal.

Unfortunately, the control protocol and specs for this system aren't
freely available, so I don't think it's possible to home-brew one.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!