RadioBanter - dipole length vs db

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dipole length vs db

hi

I ponder once again , and got a bit confused :

Currently i have a centerfed horiz dipole up pretty high

it's total length is less than 40ft, center feed via my sgc

i was thinking it'd be nice to have a SIGNIFICANT /real order of
magnatude type improvement in 'performance' or gain

my thought therefore went to making the dipole longer (as it's kinda on
the short side now)

so given the effort involved i wonder how much longer do i have to make
it to really extract a sig difference?

thanks

m

dipole length vs db

There are lots of factors to consider here. On the bands where your
antenna is longer than a half wavelength dipole, it will show gain over
the equivalent dipole. If you keep it about 40 feet, it will have a
single main lobe all the way up to 10m, where it's getting close to
being an extended double zepp (two 5/8ths wave halves)

If you make it much longer, the pattern will break up into multiple
lobes on the highest bands (which can, but not always will be, higher
gain, but in weird directions, and there will be deep nulls)

Of course, the higher bands (10, 12, to a certain extent 15) are dead
these days, so maybe we can exclude them from consideration.

- - - - -

The other thing to look at is the matching efficiency on the LOW bands.
The antenna is very, very short for 160 and 80m and is quite short for
40m operation. The tuner, if it will give you a match at all, isn't
going to be operating as efficiently as it could when you're operating
on the lower frequencies. Lengthening the antenna would help that, and
in that case, the gain could change a LOT, in the sense that you'd have
a lot less LOSS.

So it depends on what you want to do. If you're doing a lot on 80m and
40m, and want to have a dipole-like pattern all the way up to 17m, I
would suggest making the antenna maybe 74 feet total or so. This will
still put the 17m main lobe broadside to the antenna like a dipole
(though with some nonnegligible secondary lobes, but that's OK) and
will do much better on 80m as far as the tuner's ability to match.

The multi-lobed nature on 15, 12, and 10 wouldn't ruin all operation
there.

- - - - -

If you want to get gain in a particular direction using just a single
wire, you need phasing sections, but that gain isn't all that useful
unless you have a particular narrow direction that you favor, and your
gain would be single-band anyway.

So what you gain by lengthening a straight wire is more that you'll
have *less loss* on the lower bands, not so much that you'd get gain on
the higher bands (though a 74 foot doublet does have about 2.5dB gain
over a 1/2 wave dipole on 17m), and if you're trying to use a 40 foot
dipole on, say, 80m, you could expect many dB of improvement by moving
to a longer antenna.

Dan

dipole length vs db

thanks very much for taking the time to help me out dan, appreciate it

some of what you wrote sorta confused me, and maybe some left me
wondering still

i see what you ment about adding length improving the lower frequencies
80m i am 'ok' with that

but if I made the antenna length for ex 74' it's 'bad' or sort of less
than ideal things would happen on say 10m??? meaning it would be
'too' long?

so my goal here was an extreem gain 2orders of magnatude at least i
sorta thought that perhaps a wave on the lowest freq (160)might be
ok, but i get confused on how say that would negatively effect 10m

as the lobes increse their the penality is lots of nulls and radating
in odd directions?

so if i was listening to 10m and a sig was comming in on my existing
antenna say s9 and i made the antenna 74ft the signal would be lower?
maybe?

if this is true to get an 'optimal' all bad dipole you'd have to have
say 2 of them a 160-40 another for the rest?

just a little confused

In article .com,
" wrote:

There are lots of factors to consider here. On the bands where your
antenna is longer than a half wavelength dipole, it will show gain over
the equivalent dipole. If you keep it about 40 feet, it will have a
single main lobe all the way up to 10m, where it's getting close to
being an extended double zepp (two 5/8ths wave halves)

If you make it much longer, the pattern will break up into multiple
lobes on the highest bands (which can, but not always will be, higher
gain, but in weird directions, and there will be deep nulls)

Of course, the higher bands (10, 12, to a certain extent 15) are dead
these days, so maybe we can exclude them from consideration.

- - - - -

The other thing to look at is the matching efficiency on the LOW bands.
The antenna is very, very short for 160 and 80m and is quite short for
40m operation. The tuner, if it will give you a match at all, isn't
going to be operating as efficiently as it could when you're operating
on the lower frequencies. Lengthening the antenna would help that, and
in that case, the gain could change a LOT, in the sense that you'd have
a lot less LOSS.

So it depends on what you want to do. If you're doing a lot on 80m and
40m, and want to have a dipole-like pattern all the way up to 17m, I
would suggest making the antenna maybe 74 feet total or so. This will
still put the 17m main lobe broadside to the antenna like a dipole
(though with some nonnegligible secondary lobes, but that's OK) and
will do much better on 80m as far as the tuner's ability to match.

The multi-lobed nature on 15, 12, and 10 wouldn't ruin all operation
there.

- - - - -

If you want to get gain in a particular direction using just a single
wire, you need phasing sections, but that gain isn't all that useful
unless you have a particular narrow direction that you favor, and your
gain would be single-band anyway.

So what you gain by lengthening a straight wire is more that you'll
have *less loss* on the lower bands, not so much that you'd get gain on
the higher bands (though a 74 foot doublet does have about 2.5dB gain
over a 1/2 wave dipole on 17m), and if you're trying to use a 40 foot
dipole on, say, 80m, you could expect many dB of improvement by moving
to a longer antenna.

Dan

dipole length vs db

ml wrote:
but if I made the antenna length for ex 74' it's 'bad' or sort of less
than ideal things would happen on say 10m??? meaning it would be
'too' long?

Too long for what? Horizontal long wire antennas have
certain radiation characteristics. Consider the rhombic.
Some say it's the best antenna in the world.

so my goal here was an extreem gain 2orders of magnatude at least i
sorta thought that perhaps a wave on the lowest freq (160)might be
ok, but i get confused on how say that would negatively effect 10m
as the lobes increse their the penality is lots of nulls and radating
in odd directions?

Sometimes "odd" directions are the best if that's the
direction of your desired contact.

My own 130 foot dipole works like gangbusters on 17m.
It has 8 lobes each at about 8 dBi with a take-off-
angle of 19 degrees.

so if i was listening to 10m and a sig was comming in on my existing
antenna say s9 and i made the antenna 74ft the signal would be lower?
maybe?

Maybe lower but maybe higher. Unknown directions for
horizontal antennas may be good.

The g5rv designer, Mr. Varney, deliberately designed his
20m dipole to be "too long" because he desired the multi-
lobed radiation pattern.
--
73, Cecil http://www.w5dxp.com

dipole length vs db

thanks cecil, i kinda didn't fully understand some things in dan's post
my overalll takeaway was that just adding length to the antenna might be
'bad' ie not really garantee full band tremendious signal improvements
160m-10m in the same direction as i radiate now (mostly e-w) from his
post maybe he might add a few more comments to see how i can add
length and non direction gain to my setup on the higher freq side as
well as the lower

but i understood what you wrote cecil

i think for me to just try it might be most fun perhaps w/a switch
In article ,
Cecil Moore wrote:

ml wrote:
but if I made the antenna length for ex 74' it's 'bad' or sort of less
than ideal things would happen on say 10m??? meaning it would be
'too' long?

Too long for what? Horizontal long wire antennas have
certain radiation characteristics. Consider the rhombic.
Some say it's the best antenna in the world.

so my goal here was an extreem gain 2orders of magnatude at least i
sorta thought that perhaps a wave on the lowest freq (160)might be
ok, but i get confused on how say that would negatively effect 10m
as the lobes increse their the penality is lots of nulls and radating
in odd directions?

Sometimes "odd" directions are the best if that's the
direction of your desired contact.

My own 130 foot dipole works like gangbusters on 17m.
It has 8 lobes each at about 8 dBi with a take-off-
angle of 19 degrees.

so if i was listening to 10m and a sig was comming in on my existing
antenna say s9 and i made the antenna 74ft the signal would be lower?
maybe?

Maybe lower but maybe higher. Unknown directions for
horizontal antennas may be good.

The g5rv designer, Mr. Varney, deliberately designed his
20m dipole to be "too long" because he desired the multi-
lobed radiation pattern.

dipole length vs db

ml wrote:
but i understood what you wrote cecil

Walter Maxwell's advice is to make the dipole at
least 3/8 wavelength on the lowest frequency of
operation, feed it with ladder-line through a
1:1 choke, and enjoy.
--
73, Cecil http://www.w5dxp.com

dipole length vs db

In article , ml wrote:

Currently i have a centerfed horiz dipole up pretty high

it's total length is less than 40ft, center feed via my sgc

i was thinking it'd be nice to have a SIGNIFICANT /real order of
magnatude type improvement in 'performance' or gain

ML-

I have a similar question, but I'm not looking for a "real" order of
magnitude improvement. I just want to get on the air.

If I only have room for a short dipole, say 40 feet, and use a tuner such
as the SGC or Icom AH-4, what is the penalty in DB for the lower bands
(160, 75, 60, 40) compared to a half wave on each band?

73,
Fred
K4DII

dipole length vs db

Fred McKenzie wrote:
If I only have room for a short dipole, say 40 feet, and use a tuner such
as the SGC or Icom AH-4, what is the penalty in DB for the lower bands
(160, 75, 60, 40) compared to a half wave on each band?

Don't know the dB but losses would be appreciable. Why not
put up a 22 foot vertical with a good radial system? That
will work pretty well for 40m-10m using the autotuner at
the base. Install a base loading coil and it will work
reasonably well on 75m. Can't say much for 160m.
--
73, Cecil, http://www.qsl.net/w5dxp

dipole length vs db