Bandwidth of a top band dipole?
 

Never having had a 160m dipole I don't know what sort of bandwidth to
expect.
Does anyone have any direct experience of a single band 160m dipole?

I just measured the garden at 60m long but taking into account the width I
could bend in a full size dipole without it getting too silly looking.
Maybe just need to bend back five metres on each end.

Bandwidth of a top band dipole?
 

Gordon Hudson wrote:
Never having had a 160m dipole I don't know what sort of
bandwidth to expect. Does anyone have any direct experience of
a single band 160m dipole?

I just measured the garden at 60m long but taking into account
the width I could bend in a full size dipole without it getting
too silly looking. Maybe just need to bend back five metres on
each end.

The bandwidth mainly depends on the height and the wire diameter
of the dipole. Some examples, a quick simulation with MMANA:
(The bandwidth is the SWR 2 bandwidth, with reference to the
impedance at resonance. Note that it is very low at low dipole
heights. For example at 10m height and resonance, the input
impedance of the dipole is about 8 Ohms only. The given bandwidth
assumes that you somehow match that to your transmitter.)

Straight 160m Dipole over average ground, no losses, SWR2 BW in kHz

height
diam 10m 15m 20m
1mm 9 23 37
2mm 10 24 40
4mm 11 25 43
8mm 12 27 46

This sounds pretty narrow, now the same with copper wi

height
diam 10m 15m 20m
1mm 17 29 44
4mm 14 28 46

This first surprised me: The bandwidth of the 1mm diameter dipole
is higher than the 4mm diameter dipole. Only at a height of 20m,
the thicker dipole has a better bandwidth. The reason is, that
the low dipoles with a low radiation resistance have mich higher
currents on them, and by P = I^2*R, the copper losses are higher
for the thinner wire. More losses = less Q = more bandwidth.

(The above measurements don't take into account that the
resonance frequency varied with the height and the diameter of
the dipole. All BW figures with respect to resonance frequency.)

So, as you see, there is not one easy answer to your question...

73,
--
Fabian Kurz, DJ1YFK * Dresden, Germany * http://fkurz.net/
Online Log: http://dl0tud.tu-dresden.de/~dj1yfk/log.html

Bandwidth of a top band dipole?
 

On May 10, 6:26�am, Fabian Kurz wrote:
Gordon Hudson wrote:
Never having had a 160m dipole I don't know what sort of
bandwidth to expect. Does anyone have any direct experience of
a single band 160m dipole?

I just measured the garden at 60m long but taking into account
the width I could bend in a full size dipole without it getting
too silly looking. Maybe just need to bend back five metres on
each end.

The bandwidth mainly depends on the height and the wire diameter
of the dipole. Some examples, a quick simulation with MMANA:
(The bandwidth is the SWR 2 bandwidth, with reference to the
impedance at resonance. Note that it is very low at low dipole
heights. For example at 10m height and resonance, the input
impedance of the dipole is about 8 Ohms only. The given bandwidth
assumes that you somehow match that to your transmitter.)

Straight 160m Dipole over average ground, no losses, SWR2 BW in kHz

height
diam 10m 15m 20m
1mm 9 23 37
2mm 10 24 40
4mm 11 25 43
8mm 12 27 46

This sounds pretty narrow, now the same with copper wi

height
diam 10m 15m 20m
1mm 17 29 44
4mm 14 28 46

This first surprised me: The bandwidth of the 1mm diameter dipole
is higher than the 4mm diameter dipole. Only at a height of 20m,
the thicker dipole has a better bandwidth. The reason is, that
the low dipoles with a low radiation resistance have mich higher
currents on them, and by P = I^2*R, the copper losses are higher
for the thinner wire. More losses = less Q = more bandwidth.

(The above measurements don't take into account that the
resonance frequency varied with the height and the diameter of
the dipole. All BW figures with respect to resonance frequency.)

So, as you see, there is not one easy answer to your question...

73,
--
Fabian Kurz, DJ1YFK * Dresden, Germany *http://fkurz.net/
Online Log:http://dl0tud.tu-dresden.de/~dj1yfk/log.html

Just as a quick, rough comparison, the bandwidth of a lower-
frequency dipole is the inverse of the ratio of higher frequency
to lower frequency. Not absolutely accurate but close enough.

73, Len AF6AY

Bandwidth of a top band dipole?
 

"AF6AY" wrote in message
oups.com...
On May 10, 6:26?am, Fabian Kurz wrote:
Gordon Hudson wrote:
Never having had a 160m dipole I don't know what sort of
bandwidth to expect. Does anyone have any direct experience of
a single band 160m dipole?

I just measured the garden at 60m long but taking into account
the width I could bend in a full size dipole without it getting
too silly looking. Maybe just need to bend back five metres on
each end.

The bandwidth mainly depends on the height and the wire diameter
of the dipole. Some examples, a quick simulation with MMANA:
(The bandwidth is the SWR 2 bandwidth, with reference to the
impedance at resonance. Note that it is very low at low dipole
heights. For example at 10m height and resonance, the input
impedance of the dipole is about 8 Ohms only. The given bandwidth
assumes that you somehow match that to your transmitter.)

Straight 160m Dipole over average ground, no losses, SWR2 BW in kHz

height
diam 10m 15m 20m
1mm 9 23 37
2mm 10 24 40
4mm 11 25 43
8mm 12 27 46

This sounds pretty narrow, now the same with copper wi

height
diam 10m 15m 20m
1mm 17 29 44
4mm 14 28 46

This first surprised me: The bandwidth of the 1mm diameter dipole
is higher than the 4mm diameter dipole. Only at a height of 20m,
the thicker dipole has a better bandwidth. The reason is, that
the low dipoles with a low radiation resistance have mich higher
currents on them, and by P =^2*R, the copper losses are higher
for the thinner wire. More losses =ess Q =ore bandwidth.

(The above measurements don't take into account that the
resonance frequency varied with the height and the diameter of
the dipole. All BW figures with respect to resonance frequency.)

So, as you see, there is not one easy answer to your question...

73,
--
Fabian Kurz, DJ1YFK * Dresden, Germany *http://fkurz.net/
Online Log:http://dl0tud.tu-dresden.de/~dj1yfk/log.html

Just as a quick, rough comparison, the bandwidth of a lower-
frequency dipole is the inverse of the ratio of higher frequency
to lower frequency. Not absolutely accurate but close enough.

73, Len AF6AY


Thanks both,
I suspected it would be quite narrow.

Gordon
GM4SVM