In article
,
N9NEO wrote:

On Nov 30, 10:18 pm, Telamon
wrote:
In article
,





Harry7 wrote:
On Nov 28, 9:58 pm, N9NEO wrote:
I am wondering if a large ferrite rod would be good antenna for maybe
MW and 160meter band. Would there be an advantage to using a few rods
glued
together?

In the "ARRL Antenna Compendium, Vol. 6", there is an article
describing a tuned, ferrite rod, magnetic receiving loop antenna -
"The Optima 160/80-Meter Receive Antenna" by Richard Marris, G2BZQ.

THE author glues ferrite rods together exactly as you propose.

I never built or used one so I cannot comment on its perforance.

Gluing them together is a bad idea as you can not control the gap
between the rods. This small gap will ruin the inductance of the
combined rods and as a consequence the Q of this antenna.

Telemon,

The rod isn't a closed loop like a toroid so the the gap on the rod is
the distance from one face to the other. If we start with say a 7"
rod then what difference is .050" of glue going to make when we glue
to together to make a 14incher? I was thinking of maybe a series
parallel combination of a dozen or so.


Very small gaps in the rods continuity have very large magnetic field
resistance. Where the rods are glued together in series for one coil
they will behave more like two coils in series instead of just the one
coil.

--
Telamon
Ventura, California

Telamon wrote:

In article
,
N9NEO wrote:

On Nov 30, 10:18 pm, Telamon
wrote:
In article
,





Harry7 wrote:
On Nov 28, 9:58 pm, N9NEO wrote:
I am wondering if a large ferrite rod would be good antenna for
maybe
MW and 160meter band. Would there be an advantage to using a few
rods glued
together?

In the "ARRL Antenna Compendium, Vol. 6", there is an article
describing a tuned, ferrite rod, magnetic receiving loop antenna -
"The Optima 160/80-Meter Receive Antenna" by Richard Marris, G2BZQ.

THE author glues ferrite rods together exactly as you propose.

I never built or used one so I cannot comment on its perforance.

Gluing them together is a bad idea as you can not control the gap
between the rods. This small gap will ruin the inductance of the
combined rods and as a consequence the Q of this antenna.

Telemon,

The rod isn't a closed loop like a toroid so the the gap on the rod is
the distance from one face to the other. If we start with say a 7"
rod then what difference is .050" of glue going to make when we glue
to together to make a 14incher? I was thinking of maybe a series
parallel combination of a dozen or so.


Very small gaps in the rods continuity have very large magnetic field
resistance. Where the rods are glued together in series for one coil
they will behave more like two coils in series instead of just the one
coil.


I'm not sure that is correct, but even so, the two coils would be well
coupled.

I think a little math would be in order.

In article ,
craigm wrote:

Telamon wrote:

In article
,
N9NEO wrote:

On Nov 30, 10:18 pm, Telamon
wrote:
In article
,





Harry7 wrote:
On Nov 28, 9:58 pm, N9NEO wrote:
I am wondering if a large ferrite rod would be good antenna for
maybe
MW and 160meter band. Would there be an advantage to using a few
rods glued
together?

In the "ARRL Antenna Compendium, Vol. 6", there is an article
describing a tuned, ferrite rod, magnetic receiving loop antenna -
"The Optima 160/80-Meter Receive Antenna" by Richard Marris, G2BZQ.

THE author glues ferrite rods together exactly as you propose.

I never built or used one so I cannot comment on its perforance.

Gluing them together is a bad idea as you can not control the gap
between the rods. This small gap will ruin the inductance of the
combined rods and as a consequence the Q of this antenna.

Telemon,

The rod isn't a closed loop like a toroid so the the gap on the rod is
the distance from one face to the other. If we start with say a 7"
rod then what difference is .050" of glue going to make when we glue
to together to make a 14incher? I was thinking of maybe a series
parallel combination of a dozen or so.


Very small gaps in the rods continuity have very large magnetic field
resistance. Where the rods are glued together in series for one coil
they will behave more like two coils in series instead of just the one
coil.


I'm not sure that is correct, but even so, the two coils would be well
coupled.

I think a little math would be in order.

Ever gap a ferrite switching transformer so it does not saturate?

You have two rods that conduct magnetic fields well and air that doesn't.

--
Telamon
Ventura, California