Hello group -


My new interest is ferrite rod antennas.

I'm looking for a (possible) interesting doc:
UK magazine Practical Wireless, April 2000, pages 38 and 39 "An
Experimental Ferrite Rod Transmitting Antenna" by Richard Marris G2BZQ

Seems not on the net and the author doesn't have an email address or is gone.


Would be nice if someone can send it per email.


Anybody interested in ferrite antennas can contact me for info sharing.


Best regards -
Henry Kiefer

"Henry" wrote in message
...
Hello group -


My new interest is ferrite rod antennas.

I'm looking for a (possible) interesting doc:
UK magazine Practical Wireless, April 2000, pages 38 and 39 "An
Experimental Ferrite Rod Transmitting Antenna" by Richard Marris G2BZQ

Seems not on the net and the author doesn't have an email address or is
gone.


Would be nice if someone can send it per email.


Anybody interested in ferrite antennas can contact me for info sharing.


Best regards -
Henry Kiefer

Henry,

I vaguely recall reading this article also. As I recall it was claimed that
it was possible to use ferrite quite successfully to receive and transmit on
frequencies up to 7MHz or 40 metres. I believe the antenna used a couple of
six inch ferrite rods side by side with the old medium wave and long wave
windings removed and perhaps 15 or 20 turns of wire to resonate on 40 metres
wound over a sliding card sleeve. The sleeve was made loose enough to slide
along the ferrite rods to achieve the best point of operation.

I would suggest getting a couple of old ferrite rods and experimenting with
some wire and a capacitor for resonance.

The problem with ferrite is that it tends to be very lossy in transmitting
applications. The principles that concentrate received signals in a loop of
wire wound around the ferrite rod, result in transmitted signals becoming
concentrated in the ferrite rod, which then absorbs a lot of the RF energy
and reradiates it as heat. One or two six inch ferrite rods should be okay
for transmitter powers up to 10 watts.

The reason for using ferrite rods was to develop a small antenna with
similar properties to a dipole. One that could be rotated in the shack to
null out interference etc. Transmission efficiency will be very poor, but
the directional properties and the fact that you only need to radiate
milliwatts to work thousands of miles using CW may mean this type of antenna
will work fine for you.

One thing it wasn't, was a type of miracle whip. I have built one of those
following instructions on the web and it works okay at QRP powers from 3.5
MHz to 28 MHz. The transmission efficiency is rubbish, but it gets some sort
of a signal out and is fine for receiving. The miracle whip type of antenna
uses a wire wound ferrite toroid as a matching autotransformer to match the
impedence of a short whip to 50 ohms.

Try the link below for some more info on how ferrite works for receiving and
transmitting antennas

http://www.st-andrews.ac.uk/~jcgl/Sc...rt7/page5.html

This page suggests transmitter powers of less than a watt be used with
ferrite, but I think it depends on the heating effects you get with the rods
you end up using. There are many different formulations used in making
ferrite rods and toroids and some rods will work very much better than
others in this type of application.

Mike G0ULI

Hello Mike -


Thank you for the very long explanation!

Indeed, I already experimented with (unknown) ferrite rods but I'm just waiting here for new specified material (better) ferrites.
So I have time to search for more info...

Your mentioned link is one of the best I already found on the net.

In transmitting state the ui seems to fall to near 1. You can see it because the resonance frequency is going much higher (and that
will also increase harmonics)!

I'm not sure if a ferrite rod is a dipole? There is another structure possible: Ferrit-loaded helical antenna.

Unfortunately that is a kind of black art. Not much on the net to find.

The very low radiance resistance of the ferrite rod antenna is not the main problem. You must match the impedance to the
transceiver. That is easier if the antenna is an integral part of the system end amplifier, TX-RX switch and pre-amp.

If I understood you right, the "miracle whip" is not a antenna, more an impedance transformer. Whereas the typical ferrite rod
antenna is an autotransformer by itself - simply by adding or tapping another coil on the rod.


regards -
Henry


"Mike Kaliski" schrieb im Newsbeitrag ...
|
| "Henry" wrote in message
| ...
| Hello group -
|
|
| My new interest is ferrite rod antennas.
|
| I'm looking for a (possible) interesting doc:
| UK magazine Practical Wireless, April 2000, pages 38 and 39 "An
| Experimental Ferrite Rod Transmitting Antenna" by Richard Marris G2BZQ
|
| Seems not on the net and the author doesn't have an email address or is
| gone.
|
|
| Would be nice if someone can send it per email.
|
|
| Anybody interested in ferrite antennas can contact me for info sharing.
|
|
| Best regards -
| Henry Kiefer
|
| Henry,
|
| I vaguely recall reading this article also. As I recall it was claimed that
| it was possible to use ferrite quite successfully to receive and transmit on
| frequencies up to 7MHz or 40 metres. I believe the antenna used a couple of
| six inch ferrite rods side by side with the old medium wave and long wave
| windings removed and perhaps 15 or 20 turns of wire to resonate on 40 metres
| wound over a sliding card sleeve. The sleeve was made loose enough to slide
| along the ferrite rods to achieve the best point of operation.
|
| I would suggest getting a couple of old ferrite rods and experimenting with
| some wire and a capacitor for resonance.
|
| The problem with ferrite is that it tends to be very lossy in transmitting
| applications. The principles that concentrate received signals in a loop of
| wire wound around the ferrite rod, result in transmitted signals becoming
| concentrated in the ferrite rod, which then absorbs a lot of the RF energy
| and reradiates it as heat. One or two six inch ferrite rods should be okay
| for transmitter powers up to 10 watts.
|
| The reason for using ferrite rods was to develop a small antenna with
| similar properties to a dipole. One that could be rotated in the shack to
| null out interference etc. Transmission efficiency will be very poor, but
| the directional properties and the fact that you only need to radiate
| milliwatts to work thousands of miles using CW may mean this type of antenna
| will work fine for you.
|
| One thing it wasn't, was a type of miracle whip. I have built one of those
| following instructions on the web and it works okay at QRP powers from 3.5
| MHz to 28 MHz. The transmission efficiency is rubbish, but it gets some sort
| of a signal out and is fine for receiving. The miracle whip type of antenna
| uses a wire wound ferrite toroid as a matching autotransformer to match the
| impedence of a short whip to 50 ohms.
|
| Try the link below for some more info on how ferrite works for receiving and
| transmitting antennas
|
| http://www.st-andrews.ac.uk/~jcgl/Sc...rt7/page5.html
|
| This page suggests transmitter powers of less than a watt be used with
| ferrite, but I think it depends on the heating effects you get with the rods
| you end up using. There are many different formulations used in making
| ferrite rods and toroids and some rods will work very much better than
| others in this type of application.
|
| Mike G0ULI
|
|

"Henry" wrote in message
...
Hello Mike -


Thank you for the very long explanation!

Indeed, I already experimented with (unknown) ferrite rods but I'm just
waiting here for new specified material (better) ferrites.
So I have time to search for more info...

Your mentioned link is one of the best I already found on the net.

In transmitting state the ui seems to fall to near 1. You can see it
because the resonance frequency is going much higher (and that
will also increase harmonics)!

I'm not sure if a ferrite rod is a dipole? There is another structure
possible: Ferrit-loaded helical antenna.

Unfortunately that is a kind of black art. Not much on the net to find.

The very low radiance resistance of the ferrite rod antenna is not the
main problem. You must match the impedance to the
transceiver. That is easier if the antenna is an integral part of the
system end amplifier, TX-RX switch and pre-amp.

If I understood you right, the "miracle whip" is not a antenna, more an
impedance transformer. Whereas the typical ferrite rod
antenna is an autotransformer by itself - simply by adding or tapping
another coil on the rod.


regards -
Henry

Hi Henry,

The receiving (and transmission) patterns of ferrite rods are similar to a
dipole. In actual fact, the field pattern of a ferrite rod antenna is at 90
degrees to that of a dipole if both antennae were mounted with their long
axis parallel to one another. In practice, the influence of nearby buildings
and structures probably distort the pattern so much that the ferrite antenna
becomes pretty much omnidirectional.

You are absolutely right about the low impedence of small transmitting
antennae. Matching 50 ohms to perhaps 1 ohm or less will always be a major
problem. The low impedences, lead to high currents and high resistive
losses, which result in the ferrite heating up as well as the
interconnecting wiring.

The miracle whip type of antenna, uses a toroidal autotransformer
transformer which happens to be wound on ferrite to reduce the size of the
unit for portable operation. There are other ways to transform impedence to
get a match to a 54 inch whip antenna. A decent transmatch ATU will load up
just as well, but makes for a much bigger unit to carry around.

The ferrite rod is used to concentrate lines of flux within the wire coil
winding around the rod. While this works well in a receive situation, as I
understand it, the situation is effectively reversed when transmitting. The
coil of wire concentrates the transmitted signal within the ferrite rod
core. Because of the way ferrite is made up, it becomes extremely lossy when
saturated with RF and most of the energy is dissipated as heat. The higher
the frequency, the more energy is absorbed by the ferrite.

As losses are lower at lower frequencies, I would anticipate that a workable
transmitting and receiving antenna could be produced for use on the 160 and
80 metre bands, with the possibility of being able to use this type of
antenna on 40 metres. Certainly ferrite can be used to make a receiving
antenna for use up to 7MHz or so.

I would suggest experimenting to get something that receives well on the
frequency of interest. Unfortunately, receiver front ends are nearly all
high impedence so this won't necessarily guarantee a match to 50 ohms. The
proof is if you can manage to get a low SWR reading when trying to transmit
(at low power!). The ferrite rod will be doing it's level best to act as a
dummy load, but you may get enough power radiated for the system to work.
The addition of a retractable whip coupled to one end of the coil may
enhance transmission by allowing the ferrite rod and coil to provide the
matching and the whip to do the radiating. But then we are almost back to
the miracle whip idea.

If you haven't already tried one, I think you should try building a miracle
whip type of antenna. It will certainly give you an idea of the performance
you might get using a ferrite rod antenna, certainly in terms of received
signal strengths and probably transmitted output too. Buying all the
components brand new comes to under a tenner. Two twelve way switches, a
35mm diameter ferrite ring, a 54" telescopic whip antenna, a roll of 0.9 mm
enamelled copper wire and a couple of metres of hook up wire, terminals as
required and a miniature toggle switch. Don't worry too much about neat
wiring, it will all end up looking like a rats nest when all the connections
are made. Stick it in any old plastic box, you don't care if the whole
circuit radiates and receives. You can eliminate the telescopic whip and use
a random length of stiff wire if you want to reduce costs further. The grade
of ferrite ring doesn't seem to matter too much, I used one I found in my
junk box and I have no idea of the properties.

Having a good earth connection makes a world of difference to the way these
miniature antennae behave. Water and central heating pipes work okay, but
you may pick up quite a lot of local electrical noise as well. Be prepared
to hunt around for a decent quiet earthing point.

Mike G0ULI

Hi Mike -

| The receiving (and transmission) patterns of ferrite rods are similar to a
| dipole. In actual fact, the field pattern of a ferrite rod antenna is at 90
| degrees to that of a dipole if both antennae were mounted with their long
| axis parallel to one another. In practice, the influence of nearby buildings
| and structures probably distort the pattern so much that the ferrite antenna
| becomes pretty much omnidirectional.
|
| You are absolutely right about the low impedence of small transmitting
| antennae. Matching 50 ohms to perhaps 1 ohm or less will always be a major
| problem. The low impedences, lead to high currents and high resistive
| losses, which result in the ferrite heating up as well as the
| interconnecting wiring.

There is a difference between ferrite heating because of ohmic losses in the coils, and
ferrite losses. Both will rise temperature in ferrite rod and coil.


|
| The miracle whip type of antenna, uses a toroidal autotransformer
| transformer which happens to be wound on ferrite to reduce the size of the
| unit for portable operation. There are other ways to transform impedence to
| get a match to a 54 inch whip antenna. A decent transmatch ATU will load up
| just as well, but makes for a much bigger unit to carry around.

Where can I see an explanation of the miracle whip antenna? Mechanical construction.


|
| The ferrite rod is used to concentrate lines of flux within the wire coil
| winding around the rod. While this works well in a receive situation, as I
| understand it, the situation is effectively reversed when transmitting. The
| coil of wire concentrates the transmitted signal within the ferrite rod
| core. Because of the way ferrite is made up, it becomes extremely lossy when
| saturated with RF and most of the energy is dissipated as heat. The higher
| the frequency, the more energy is absorbed by the ferrite.
|
| As losses are lower at lower frequencies, I would anticipate that a workable
| transmitting and receiving antenna could be produced for use on the 160 and
| 80 metre bands, with the possibility of being able to use this type of
| antenna on 40 metres. Certainly ferrite can be used to make a receiving
| antenna for use up to 7MHz or so.

Yeah. At about 2MHz there is a first corner frequency for ferrits.


| Having a good earth connection makes a world of difference to the way these
| miniature antennae behave. Water and central heating pipes work okay, but
| you may pick up quite a lot of local electrical noise as well. Be prepared
| to hunt around for a decent quiet earthing point.

Mike, I don't have any earth. That is a portable design.

regards -
Henry

Henry wrote:

...
Where can I see an explanation of the miracle whip antenna? Mechanical construction.
...

Henry:

Here is a homemade "miracle whip:"

http://www.qsl.net/g4fon/Musings.htm

and here is the commercial version:

http://www.miracleantenna.com/

Regards,
JS