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lsmyer June 11th 04 01:53 AM

Question about Ferrite Antennas
 
I enjoy AM dxing, and I've noticed that the radios with larger ferrite rods
seem to be better for dxing than those with small ones.

I did some research on the subject, and I kept running into terms such
q-factor and flux. My 45-year-old mind only has room for so much, and I'm
afraid that anything I try to learn about electronic theory will just push
out some of the more important stuff already stored in there such as
anniversary dates and current wife's name.

So maybe somebody can answer a couple of questions for me in simple English,
and maybe help me save what few brain cells I still have left.

1) Is there an optimal length for an internal ferrite antenna?

2) If so, then why don't all radios have one that size?

3) Is ferrite expensive or something?

4) How can my little Degen 1102 (tiny ferrite antenna) do so well on MW
while my ATS505 does so poorly?

Thank you in advance for all who reply.



Gray Shockley June 11th 04 04:10 AM

On Thu, 10 Jun 2004 19:53:30 -0500, lsmyer wrote
(in article ):

4) How can my little Degen 1102 (tiny ferrite antenna) do so well on MW
while my ATS505 does so poorly?



How much difference does the "DX/Local" switch make?

In other words, what effect does the switch have on a strong
local station and what effect does it have on a weak, distant
station.

The "Local" position will make it just about insensitive so that
the "Local" stations won't overload it.

In the "DX" position, "Local" stations will overload the radio.
It's a good feature but ya have to remember to switch.



Gray Shockley
----------------
DX-392 DX-398
RX-320 DX-399
CCradio+ w/RS Loop
Justice AM Antenna
Torus Tuner (3-13 MHz)
Select-A-Tenna
---------------------
Vicksburg, MS US



Matti Ponkamo June 11th 04 12:42 PM

"lsmyer" kirjoitti viestissä
...
I enjoy AM dxing, and I've noticed that the radios with larger ferrite

rods
seem to be better for dxing than those with small ones.
I did some research on the subject, and I kept running into terms such
q-factor and flux. My 45-year-old mind only has room for so much, and I'm
afraid that anything I try to learn about electronic theory will just push
out some of the more important stuff already stored in there such as
anniversary dates and current wife's name.

So maybe somebody can answer a couple of questions for me in simple

English,
and maybe help me save what few brain cells I still have left.

1) Is there an optimal length for an internal ferrite antenna?
2) If so, then why don't all radios have one that size?
3) Is ferrite expensive or something?
4) How can my little Degen 1102 (tiny ferrite antenna) do so well on MW
while my ATS505 does so poorly?

Thank you in advance for all who reply.


All the receivers have a limited space for the ferrite antenna. I am no
expert in antennas, but what little I know is that

1) The total physical length of an antenna (ref: wavelength) is important:
usually the longer the better
2) The tuning of the antenna is important, too. Is the antenna "fitted"
to the "front end" of the receiver and how well... e.t.c. ?
If a receiver is "tuned" to work fine on shortwave it may not work
fine on MW
3) Ferrite itself is not expensive, though the retail price for a piece
of antenna can be high
4) My little Kenwood TH-F7 is more sensitive with its tiny
ferrite rod and my old Grundig YB207 is not with its longer
piece of ferrite. Kenwood, though, is too sensitive for all
kind of noise and "parasites", too.

73's, Matti Ponkamo, Naantali, Finland



Jay Heyl June 13th 04 11:28 AM

In article ,
says...
1) Is there an optimal length for an internal ferrite antenna?


Within limits, the bigger the better.

2) If so, then why don't all radios have one that size?


Not everyone wants to lug around a radio the size of a steamer trunk.

3) Is ferrite expensive or something?


Larger ferrite rods are considerably more expensive than smaller ones.
This was just a quick spot check, but one site was offering 2" ferrite
rods for $2, 7.5" for $12, and 12" for $75.

4) How can my little Degen 1102 (tiny ferrite antenna) do so well on MW
while my ATS505 does so poorly?


There could be any number of reasons. I know some of the other Sangeans
are purposely designed with a less than optimal antenna interface to
reduce overload problems in Europe where enormous transmitters are
fairly common. It could be simply that Degen put more effort into MW.

WagnerND June 13th 04 05:44 PM

Ismyer, I'll be glad to help you with ferrite antennas. 1) No, there is no
optimal ferrite rod length. For your Sangean 505 try a ferrite plus coil
antenna such as the Terk or Select-a-Tenna. These antennas couple to your
receiver inductively (magneticially-no wire connections).
2) Ferrite rods are expensive so the bigger rods are on the better receivers.
But, you can easily add one. But, you really don't need to if you use one of
the above MW antennas. See Univesal Radios web site & look up the Palomar LC-1
& RF Systems AA-2 add on ferrite rods.
3) Yes, Ferrite rods are expensive & hard to find. For MW you can easily make
one. See the web site of "National Radio Club", a MW DX Club with rod designs.
4) If you use a Select-A-Tenna the 505 will out perfrom the smaller one. It is
all in knowing how to couple an exterior loop to the receiver. You need an
exterior loop that couples (transfers signals to) your 505.
5) Flux is the type of ferrite used. It is sold by an assigned number. #61 is
good for MW.
6) "Q" stands for the "Quality" of the circuit, not always agood thing. For
example a "Hi-Q" provides a narrow band width. You want a wider band width.

Need more help let me know. You really need a Select-A-Tenna with the mini jack
on it's base, or the locally available Terk.

73 John T. Wagner, Ohio

lsmyer June 13th 04 06:24 PM

Thanks to everyone for their help about ferrite antennas. Now I know enough
to start experimenting, and that's what a hobby is all about!



GrtPmpkin32 June 13th 04 09:06 PM

Now I know enough
to start experimenting, and that's what a hobby is all about!


Damn straight. I've been into antenna tinkering for years, and I have as much
fun failing as I do succeeding (well, within reason, haha!) with any given
project. I learn from both, and get a lot of help from this group too.
Have a blast-
Linus

H. Dziardziel June 14th 04 12:01 AM

On Thu, 10 Jun 2004 20:53:30 -0400, "lsmyer"
wrote:

I enjoy AM dxing, and I've noticed that the radios with larger ferrite rods
seem to be better for dxing than those with small ones.

I did some research on the subject, and I kept running into terms such
q-factor and flux. My 45-year-old mind only has room for so much, and I'm
afraid that anything I try to learn about electronic theory will just push
out some of the more important stuff already stored in there such as
anniversary dates and current wife's name.

So maybe somebody can answer a couple of questions for me in simple English,
and maybe help me save what few brain cells I still have left.

It's been years so the erudite here will please set me straight.

The coil-antenna combines signal gathering with tuning and
directivity. The ferrite core just increases the antenna-coil
inductance. This results in a smaller coil for tuning frequency
coverage but less antenna (the physical coil proper) for actual
signal reception. It adds to core losses but there is less wire
loss. It makes a much smaller transformer. So, there are
several tradeoffs.

The most efficient AM band ferrite coils for external antenna use
were only about an inch and a half or so as I recall. They are
variable inductance too for tweaking. Some old radios may have
them.


1) Is there an optimal length for an internal ferrite antenna?

2) If so, then why don't all radios have one that size?

3) Is ferrite expensive or something?

4) How can my little Degen 1102 (tiny ferrite antenna) do so well on MW
while my ATS505 does so poorly?

Thank you in advance for all who reply.



Telamon June 14th 04 12:50 AM

In article ,
H. Dziardziel wrote:

On Thu, 10 Jun 2004 20:53:30 -0400, "lsmyer"
wrote:

I enjoy AM dxing, and I've noticed that the radios with larger
ferrite rods seem to be better for dxing than those with small ones.

I did some research on the subject, and I kept running into terms
such q-factor and flux. My 45-year-old mind only has room for so
much, and I'm afraid that anything I try to learn about electronic
theory will just push out some of the more important stuff already
stored in there such as anniversary dates and current wife's name.

So maybe somebody can answer a couple of questions for me in simple
English, and maybe help me save what few brain cells I still have
left.

1) Is there an optimal length for an internal ferrite antenna?

2) If so, then why don't all radios have one that size?

3) Is ferrite expensive or something?

4) How can my little Degen 1102 (tiny ferrite antenna) do so well on
MW while my ATS505 does so poorly?

Thank you in advance for all who reply.



It's been years so the erudite here will please set me straight.

The coil-antenna combines signal gathering with tuning and
directivity. The ferrite core just increases the antenna-coil
inductance. This results in a smaller coil for tuning frequency
coverage but less antenna (the physical coil proper) for actual
signal reception. It adds to core losses but there is less wire loss.
It makes a much smaller transformer. So, there are several tradeoffs.

The most efficient AM band ferrite coils for external antenna use
were only about an inch and a half or so as I recall. They are
variable inductance too for tweaking. Some old radios may have them.


This sounds right to me. I don't see how a larger ferrite rod would
necessarily work better other than change the number of turns for a
given frequency range. A larger rod would have more inductance per
turn.

I would add the type of ferrite is important, which will determine the
inductance per turn and core loss.

1. No optimal length.

2. The antenna rod works with other components chosen in the design of
the radio and so must be different.

3. Ferrite is not expensive but it is brittle and the longer the rod the
easier it is to break.

4. The design of the front end of the radio of which the rod antenna is
just one part of determines the difference in performance.

--
Telamon
Ventura, California

Telamon June 14th 04 04:59 AM

In article
,
Telamon wrote:

In article ,
H. Dziardziel wrote:

On Thu, 10 Jun 2004 20:53:30 -0400, "lsmyer"
wrote:

I enjoy AM dxing, and I've noticed that the radios with larger
ferrite rods seem to be better for dxing than those with small ones.

I did some research on the subject, and I kept running into terms
such q-factor and flux. My 45-year-old mind only has room for so
much, and I'm afraid that anything I try to learn about electronic
theory will just push out some of the more important stuff already
stored in there such as anniversary dates and current wife's name.

So maybe somebody can answer a couple of questions for me in simple
English, and maybe help me save what few brain cells I still have
left.

1) Is there an optimal length for an internal ferrite antenna?

2) If so, then why don't all radios have one that size?

3) Is ferrite expensive or something?

4) How can my little Degen 1102 (tiny ferrite antenna) do so well on
MW while my ATS505 does so poorly?

Thank you in advance for all who reply.



It's been years so the erudite here will please set me straight.

The coil-antenna combines signal gathering with tuning and
directivity. The ferrite core just increases the antenna-coil
inductance. This results in a smaller coil for tuning frequency
coverage but less antenna (the physical coil proper) for actual
signal reception. It adds to core losses but there is less wire loss.
It makes a much smaller transformer. So, there are several tradeoffs.

The most efficient AM band ferrite coils for external antenna use
were only about an inch and a half or so as I recall. They are
variable inductance too for tweaking. Some old radios may have them.


This sounds right to me. I don't see how a larger ferrite rod would
necessarily work better other than change the number of turns for a
given frequency range. A larger rod would have more inductance per
turn.

I would add the type of ferrite is important, which will determine the
inductance per turn and core loss.

1. No optimal length.

2. The antenna rod works with other components chosen in the design of
the radio and so must be different.

3. Ferrite is not expensive but it is brittle and the longer the rod the
easier it is to break.

4. The design of the front end of the radio of which the rod antenna is
just one part of determines the difference in performance.


Hey check this out they have an electronic kit for just about anything.
http://www.kitsusa.net

If you want to experiment with different rod antennas you could build
this kit and try different rod antennas. Connect an inexpensive DVM to
measure the AGC voltage from this little breadboard radio and you will
be able to tell if the experimental rod is better or worse.

http://www.kitsusa.net/phpstore/inde...8&prevaction=c
ategory&previd=2&prevstart=12

Then you will know more than the blow hards that recently cross posted
in here that endlessly talk out their you know what.

--
Telamon
Ventura, California

Stephen June 17th 04 04:38 PM

"H. Dziardziel" wrote in message
...

It's been years so the erudite here will please set me straight.

The coil-antenna combines signal gathering with tuning and
directivity. The ferrite core just increases the antenna-coil
inductance. This results in a smaller coil for tuning frequency
coverage but less antenna (the physical coil proper) for actual
signal reception. It adds to core losses but there is less wire
loss. It makes a much smaller transformer. So, there are
several tradeoffs.

The most efficient AM band ferrite coils for external antenna use
were only about an inch and a half or so as I recall. They are
variable inductance too for tweaking. Some old radios may have
them.



You're right about the ferrite core increasing the inductance of the antenna
coil, however, it does something else as well - it provides a 'low
resistance' (in a magnetic sense) path for the signal's magnetic field to
travel through. Suppose you're facing the transmitter, and suppose the
magnetic field lines from the station's signal are horizontally oriented
(which I think is likely to be the case for a signal traveling along the
ground). This means that a particular field line would approach you from
the right and leave you going to the left (or vice versa since these are
alternating fields - it just depends on the instant when you look). Given
all of this, the MW antenna should be oriented such that the maximum number
of field lines pass through the inside of the coil (which will maximize the
current that gets induced in the coil windings). If the antenna uses a
ferrite bar, this orientation means that the length of the bar is lined up
with the magnetic field lines.

Now for the interesting part ( :-) ). If there were no ferrite bar, the
magnetic field lines would travel in fairly straight paths (in your local
vicinity), and the coil would intercept a cross-section of the field
determined by the cross sectional area of the coil. However, when a ferrite
bar is used, many of the magnetic field lines in the vicinity of the antenna
take a detour so as to pass through the ferrite bar, because travelling
through the ferrite bar is easier than travelling through the air. This has
the effect of increasing the number of magnetic field lines that pass
through the inside of the coil, thereby increasing the antenna's signal
pickup. If the bar is short, only a small number of field lines will decide
it's worth their while to take the detour. If the bar is longer, a larger
number of field lines will end up travelling a shorter distance *through
air* as a result of taking the detour and travelling through the ferrite bar
for its length. So a longer bar does work better because it creates a
bigger distortion in the local magnetic field, and, in effect, catches a
larger number of magnetic field lines and sends them through the center of
the coil.

So there you go - I may have left a few physicists cringing over some of the
terminology, but you get the general idea...

-- Stephen


--
Please remove no and spam from my email address if replying by email.



H. Dziardziel June 19th 04 08:08 AM

On Thu, 17 Jun 2004 11:38:23 -0400, "Stephen"
wrote:

rotated out portion

You're right about the ferrite core increasing the inductance of the antenna
coil, however, it does something else as well - it provides a 'low
resistance' (in a magnetic sense) path for the signal's magnetic field to
travel through. Suppose you're facing the transmitter, and suppose the
magnetic field lines from the station's signal are horizontally oriented
(which I think is likely to be the case for a signal traveling along the
ground). This means that a particular field line would approach you from
the right and leave you going to the left (or vice versa since these are
alternating fields - it just depends on the instant when you look). Given
all of this, the MW antenna should be oriented such that the maximum number
of field lines pass through the inside of the coil (which will maximize the
current that gets induced in the coil windings). If the antenna uses a
ferrite bar, this orientation means that the length of the bar is lined up
with the magnetic field lines.

Now for the interesting part ( :-) ). If there were no ferrite bar, the
magnetic field lines would travel in fairly straight paths (in your local
vicinity), and the coil would intercept a cross-section of the field
determined by the cross sectional area of the coil. However, when a ferrite
bar is used, many of the magnetic field lines in the vicinity of the antenna
take a detour so as to pass through the ferrite bar, because travelling
through the ferrite bar is easier than travelling through the air. This has
the effect of increasing the number of magnetic field lines that pass
through the inside of the coil, thereby increasing the antenna's signal
pickup. If the bar is short, only a small number of field lines will decide
it's worth their while to take the detour. If the bar is longer, a larger
number of field lines will end up travelling a shorter distance *through
air* as a result of taking the detour and travelling through the ferrite bar
for its length. So a longer bar does work better because it creates a
bigger distortion in the local magnetic field, and, in effect, catches a
larger number of magnetic field lines and sends them through the center of
the coil.

So there you go - I may have left a few physicists cringing over some of the
terminology, but you get the general idea...

-- Stephen


Your nearly poetic license disclamer is well appreciated although
I am mystified at how the flux "knows" it should detour? Most
intriguing and Nobel prize stuff perhap?.

This site has a dandy handbook style lightly theoretical
description and fine images.:
..http://www.st-andrews.ac.uk/~www_pa/...rt7/page5.html

Keeping in mind the facts that: transmission and reception is in
theory reciprocal, and essentially so in reality for low power
applications: the meaning of radiation resistance, effective
area, and gain, the ferrite results in higher output for the
identical input i.e. the impinging EM energy on the coil. It's
more efficient: a better antenna impedance match thus minimizing
effects of the coil etc losses.

A larger core and coil, just like a larger loop only etc thus
gives more output. A longer bar _only_ has no effect as it is
insignificant compared to the total flux path which is all air.
It will change the inductance however. Note too that the coil
(the ferrite only enhances this) changes the loop reception from
electric to magnetic field and thus the orientation for maximum by
90 degrees.

That gain could be up to a million explains why my nifty 20 year
old great sounding credit card thick Sanyo AM/FM (stereo too) has
sensitivity nearly equal to my 2010.

Regards

Telamon June 19th 04 08:47 AM

In article ,
H. Dziardziel wrote:

On Thu, 17 Jun 2004 11:38:23 -0400, "Stephen"
wrote:

rotated out portion

You're right about the ferrite core increasing the inductance of the antenna
coil, however, it does something else as well - it provides a 'low
resistance' (in a magnetic sense) path for the signal's magnetic field to
travel through. Suppose you're facing the transmitter, and suppose the
magnetic field lines from the station's signal are horizontally oriented
(which I think is likely to be the case for a signal traveling along the
ground). This means that a particular field line would approach you from
the right and leave you going to the left (or vice versa since these are
alternating fields - it just depends on the instant when you look). Given
all of this, the MW antenna should be oriented such that the maximum number
of field lines pass through the inside of the coil (which will maximize the
current that gets induced in the coil windings). If the antenna uses a
ferrite bar, this orientation means that the length of the bar is lined up
with the magnetic field lines.

Now for the interesting part ( :-) ). If there were no ferrite bar, the
magnetic field lines would travel in fairly straight paths (in your local
vicinity), and the coil would intercept a cross-section of the field
determined by the cross sectional area of the coil. However, when a ferrite
bar is used, many of the magnetic field lines in the vicinity of the antenna
take a detour so as to pass through the ferrite bar, because travelling
through the ferrite bar is easier than travelling through the air. This has
the effect of increasing the number of magnetic field lines that pass
through the inside of the coil, thereby increasing the antenna's signal
pickup. If the bar is short, only a small number of field lines will decide
it's worth their while to take the detour. If the bar is longer, a larger
number of field lines will end up travelling a shorter distance *through
air* as a result of taking the detour and travelling through the ferrite bar
for its length. So a longer bar does work better because it creates a
bigger distortion in the local magnetic field, and, in effect, catches a
larger number of magnetic field lines and sends them through the center of
the coil.

So there you go - I may have left a few physicists cringing over some of the
terminology, but you get the general idea...

-- Stephen


Your nearly poetic license disclamer is well appreciated although
I am mystified at how the flux "knows" it should detour? Most
intriguing and Nobel prize stuff perhap?.


The permeability of ferrite is much greater than air. Ferrite become a
path of least resistance to magnetic fields.

The Nobel prize was given out long ago on this subject. This is just a
basic concept. Nothing new here.

--
Telamon
Ventura, California

H. Dziardziel June 20th 04 02:31 PM

On Sat, 19 Jun 2004 07:47:46 GMT, Telamon
wrote:




The permeability of ferrite is much greater than air. Ferrite become a
path of least resistance to magnetic fields.

Yes..

The Nobel prize was given out long ago on this subject. This is just a
basic concept. Nothing new here.


Only gravity bends EM waves. GUT
..
The higher permeabillity does not "suck" in EM waves. Nor do EM
waves have a uncanny ability to seek out the path of least
resistance.

The higher permeabillity means a greater flux density is
possible within that medium. So, for example, once absorbed
they stay in that medium, the path of least resistance and more
of the energy can be transformed.

First however, the EM waves must arrive at the core-coil..
Just like a black body absorber.

And the reciprocal case when the ferrite loop is used for
transmission: The denser field is created by the coil -core
medium and radiates out into space.

What the permeability does is improve EM and electrical power
_transformation_ efficiency within it.





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