Ferrite bar antenna for car radio?

[[email protected]]

Any idea the best way to couple a ferrite loopstick antenna
to a car radio input for AM reception?

I experimeted using a 6 inch loopstick (230uH) and 365pF
parallel tunning cap from antenna input to ground (chassis)
with reasonable results, but I'm wondering what the best
approach is.

The tuning is very broad and I don't get much of a peak
when adjusting the capacitor, but all the local stations
come in.

How should I wind the loopstick for best results?

-Bill

 

[Pooh Bear]

Any idea the best way to couple a ferrite loopstick antenna
to a car radio input for AM reception?

You still listen to AM ! ?

Awesome.

Most poor ppl I know use wire coathangers to replace the car aerial
when the original gets trashed by kids or whoever..


Graham

 

[Dave]

Any idea the best way to couple a ferrite loopstick antenna
to a car radio input for AM reception?

I experimeted using a 6 inch loopstick (230uH) and 365pF
parallel tunning cap from antenna input to ground (chassis)
with reasonable results, but I'm wondering what the best
approach is.

The tuning is very broad and I don't get much of a peak
when adjusting the capacitor, but all the local stations
come in.

How should I wind the loopstick for best results?

-Bill

IIRC the normal approach if you wish to make it tuneable is to have a
large winding which is tuned with the cap, and a smaller winding with
less turns, so there is an impedance transformation.

I suspect very much depends on the device used as the front end -
whether it is a high Z fet or a lower impedance device.

It sounds like the Q is low if the tuning is broad, but do you really
want the hassle of returning the capacitor every time?

 

[John Woodgate]

I read in sci.electronics.design that [email protected] wrote (in

Any idea the best way to couple a ferrite loopstick antenna to a car
radio input for AM reception?

I experimeted using a 6 inch loopstick (230uH) and 365pF parallel
tunning cap from antenna input to ground (chassis) with reasonable
results, but I'm wondering what the best approach is.

The tuning is very broad and I don't get much of a peak when adjusting
the capacitor, but all the local stations come in.

How should I wind the loopstick for best results?

You need to tap down the coil or wind a secondary winding on the rod.
The car radio antenna input is a lowish impedance, not 50 ohms or
anything like, but much lower than the resonant impedance of your tuned
circuit. But if you tap down too far, you will need to retune the
loopstick for each station.

Experiment with taps or secondary windings. Alternatively, you could put
a larger fixed cap in series with your 365 pF at the earthy end, and
connect across it to the antenna socket. You might try a number of
values from 1000 pF upwards.

 

[Robert Scott]

Any idea the best way to couple a ferrite loopstick antenna
to a car radio input for AM reception?

Why bother with "best", unless you mean "easiest". There is no sense
in trying to improve sensitivity beyond the point where you can hear
the background RF noise. And on the AM band there is a lot of it.
The radio itself is probably already doing as well as it can using
selectivity to limit background noise. So if you connect the
loopstick antenna any way at all that produces enough signal to hear
the background hiss, then that is good enough, and no further overall
improvement can be had by improved impedance matching or tuning. To
check if your connection is adequate, just turn up the volume until
you hear a good deal of hiss, while tuned to a frequency where there
is no local station. Then disconnect the antenna completely. If the
hiss drops to almost nothing, then you have as good an antenna as is
possible. But if the hiss remains the same or drops only a little,
then that hiss is coming from the radio itself, and a better antenna
match could improve things.


-Robert Scott
Ypsilanti, Michigan

 

[Joerg]

Hello Bill,

The tuning is very broad and I don't get much of a peak
when adjusting the capacitor, but all the local stations
come in.

Hard to guess from the distance. Most likely your ferrite antenna is
fine but the impedance of the radio is a bit low. That loads down the LC
circuit formed by your ferrite coil and capacitor, reducing its Q and
thus making the tuning "broad".

I am afraid you need a FET follower at the antenna, to provide a Hi-Z to
the ferrite antenna and a lower Z to the cable that goes into the radio.

Regards, Joerg

 

[Joerg]

Hello Graham,

You still listen to AM ! ?

I think Bill lives in the US. Out here AM is very much alive and
kicking. While on the long drive to the airport I listen to it all the
time. Same when doing some "real" hardware in the shop.

Regards, Joerg

 

[Michael A. Terrell]

IIRC the normal approach if you wish to make it tuneable is to have a
large winding which is tuned with the cap, and a smaller winding with
less turns, so there is an impedance transformation.

I suspect very much depends on the device used as the front end -
whether it is a high Z fet or a lower impedance device.

It sounds like the Q is low if the tuning is broad, but do you really
want the hassle of returning the capacitor every time?

Car radios used to be designed for a 93 ohm input impedance, and
already has a tuned front end. Unless there is something to buffer the
tuned antenna, you will detune the existing front end circuit. The whip
"Antenna is really a RF probe fed to the top end of the tuned circuit.
Good designs used a variable cap in the circuit to null out the cable
capacitance's effects on the tuned circuit. You tuned the radio to a
station near 1300 KHz and adjusted it for peak reception. I could scan
the input circuit from one of the old Sams AR series car radio manuals
and post it on ABSE if anyone wants to see it.

 

[[email protected]]

You still listen to AM ! ?
I used to listen to FM music when I was a teenager, but nowadays, I
just listen to right wing AM talk shows:

Michael Savage
Larry Elder
Rush Limbaugh
Shawn Hannidy
Michael Medvits
Dennis Prager
Al Rantell
Bill Handle
etc.

 

[Ross Herbert]

Any idea the best way to couple a ferrite loopstick antenna
to a car radio input for AM reception?

I experimeted using a 6 inch loopstick (230uH) and 365pF
parallel tunning cap from antenna input to ground (chassis)
with reasonable results, but I'm wondering what the best
approach is.

The tuning is very broad and I don't get much of a peak
when adjusting the capacitor, but all the local stations
come in.

How should I wind the loopstick for best results?

-Bill

Why?

Doesn't your normal car antenna do this already? It does on my car
radio.

Most cars since around 1992 use diversity antenna's which work better
for AM reception. If your car has a rear window heater it may also
double as an AM antenna.

I would also think that trying to use an add-on ferrite loopstick
antenna would allow pick-up of all sorts of local interference coming
from car ignitions etc. And it would also be directional thus making
sensitivity dependant on orientation to the transmitter while driving.

 

[Pooh Bear]

Hello Graham,


I think Bill lives in the US. Out here AM is very much alive and
kicking. While on the long drive to the airport I listen to it all the
time. Same when doing some "real" hardware in the shop.

It's so, so different over here.

The AM band has been virtually abandoned.

The FM band has whole MHz worth of bandwidth hi-jacked by the BBC so as to
provide nationwide coverage but it strikes me as over-kill. Each BBC FM
service uses about 2 MHz. I can often pick up one of their stations on 3
different frequencies. E.g. I can get Radio 4 on 93, 93.2 and 93.5 MHz.

Stupid regulations intended to ensure breadth of programming simply mean
that most commercial stations are virtual clones of each other with bland
look-alike programming. In a similar vein 'narrow-casting' is discouraged,
the only 2 stations offering a unique and specialised programming style
being Jazz FM and Classic FM. There's no 'rock channel' at all ! Oh - and
BBC's Radio 3 already offers a full classical music service anyway.

No shortage of phone-ins to let the local retards spout off about rubbish
though !

BBC's Radio 1 which is their 'contemporary music' channel plays the kind
of stuff that you'd expect to hear at the kids' dance raves mainly ( and
almost exclusively - to the extent that a spokesman for that channel once
stated that they weren't intereted in an audience aged over 25 ? ) whilst
their Radio 2 offers MOR for oldies that's 80s weighted - Yuk.

No wonder that pirating is popular in London.

A really screwed up radio service here.

Graham

 

[Joerg]

Hello Graham,

The AM band has been virtually abandoned.

Sad. Maybe it can be revived with some local stations.

FM is bland here as well. IMHO that is because of conglomeration, large
companies owning a whole slew of stations and "adjusting" the music to
mainstream, the same songs over and over. But the local ones is where
you can occasionally find the real blue grass or old style country. AM
is a bit better, lots of ethnic broadcasts but don't count on
understanding the languages.

AM talk radio is popular here, mostly conservative. Some of it has
pretty good quality content so I listen to that once in a while.
Surprisingly most of the contractors seem to listen to it as well when
on a remote job. Also, the driving distances are huge out here. When you
are going clear across a place like Nevada AM is the only thing that
really works in many areas. Actually, when I drove in north eastern
Scotland in the 80's it was similar. Not many FM stations but this was
in an old Ford Cortina with a weak radio.

Regards, Joerg

 

[[email protected]]

Why?

Doesn't your normal car antenna do this already? It does on my car
radio.

The radio is used indoors, not in the car.

Most cars since around 1992 use diversity antenna's which work better
for AM reception. If your car has a rear window heater it may also
double as an AM antenna.

I would also think that trying to use an add-on ferrite loopstick
antenna would allow pick-up of all sorts of local interference coming
from car ignitions etc. And it would also be directional thus making
sensitivity dependant on orientation to the transmitter while driving.

Yes, I want it to be directional so I can null out
strong stations adjacient to weak ones I want to hear.

-Bill

 

[Mark]

try a tap on the coil to create a lower z output to feed to the
radio...

or a small C coupling to the radio from the top of the coil.

A "real" whip anteanna on a car looks like a capacitor at AM
frequencies.

Mark

 

[Glenn Gundlach]

I used to listen to FM music when I was a teenager, but nowadays, I
just listen to right wing AM talk shows:

Michael Savage
Larry Elder
Rush Limbaugh
Sean Hannity <<
Michael Medved <<
Dennis Prager
Al Rantel <<
Bill Handle
etc.

You forgot Hugh Hewitt.

The first 6 are nationally syndicated. I don't think Al or Bill are so
you must be in the LA area, Right ? (I fixed your spelling)
GG

 

[Jim Thompson]

You forgot Hugh Hewitt.

The first 6 are nationally syndicated. I don't think Al or Bill are so
you must be in the LA area, Right ? (I fixed your spelling)
GG

While Bill Handle (Handle on the Law) is on KFYI, I would hardly class
him as right wing... just seems to be really savvy about law.

Actually Handle is the only one on the list that I listen to.

Mornings, I listen to Barry Young (here in Phoenix), then I switch to
Air America just for groans and to keep the "canal" cleaned out ;-)

...Jim Thompson

 

[Mike]

Any idea the best way to couple a ferrite loopstick antenna
to a car radio input for AM reception?

I experimeted using a 6 inch loopstick (230uH) and 365pF
parallel tunning cap from antenna input to ground (chassis)
with reasonable results, but I'm wondering what the best
approach is.

The tuning is very broad and I don't get much of a peak
when adjusting the capacitor, but all the local stations
come in.

How should I wind the loopstick for best results?

-Bill

I bought this new microwave oven that trashes every AM radio in the
house while it's running, So I built a Shielded loopstick antenna for
my old RCA Radiola. It is untuned, Faraday shielded, and I used a
mosfet amplifier with the drain capacitor coupled to the external ant
input to the set. No impedance matching to speak of, but it works
really well! No noise from the microwave and it picks up more stations
than I care to listen to.

Mike

 

[[email protected]]

You forgot Hugh Hewitt.

you must be in the LA area, Right ?

Yes, I'm in the LA area, I can walk to Disneyland.
I have a year round pass.

I forgot a couple others in addition to Hewitt.

Kevin James late at night on KABC.
Also, Doug McIntyre and Bill O'Reilly
in the morning on KABC.

-Bill

 

[Keith Williams]

I used to listen to FM music when I was a teenager, but nowadays, I
just listen to right wing AM talk shows:

Michael Savage
Larry Elder

Didn't know he had a radio show.

Rush Limbaugh
Shawn Hannidy

Hannity - like the TV show, not the radio version

Michael Medvits

Medved - not my style.

Dennis Prager

Didn't know he had a show either.

Al Rantell
?

Bill Handle
etc.

G. Gordon Liddy
And don't forget Phil Hendrie. ;-)

I've become hooked on Bill Bennet's "Morning in America". XM dropped
the show 9/1 so I had do buy a subscription (via the internet) and an
MP3 player with an FM modulator to get my daily fix. :-(

 

[[email protected]]

I read in sci.electronics.design that [email protected] wrote (in


You need to tap down the coil or wind a secondary winding on the rod.
The car radio antenna input is a lowish impedance, not 50 ohms or
anything like, but much lower than the resonant impedance of your tuned
circuit. But if you tap down too far, you will need to retune the
loopstick for each station.

Experiment with taps or secondary windings. Alternatively, you could put
a larger fixed cap in series with your 365 pF at the earthy end, and
connect across it to the antenna socket. You might try a number of
values from 1000 pF upwards.

Yes, a separate short winding on the loopstick improves operation. The
main winding is about 80 turns, and I added another winding of about 20
turns feeding the antenna input. I get a sharp peak on weak stations,
and it picks up stations I can't get in the car, so it seems to be
working better than the normal car radio setup.

There are 8 tunable coils inside the radio which is a Ford modle from
1980s. I tried tuning a couple coils near the antenna input, hoping to
improve it further, but didn't have much effect.

I might try adding or subtracting a few turns from the secondary
winding to see if I can improve it further.

-Bill