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From: Joerg on 14 Sep 2005 10:31
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

http://www.analogconsultants.com
From: Joerg on 14 Sep 2005 10:33
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

http://www.analogconsultants.com
From: Michael A. Terrell on 14 Sep 2005 15:48
Dave wrote:
>
> wrongaddress(a)att.net wrote:
> > 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?

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.


--
?

Michael A. Terrell
Central Florida
From: wrongaddress on 14 Sep 2005 22:15
>> You still listen to AM ! ?
>> Awesome.

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.

From: Pooh Bear on 15 Sep 2005 00:53

Joerg wrote:

> 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.

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

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