Coil
 

Is their a set rule on how meny turns of the antenna coil is to the
tuneing coil? And would it depend on if you wind it over or next to the
tuneing coil?

Bill Hennessy wrote:

Is their a set rule on how meny turns of the antenna coil is to the
tuneing coil? And would it depend on if you wind it over or next to the
tuneing coil?

Yes, it makes a difference if it's over vs. next to the tuning coil,
because your coupling will change with distance.

No there isn't a set rule (or shouldn't be) -- you should design your
transformer for the desired input impedance of the devices you're going
into, the intended input impedance of your radio, etc., etc.

Ideally you'd decide on what kind of noise & intermodulation performance
you wanted from your set, decide what impedance your 1st stage should
see, and design your antenna coil from that.

Realistically you can just look for similar radios to the one you're
wanting to build and use an average of their input coils as a starting
point, then dink with it if you feel motivated.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Bill Hennessy wrote:

Is their a set rule on how meny turns of the antenna coil is to the
tuneing coil? And would it depend on if you wind it over or next to the
tuneing coil?

Yes, it makes a difference if it's over vs. next to the tuning coil,
because your coupling will change with distance.

No there isn't a set rule (or shouldn't be) -- you should design your
transformer for the desired input impedance of the devices you're going
into, the intended input impedance of your radio, etc., etc.

Ideally you'd decide on what kind of noise & intermodulation performance
you wanted from your set, decide what impedance your 1st stage should
see, and design your antenna coil from that.

Realistically you can just look for similar radios to the one you're
wanting to build and use an average of their input coils as a starting
point, then dink with it if you feel motivated.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

"Bill Hennessy" wrote
Is their a set rule on how meny turns of the antenna coil is to the
tuneing coil? And would it depend on if you wind it over or next to the
tuneing coil?

=================================

There are no rules except normal network analysis rules.

The generator is the antenna with its internal impedance Ra - jXa.

Generator volts is field strength times effective height of antenna.

The primary coil has optimum inductance when it resonates with -Xa.

The secondary coil inductance resonates with its parallel tuning capacitor
at the same frequency.

The coefficient of coupling beween the two coils is set to its optimum value
of -

K = 1 / Sqrt( Q1 * Q2 ) or somewhat greater.

where Q1 is the primary circuit Q taking antenna resistance Ra into account,
and Q2 is the Q of the secondary circuit coil.

So everything depends on frequency, antenna length, ground loss resistance,
coil Q, coupling coefficient, and value of tuning capacitor. The
calculations are quite simple.

For the medium waves and a 40 feet antenna, the primary coil has a
wave-winding of many turns spaced a little apart from the secondary coil.
The coupling is fairly loose, K about 0.1

The secondary coil is wound on the same former and is usually a
single-layer, high Q solenoid. But everything is very non-critical and
almost anything will work. Over the wide medium wave band it is impossible
to keep anything near optimum. Just find some wire and start winding.
----
Reg, G4FGQ

"Bill Hennessy" wrote
Is their a set rule on how meny turns of the antenna coil is to the
tuneing coil? And would it depend on if you wind it over or next to the
tuneing coil?

=================================

There are no rules except normal network analysis rules.

The generator is the antenna with its internal impedance Ra - jXa.

Generator volts is field strength times effective height of antenna.

The primary coil has optimum inductance when it resonates with -Xa.

The secondary coil inductance resonates with its parallel tuning capacitor
at the same frequency.

The coefficient of coupling beween the two coils is set to its optimum value
of -

K = 1 / Sqrt( Q1 * Q2 ) or somewhat greater.

where Q1 is the primary circuit Q taking antenna resistance Ra into account,
and Q2 is the Q of the secondary circuit coil.

So everything depends on frequency, antenna length, ground loss resistance,
coil Q, coupling coefficient, and value of tuning capacitor. The
calculations are quite simple.

For the medium waves and a 40 feet antenna, the primary coil has a
wave-winding of many turns spaced a little apart from the secondary coil.
The coupling is fairly loose, K about 0.1

The secondary coil is wound on the same former and is usually a
single-layer, high Q solenoid. But everything is very non-critical and
almost anything will work. Over the wide medium wave band it is impossible
to keep anything near optimum. Just find some wire and start winding.
----
Reg, G4FGQ