"Brian Howie" wrote in message
...

I've a 5 foot Octagonal loop for MF. The shield is copper water pipe, with
a gap , 7 turns inside plus a coupling winding. It does a good job
eliminating local noise (mostly ASDL hash from the phone lines) compared
with a vertical. However the capacitance between the shield and turns
seems to load it quite a bit meaning I can't get the tuning range I'd
like.

Brian GM4DIJ
--
Brian Howie
Hi
My own experience is that ,at least for receive, multi turn loops are
useless.
Instead you can use a single turn one with a good coil in serial.
The tuning range for a given variable capacitor is much greater
especially if ,at low frequency, the coil is using ferrite .
Switching the coil can increase the tuning range easily.
The coil, with a secondary winding,is also very useful to
adjust the coupling to the receiver.

In message , bilou
writes

"Brian Howie" wrote in message
...

I've a 5 foot Octagonal loop for MF. The shield is copper water pipe, with
a gap , 7 turns inside plus a coupling winding. It does a good job
eliminating local noise (mostly ASDL hash from the phone lines) compared
with a vertical. However the capacitance between the shield and turns
seems to load it quite a bit meaning I can't get the tuning range I'd
like.

Brian GM4DIJ
--
Brian Howie
Hi
My own experience is that ,at least for receive, multi turn loops are
useless.
Instead you can use a single turn one with a good coil in serial.
The tuning range for a given variable capacitor is much greater
especially if ,at low frequency, the coil is using ferrite .
Switching the coil can increase the tuning range easily.
The coil, with a secondary winding,is also very useful to
adjust the coupling to the receiver.

I'd have thought I'd get a better signal from more turns, but maybe
better coupling and a higher Q from your suggestion would do the same.

Brian
--
Brian Howie

On 10/19/2015 3:34 AM, Brian Howie wrote:
In message , bilou
writes

"Brian Howie" wrote in message
...

I've a 5 foot Octagonal loop for MF. The shield is copper water pipe,
with
a gap , 7 turns inside plus a coupling winding. It does a good job
eliminating local noise (mostly ASDL hash from the phone lines) compared
with a vertical. However the capacitance between the shield and turns
seems to load it quite a bit meaning I can't get the tuning range I'd
like.

Brian GM4DIJ
--
Brian Howie
Hi
My own experience is that ,at least for receive, multi turn loops are
useless.
Instead you can use a single turn one with a good coil in serial.
The tuning range for a given variable capacitor is much greater
especially if ,at low frequency, the coil is using ferrite .
Switching the coil can increase the tuning range easily.
The coil, with a secondary winding,is also very useful to
adjust the coupling to the receiver.

I'd have thought I'd get a better signal from more turns, but maybe
better coupling and a higher Q from your suggestion would do the same.

I can't imagine why more turns won't help a receiving loop. I guess it
depends on what is limiting reception. Adding a coil may improve the Q
or it make make it worse depending on the Q of the coil. More turns
won't help the Q of a receiving loop, other than reducing the
significance of the resistance of connections and other components.
More turns *will* increase the signal strength.

How does the coil affect the tuning range of the cap? A cap is limited
by the ratio of the minimum to maximum capacitance. The ratio of
frequency is limited to the same ratio.

--

Rick

"rickman" wrote in message
...
On 10/19/2015 3:34 AM, Brian Howie wrote:
How does the coil affect the tuning range of the cap? A cap is limited by
the ratio of the minimum to maximum capacitance. The ratio of frequency
is limited to the same ratio.
In a multiturn loop you get huge capacitance between turns.
For a given variable capacitor it appears in parallel.
The Q of that big coil might be higher but as you need to add
fixed capacitors to the variable one to get useful tuning range
you loose almost what you gain.
I saw descriptions using a 128 pairs telephone cable and spending
several days to wire it as a 256 turns loop.
A bad idea IMHO.

On 10/19/2015 3:50 PM, bilou wrote:
"rickman" wrote in message
...
On 10/19/2015 3:34 AM, Brian Howie wrote:
How does the coil affect the tuning range of the cap? A cap is limited by
the ratio of the minimum to maximum capacitance. The ratio of frequency
is limited to the same ratio.
In a multiturn loop you get huge capacitance between turns.
For a given variable capacitor it appears in parallel.
The Q of that big coil might be higher but as you need to add
fixed capacitors to the variable one to get useful tuning range
you loose almost what you gain.

I sort of lost the thought here. If you up the inductance of the loop,
it lowers the required tuning capacitance, so why would fixed capacitors
be needed? Are you saying the parasitic capacitance of the loop is
enough to significantly reduce the tuning range of the variable cap?
Maybe, but there are construction methods that minimize the parasitic
capacitance of multi-turn loops. Wide spacing is important. I've seen
spiral loops wound on wooden frames that look like God's Eyes, very
attractive.


I saw descriptions using a 128 pairs telephone cable and spending
several days to wire it as a 256 turns loop.
A bad idea IMHO.

I'm not sure what problem you would be trying to solve by using a 256
turn loop. There are middle grounds...

--

Rick

On 10/19/2015 10:53 PM, rickman wrote:
On 10/19/2015 3:50 PM, bilou wrote:
"rickman" wrote in message
...
On 10/19/2015 3:34 AM, Brian Howie wrote:
How does the coil affect the tuning range of the cap? A cap is
limited by
the ratio of the minimum to maximum capacitance. The ratio of frequency
is limited to the same ratio.
In a multiturn loop you get huge capacitance between turns.
For a given variable capacitor it appears in parallel.
The Q of that big coil might be higher but as you need to add
fixed capacitors to the variable one to get useful tuning range
you loose almost what you gain.

I sort of lost the thought here. If you up the inductance of the loop,
it lowers the required tuning capacitance, so why would fixed capacitors
be needed? Are you saying the parasitic capacitance of the loop is
enough to significantly reduce the tuning range of the variable cap?
Maybe, but there are construction methods that minimize the parasitic
capacitance of multi-turn loops. Wide spacing is important. I've seen
spiral loops wound on wooden frames that look like God's Eyes, very
attractive.


I saw descriptions using a 128 pairs telephone cable and spending
several days to wire it as a 256 turns loop.
A bad idea IMHO.

I'm not sure what problem you would be trying to solve by using a 256
turn loop. There are middle grounds...


Often a 60kHz WWVB time receiver.

Mikek

On 10/20/2015 10:44 AM, amdx wrote:
On 10/19/2015 10:53 PM, rickman wrote:
On 10/19/2015 3:50 PM, bilou wrote:
"rickman" wrote in message
...
On 10/19/2015 3:34 AM, Brian Howie wrote:
How does the coil affect the tuning range of the cap? A cap is
limited by
the ratio of the minimum to maximum capacitance. The ratio of
frequency
is limited to the same ratio.
In a multiturn loop you get huge capacitance between turns.
For a given variable capacitor it appears in parallel.
The Q of that big coil might be higher but as you need to add
fixed capacitors to the variable one to get useful tuning range
you loose almost what you gain.

I sort of lost the thought here. If you up the inductance of the loop,
it lowers the required tuning capacitance, so why would fixed capacitors
be needed? Are you saying the parasitic capacitance of the loop is
enough to significantly reduce the tuning range of the variable cap?
Maybe, but there are construction methods that minimize the parasitic
capacitance of multi-turn loops. Wide spacing is important. I've seen
spiral loops wound on wooden frames that look like God's Eyes, very
attractive.


I saw descriptions using a 128 pairs telephone cable and spending
several days to wire it as a 256 turns loop.
A bad idea IMHO.

I'm not sure what problem you would be trying to solve by using a 256
turn loop. There are middle grounds...


Often a 60kHz WWVB time receiver.

So why would that be a "bad idea"?

--

Rick

In message , rickman
writes
On 10/19/2015 3:34 AM, Brian Howie wrote:
In message , bilou
writes

"Brian Howie" wrote in message
...

I've a 5 foot Octagonal loop for MF. The shield is copper water pipe,
with
a gap , 7 turns inside plus a coupling winding. It does a good job
eliminating local noise (mostly ASDL hash from the phone lines) compared
with a vertical. However the capacitance between the shield and turns
seems to load it quite a bit meaning I can't get the tuning range I'd
like.

Brian GM4DIJ
--
Brian Howie
Hi
My own experience is that ,at least for receive, multi turn loops are
useless.
Instead you can use a single turn one with a good coil in serial.
The tuning range for a given variable capacitor is much greater
especially if ,at low frequency, the coil is using ferrite .
Switching the coil can increase the tuning range easily.
The coil, with a secondary winding,is also very useful to
adjust the coupling to the receiver.

I'd have thought I'd get a better signal from more turns, but maybe
better coupling and a higher Q from your suggestion would do the same.

I can't imagine why more turns won't help a receiving loop. I guess it
depends on what is limiting reception. Adding a coil may improve the Q
or it make make it worse depending on the Q of the coil. More turns
won't help the Q of a receiving loop, other than reducing the
significance of the resistance of connections and other components.
More turns *will* increase the signal strength.

How does the coil affect the tuning range of the cap? A cap is limited
by the ratio of the minimum to maximum capacitance. The ratio of
frequency is limited to the same ratio.


The capacitance of the loop to the screen meant that at the minimum
variable C setting ,I couldn't get the maximum frequency of about
500KHz I wanted, so I had to take turns off. I now need more parallel C
to tune the look down to 136KHz.

Brian



--
Brian Howie

On 10/21/2015 2:18 AM, Brian Howie wrote:
In message , rickman writes
On 10/19/2015 3:34 AM, Brian Howie wrote:
In message , bilou
writes

"Brian Howie" wrote in message
...

I've a 5 foot Octagonal loop for MF. The shield is copper water pipe,
with
a gap , 7 turns inside plus a coupling winding. It does a good job
eliminating local noise (mostly ASDL hash from the phone lines)
compared
with a vertical. However the capacitance between the shield and turns
seems to load it quite a bit meaning I can't get the tuning range I'd
like.

Brian GM4DIJ
--
Brian Howie
Hi
My own experience is that ,at least for receive, multi turn loops are
useless.
Instead you can use a single turn one with a good coil in serial.
The tuning range for a given variable capacitor is much greater
especially if ,at low frequency, the coil is using ferrite .
Switching the coil can increase the tuning range easily.
The coil, with a secondary winding,is also very useful to
adjust the coupling to the receiver.

I'd have thought I'd get a better signal from more turns, but maybe
better coupling and a higher Q from your suggestion would do the same.

I can't imagine why more turns won't help a receiving loop. I guess
it depends on what is limiting reception. Adding a coil may improve
the Q or it make make it worse depending on the Q of the coil. More
turns won't help the Q of a receiving loop, other than reducing the
significance of the resistance of connections and other components.
More turns *will* increase the signal strength.

How does the coil affect the tuning range of the cap? A cap is
limited by the ratio of the minimum to maximum capacitance. The ratio
of frequency is limited to the same ratio.


The capacitance of the loop to the screen meant that at the minimum
variable C setting ,I couldn't get the maximum frequency of about
500KHz I wanted, so I had to take turns off. I now need more parallel C
to tune the look down to 136KHz.

Wow, that loop must have a *lot* of capacitance. Is there a way to
space the conductors away from the copper tubing in the run?

I'm curious why you would use copper pipe for the shield. Because it
provides both shield and support? I guess there are a million ways to
build a shielded loop. I like the idea of using coax, but I don't know
if that also has serious limitations from the capacitance between loop
conductor and shield.

--

Rick

In message , rickman
writes

The capacitance of the loop to the screen meant that at the minimum
variable C setting ,I couldn't get the maximum frequency of about
500KHz I wanted, so I had to take turns off. I now need more parallel C
to tune the look down to 136KHz.

Wow, that loop must have a *lot* of capacitance. Is there a way to
space the conductors away from the copper tubing in the run?

Not easy

I'm curious why you would use copper pipe for the shield. Because it
provides both shield and support? I guess there are a million ways to
build a shielded loop. I like the idea of using coax, but I don't know
if that also has serious limitations from the capacitance between loop
conductor and shield.


It seemed a good idea at the time. The original design used plastic pipe
covered with tin-foil ,but I wanted something that would survive a
Scottish winter outdoors.

PVC 4-7 Loop Antenna Al Burzynski KA5JGV ( it's on the NDB yahoo group)

it used 12 turns. I think the use of plastic pipe and external tinfoil
reduces the C.

My loop does work quite well, and has survived outdoors but I think it
could be improved

Brian



--
Brian Howie