Driver to drive?

[Martin Brown]

On 17/03/2017 09:35, tabbypurr@gmail.com wrote:

On Friday, 17 March 2017 03:56:37 UTC, David Eather wrote:
On Fri, 17 Mar 2017 13:56:13 +1000, David Eather <eather@tpg.com.au> wrote:
On Wed, 15 Mar 2017 22:39:48 +1000, <tabbypurr> wrote:
On Wednesday, 15 March 2017 12:10:36 UTC, Martin Brown wrote:
On 14/03/2017 13:58, tabbypurr wrote:
On Tuesday, 14 March 2017 09:22:05 UTC, Martin Brown wrote:

There used to be old school analogue function generator chips that
made a triangle wave and then applied diode shaping to get a
pseudo-sine wave. HP made one design implementation that was
surprisingly good. Intersils 8038 was the poor mans alternative for
DIY.


http://www.intersil.com/content/dam/intersil/documents/icl8/icl8038.pdf


I built one of those decades ago. What a car crash. The wave forms
were hopeless. I don't remember the details to know why, I presume
the problem was the 8038 though.

It was never anything like as good as a Wein bridge sine wave but it
was
good for about 0.5% THD if you trimmed it properly. I suspect
manufacturing tolerances made it inconsistent batch to batch.

Cute chip in its day, but that was a long time ago.

I doubt it managed 50%, let alone 0.5%. It had 3 outputs, sine square &
triangle. At some frequencies one output looked more like one of the
others should, and the others were just a mess. It was dire, and yes I
followed the advised circuit. It might manage 0.5% at some frequency,
but as a sig gen it was a real failure. If I ever get the time I'll
look at it again one day, it's on a shelf somewhere.

there were a few kits designed with it - they really did manage 0.5%

Presumably they used only part of its frequency range.

Yes. It was fine up to around 20kHz but at higher frequencies the
triangle wave linearity degraded taking down the sine wave with it.

You had to work at the waveform symmetry to get 0.5% but <1% was easy.

--
Regards,
Martin Brown

 

[DemonicTubes]

What are some modern equivalents to the XR2206 and ICL8038? Other than already soldered into ebay junk, they are non-stocked/obsolete/discontinued...Surely we have something cheaper-faster-better now?

 

[DemonicTubes]

On Friday, March 17, 2017 at 8:27:59 AM UTC-6, John Larkin wrote:

On Thu, 16 Mar 2017 17:36:12 -0700 (PDT), Phil Allison
pallison49@gmail.com> wrote:

George Herold wrote:



I've got an AM radio that came with an air core antenna.
(1990's vintage)
~4" (10 cm) squarish loop. Not sure how many turns.
Works fine.


** So it's an external loop for a main powered receiver ?

Right, It's a JVC "ultra compact component system"
FS-1000


** So why didn't you post that info before?

It's a fucking frame antenna, already discussed here in this thread and been around since the dawn of radio.



Knowing almost nothing about AM, (and assuming I don't care about price.)
I figure I want the highest Q possible on the front end..


** Nope.

You need at least 10kHz of bandwidth at the antenna so the Q must not exceed 50 to 100 across the AM band. You will find that antenna has a fairly low Q in practice.



You need to learn how to post unambiguously too.

IOW not smartarse style like Larkin.

Larkin is great,

** Larkin is a smug pig and a troll.

He is so narcissistic he thinks he owns the NG and everyone on it.



Hey, if anybody wants Allison, you can gave him cheap. As-is, Free
shipping.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

That reminds me...anybody else notice DecadentLinuxUserNumeroUno suddenly went silent some time last summer?

 

On Wednesday, March 15, 2017 at 12:18:38 AM UTC-4, Bill Bowden wrote:

Which is a better design. Suppose you have a 6 inch length of PVC pipe with
numerous turns of wire that has an inductance of say 200uH. Now suppose you
use the same (6 inch) piece of PVC with a ferrite rod in the core with
considerably fewer turns of wire. Which one would capture the most signal
at the AM Broadcast frequencies (500K to 2 Megs) and poduce the greatest
signal output? Would it be more ferrite, or more wire?

There are many variables you're not considering, but maybe this will spark
some ideas.

AIUI, in a uniform magnetic field (such as far from a radio transmitting
source), a loop antenna produces a voltage proportional to the area the
loop encloses. A ferrite rod will increase a loop's effective area by a
factor equal to the effective permeability of the ferrite rod.

So, a 8mm^2 loop wound on a core with an effective permeability of 50
produces the same output voltage as an 400mm^2 loop with no core.

The effective permeability of a ferrite rod, in turn, is mostly a property
of its length-to-diameter ratio.

e.g.,

http://caves.org/section/commelect/mm/mm04.html

Coil geometry also affects a rod's effective permeability. Highest
effective mu is attained by short coils, in the center of the rod.

e.g. Fig. 1,
makearadio.com/tech/files/Ferrite_Rod_Inductance.pdf


Cheers,
James Arthur

 

[John Larkin]

On Thu, 16 Mar 2017 17:36:12 -0700 (PDT), Phil Allison
<pallison49@gmail.com> wrote:

George Herold wrote:



I've got an AM radio that came with an air core antenna.
(1990's vintage)
~4" (10 cm) squarish loop. Not sure how many turns.
Works fine.


** So it's an external loop for a main powered receiver ?

Right, It's a JVC "ultra compact component system"
FS-1000


** So why didn't you post that info before?

It's a fucking frame antenna, already discussed here in this thread and been around since the dawn of radio.



Knowing almost nothing about AM, (and assuming I don't care about price.)
I figure I want the highest Q possible on the front end..


** Nope.

You need at least 10kHz of bandwidth at the antenna so the Q must not exceed 50 to 100 across the AM band. You will find that antenna has a fairly low Q in practice.



You need to learn how to post unambiguously too.

IOW not smartarse style like Larkin.

Larkin is great,

** Larkin is a smug pig and a troll.

He is so narcissistic he thinks he owns the NG and everyone on it.

Hey, if anybody wants Allison, you can gave him cheap. As-is, Free
shipping.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[John Larkin]

On Thu, 16 Mar 2017 18:46:06 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Thursday, March 16, 2017 at 8:36:16 PM UTC-4, Phil Allison wrote:
George Herold wrote:



I've got an AM radio that came with an air core antenna.
(1990's vintage)
~4" (10 cm) squarish loop. Not sure how many turns.
Works fine.


** So it's an external loop for a main powered receiver ?

Right, It's a JVC "ultra compact component system"
FS-1000


** So why didn't you post that info before?

'cos I'm now at home and not at work.
It's a fucking frame antenna, already discussed here in this thread and been around since the dawn of radio.



Knowing almost nothing about AM, (and assuming I don't care about price.)
I figure I want the highest Q possible on the front end..


** Nope.

You need at least 10kHz of bandwidth at the antenna so the Q must not exceed 50 to 100 across the AM band. You will find that antenna has a fairly low Q in practice.
OK I was thinking of best signal to noise, and figuring that ~1-2 kHz would
be enough.. Everyones "best/ optimal" is a bit different.

An AM antenna doesn't need to be tuned at all. An untuned coil will
snoop the ambient h-field.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

That reminds me...anybody else notice DecadentLinuxUserNumeroUno
suddenly went silent some time last summer?

Yeah, we talked about it a couple of months afterwards, but iirc nobody turned up any leads.

Cheers

Phil Hobbs

 

[rickman]

On 3/17/2017 5:35 AM, tabbypurr@gmail.com wrote:

On Friday, 17 March 2017 03:56:37 UTC, David Eather wrote:
On Fri, 17 Mar 2017 13:56:13 +1000, David Eather <eather@tpg.com.au> wrote:
On Wed, 15 Mar 2017 22:39:48 +1000, <tabbypurr> wrote:
On Wednesday, 15 March 2017 12:10:36 UTC, Martin Brown wrote:
On 14/03/2017 13:58, tabbypurr wrote:
On Tuesday, 14 March 2017 09:22:05 UTC, Martin Brown wrote:

There used to be old school analogue function generator chips that
made a triangle wave and then applied diode shaping to get a
pseudo-sine wave. HP made one design implementation that was
surprisingly good. Intersils 8038 was the poor mans alternative for
DIY.


http://www.intersil.com/content/dam/intersil/documents/icl8/icl8038.pdf


I built one of those decades ago. What a car crash. The wave forms
were hopeless. I don't remember the details to know why, I presume
the problem was the 8038 though.

It was never anything like as good as a Wein bridge sine wave but it
was
good for about 0.5% THD if you trimmed it properly. I suspect
manufacturing tolerances made it inconsistent batch to batch.

Cute chip in its day, but that was a long time ago.

I doubt it managed 50%, let alone 0.5%. It had 3 outputs, sine square &
triangle. At some frequencies one output looked more like one of the
others should, and the others were just a mess. It was dire, and yes I
followed the advised circuit. It might manage 0.5% at some frequency,
but as a sig gen it was a real failure. If I ever get the time I'll
look at it again one day, it's on a shelf somewhere.


NT

there were a few kits designed with it - they really did manage 0.5%

Presumably they used only part of its frequency range.

Yeah, the audio portion.

--

Rick C

 

[Phil Hobbs]

On 03/17/2017 11:28 AM, George Herold wrote:

On Friday, March 17, 2017 at 10:30:32 AM UTC-4, John Larkin wrote:
On Thu, 16 Mar 2017 18:46:06 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Thursday, March 16, 2017 at 8:36:16 PM UTC-4, Phil Allison wrote:
George Herold wrote:



I've got an AM radio that came with an air core antenna.
(1990's vintage)
~4" (10 cm) squarish loop. Not sure how many turns.
Works fine.


** So it's an external loop for a main powered receiver ?

Right, It's a JVC "ultra compact component system"
FS-1000


** So why didn't you post that info before?

'cos I'm now at home and not at work.
It's a fucking frame antenna, already discussed here in this thread and been around since the dawn of radio.



Knowing almost nothing about AM, (and assuming I don't care about price.)
I figure I want the highest Q possible on the front end..


** Nope.

You need at least 10kHz of bandwidth at the antenna so the Q must not exceed 50 to 100 across the AM band. You will find that antenna has a fairly low Q in practice.
OK I was thinking of best signal to noise, and figuring that ~1-2 kHz would
be enough.. Everyones "best/ optimal" is a bit different.

An AM antenna doesn't need to be tuned at all. An untuned coil will
snoop the ambient h-field.
I guess that's right. As long as most of the noise is "in the air" it doesn't
really matter where the band pass filter is. (Except for dynamic range issues.)

As you say, dynamic range. An untuned input needs a stronger mixer. A
Q of 10 or 20 would help a lot.

On the other hand, one could just use a Mini Circuits mixer with a +17
dBm LO, or a nice analogue mux with square wave drive. It takes a lot
to screw one of those up.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[Martin Brown]

On 17/03/2017 15:55, DemonicTubes wrote:

What are some modern equivalents to the XR2206 and ICL8038? Other
than already soldered into ebay junk, they are
non-stocked/obsolete/discontinued...Surely we have something
cheaper-faster-better now?

Hobby kits using the XR2206 are still available but they have been
largely out evolved by DDS chips and fast DACs. eg.

https://www.amazon.co.uk/TOOGOO-1HZ-500KHz-Function-Generator-Triangle/dp/B015X7OJT2/

No idea if that one is any good or not.

--
Regards,
Martin Brown

 

[bitrex]

On 03/16/2017 08:36 PM, Phil Allison wrote:

George Herold wrote:



I've got an AM radio that came with an air core antenna.
(1990's vintage)
~4" (10 cm) squarish loop. Not sure how many turns.
Works fine.


** So it's an external loop for a main powered receiver ?

Right, It's a JVC "ultra compact component system"
FS-1000


** So why didn't you post that info before?

It's a fucking frame antenna, already discussed here in this thread and been around since the dawn of radio.



Knowing almost nothing about AM, (and assuming I don't care about price.)
I figure I want the highest Q possible on the front end..


** Nope.

You need at least 10kHz of bandwidth at the antenna so the Q must not exceed 50 to 100 across the AM band. You will find that antenna has a fairly low Q in practice.



You need to learn how to post unambiguously too.

IOW not smartarse style like Larkin.

Larkin is great,

** Larkin is a smug pig and a troll.

He is so narcissistic he thinks he owns the NG and everyone on it.

To be fair he probably knows that Usenet was designed to not have a
central administrator...

 

[John Larkin]

On Fri, 17 Mar 2017 11:38:33 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 03/17/2017 11:28 AM, George Herold wrote:
On Friday, March 17, 2017 at 10:30:32 AM UTC-4, John Larkin wrote:
On Thu, 16 Mar 2017 18:46:06 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Thursday, March 16, 2017 at 8:36:16 PM UTC-4, Phil Allison wrote:
George Herold wrote:



I've got an AM radio that came with an air core antenna.
(1990's vintage)
~4" (10 cm) squarish loop. Not sure how many turns.
Works fine.


** So it's an external loop for a main powered receiver ?

Right, It's a JVC "ultra compact component system"
FS-1000


** So why didn't you post that info before?

'cos I'm now at home and not at work.
It's a fucking frame antenna, already discussed here in this thread and been around since the dawn of radio.



Knowing almost nothing about AM, (and assuming I don't care about price.)
I figure I want the highest Q possible on the front end..


** Nope.

You need at least 10kHz of bandwidth at the antenna so the Q must not exceed 50 to 100 across the AM band. You will find that antenna has a fairly low Q in practice.
OK I was thinking of best signal to noise, and figuring that ~1-2 kHz would
be enough.. Everyones "best/ optimal" is a bit different.

An AM antenna doesn't need to be tuned at all. An untuned coil will
snoop the ambient h-field.
I guess that's right. As long as most of the noise is "in the air" it doesn't
really matter where the band pass filter is. (Except for dynamic range issues.)

As you say, dynamic range. An untuned input needs a stronger mixer. A
Q of 10 or 20 would help a lot.

Resonating an AM antenna needs a giant variable cap, or a varicap and
some sort of tracking voltage source for that. In these days of cheap
gain and signal processing, a mediocre AM receiver (who needs more?)
could well use a simple loop, maybe on the PC board.

Is there anything on AM these days? I haven't tuned into the AM band
in a decade or two.

Amazon has an am/fm radio with earbuds for $6.99.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[John Larkin]

On Fri, 17 Mar 2017 12:29:05 -0400, bitrex
<bitrex@de.lete.earthlink.net> wrote:

On 03/16/2017 08:36 PM, Phil Allison wrote:
George Herold wrote:



I've got an AM radio that came with an air core antenna.
(1990's vintage)
~4" (10 cm) squarish loop. Not sure how many turns.
Works fine.


** So it's an external loop for a main powered receiver ?

Right, It's a JVC "ultra compact component system"
FS-1000


** So why didn't you post that info before?

It's a fucking frame antenna, already discussed here in this thread and been around since the dawn of radio.



Knowing almost nothing about AM, (and assuming I don't care about price.)
I figure I want the highest Q possible on the front end..


** Nope.

You need at least 10kHz of bandwidth at the antenna so the Q must not exceed 50 to 100 across the AM band. You will find that antenna has a fairly low Q in practice.



You need to learn how to post unambiguously too.

IOW not smartarse style like Larkin.

Larkin is great,

** Larkin is a smug pig and a troll.

He is so narcissistic he thinks he owns the NG and everyone on it.

To be fair he probably knows that Usenet was designed to not have a
central administrator...

There are moderated NGs. This ain't one.

Most of usenet is dead. SED is unusually active, some of it actually
on topic.





--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

On Friday, March 17, 2017 at 7:33:04 PM UTC-4, Clifford Heath wrote:

On 18/03/17 06:21, John Larkin wrote:
Resonating an AM antenna needs a giant variable cap, or a varicap and
some sort of tracking voltage source for that.

They don't make big enough varicaps for that, but those Superjunction
FETs discussed here recently would work.

A friend designed a specialised hand-held pickup head that had
to tune 1-5MHz, and used 480(!) small varicaps. It was measuring
micro-ohms of dynamic impedance using transformer coupling
(about 8mm square) across a small air gap. The DUT had dozens
of resonances with Q of 1000-5000 across the band.

I suggested using the Superjunction FETs, but the device is finished.

Clifford Heath.

A perfect application for Y5V / Z5U / X5R ceramic caps. 2uF varicap? Can do!

Cheers,
James Arthur

 

[George Herold]

On Friday, March 17, 2017 at 11:38:44 AM UTC-4, Phil Hobbs wrote:

On 03/17/2017 11:28 AM, George Herold wrote:
On Friday, March 17, 2017 at 10:30:32 AM UTC-4, John Larkin wrote:
On Thu, 16 Mar 2017 18:46:06 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Thursday, March 16, 2017 at 8:36:16 PM UTC-4, Phil Allison wrote:
George Herold wrote:



I've got an AM radio that came with an air core antenna.
(1990's vintage)
~4" (10 cm) squarish loop. Not sure how many turns.
Works fine.


** So it's an external loop for a main powered receiver ?

Right, It's a JVC "ultra compact component system"
FS-1000


** So why didn't you post that info before?

'cos I'm now at home and not at work.
It's a fucking frame antenna, already discussed here in this thread and been around since the dawn of radio.



Knowing almost nothing about AM, (and assuming I don't care about price.)
I figure I want the highest Q possible on the front end..


** Nope.

You need at least 10kHz of bandwidth at the antenna so the Q must not exceed 50 to 100 across the AM band. You will find that antenna has a fairly low Q in practice.
OK I was thinking of best signal to noise, and figuring that ~1-2 kHz would
be enough.. Everyones "best/ optimal" is a bit different.

An AM antenna doesn't need to be tuned at all. An untuned coil will
snoop the ambient h-field.
I guess that's right. As long as most of the noise is "in the air" it doesn't
really matter where the band pass filter is. (Except for dynamic range issues.)

As you say, dynamic range. An untuned input needs a stronger mixer. A
Q of 10 or 20 would help a lot.

On the other hand, one could just use a Mini Circuits mixer with a +17
dBm LO, or a nice analogue mux with square wave drive. It takes a lot
to screw one of those up.

Hah, I made an AM radio just that way. Not with a loop, but just
a length of wire. (It's probably the worlds's worst AM radio.)
I had to add series L's (selected for range) to make it work.
Circuit from Terman's radio electronics book.

So a loop (with parallel C) into a TIA? ... (I'd rather use an opamp.)
or will that wig out at the C side of the resonance?

George H.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

On Wednesday, March 15, 2017 at 12:18:38 AM UTC-4, Bill Bowden wrote:

Which is a better design. Suppose you have a 6 inch length of PVC pipe with
numerous turns of wire that has an inductance of say 200uH. Now suppose you
use the same (6 inch) piece of PVC with a ferrite rod in the core with
considerably fewer turns of wire. Which one would capture the most signal
at the AM Broadcast frequencies (500K to 2 Megs) and poduce the greatest
signal output? Would it be more ferrite, or more wire?

The Antenna Ferrite Loopstick Verses
(an exercise in mixed metaphors)
--------------------------------

I raised an aerial into the air,
Pumped in some watts; they landed, but where?
For, so swiftly they flew, the sight
Could not follow the watts in their flight.

But now we all know
(thanks to Edward J. Snowden)
They were scooped from the ether
By one William ('Bill') Bowden.

Whose giant loop, all loaded with ferrite
Had grabbed all my flux (that ain't fair, right?)
To warm up his home, and light LEDS,
And listen to Rush whenever he pleased.

 

[George Herold]

On Friday, March 17, 2017 at 8:13:13 PM UTC-4, dagmarg...@yahoo.com wrote:

On Friday, March 17, 2017 at 7:33:04 PM UTC-4, Clifford Heath wrote:
On 18/03/17 06:21, John Larkin wrote:
Resonating an AM antenna needs a giant variable cap, or a varicap and
some sort of tracking voltage source for that.

They don't make big enough varicaps for that, but those Superjunction
FETs discussed here recently would work.

A friend designed a specialised hand-held pickup head that had
to tune 1-5MHz, and used 480(!) small varicaps. It was measuring
micro-ohms of dynamic impedance using transformer coupling
(about 8mm square) across a small air gap. The DUT had dozens
of resonances with Q of 1000-5000 across the band.

I suggested using the Superjunction FETs, but the device is finished.

Clifford Heath.

A perfect application for Y5V / Z5U / X5R ceramic caps. 2uF varicap? Can do!

Cheers,
James Arthur

Oh boy! Can't wait... how do you feed the drive in?
I've always pictured two caps driven in the middle.

George H.

 

[Cursitor Doom]

On Thu, 16 Mar 2017 22:22:33 -0400, krw wrote:

Nothing like that. I knew the surgery would be bad but it wasn't nearly
as bad as they said.

I find coming round after the op is the worst part. It's not like normal
waking up. I panic like hell! "Where am I? What the fuck happened? What
are all these fucking tubes for?" That kind of thing. Nasty!

 

[billbowden]

"John Larkin" <jjlarkinxyxy@highlandtechnology.com> wrote in message
news:qcdocc5iec6gv362jo93hq45tlib1sgruh@4ax.com...

On Fri, 17 Mar 2017 11:38:33 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 03/17/2017 11:28 AM, George Herold wrote:
I guess that's right. As long as most of the noise is "in the air" it
doesn't
really matter where the band pass filter is. (Except for dynamic range
issues.)

As you say, dynamic range. An untuned input needs a stronger mixer. A
Q of 10 or 20 would help a lot.


Resonating an AM antenna needs a giant variable cap, or a varicap and
some sort of tracking voltage source for that. In these days of cheap
gain and signal processing, a mediocre AM receiver (who needs more?)
could well use a simple loop, maybe on the PC board.

Is there anything on AM these days? I haven't tuned into the AM band
in a decade or two.

Rush Limbaugh, Mark Levin, Dennis Prager, Michael Medved, George Noory, Bill
Handel, John and Ken, Tim Conway Jr. and other political hacks. Also there
are financial shows like Ric Edelman, George Chamberlain, Ken Moraif, and
others. Keeps me busy 24/7
..

Amazon has an am/fm radio with earbuds for $6.99.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

On Friday, March 17, 2017 at 8:36:33 PM UTC-4, George Herold wrote:

On Friday, March 17, 2017 at 8:13:13 PM UTC-4, dagmarg...@yahoo.com wrote:
On Friday, March 17, 2017 at 7:33:04 PM UTC-4, Clifford Heath wrote:
On 18/03/17 06:21, John Larkin wrote:
Resonating an AM antenna needs a giant variable cap, or a varicap and
some sort of tracking voltage source for that.

They don't make big enough varicaps for that, but those Superjunction
FETs discussed here recently would work.

A friend designed a specialised hand-held pickup head that had
to tune 1-5MHz, and used 480(!) small varicaps. It was measuring
micro-ohms of dynamic impedance using transformer coupling
(about 8mm square) across a small air gap. The DUT had dozens
of resonances with Q of 1000-5000 across the band.

I suggested using the Superjunction FETs, but the device is finished.

Clifford Heath.

A perfect application for Y5V / Z5U / X5R ceramic caps. 2uF varicap? Can do!


Oh boy! Can't wait... how do you feed the drive in?
I've always pictured two caps driven in the middle.

That's typical. Varicaps are usually used back-to-back, or with a d.c.
blocking cap.

Cheers,
James Arthur