On 02/04/2015 15:10, amdx wrote:
Any fix for the sinewave distortion in the second and third scope traces.

Infinite impedance detectors are said to have very low demod distortion
by AM aficionados.

piglet

I wrote:

The thing to watch is the Q factor,
the detector circuit can be seen asa resistor parallel with the ferrite rod and tuning cap.
----------
|( | |
|( === [ ] Rp
|( | |
---------

The higher Rp, the higher the Q factor, the more signal, the narrower the bandwidth
B = f / Q

http://en.wikipedia.org/wiki/RLC_circuit
scroll down to 'parallel RLC circuit'.

PS
so a high Q gives a narrow bandwidth, better 'selectivity'.
That may be needed if you receive 2 stations close together in frequency.
Especially in the evening on the AM broadcast band you may get very strong signals from far away stations
at the same or right next to the frequency of the one you are listening to,
you then hear both at the same time, or this gives a few kHz interference.

But, too high a Q (hard to obtain [1]) will attenuate the high frequency sidebands of the station you
are listening to, reducing high frequency sound components.


[1] RF feedback can be used in a RF stage to increase Q,

Am stations are spaced 9 kHz or 10kHz apart depending on location,
so all sorts of interference from far away stations exists.
This site is worth reading:
http://en.wikipedia.org/wiki/AM_broadcasting


RR and IF stages with tuned circuits or bandfilters of any kind (mechanical, crystal, piezo, LC, etc) can help
create an accurate bandpass curve.

I think you should perhaps get hold of one of the RSGB radio books,
and start from the
http://www.rsgbshop.org/acatalog/Onl...___CDs_29.html

amdx wrote:
On 4/2/2015 3:43 PM, Allodoxaphobia wrote:
On Thu, 02 Apr 2015 09:10:47 -0500, amdx wrote:
"Critic of circuit before I build it."

heh...
This place is infested with critics.
What you want is a critique.


I'll do better next time.
I'm going to my room now.
Mikek
....without supper.

On 4/3/2015 2:02 AM, Jan Panteltje wrote:
I wrote:

The thing to watch is the Q factor,
the detector circuit can be seen asa resistor parallel with the ferrite rod and tuning cap.
----------
|( | |
|( === [ ] Rp
|( | |
---------

The higher Rp, the higher the Q factor, the more signal, the narrower the bandwidth
B = f / Q

http://en.wikipedia.org/wiki/RLC_circuit
scroll down to 'parallel RLC circuit'.

PS
so a high Q gives a narrow bandwidth, better 'selectivity'.
That may be needed if you receive 2 stations close together in frequency.
Especially in the evening on the AM broadcast band you may get very strong signals from far away stations
at the same or right next to the frequency of the one you are listening to,
you then hear both at the same time, or this gives a few kHz interference.

But, too high a Q (hard to obtain [1]) will attenuate the high frequency sidebands of the station you
are listening to, reducing high frequency sound components.


Yes, I'm aware of how Q affects selectivity, I can only hope for too
high of a Q, easy enough to spoil. I've been following a crystal radio
group for a few years, they recently got hold of a low loss ferrite and
getting Q's in the 1000 to 1200 range over the broadcast band. Using
Litz wire.
The material I'm using is some in my stock, and not real good Q at
AM band frequencies.
What I have is twelve-1/2 potcores stacked as a rod. A coil is
wrapped on that and resonated with a cap. With a radio near the core
You get an increase in the signal as you tune to resonance.
The rod is 67.5mm Dia. x 335mm long, or 2.66 in dia. x 13.2 in long.

-
[1] RF feedback can be used in a RF stage to increase Q,

I just yesterday, tried a Hartley oscillator on part of the winding in
an attempt to raise Q and get more selectivity. It didn't oscillate,
but I only spent a few minutes before supper, I'll be trying again.


Am stations are spaced 9 kHz or 10kHz apart depending on location,
so all sorts of interference from far away stations exists.
This site is worth reading:
http://en.wikipedia.org/wiki/AM_broadcasting


RR and IF stages with tuned circuits or bandfilters of any kind (mechanical, crystal, piezo, LC, etc) can help
create an accurate bandpass curve.

I think you should perhaps get hold of one of the RSGB radio books,
and start from the
http://www.rsgbshop.org/acatalog/Onl...___CDs_29.html

Oh that one! I have the ARRL Handbook. :-)

Thanks, Mikek


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On 4/3/2015 1:08 AM, Jan Panteltje wrote:
AGC (Automatic Gain Correction[1]) will keep that voltage high as long as possible with weakening signals.

Yes, I can hear that work if I hit resonance quick, the volume jumps
up, but then settles back down.



I'll be measuring across a resonant ferrite rod, I don't know what a
minimum usable voltage would be. I'll go check.
Mikek

Depends how far you are from any transmitter, and the direction the ferrite rod is pointing.
For maximum signal it should be like this:

|
| ------- 0 transmitter
|
rod


Yes, the long rod I reference before has a wide null off the ends.
I have listened to two different stations on the same frequency, just by
rotating the rod. I have it on a Lazy Susan.


The thing to watch is the Q factor,
the detector circuit can be seen as a resistor in parallel with the ferrite rod and tuning cap.
----------
|( | |
|( === [ ] Rp
|( | |
---------

The higher Rp, the higher the Q factor, the more signal, the narrower the bandwidth
B = f / Q

Yep, I have an old Booton 260A for measuring Q.
Thanks, Mikek


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On Thu, 02 Apr 2015 09:10:47 -0500, amdx wrote:

I'm about to build this circuit to compare output from different
ferrite receive antennas. I will be using it with the the FET amplifier
referenced at the bottom of the page, so the input impedance is not a
concern. I'm mostly interested in the DC output to monitor signal
levels. AM band frequencies.

http://www.crystal-radio.eu/diodedet...dedetector.htm

Any fix for the sinewave distortion in the second and third scope traces.
Mikek

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At AM band frequencies there now exist fast enough OpAmp's to make a
nearly ideal diode detector.

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

On Thu, 02 Apr 2015 09:10:47 -0500, amdx wrote:

I'm about to build this circuit to compare output from different
ferrite receive antennas. I will be using it with the the FET amplifier
referenced at the bottom of the page, so the input impedance is not a
concern. I'm mostly interested in the DC output to monitor signal
levels. AM band frequencies.

http://www.crystal-radio.eu/diodedet...dedetector.htm

Any fix for the sinewave distortion in the second and third scope traces.
Mikek


At AM band frequencies there now exist fast enough OpAmp's to make a
nearly ideal diode detector.

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.