Topics

uBITX ... AGC or AVC?


 

Loris,

Try something else..

Use a SBL-1 or similar. DBM. it is a BiDi device

Connect one  RF port to signal INput and second to OUTput or other way.

Feed a DC control voltage through a resistor to the IF port. Try with 1-10K.
Vary the voltage and see the signal level change. The behavior is opposite
of the varicap control voltage.

We can use this for AGC and ALC in either direction.

Raj


At 28/10/2020, you wrote:
On Wed, Oct 28, 2020 at 12:31 PM, Raj vu2zap wrote:
I had experimented with a AGC which was very simple. Disconnect R23 and R43 from ground and introduce
a varicap which I had MV2109. A series resistor to the varicap through which you varied the capacitance
and thereby the gain. This method worked very well with both IF stages and even on the TX branch.

I wish some members would experiment on this approach.

Hello Raj ...
Interesting solution, if I have some free time I could try it!
I would like to have an explanation from you:
what is the function of AGC  transmission for uBITX? ... perhaps as a compressor instead of an external speech-processor?
Thank you, 73 Loris - IW4AJR


Biju Apkrcl
 

Please post the circuit diagram also with your suggestions, that will helpful to us.

VU2TDD , Biju

On Thu, 29 Oct 2020, 12:00 Raj vu2zap, <rajendrakumargg@...> wrote:
Loris,

Try something else..

Use a SBL-1 or similar. DBM. it is a BiDi device

Connect one  RF port to signal INput and second to OUTput or other way.

Feed a DC control voltage through a resistor to the IF port. Try with 1-10K.
Vary the voltage and see the signal level change. The behavior is opposite
of the varicap control voltage.

We can use this for AGC and ALC in either direction.

Raj

At 28/10/2020, you wrote:
On Wed, Oct 28, 2020 at 12:31 PM, Raj vu2zap wrote:
I had experimented with a AGC which was very simple. Disconnect R23 and R43 from ground and introduce
a varicap which I had MV2109. A series resistor to the varicap through which you varied the capacitance
and thereby the gain. This method worked very well with both IF stages and even on the TX branch.

I wish some members would experiment on this approach.

Hello Raj ...
Interesting solution, if I have some free time I could try it!
I would like to have an explanation from you:
what is the function of AGC  transmission for uBITX? ... perhaps as a compressor instead of an external speech-processor?
Thank you, 73 Loris - IW4AJR


 

On Thu, Oct 29, 2020 at 07:30 AM, Raj vu2zap wrote:
Try something else..

Use a SBL-1 or similar. DBM. it is a BiDi device

Connect one  RF port to signal INput and second to OUTput or other way.

Feed a DC control voltage through a resistor to the IF port. Try with 1-10K.
Vary the voltage and see the signal level change. The behavior is opposite
of the varicap control voltage.

We can use this for AGC and ALC in either direction.
WOW !!! I had never thought about it ! it's almost brilliant! with a little time, as soon as the job allows me, I could try!
Thanks Raj ... it's as simple as it is brilliant!
73 de IW4AJR Loris


iz oos
 

Not really sure I got it. If It works well, please share the added schematics also drawn with a pencil on paper.


Il gio 29 ott 2020 10:53 AM IW4AJR Loris <lorisbollina@...> ha scritto:
On Thu, Oct 29, 2020 at 07:30 AM, Raj vu2zap wrote:
Try something else..

Use a SBL-1 or similar. DBM. it is a BiDi device

Connect one  RF port to signal INput and second to OUTput or other way.

Feed a DC control voltage through a resistor to the IF port. Try with 1-10K.
Vary the voltage and see the signal level change. The behavior is opposite
of the varicap control voltage.

We can use this for AGC and ALC in either direction.
WOW !!! I had never thought about it ! it's almost brilliant! with a little time, as soon as the job allows me, I could try!
Thanks Raj ... it's as simple as it is brilliant!
73 de IW4AJR Loris


 

Emacs!

At 29/10/2020, you wrote:
Please post the circuit diagram also with your suggestions, that will helpful to us.

VU2TDD , Biju

On Thu, 29 Oct 2020, 12:00 Raj vu2zap, < rajendrakumargg@...> wrote:
Loris,

Try something else..

Use a SBL-1 or similar. DBM. it is a BiDi device

Connect one  RF port to signal INput and second to OUTput or other way.

Feed a DC control voltage through a resistor to the IF port. Try with 1-10K.
Vary the voltage and see the signal level change. The behavior is opposite
of the varicap control voltage.

We can use this for AGC and ALC in either direction.

Raj


 

I just did Ooz, some days my hands are not steady..

Raj


At 29/10/2020, you wrote:
Not really sure I got it. If It works well, please share the added schematics also drawn with a pencil on paper.

Il gio 29 ott 2020 10:53 AM IW4AJR Loris <lorisbollina@...> ha scritto:
On Thu, Oct 29, 2020 at 07:30 AM, Raj vu2zap wrote:
Try something else..

Use a SBL-1 or similar. DBM. it is a BiDi device

Connect one  RF port to signal INput and second to OUTput or other way.

Feed a DC control voltage through a resistor to the IF port. Try with 1-10K.
Vary the voltage and see the signal level change. The behavior is opposite
of the varicap control voltage.

We can use this for AGC and ALC in either direction.

WOW !!! I had never thought about it ! it's almost brilliant! with a little time, as soon as the job allows me, I could try!
Thanks Raj ... it's as simple as it is brilliant!
73 de IW4AJR Loris


Vince Vielhaber
 

Amplifier Research did this in their RF Levelers. They used a minicircuits mixer as an attenuator using a control voltage.

Vince - K8ZW.

On 10/29/2020 02:30 AM, Raj vu2zap wrote:
Loris,

Try something else..

Use a SBL-1 or similar. DBM. it is a BiDi device

Connect one RF port to signal INput and second to OUTput or other way.

Feed a DC control voltage through a resistor to the IF port. Try with 1-10K.
Vary the voltage and see the signal level change. The behavior is opposite
of the varicap control voltage.

We can use this for AGC and ALC in either direction.

Raj

At 28/10/2020, you wrote:
On Wed, Oct 28, 2020 at 12:31 PM, Raj vu2zap wrote:

I had experimented with a AGC which was very simple. Disconnect
R23 and R43 from ground and introduce
a varicap which I had MV2109. A series resistor to the varicap
through which you varied the capacitance
and thereby the gain. This method worked very well with both IF
stages and even on the TX branch.

I wish some members would experiment on this approach.

Hello Raj ...
Interesting solution, if I have some free time I could try it!
I would like to have an explanation from you:
what is the function of AGC transmission for uBITX? ... perhaps as a
compressor instead of an external speech-processor?
Thank you, 73 Loris - IW4AJR


 

Here is my attenuator - simple and useful tool.

Emacs!


At 29/10/2020, you wrote:
Amplifier Research did this in their RF Levelers.  They used a minicircuits mixer as an attenuator using a control voltage.

Vince - K8ZW.



On 10/29/2020 02:30 AM, Raj vu2zap wrote:
Loris,

Try something else..

Use a SBL-1 or similar. DBM. it is a BiDi device

Connect one  RF port to signal INput and second to OUTput or other way.

Feed a DC control voltage through a resistor to the IF port. Try with 1-10K.
Vary the voltage and see the signal level change. The behavior is opposite
of the varicap control voltage.

We can use this for AGC and ALC in either direction.

Raj

At 28/10/2020, you wrote:
On Wed, Oct 28, 2020 at 12:31 PM, Raj vu2zap wrote:

    I had experimented with a AGC which was very simple. Disconnect
    R23 and R43 from ground and introduce
    a varicap which I had MV2109. A series resistor to the varicap
    through which you varied the capacitance
    and thereby the gain. This method worked very well with both IF
    stages and even on the TX branch.

    I wish some members would experiment on this approach.

Hello Raj ...
Interesting solution, if I have some free time I could try it!
I would like to have an explanation from you:
what is the function of AGC  transmission for uBITX? ... perhaps as a
compressor instead of an external speech-processor?
Thank you, 73 Loris - IW4AJR

--
  K8ZW  http://www.metalworkingfun.com  http://www.hamradio.fun





iz oos
 

Hi Raj, how much voltage would you suggest to be out on the 10kohm at the IF port of the mixer. Is a potentiometer necessary or would a 10kohm fixed resistor suffice?


Il gio 29 ott 2020 11:48 AM Raj vu2zap <rajendrakumargg@...> ha scritto:


At 29/10/2020, you wrote:
Please post the circuit diagram also with your suggestions, that will helpful to us.

VU2TDD , Biju

On Thu, 29 Oct 2020, 12:00 Raj vu2zap, < rajendrakumargg@...> wrote:
Loris,

Try something else..

Use a SBL-1 or similar. DBM. it is a BiDi device

Connect oneĀ  RF port to signal INput and second to OUTput or other way.

Feed a DC control voltage through a resistor to the IF port. Try with 1-10K.
Vary the voltage and see the signal level change. The behavior is opposite
of the varicap control voltage.

We can use this for AGC and ALC in either direction.

Raj


 

You will have to experiment a bit. I dont have any info here. I had to get my son to
photograph the attenuator for the group. Its part of my tool box now. Try a pot
with say 5-10V and see where you get max and min attenuation and work from
there.

Use #1
I did some complex AGC system some years ago and to test his AGC I came up with this
tool. RF from signal generator -> to receiver. The IF port was connected to a function
generator. I gave a little DC bias on my Siemens so that the SBL was allowing some
signal to pass, then mixed in a 1Hz sine wave / square wave to simulate fading and
square wave for observing the attack and decay of the agc. Worked out well.
In the files section of homebrewers at groups.io there is an RX2 schematic with
the AGC etc.

Use #2
I have a GPS based 10MHz oscillator and I connect one input to that and the other
input to an 10MHz oscillator like an oven / rubidium clock. The IF out is connected
through a 10K pot to a center zero micro ammeter. You can see the zero beat by
the needle swing left to right and all I do is minimize it.

Raj


At 30/10/2020, you wrote:
Hi Raj, how much voltage would you suggest to be out on the 10kohm at the IF port of the mixer. Is a potentiometer necessary or would a 10kohm fixed resistor suffice?

Il gio 29 ott 2020 11:48 AM Raj vu2zap < rajendrakumargg@...> ha scritto:


Curt
 

I did see the concept of using a double balanced diode mixer as a voltage variable attenuator. Funny thing I was a young engineer, and an older guy had me take data on it at a range of low vhf. I can't recall the useful range, maybe around 25 dB or more.

The only real limitation is that for a variable biased diode it generates more harmonics and intermods when operated in between on or off.

Diodes are fascinating indeed. Switch action, limiting, variable capacitance, zener, mixing, light emitting, maybe even fanatics finding the LED can drive a LDR to create a little agc action. Some transistor circuits might be boring without these 2 terminal junctions. Based upon using sand and part of its substance.

Enjoy biasing whatever circuits you craft.

Curt


 

These SBL ones are much better:
  • high L-R isolation, 45 dB typ. L-I isolation, 40 dB typ.
That would be the max range.

Raj


At 31/10/2020, you wrote:
I did see the concept of using a double balanced diode mixer as a voltage variable attenuator. Funny thing I was a young engineer, and an older guy had me take data on it at a range of low vhf. I can't recall the useful range, maybe around 25 dB or more.

The only real limitation is that for a variable biased diode it generates more harmonics and intermods when operated in between on or off.

Diodes are fascinating indeed. Switch action, limiting, variable capacitance, zener, mixing, light emitting, maybe even fanatics finding the LED can drive a LDR to create a little agc action. Some transistor circuits might be boring without these 2 terminal junctions. Based upon using sand and part of its substance.

Enjoy biasing whatever circuits you craft.

Curt