Date   

Re: #bitx40 Help needed with compiler error #bitx40

Mike Woods
 

Keith

You need to install the PinChangeInterrupt library first.  Then restart the Arduino IDE and all should be well.   Go to "Tools" and "Include library" in the menu system.

Mike ZL1AXG

On 8/04/18 1:17 PM, AGØH wrote:
I've downloaded v1.27.7 sketch to the Arduino IDE.  Installed the necessary driver (Ch340/341).  My OS is WIN10.  Installed the PinChangeInterrupt library  to the same directory that raduino_v1.27.7.ino is in.  Hooked up the raduino and then tried to compile the sketch.  I got the following:  

I removed the word '-master' from the title as suggested by  the readme file but to no avail.  as you can see it stopped after starting the compile telling me that the compilation stopped because of an error.  When I scrolled up, you can see it's listing the #include <PinChangeInterrupt.h> as the error.  There are three other lines in that sketch but it looks like it stopped after not being able to find the first one.  
I verified that the raduino was working earlier by loading/running  the blink example.  So,I'm in sore need of suggestions on how to load in this program.
A little background:   I did go by a set of instructions by Pat AA4PG (updated by VE3RRD). My main directory for the Arduino IDE is C:\\.  I created another directory in C:\\ for Bitx40Software where I placed the raduino_v1.27.7 sub directory.  I copied the unzipped raduino_v1.27.7.ino in that directory along with the PinChangeInterrupt directory. Clicking on the Sketch file automatically starts the IDE and the result you see in the above capture.
Thanks es 73 for any and all help, 
Keith - AGØH 


--
Mike Woods
mhwoods@...


Re: AGC circuit to try?

Tim Gorman
 

Allison,

These amplifier circuits are very carefully designed to provide 50ohm
inputs and outputs so that proper terminations are provided to the
mixers in order to maximize rejection of unwanted carriers. The output
of the second amplifier is to provide the proper termination to the
crystal filter.

If you replace the emitter resistors with a diode then you have
effectively changed the input and output impedances of the amplifiers.
This would be especially bad for the termination into the crystal
filter.

Google "w7zoi" and "termination insensitive amplifiers" for a
discussion.

What you suggest would probably work but without testing it is
difficult to determine the actual result on the overall operation of
the receiver.

tim ab0wr



On Sat, 07 Apr 2018 12:15:15 -0700
"ajparent1" <kb1gmx@...> wrote:

It is incomplete..

You have the audio detection to get an AGC control voltage but you
don't show what your controlling.

What I find odd in general every one seems to be bent on leveling the
audio volume in the audio circuit. Why?  I understand protecting ones
ears and all but what an audio compressor?  

The Bitx or uBitx has enough gain and handy places that RF gain
control based on audio detection works very well.  The easy way is
replace R13 (ubitx) with a diode such as 1n400x (x=1 to 7) and
controlling the current through the diode to make it behave as a
variable resistance at RF.  

The current would be about 4-6ma at max gain and decrease to zero (0)
at minimum gain.  For that design the AGC range is about 26 to 32db
depening on band.  If you feel that is not enough agc range then add
the same mod at R35 then with both the agc range is near 60+ DB,
generally enough.  AGC in this form is less prone to overload
distortion as you are lowering gain.  The control could be a pot
between 8V (or RX-V) and ground and a series 1K resistor to the he
diode (x2 of your using both diodes).  That is a manual gain
control.   To make it automatic use a circuit like just published to
detect the voltage at the top of the audio gain pot and feed that
voltage to the gain control diodes.  The circuit should be arranged
to put 4-8V out at NO Audio and decrease to zero volts with
increasing audio.

Side note the 1n400x series with minor reservations makes a fine
substitute for a PIN diode, the prefered but more costly device for
this function.  Beside being widely available and cheap ( I buy them
in quantities of 100 for pennies each) makes it useful.  It also
makes a good 20pf varicap and a 1A rectifier to 1000V (1n4007).

This was tested on the first bitx20 I built over a decade ago to test
AGC and is used on several  older Tentec radios and more than few of
my own design.   That said its far from a new idea or design as its
documented in EMRFD and the older SSD (Solid State Design AARL press,
out of print).   

Allison


#bitx40 Help needed with compiler error #bitx40

AGØH
 

I've downloaded v1.27.7 sketch to the Arduino IDE.  Installed the necessary driver (Ch340/341).  My OS is WIN10.  Installed the PinChangeInterrupt library  to the same directory that raduino_v1.27.7.ino is in.  Hooked up the raduino and then tried to compile the sketch.  I got the following:  

I removed the word '-master' from the title as suggested by  the readme file but to no avail.  as you can see it stopped after starting the compile telling me that the compilation stopped because of an error.  When I scrolled up, you can see it's listing the #include <PinChangeInterrupt.h> as the error.  There are three other lines in that sketch but it looks like it stopped after not being able to find the first one.  
I verified that the raduino was working earlier by loading/running  the blink example.  So,I'm in sore need of suggestions on how to load in this program.
A little background:   I did go by a set of instructions by Pat AA4PG (updated by VE3RRD). My main directory for the Arduino IDE is C:\\.  I created another directory in C:\\ for Bitx40Software where I placed the raduino_v1.27.7 sub directory.  I copied the unzipped raduino_v1.27.7.ino in that directory along with the PinChangeInterrupt directory. Clicking on the Sketch file automatically starts the IDE and the result you see in the above capture.
Thanks es 73 for any and all help, 
Keith - AGØH 


Re: Variation on Ian's KD8CEC uBitx software (based on his 1.04 release for now) and ATU sketch. #ubitx

W2CTX
 

You also need to know the I2C address

rOn



From: John <passionfruit88@...>
To: BITX20@groups.io
Sent: Saturday, April 7, 2018 8:42 PM
Subject: Re: [BITX20] Variation on Ian's KD8CEC uBitx software (based on his 1.04 release for now) and ATU sketch. #ubitx

Hello Tim,

If I remember well it is only a one liner or so. I will add it as an option.

73, John  (VK2ETA)



Re: Variation on Ian's KD8CEC uBitx software (based on his 1.04 release for now) and ATU sketch. #ubitx

John <passionfruit88@...>
 

Hello Tim,

If I remember well it is only a one liner or so. I will add it as an option.

73, John  (VK2ETA)


Re: AGC circuit to try?

Jerry Gaffke
 

That was a general "you", addressed to the now thousands of uBitx owners. 
I'm still concerned that a random 1n400* off an ebay site could do most anything at 45mhz
There are lots of different manufacturers using lots of different processes. 

So if ordering parts for this, I'd get a BAP64 or similar.
The BAP64-03 is in a bigger package than the -02, still plenty small.
If what's on hand are some one amp power rectifiers mostly used at 60hz,
by all means give them a try first.

Very encouraging that Allison usually finds these 1n400*'s to work well at RF. 

Jerry 


On Sat, Apr 7, 2018 at 02:29 pm, ajparent1 wrote:
Rare is an order for just one part here.  Typical order for my lab are 4-20 parts and quantity.
Stock devices like 1n4007 a hundred in a order is common, same for 2n2222A, 2n3906, 2n3904
as they are cheaper when purchased in volume.  I do have the BAP64 in various packages and
several others as well. Even some exotic Avago PIN parts.  I maintain a stock that allows me
to build then optimize.  I get annoyed when I don't have something unless exotic like 10ghz
gain blocks.
On Sat, Apr 7, 2018 at 01:32 pm, Jerry Gaffke wrote:

If you are paying $5 postage to ship in some 1n4007's, you might consider
also getting some BAP64-02's at $0.43 each single unit pricing, Mouser 771-BAP64-02-T/R.
Down to $0.10 or so if you buy a reel.
Fully spec'd for use as an RF PIN diode. 


Re: AGC circuit to try?

ajparent1 <kb1gmx@...>
 

How many cubic feet?  Best guess something on the order of 250-400 cubic feet.
Mind you not all of that is junk in the classic sense.  Much of that is what I'd call
stockpiles.

I use 50 drawer bins and some with larger drawers that are only 18 drawers in the same
overall size.  There are 8 of those for just routine stuff like screws, resistors, caps, diodes,
connectors, LEDs, common transistors, and so on.  ITs part of the non-junk part.  Tackle boxes
are not space efficient.   However there are maybe 12 of the variable pocket size clear
polyethylene boxes of varying heights for things like batteries, electrolytic caps, crystals, 
small relays and the like.

Junk aka random assemblies, chassis and boards, mechanical, cable and wire
are in large tubs maybe of the 30 gallon size.  FIgure 10 of those.  Plus another 15 
printer paper boxes (10 ream size) many are marked as to content.  

Its organized so the two car garage can hold two cars, and a workbench there
for messy activities, even after 35 years.  

The running joke with friends is, I likely have unobtainium.

Regarding the X1M info I have that and its good but cannot be used directly
with BITX as it was designed based on the MC1350 IF chip.  That would be
tough to shoe horn into the BITX design.  The basic idea is worth understanding
and with some changes could be applied would be very useful.

Allison 


Re: POP fix

Gary Anderson
 

From a visual inspection of Wayne’s original VA7AT “9-component” Pop Fix circuit (awesome document by Don ND6T on his website), I see the potential issue with why a loud noise to the microphone could ‘sneak’ into the uBITX audio output in RX mode. The Source and Drain of the n-FET Q1 (To C50, Audio receive) are swapped in the design.  There’s a body diode from source (pin 3) to drain (pin 2).  As drawn, there is still an attenuated signal path from the microphone to the receive audio amplifier though this body diode. Swapping the Source and Drain will eliminate this path, with no negative consequences that I can see.  I am curious if this would fix this “glitch”.


I am not at a point where I can try this out.  But since I spied a possible simple circuit enhancement, I thought it better to share my thoughts and be wrong, then to be correct and not share.  That wouldn’t be of any use.


Best Regards,
Gary
AG5TX


Re: EMRFD Butler VXO for Intermod Testing

emi constantino
 

Hi Nigel, I am working on  vfo butler osc but with series L C instead of a crystal.I dont have the EMRFD book so i cant give an opinion.If you can email me that particular page maybe i can give a cent of experience.
I am looking for a stable vfo since the original vfo of Bitx40 is now replaced with digital and i dont know how to program.

Best regards,

Emi Constantino,DW3 CBO

On Sun, Apr 8, 2018 at 6:15 AM, Nigel Maund
<maund.n@...> wrote:
Hi,

 I am building the Oscillator from EMRFD,page 7.19 Fig. 7.32.  I have reviewed the corrections from the W7ZOI EMRFD Errata site.
 Designing for 7 MHz, I plan to adjust by using the formula Fold/Fnew and multiply (i.e. by 2) all the required LC components.  This works for the pi filter, fine enough.
My question: (1) how do I modify the Transformer that is in the Oscillator Collector circuit?  I see that for 14 MHz, the inductance is actually giving a 44 Ohm impedance; would I simply calculate the primary inductance of the transformer, to try and obtain the same impedance, but for 7 MHz?  I haven't found much info on Butler oscillator design,  and how its LC values are set, and cannot find a good site on the web to refer to.  Can I use the same 220 pF and 440 pF capacitors?  Butler VXOs seem to be often used for overtones of the crystal.   (2) why are there 2 x 0.1 microFarad bypass capacitors on the Base of the Final transistor?   

Thanks,
Nigel
VA2NM




EMRFD Butler VXO for Intermod Testing

Nigel Maund
 

Hi,

 I am building the Oscillator from EMRFD,page 7.19 Fig. 7.32.  I have reviewed the corrections from the W7ZOI EMRFD Errata site.
 Designing for 7 MHz, I plan to adjust by using the formula Fold/Fnew and multiply (i.e. by 2) all the required LC components.  This works for the pi filter, fine enough.
My question: (1) how do I modify the Transformer that is in the Oscillator Collector circuit?  I see that for 14 MHz, the inductance is actually giving a 44 Ohm impedance; would I simply calculate the primary inductance of the transformer, to try and obtain the same impedance, but for 7 MHz?  I haven't found much info on Butler oscillator design,  and how its LC values are set, and cannot find a good site on the web to refer to.  Can I use the same 220 pF and 440 pF capacitors?  Butler VXOs seem to be often used for overtones of the crystal.   (2) why are there 2 x 0.1 microFarad bypass capacitors on the Base of the Final transistor?   

Thanks,
Nigel
VA2NM




Re: RadioKits.in Case #ubitx Encoder knob fit #ubitx

K Buehler
 

Back of the hex on the front of the knob & it expands the internal collect & it falls on (it clamps on shaft when you tighten it

73
Ken VE3KCY


Re: AGC circuit to try?

Lee
 

I also have a X1M with the AGC board installed. I attached the install manual from the X1M group for those interested.


Re: AGC circuit to try?

Gordon Gibby <ggibby@...>
 

​how many cubic feet, perchance?

Do you use fishing tackle boxes to sort?



I have a bunch of junk, but not nearly the range of stuff you seem to have and I need to figure out how to allocate space in the "bonus room"


Gordon




From: BITX20@groups.io <BITX20@groups.io> on behalf of ajparent1 <kb1gmx@...>
Sent: Saturday, April 7, 2018 5:50 PM
To: BITX20@groups.io
Subject: Re: [BITX20] AGC circuit to try?
 
Retired engineer,  about 45 years of commercial antenna design, RF, Digital, Audio
add a decade or so more for my hobby work.

I have the mother of all junk boxes, from accumulating for that long.

Allison


Re: AGC circuit to try?

ajparent1 <kb1gmx@...>
 

Retired engineer,  about 45 years of commercial antenna design, RF, Digital, Audio
add a decade or so more for my hobby work.

I have the mother of all junk boxes, from accumulating for that long.

Allison


Re: AGC circuit to try?

Gordon Gibby <ggibby@...>
 

​Allison, what on earth do you do for a living, and for WHOM???

gordon



From: BITX20@groups.io <BITX20@groups.io> on behalf of ajparent1 <kb1gmx@...>
Sent: Saturday, April 7, 2018 5:29 PM
To: BITX20@groups.io
Subject: Re: [BITX20] AGC circuit to try?
 
Jerry,

Rare is an order for just one part here.  Typical order for my lab are 4-20 parts and quantity.
Stock devices like 1n4007 a hundred in a order is common, same for 2n2222A, 2n3906, 2n3904
as they are cheaper when purchased in volume.  I do have the BAP64 in various packages and
several others as well. Even some exotic Avago PIN parts.  I maintain a stock that allows me
to build then optimize.  I get annoyed when I don't have something unless exotic like 10ghz
gain blocks.

When I write for open audiences I tend to use parts I know they can get or easily and effortlessly 
substitute and not require shipping for 5 pieces. 

The junction capacitance is about 15-25PF at -4V depending on vendor. Vishay says 15pf and
Motorola says 20.  For the application that's small enough to not be a factor.  Reason is rare
will it be at zero bias as it is being use in the forward direction.  However, if bias is zero, the
capacitance measured for a few 1n4007s is around 25 pf and compared to the nominal
bypass for that stage it is larger than the emitter resistance used and far higher than the
gain set resistor that was there.  At 30mhz thats a capacitive reactance of around 200
ohms and the resistor was only 10, so gain reduction is still very significant.  

Regarding  "That should probably be R33, not R35"  depends on the version of the schematic
you have.   It is annoying but it is what it is.  For the latest dump of the manual 33 would be it.
When you follow a design for over 12 years to accumulate all the flavors and variants, big disks
are cheap so I keep information going back to the flood.  The Bitx folder is small only 43MB
and history is interesting.  

One of my radios has a twin-Tee attenuator in the front end as image reject DC receivers 
have few places at RF to put variable attenuation in.  It works very well in that place but might be
harder to insert into the (u)BITX board. 

It allows the BITX ( all variants) to have RF agc and on a trial version of a bitx20 about 10 years ago
I have used it in the TX path to allow ALC for power compression to allow increased talk power.
The agc signal in that case was rectified RF out.   IT has another useful characteristic in that any
time the SWR is unacceptable the RF at that point will climb and clamp the TX power.  Its not a 
true SWR protection but it helps.

Its a really neat design for those that like to mod.

FYI that opamp AGC mod was published by W4OP and also a Y0 a while ago as applicable to 
KNQ7A, KN10, and the X1M all of which use a MC1350 for the RX IF and require a 4 to 8V signal
for AGC where 4V is max gain and 8V is min (about -50DB) gain.  It would take a transistor
and a few resistors to invert the signal and apply it to the diodes.  An opamp can do that too
and a quad device would be convenient.  

Allison


Re: AGC circuit to try?

ajparent1 <kb1gmx@...>
 

Jerry,

Rare is an order for just one part here.  Typical order for my lab are 4-20 parts and quantity.
Stock devices like 1n4007 a hundred in a order is common, same for 2n2222A, 2n3906, 2n3904
as they are cheaper when purchased in volume.  I do have the BAP64 in various packages and
several others as well. Even some exotic Avago PIN parts.  I maintain a stock that allows me
to build then optimize.  I get annoyed when I don't have something unless exotic like 10ghz
gain blocks.

When I write for open audiences I tend to use parts I know they can get or easily and effortlessly 
substitute and not require shipping for 5 pieces. 

The junction capacitance is about 15-25PF at -4V depending on vendor. Vishay says 15pf and
Motorola says 20.  For the application that's small enough to not be a factor.  Reason is rare
will it be at zero bias as it is being use in the forward direction.  However, if bias is zero, the
capacitance measured for a few 1n4007s is around 25 pf and compared to the nominal
bypass for that stage it is larger than the emitter resistance used and far higher than the
gain set resistor that was there.  At 30mhz thats a capacitive reactance of around 200
ohms and the resistor was only 10, so gain reduction is still very significant.  

Regarding  "That should probably be R33, not R35"  depends on the version of the schematic
you have.   It is annoying but it is what it is.  For the latest dump of the manual 33 would be it.
When you follow a design for over 12 years to accumulate all the flavors and variants, big disks
are cheap so I keep information going back to the flood.  The Bitx folder is small only 43MB
and history is interesting.  

One of my radios has a twin-Tee attenuator in the front end as image reject DC receivers 
have few places at RF to put variable attenuation in.  It works very well in that place but might be
harder to insert into the (u)BITX board. 

It allows the BITX ( all variants) to have RF agc and on a trial version of a bitx20 about 10 years ago
I have used it in the TX path to allow ALC for power compression to allow increased talk power.
The agc signal in that case was rectified RF out.   IT has another useful characteristic in that any
time the SWR is unacceptable the RF at that point will climb and clamp the TX power.  Its not a 
true SWR protection but it helps.

Its a really neat design for those that like to mod.

FYI that opamp AGC mod was published by W4OP and also a Y0 a while ago as applicable to 
KNQ7A, KN10, and the X1M all of which use a MC1350 for the RX IF and require a 4 to 8V signal
for AGC where 4V is max gain and 8V is min (about -50DB) gain.  It would take a transistor
and a few resistors to invert the signal and apply it to the diodes.  An opamp can do that too
and a quad device would be convenient.  

Allison


Re: AGC circuit to try?

Jerry Gaffke
 

Allison said:
>  If you feel that is not enough agc range then add the same mod at R35

That should probably be R33, not R35

I have no idea what the capacitance of a slightly forward biased 1n400x is,
figure 6 here suggests it's north of 30pf:  https://www.vishay.com/docs/88503/1n4001.pdf
Might be marginal at 45mhz, can vary wildly with diode type and brand.

Consensus seems to be that a 1n4007 is preferred over other 1n400x flavors for use as a PIN.
Some experimentation may be required using diodes from different manufacturers:
    https://groups.io/g/BITX20/message/32099
That entire thread is worth looking over.

If you are paying $5 postage to ship in some 1n4007's, you might consider
also getting some BAP64-02's at $0.43 each single unit pricing, Mouser 771-BAP64-02-T/R.
Down to $0.10 or so if you buy a reel.
Fully spec'd for use as an RF PIN diode. 
We've discussed the BAP64Q array of four PIN diodes in the forum previously
for use as a (roughy) 50 ohm conrolled impedance bridge attenuator.
Easily searched for on the forum website.

Jerry, KE7ER


On Sat, Apr 7, 2018 at 12:15 pm, ajparent1 wrote:
You have the audio detection to get an AGC control voltage but you don't show what your controlling.

What I find odd in general every one seems to be bent on leveling the audio volume in the audio circuit.
Why?  I understand protecting ones ears and all but what an audio compressor?  

The Bitx or uBitx has enough gain and handy places that RF gain control based on audio detection works
very well.  The easy way is replace R13 (ubitx) with a diode such as 1n400x (x=1 to 7) and controlling the
current through the diode to make it behave as a variable resistance at RF.  

The current would be about 4-6ma at max gain and decrease to zero (0) at minimum gain.  For that design
the AGC range is about 26 to 32db depening on band.  If you feel that is not enough agc range then add
the same mod at R35 then with both the agc range is near 60+ DB, generally enough.  AGC in this form
is less prone to overload distortion as you are lowering gain.  The control could be a pot between 8V
(or RX-V) and ground and a series 1K resistor to the he diode (x2 of your using both diodes).  That is a
manual gain control.   To make it automatic use a circuit like just published to detect the voltage at the
top of the audio gain pot and feed that voltage to the gain control diodes.  The circuit should be
arranged to put 4-8V out at NO Audio and decrease to zero volts with increasing audio.

Side note the 1n400x series with minor reservations makes a fine substitute for a PIN diode, the
prefered but more costly device for this function.  Beside being widely available and cheap
( I buy them in quantities of 100 for pennies each) makes it useful.  It also makes a good
20pf varicap and a 1A rectifier to 1000V (1n4007).

This was tested on the first bitx20 I built over a decade ago to test AGC and is used on several  older Tentec
radios and more than few of my own design.   That said its far from a new idea or design as its documented
in EMRFD and the older SSD (Solid State Design AARL press, out of print).   


Re: RadioKits.in Case #ubitx

lou_w2row
 

I also had trouble fitting the power pcb between the fuse and switch. I bent the fuse lead so that it sort of fit together. My switch survived the soldering but just barely. I could see the plastic softening.

Has anyone tried to fit the tuning knob (provided with the case) to the encoder (provided with the radio)? The hole in the knob is much to small to fit on the encoder shaft. I could not see anyway to adjust the knob opening.

73,  Lou W2ROW


Re: AGC circuit to try?

Gordon Gibby <ggibby@...>
 

​Allison --- THanks VERY VERY much for that informative post about using a 1n400X diode as a rf gain control!!!!


Gordon




From: BITX20@groups.io <BITX20@groups.io> on behalf of ajparent1 <kb1gmx@...>
Sent: Saturday, April 7, 2018 3:15 PM
To: BITX20@groups.io
Subject: Re: [BITX20] AGC circuit to try?
 
It is incomplete..

You have the audio detection to get an AGC control voltage but you don't show what your controlling.

What I find odd in general every one seems to be bent on leveling the audio volume in the audio circuit.
Why?  I understand protecting ones ears and all but what an audio compressor?  

The Bitx or uBitx has enough gain and handy places that RF gain control based on audio detection works
very well.  The easy way is replace R13 (ubitx) with a diode such as 1n400x (x=1 to 7) and controlling the
current through the diode to make it behave as a variable resistance at RF.  

The current would be about 4-6ma at max gain and decrease to zero (0) at minimum gain.  For that design
the AGC range is about 26 to 32db depening on band.  If you feel that is not enough agc range then add
the same mod at R35 then with both the agc range is near 60+ DB, generally enough.  AGC in this form
is less prone to overload distortion as you are lowering gain.  The control could be a pot between 8V
(or RX-V) and ground and a series 1K resistor to the he diode (x2 of your using both diodes).  That is a
manual gain control.   To make it automatic use a circuit like just published to detect the voltage at the
top of the audio gain pot and feed that voltage to the gain control diodes.  The circuit should be
arranged to put 4-8V out at NO Audio and decrease to zero volts with increasing audio.

Side note the 1n400x series with minor reservations makes a fine substitute for a PIN diode, the
prefered but more costly device for this function.  Beside being widely available and cheap
( I buy them in quantities of 100 for pennies each) makes it useful.  It also makes a good
20pf varicap and a 1A rectifier to 1000V (1n4007).

This was tested on the first bitx20 I built over a decade ago to test AGC and is used on several  older Tentec
radios and more than few of my own design.   That said its far from a new idea or design as its documented
in EMRFD and the older SSD (Solid State Design AARL press, out of print).   


Allison


Re: AGC circuit to try?

ajparent1 <kb1gmx@...>
 

It is incomplete..

You have the audio detection to get an AGC control voltage but you don't show what your controlling.

What I find odd in general every one seems to be bent on leveling the audio volume in the audio circuit.
Why?  I understand protecting ones ears and all but what an audio compressor?  

The Bitx or uBitx has enough gain and handy places that RF gain control based on audio detection works
very well.  The easy way is replace R13 (ubitx) with a diode such as 1n400x (x=1 to 7) and controlling the
current through the diode to make it behave as a variable resistance at RF.  

The current would be about 4-6ma at max gain and decrease to zero (0) at minimum gain.  For that design
the AGC range is about 26 to 32db depening on band.  If you feel that is not enough agc range then add
the same mod at R35 then with both the agc range is near 60+ DB, generally enough.  AGC in this form
is less prone to overload distortion as you are lowering gain.  The control could be a pot between 8V
(or RX-V) and ground and a series 1K resistor to the he diode (x2 of your using both diodes).  That is a
manual gain control.   To make it automatic use a circuit like just published to detect the voltage at the
top of the audio gain pot and feed that voltage to the gain control diodes.  The circuit should be
arranged to put 4-8V out at NO Audio and decrease to zero volts with increasing audio.

Side note the 1n400x series with minor reservations makes a fine substitute for a PIN diode, the
prefered but more costly device for this function.  Beside being widely available and cheap
( I buy them in quantities of 100 for pennies each) makes it useful.  It also makes a good
20pf varicap and a 1A rectifier to 1000V (1n4007).

This was tested on the first bitx20 I built over a decade ago to test AGC and is used on several  older Tentec
radios and more than few of my own design.   That said its far from a new idea or design as its documented
in EMRFD and the older SSD (Solid State Design AARL press, out of print).   


Allison