Topics

has anyone built this kit AGC from Amateur Radio Kits?

Erik Hokansson
 

I ordered 2 kits thankfully because both were missing parts and I could make 1 kit from the 2 ..seller non-responsive..  can anyone  tell a newbee  how/where to connect the "audio" and "to AGC" to the bitx40? each has 2 wires 


MVS Sarma
 

What is your concern with the kit?
 Sunil has put information on his site.
 please go through and try to use. . Still you have a problem,  perhaps I to could be of some help.
 all the best
  sarma
vu3zmv

On Sat, Apr 8, 2017 at 5:14 AM, Erik Hokansson <hokan@...> wrote:
I ordered 2 kits thankfully because both were missing parts and I could make 1 kit from the 2 ..seller non-responsive..  can anyone  tell a newbee  how/where to connect the "audio" and "to AGC" to the bitx40? each has 2 wires 





--
Regards
Sarma
 

thomas.donoghue@...
 

I too was hoping to find answers to this same question.  I have looked through Sunil's documents and I think the question above needs clarification.  We are interested in how/where to connect the plugs/wires from the AGC kit to the Bitx40 board.  Some other models show Bitx20 boards having circuit oard traces cut and pins soldered in to "receive" the plugs from the AGC board.  In bringing this AGC board tothe Bitx40, one does not want to cut or modify the board without some awareness that the process is correct.  Other AGC circuits call for removing wire(s) from the volume pot for audio "in" then runing "out" from the AGC boardack to thevolume pot.  Again, that is for a different circuit, but we recognise the wire-up could be similar.  One just is not interested in finding out by way of smoke, that connections were incorrect.....many thanks for any input to a 2 year old posting...73

Jack, W8TEE
 

The AGC issue is part apples and part oranges. Some AGC circuits work off the volume control while others work off the IF chain. If you're using the IF chain, chances are there's going to be some messing around with the PCB itself. If you're happy with an automatic volume control, working off the volume control is less invasive to the board itself. The IF surgery need not be too invasive, however. The JackAl board (hamradiodesigns.com) provides both IF and audio AGC. The IF surgery requires removing an SMD resistor and moving an on-board cap to that resistor's position and then attaching a cable to the old cap location. There is no audio AGC surgery, since the board has its own 6W audio amp on board. (It preserves the old µBITX audio so you can compare the results.)

Anyway, you need to decide which kind of AGC you want and be prepared to perform some minor surgery for IF AGC and perhaps minor "wire moving" for audio AGC. Always remember that no decision is a decision--thousands are using the µBITX with no AGC. Pick what makes you happy!

Jack, W8TEE

On Thursday, February 21, 2019, 9:44:32 AM EST, thomas.donoghue@... <thomas.donoghue@...> wrote:


I too was hoping to find answers to this same question.  I have looked through Sunil's documents and I think the question above needs clarification.  We are interested in how/where to connect the plugs/wires from the AGC kit to the Bitx40 board.  Some other models show Bitx20 boards having circuit oard traces cut and pins soldered in to "receive" the plugs from the AGC board.  In bringing this AGC board tothe Bitx40, one does not want to cut or modify the board without some awareness that the process is correct.  Other AGC circuits call for removing wire(s) from the volume pot for audio "in" then runing "out" from the AGC boardack to thevolume pot.  Again, that is for a different circuit, but we recognise the wire-up could be similar.  One just is not interested in finding out by way of smoke, that connections were incorrect.....many thanks for any input to a 2 year old posting...73

Robert D. Bowers
 

I added an external DSP noise filter to my bitx40... it has awesome AGC built-in, and can really cut back on noise without garbling voice (as long as I don't turn it up too far).  The audio out is also quite strong and clear - great for mobile use. 

Since people are often dumping the filters (as they're usually built-in these days to the commercial rigs), they're available used (and usually still working fine) for cheap, as well as still being sold if you have that sort of income (probably not that bad a price for most hams).

This could be another answer regarding AGC.

The only thing I miss is an external squelch circuit - I've got the schematic for one that is based on voice characteristics, but have too many pans in the fire so to speak, to build it and try it out.

Bob

N4FBZ

On 2/21/19 10:03 AM, Jack Purdum via Groups.Io wrote:
The AGC issue is part apples and part oranges. Some AGC circuits work off the volume control while others work off the IF chain. If you're using the IF chain, chances are there's going to be some messing around with the PCB itself. If you're happy with an automatic volume control, working off the volume control is less invasive to the board itself. The IF surgery need not be too invasive, however. The JackAl board (hamradiodesigns.com) provides both IF and audio AGC. The IF surgery requires removing an SMD resistor and moving an on-board cap to that resistor's position and then attaching a cable to the old cap location. There is no audio AGC surgery, since the board has its own 6W audio amp on board. (It preserves the old µBITX audio so you can compare the results.)

Anyway, you need to decide which kind of AGC you want and be prepared to perform some minor surgery for IF AGC and perhaps minor "wire moving" for audio AGC. Always remember that no decision is a decision--thousands are using the µBITX with no AGC. Pick what makes you happy!

Jack, W8TEE

On Thursday, February 21, 2019, 9:44:32 AM EST, thomas.donoghue@... <thomas.donoghue@...> wrote:


I too was hoping to find answers to this same question.  I have looked through Sunil's documents and I think the question above needs clarification.  We are interested in how/where to connect the plugs/wires from the AGC kit to the Bitx40 board.  Some other models show Bitx20 boards having circuit oard traces cut and pins soldered in to "receive" the plugs from the AGC board.  In bringing this AGC board tothe Bitx40, one does not want to cut or modify the board without some awareness that the process is correct.  Other AGC circuits call for removing wire(s) from the volume pot for audio "in" then runing "out" from the AGC boardack to thevolume pot.  Again, that is for a different circuit, but we recognise the wire-up could be similar.  One just is not interested in finding out by way of smoke, that connections were incorrect.....many thanks for any input to a 2 year old posting...73

James Zdunic
 

Here’s an example photo of the surgery Jack mentioned...

image1.jpeg

Jim KM4TXR

On Feb 21, 2019, at 10:03 AM, Jack Purdum via Groups.Io <jjpurdum@...> wrote:

The AGC issue is part apples and part oranges. Some AGC circuits work off the volume control while others work off the IF chain. If you're using the IF chain, chances are there's going to be some messing around with the PCB itself. If you're happy with an automatic volume control, working off the volume control is less invasive to the board itself. The IF surgery need not be too invasive, however. The JackAl board (hamradiodesigns.com) provides both IF and audio AGC. The IF surgery requires removing an SMD resistor and moving an on-board cap to that resistor's position and then attaching a cable to the old cap location. There is no audio AGC surgery, since the board has its own 6W audio amp on board. (It preserves the old µBITX audio so you can compare the results.)

Anyway, you need to decide which kind of AGC you want and be prepared to perform some minor surgery for IF AGC and perhaps minor "wire moving" for audio AGC. Always remember that no decision is a decision--thousands are using the µBITX with no AGC. Pick what makes you happy!

Jack, W8TEE

On Thursday, February 21, 2019, 9:44:32 AM EST, thomas.donoghue@... <thomas.donoghue@...> wrote:


I too was hoping to find answers to this same question.  I have looked through Sunil's documents and I think the question above needs clarification.  We are interested in how/where to connect the plugs/wires from the AGC kit to the Bitx40 board.  Some other models show Bitx20 boards having circuit oard traces cut and pins soldered in to "receive" the plugs from the AGC board.  In bringing this AGC board tothe Bitx40, one does not want to cut or modify the board without some awareness that the process is correct.  Other AGC circuits call for removing wire(s) from the volume pot for audio "in" then runing "out" from the AGC boardack to thevolume pot.  Again, that is for a different circuit, but we recognise the wire-up could be similar.  One just is not interested in finding out by way of smoke, that connections were incorrect.....many thanks for any input to a 2 year old posting...73

MadRadioModder
 

Maybe a few words about the technical differences  in AF and IF AGC.  An audio AGC (better called AVC:  Auto Volume Control)  just keeps the volume at or below a specified level.  A good IF AGC on the other hand will turn the gain down of the receiver’s IF gain stages so that loud signals don’t cause those stages (including the AF stage) to go into compression (flat topping etc.) causing loud DISTORTED signals to come through. There are good thing and bad things that go with both methodologies.   You should decide what you are really trying to accomplish with the circuitry before you start building.

 

AVC

Pros:  Simple, easy to understand and implement.  Can be done at the speaker.

Cons:  Loud signals may distort/ overload IF and front end of the radio

 

AGC

Pros:  Limits IF and AF compression when implemented properly

Cons:  Is more difficult to build.  Is bandwidth dependent so a loud signal up the band could cause active AGC if the filtered IF bandwidth is wide.

 

I’ve designed many commercial AC circuits and they can be more complicated to pull off than the actual receiving circuitry.

 

MRM

 


Virus-free. www.avg.com

--

…_. _._

Alf Baranda
 

 
 
 
 
 
That's right, exactly the same as I think.
For those of us who have built receivers from the beginning, we know that a good AGC circuit with a good dynamic range is one of the most complicated parts of a good radio receiver.
The AGC must always act on the first input circuits and on IF, of course.
In this way, saturations that involve clipping and distortion of the signal are avoided.
For me, this circuit has always been a great challenge and a big headache, due to its importance and complexity.
 
 
 
 
 

Ted
 

Here's another solution. Get one of these RF preamp kits and install it between the TX/RX relay and the front end, just as for the popular AGC circuits. The output can be clamped down with a transistor fed with control voltage from an audio module.

I used a spare module lying around, and added a diode and capacitor to rectify the output to [near] DC that varies by audio amplitude. That feeds the clamping transistor, which shunts the preamp output [which has traces for an attenuation pad already] through a 47k capacitor.  A manual control pot to feed clamping energy was added as well.

This near-short at the preamp output (isolated from the preamp by 100-ohms as R6 below, first) more than handles the preamped RF; it shuts all RF down to well below naked, factory sensitivity AND still allows the extra pickup some operators may enjoy. Not that he ubitx lacks sensitivity, but preferences vary.







Ted
K3RTA

Gordon Gibby <ggibby@...>
 

Wow that’s a slick idea!  But can you clarify the value of that clamp and capacitor? 47K doesn’t make sense


On Feb 22, 2019, at 06:10, Ted via Groups.Io <k3rta@...> wrote:

Here's another solution. Get one of these RF preamp kits and install it between the TX/RX relay and the front end, just as for the popular AGC circuits. The output can be clamped down with a transistor fed with control voltage from an audio module.

I used a spare module lying around, and added a diode and capacitor to rectify the output to [near] DC that varies by audio amplitude. That feeds the clamping transistor, which shunts the preamp output [which has traces for an attenuation pad already] through a 47k capacitor.  A manual control pot to feed clamping energy was added as well.

This near-short at the preamp output (isolated from the preamp by 100-ohms as R6 below, first) more than handles the preamped RF; it shuts all RF down to well below naked, factory sensitivity AND still allows the extra pickup some operators may enjoy. Not that he ubitx lacks sensitivity, but preferences vary.



<rfamp1.3.png>



Ted
K3RTA

Ted
 

Oh, me and my haste.... 47uF but mainly because it was available. Basically, any value that successfully causes all or, nearly all, energy coming from the preamp to disappear into the 100-ohm (or your experimental value) resistor will do. 

Tnx,  

Ted

Ted
 

I should also add that using a 2N7002 rather than a 2N2222 would be worthy of a trial; that's what the popular ND6T design uses.

Once ready to destroy the new V5 kit just received, I plan to build the ND6T board in hand and have it's output applied to the KitsandParts preamp in place of an R7 & with an R6 of yet-to-be-determined value. The current trial on a V3 radio uses (as mentioned) a 100-ohm resistor just to keep from shorting out the preamp transistor direct to earth.