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AGC Circuit for uBITX Featured in July 2019 QST Magazine

Dennis Zabawa
 

On page 45 of the July 2019 issue of QST magazine there is an article on an AGC Circuit for uBITX.  The circuit replaces the uBITX audio amp and adds the AGC functionality.

Curt
 

Cool maybe.  Remember this list is global -- many in India, Europe, Asia, South America, even Canada don't have access to QST (nor do I - my copy hasn't arrived yet) --

can you at least mention the type of audio amplifier, how they are implementing AGC and anything else that is different about this mechanization? 

please think global -- the US may be 'central' to me -- but not everyone here. 

Curt

pat griffin
 

I have only glanced at the circuit but it appears similar to the various ubitx agc circuits we have seen with some nice enhancements.  In fact, the author, K1BQT (email: k1bqt at arrl dot net), built it for a ubitx.  It uses 2n5486, 2N7000 and LM386.
73, AA4PG

http://www.cahabatechnology.com/aa4pg.html


From: BITX20@groups.io <BITX20@groups.io> on behalf of Curt via Groups.Io <wb8yyy@...>
Sent: Tuesday, June 11, 2019 6:37 AM
To: BITX20@groups.io
Subject: Re: [BITX20] AGC Circuit for uBITX Featured in July 2019 QST Magazine
 
Cool maybe.  Remember this list is global -- many in India, Europe, Asia, South America, even Canada don't have access to QST (nor do I - my copy hasn't arrived yet) --

can you at least mention the type of audio amplifier, how they are implementing AGC and anything else that is different about this mechanization? 

please think global -- the US may be 'central' to me -- but not everyone here. 

Curt

Jack, W8TEE
 

The JackAl circuit has both audio and IF AGC, is Open Source, and designed for the µBITX. The manuals can be downloaded from QRP Guys. Anyone who wants to build it is free to do so. See attached.

Jack, W8TEE

On Tuesday, June 11, 2019, 9:59:21 AM EDT, pat griffin <patgriffin@...> wrote:


I have only glanced at the circuit but it appears similar to the various ubitx agc circuits we have seen with some nice enhancements.  In fact, the author, K1BQT (email: k1bqt at arrl dot net), built it for a ubitx.  It uses 2n5486, 2N7000 and LM386.
73, AA4PG

_._,_._,_

MadRadioModder
 

The advantage of the JackAL is that it is a true AGC, controlling the gain of the AF and RF stages of the radio… and thus preventing overload and distortion of the RF stages before the audio gain adjustment.  The circuit in the in QST is just a simple volume control/ limiter that could work on “any audio line” to keep the volume below a specified point.

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Jack Purdum via Groups.Io
Sent: Tuesday, June 11, 2019 9:11 AM
To: BITX20@groups.io
Subject: Re: [BITX20] AGC Circuit for uBITX Featured in July 2019 QST Magazine

 

The JackAl circuit has both audio and IF AGC, is Open Source, and designed for the µBITX. The manuals can be downloaded from QRP Guys. Anyone who wants to build it is free to do so. See attached.

 

Jack, W8TEE

 

On Tuesday, June 11, 2019, 9:59:21 AM EDT, pat griffin <patgriffin@...> wrote:

 

 

I have only glanced at the circuit but it appears similar to the various ubitx agc circuits we have seen with some nice enhancements.  In fact, the author, K1BQT (email: k1bqt at arrl dot net), built it for a ubitx.  It uses 2n5486, 2N7000 and LM386.

73, AA4PG

 


Virus-free. www.avg.com

--

…_. _._

Jerry Gaffke
 

If in your location you get stations you want to hear that are strong enough
to still sound distorted when the volume control is turned down, then
you do need the dynamic range that RF attenuation gives you.
If not (or if your primary concern is that you not damage your ears),
then a simple AGC with audio attenuation is perfectly fine.
Many many many *Bitx* owners are perfectly happy with audio AGC,
and perhaps a pot where RF comes in from the antenna for use as a manual RF gain control.

Mad and I have had this argument before over what "true AGC" might be:
    https://groups.io/g/BITX20/topic/31238211
It's AGC regardless of the frequency at which attenuation takes place.  Period.
There have not been any takers yet to this challenge:
    https://groups.io/g/BITX20/message/68083

Jerry, KE7ER



On Tue, Jun 11, 2019 at 09:08 AM, MadRadioModder wrote:
The advantage of the JackAL is that it is a true AGC, controlling the gain of the AF and RF stages of the radio… and thus preventing overload and distortion of the RF stages before the audio gain adjustment.  The circuit in the in QST is just a simple volume control/ limiter that could work on “any audio line” to keep the volume below a specified point.

MadRadioModder
 

Or…. Just turn the volume down.

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Jerry Gaffke via Groups.Io
Sent: Tuesday, June 11, 2019 2:04 PM
To: BITX20@groups.io
Subject: Re: [BITX20] AGC Circuit for uBITX Featured in July 2019 QST Magazine

 

If in your location you get stations you want to hear that are strong enough
to still sound distorted when the volume control is turned down, then
you do need the dynamic range that RF attenuation gives you.
If not (or if your primary concern is that you not damage your ears),
then a simple AGC with audio attenuation is perfectly fine.
Many many many *Bitx* owners are perfectly happy with audio AGC,
and perhaps a pot where RF comes in from the antenna for use as a manual RF gain control.

Mad and I have had this argument before over what "true AGC" might be:
    https://groups.io/g/BITX20/topic/31238211
It's AGC regardless of the frequency at which attenuation takes place.  Period.
There have not been any takers yet to this challenge:
    https://groups.io/g/BITX20/message/68083

Jerry, KE7ER



On Tue, Jun 11, 2019 at 09:08 AM, MadRadioModder wrote:

The advantage of the JackAL is that it is a true AGC, controlling the gain of the AF and RF stages of the radio… and thus preventing overload and distortion of the RF stages before the audio gain adjustment.  The circuit in the in QST is just a simple volume control/ limiter that could work on “any audio line” to keep the volume below a specified point.


Virus-free. www.avg.com

--

…_. _._

Jerry Gaffke
 

Mad is right.
Just turning down the volume is good enough for the majority of *Bitx* owners.
And how designer meant for this minimalist rig was meant to be used.

But if you got the gain way up to hear a weak station
and then suddenly some +40dB local steps on top of him,
it can be hard to tear the headphones off fast enough.

Jerry


On Tue, Jun 11, 2019 at 12:10 PM, MadRadioModder wrote:

Or…. Just turn the volume down.

 

Curt
 

As we almost started to debate this, ubitx works with no agc, and somewhat better with audio AGC. Glad I figured out finally the vk3ye agc, its nice enough. Those adding the jackal get something even better, Jack invited me to look at it a while back. It has some elements of the hybrid cascode IF AGC. We can each manage our degree of addiction in modifying this nice rig.

I don't miss agc much sitting on a frequency,  but in tuning its nice. While I have an agc off switch I find no reason to turn it off. My tweaks to the vk3ye agc are on the k3pzn website, but I confess I see a resistor value is off, the same one in Peter's schematic. Need to fix that.

Curt

Curt
 

Back to topic -- I see it uses a LM386 output with a JFET input conditioning stage.  A MOSFET is across the differential input of the LM386 to provide attenuation.  audio is sensed by a diode, that directly biases the MOSFET gate with a little RC conditioning.  It does require a little more surgery than the ND6T (minimal surgery) or VK3YE (no surgery) designs.  Useful solution perhaps for someone who has or wants to remove their audio amplifier. 

I confess my ubitx currently feeds a NESCAF with a LM386, now external. 

73 Curt

Richard Spohn
 

Jack, any luck with your website? I am starting to take a serious
look at the JackAl board, would love to find out more info before
buying...as in the BOM and Prices, etc. - Rich WB2GXM

On 6/11/19, Jack Purdum via Groups.Io <jjpurdum=yahoo.com@groups.io> wrote:
The JackAl circuit has both audio and IF AGC, is Open Source, and designed
for the µBITX. The manuals can be downloaded from QRP Guys. Anyone who wants
to build it is free to do so. See attached.
Jack, W8TEE

On Tuesday, June 11, 2019, 9:59:21 AM EDT, pat griffin
<patgriffin@...> wrote:

I have only glanced at the circuit but it appears similar to the various
ubitx agc circuits we have seen with some nice enhancements.  In fact, the
author, K1BQT (email: k1bqt at arrl dot net), built it for a ubitx.  It uses
2n5486, 2N7000 and LM386.73, AA4PG
_._,_._,_



Jack, W8TEE
 

We have not worked on the site, mainly because I was spending time on my FDIM talk and now our club hamfest is Saturday and Al and I are working on the book. One chapter is a different mag loop and controller, so the site has fallen down on the priorities list. However, we have moved everything to our group web site:


Check that out and see if it helps.

Jack, W8TEE

On Tuesday, June 11, 2019, 10:05:00 PM EDT, Richard Spohn <wb2gxm@...> wrote:


Jack, any luck with your website?  I am starting to take a serious
look at the JackAl board, would love to find out more info before
buying...as in the BOM and Prices, etc. - Rich WB2GXM

On 6/11/19, Jack Purdum via Groups.Io <jjpurdum=yahoo.com@groups.io> wrote:
>  The JackAl circuit has both audio and IF AGC, is Open Source, and designed
> for the µBITX. The manuals can be downloaded from QRP Guys. Anyone who wants
> to build it is free to do so. See attached.
> Jack, W8TEE
>
>    On Tuesday, June 11, 2019, 9:59:21 AM EDT, pat griffin
> <patgriffin@...> wrote:
>
>  I have only glanced at the circuit but it appears similar to the various
> ubitx agc circuits we have seen with some nice enhancements.  In fact, the
> author, K1BQT (email: k1bqt at arrl dot net), built it for a ubitx.  It uses
> 2n5486, 2N7000 and LM386.73, AA4PG

> _._,_._,_
>
>
>
>


Olivier Grand
 

Hello Dennis.
I wondering if you can send me a copy of the K1BQT's article on the AGC Circuit for uBITX on page 45 of the July 2019 issue of QST magazine, I am ARRL registered but I can't download it from France.
As you can see on the picture attached, I don't have enough room (even with the IRF510 out of the box) to install the Jack Al Board. I already installed an audio amp with tone control, the VK3YE's AVC, a mike compressor,  the standalone analyser, two 5V rails (one for TX and one for RX) and a Li-Ion battery with protection bard, the rig is still under construction so please excuse the anarchic way of wiring.
Regards.
Olivier

Garanti sans virus. www.avast.com


Le mar. 11 juin 2019 à 06:19, Dennis Zabawa <kg4rul@...> a écrit :
On page 45 of the July 2019 issue of QST magazine there is an article on an AGC Circuit for uBITX.  The circuit replaces the uBITX audio amp and adds the AGC functionality.

Rob French (KC4UPR)
 

I'm looking at possibly lifting just the AGC circuit out of the JackAl design, and seeing if I can stock it out of my junk box.  But... the only JFET's I have are MPF102, J201, 2N5486, and 2N4393... will any of those work?  Other than the MPF102, the rest were all originally purchased for audio work, so I can totally imagine them not being suitable.

Thanks!
-Rob

MadRadioModder
 

As I recall, the JackAl AGC circuit is just the Hycas AGC circuit lifted from QST December 2007.  Al added a couple of things like a switch to turn it off.  The FETs are nothing special.  A 201 and a 102 will work fine.

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Rob French (KC4UPR)
Sent: Sunday, August 11, 2019 10:57 PM
To: BITX20@groups.io
Subject: Re: [BITX20] AGC Circuit for uBITX Featured in July 2019 QST Magazine

 

I'm looking at possibly lifting just the AGC circuit out of the JackAl design, and seeing if I can stock it out of my junk box.  But... the only JFET's I have are MPF102, J201, 2N5486, and 2N4393... will any of those work?  Other than the MPF102, the rest were all originally purchased for audio work, so I can totally imagine them not being suitable.

Thanks!
-Rob


Virus-free. www.avg.com

--

…_. _._

Rob French (KC4UPR)
 

Thanks.  Any thoughts on voltage rating for the capacitors, especially the "big" electrolytic ones?  (10uF, 100uF, 470uF... I'm assuming they're electrolytics.)  I looked at the Hycas schematic, and that calls out 50v for all the caps, but I don't have many of those... got lots of 16v though!

MadRadioModder
 

Since the entire circuit set is 12V or less, your 16V caps should work just fine.

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Rob French (KC4UPR)
Sent: Monday, August 12, 2019 12:40 AM
To: BITX20@groups.io
Subject: Re: [BITX20] AGC Circuit for uBITX Featured in July 2019 QST Magazine

 

Thanks.  Any thoughts on voltage rating for the capacitors, especially the "big" electrolytic ones?  (10uF, 100uF, 470uF... I'm assuming they're electrolytics.)  I looked at the Hycas schematic, and that calls out 50v for all the caps, but I don't have many of those... got lots of 16v though!


Virus-free. www.avg.com

--

…_. _._

David Wilcox
 

Can someone explain the reasons for certain voltages listed on any schematic for the electrolytic caps, AND what problems could arise if one used a cap with a larger voltage rating? How much higher a voltage cap could be substituted without causing a problem?

Dave K8WPE 

David J. Wilcox K8WPE’s iPad

On Aug 12, 2019, at 2:18 AM, MadRadioModder <madradiomodder@...> wrote:

Since the entire circuit set is 12V or less, your 16V caps should work just fine.

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Rob French (KC4UPR)
Sent: Monday, August 12, 2019 12:40 AM
To: BITX20@groups.io
Subject: Re: [BITX20] AGC Circuit for uBITX Featured in July 2019 QST Magazine

 

Thanks.  Any thoughts on voltage rating for the capacitors, especially the "big" electrolytic ones?  (10uF, 100uF, 470uF... I'm assuming they're electrolytics.)  I looked at the Hycas schematic, and that calls out 50v for all the caps, but I don't have many of those... got lots of 16v though!


Virus-free. www.avg.com

--

…_. _._

Ian Reeve
 

The voltage rating on the capacitor is the maximum the component can “deal with”. It works absolutely fine at lower voltages of course and it is best to give some headroom for example on a 12v rail,use 16v capacitors.

There is no problem going up to say 25 or higher voltage rating,just expect a physically larger component which might not fit in the desired space.

Electrolytics are happiest when run at 50%  and above of their stated voltage, they tend to deteriorate if say a 100v component is used on a 12v rail. The low voltage in comparison to their rating does not properly keep the component and its chemicals in proper balance.

 

This is why equipment not used for some considerable time needs careful powering up because of the deterioration of electrolytics deprived of polarising voltage.

 

For a 12v DC  rail use 16v or 25v components.

 

Hope this helps

 

Ian M0IDR

 

Sent from Mail for Windows 10

 


From: BITX20@groups.io <BITX20@groups.io> on behalf of David Wilcox via Groups.Io <Djwilcox01@...>
Sent: Monday, August 12, 2019 11:21:17 AM
To: BITX20@groups.io <BITX20@groups.io>
Subject: Re: [BITX20] AGC Circuit for uBITX Featured in July 2019 QST Magazine
 
Can someone explain the reasons for certain voltages listed on any schematic for the electrolytic caps, AND what problems could arise if one used a cap with a larger voltage rating? How much higher a voltage cap could be substituted without causing a problem?

Dave K8WPE 

David J. Wilcox K8WPE’s iPad

On Aug 12, 2019, at 2:18 AM, MadRadioModder <madradiomodder@...> wrote:

Since the entire circuit set is 12V or less, your 16V caps should work just fine.

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Rob French (KC4UPR)
Sent: Monday, August 12, 2019 12:40 AM
To: BITX20@groups.io
Subject: Re: [BITX20] AGC Circuit for uBITX Featured in July 2019 QST Magazine

 

Thanks.  Any thoughts on voltage rating for the capacitors, especially the "big" electrolytic ones?  (10uF, 100uF, 470uF... I'm assuming they're electrolytics.)  I looked at the Hycas schematic, and that calls out 50v for all the caps, but I don't have many of those... got lots of 16v though!


Virus-free. www.avg.com

--

…_. _._

Jakobus van der Merwe
 

All caps have a rated voltage. That is the max voltage you apply to it. If you exceed this voltage the insulation between the "plates" of the cap will break down and the magical smoke will be released out of it. It will blow. Alliminium  caps are very sensitive to this max voltage. Therefore the max voltages are printed on them so you are can be aware of it. And the circuit designer also jods it down on the cct diagram. If your supply voltage is say 12V, it is safe to use a 16V rated cap. You do then have a safety margin for 'n slight mishap in the supply voltage if it occur. The cap will only charge up to the supply voltage. So using a higher voltage rated cap will make no difference. The cap can not generate a higher voltage than what is supplied to it. Your safety margin will just be greater. Using a 50V cap in a 12V system ? So what. The capacitance of the cap is worth watching and to adhere to. Also the voltage rating of the cap determines its fiscall  dimensions. 

J van der Merwe

On Mon, 12 Aug 2019, 12:21 David Wilcox via Groups.Io <Djwilcox01=yahoo.com@groups.io> wrote:
Can someone explain the reasons for certain voltages listed on any schematic for the electrolytic caps, AND what problems could arise if one used a cap with a larger voltage rating? How much higher a voltage cap could be substituted without causing a problem?

Dave K8WPE 

David J. Wilcox K8WPE’s iPad

On Aug 12, 2019, at 2:18 AM, MadRadioModder <madradiomodder@...> wrote:

Since the entire circuit set is 12V or less, your 16V caps should work just fine.

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Rob French (KC4UPR)
Sent: Monday, August 12, 2019 12:40 AM
To: BITX20@groups.io
Subject: Re: [BITX20] AGC Circuit for uBITX Featured in July 2019 QST Magazine

 

Thanks.  Any thoughts on voltage rating for the capacitors, especially the "big" electrolytic ones?  (10uF, 100uF, 470uF... I'm assuming they're electrolytics.)  I looked at the Hycas schematic, and that calls out 50v for all the caps, but I don't have many of those... got lots of 16v though!


Virus-free. www.avg.com

--

…_. _._