Date   
Add S-meter to VK3YE AGC

Curt
 

I have been pleased with this unusual AGC circuit as it nicely removes the top of large signals.  VK3YE has suggested measuring current in parallel with the LED that drives the AGC action, but I found this gave little indication of relative signal strength.  it works much better measuring current in series with the LED. 

I am using a small meter movement supplied by Sunil, about 250 uV peak current.  A shunt resistor across the meter is necessary since the LED current at peak is at least 20 mA per my research.  The approximate value of the shunt resistor Rsh = ( Im x Rm ) / Ish

Rm was unknown but I am able to measure it with my DVM at around 500 ohms.  Inserting these values gives 6.25 ohms.  i found a resistor around 5 ohms and it working nicely.  Its not a real S-meter response - let's call it a signal strength meter.  I sense I can discern signals from approx S5 to S9 with it.  Now if someone does not have a meter movement, the LED itself could be observed to sense signal strength - but the meter is a nice touch. 

I have previously tried s-meter sensing circuits but the action of this particular AGC circuit prohibits them from functioning - so this simple current meter does decently. 

73 Curt

Re: External Amp

Sajid Rahum
 

Hi Richie

Were you able to get the 22ohm 1 watt resistor added?  can you share the exact place you soldered over from the gate to target solder point.  That is where it is not clear.

Sajid

Re: AGC Circuit for uBITX Featured in July 2019 QST Magazine

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
_._,_._,_



Re: AGC Circuit for uBITX Featured in July 2019 QST Magazine

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

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


Re: Antuino and SWR

Ashhar Farhan
 

Mike,
This is unusual. Do you have a signal source that can be used to provide variable level signals such as a step attenuator or an amplitude controlled signal generator?
It could be that the frequency calibration is off. Have you checked the frequency calibration too?
What frequency are you using for swr measurement?
- f

On Wed 12 Jun, 2019, 6:23 AM Michael Aiello, <n2htt.mike@...> wrote:
Has anyone experimented with the Antuino as an SWR meter?
I have noticed it reads consistently high, even after repeated return loss calibrations.

Using a set of calibrated dummy loads, I get these readings:
1:1, 50 ohms  - Antuino reads 1.0
2:1, 100 ohms - reads 3.0
5:1, 250 ohms - reads 8.7
100:1, 5000 ohms - reads 99.9

So we have good agreement at each end of the scale, not so much in the middle. Using my commercial SWR analyzer, these loads read exactly as marked.

Anyone have a similar experience?

73,
Mike N2HTT

Re: Antuino

KE2GKB
 

has anyone gotten a chance to test this? It seems there are quite a few of us with this problem. I need to get an attenuator set on hand to try this my self but I have noticed this problem with my antuino as well mostly where the the SNA measures -15 with a short piece of Coax hooked up.

-- Tim Keller - KE2GKB https://shop.kit-projects.com

Re: Amateurradiokits Chassis and Grounding

Dexter N Muir
 

Modern wood-drills (used to be called 'bits' for brace-and-bit use) might help, in an ordinary drill (hand- or low-speed) to 'peel off ' a circular 'land' of paint (or whatever). They have a flat 'cutting' edge with a centralizing peak that ought to be the right size/proportion.

Re: bitx40: low RF ower an dead part in RX path?

Stephan Lauffer
 

Dear Jerry,

thanks for your help!

For Pwr I use diode to prevent wrong polarization. Then into the LM2940 12V with 0.1uF on input and 100uF on output side. The PA is connected after the diode. I will add another, bigger C at input for some tests.

Yesterday I noticed an other "funny" thing: If the input power is lower than about 12.9V I can hear strong the tuning ticks. But I have no high freq hiss. If I increase the voltage the ticks went of and the hiss begings. (:

Ok, my RF input part seems to be OK I guess. I checked it out with a ~2m wire like Farhan in the video below. The sound here is not that loud (f.e. at C11) and not that high and crispy but I guess this is in the specs. I can hear weak signals, thats good, my bitx has good ears. Just could a bit more louder. Hm... Checked four different small speakers.

Would ne nice to fix the hiss and tuning click thing... some day! :)

Am 10.06.2019 um 04:43 schrieb Jerry Gaffke via Groups.Io:

Stephan,
Driving 1khz into C31 is not going to give much response because the amplifier at Q3
is operating at 12mhz, and the 0.1uF at C33 will mostly block the 1khz audio frequency.
The signals through Q3 remain at 12mhz until after going through the mixer at D15,D16,T4,
after which they are at audio frequencies.
Here's an easy way to do a rough check of the gain of each stage of a receiver:
http://bitxhacks.blogspot.com/2016/12/troubleshooting-bitx40.html
Farhan uses a piece of wire that's maybe a meter or two long as an antenna, nothing attached to the far end of the wire.
Your household environment will have 60hz power hum and lots of RF signals from digital clocks and light dimmers
and natural atmospheric disturbances, all of which get picked up by the wire to provide the test signal.
If the Bitx40 is getting signals strong enough that you need the AGC circuit to prevent the audio from distorting,
that distortion is probably coming from too large of a signal into the Q12 audio pre-amp stage.
The LM386 audio amplifier should then give plenty of volume.
I suggest you triple check the way the volume control and speaker have been wired up,
perhaps try a larger speaker.
The three terminal Low-Dropout-Regulator should work fine if used with the recommended bypass caps.
You don't say which LDO you are using, here's a datasheet for the popular LM7812 (and many variants of it).
They recommend a 0.22uF cap to ground at the input pin of the regulator to avoid oscillation,
which may very well be the source of your noise problem.  (Maybe just two common 0.1uF caps in parallel.)
A 0.1uF cap from output pin to ground is not a bad idea.
Jerry, KE7ER
On Sun, Jun 9, 2019 at 09:32 AM, Stephan Lauffer wrote:
Hello!
With the AGC mod from Don nd6t I have a lot of fun with my bitx40
again. Without this strong signals overdrive my RX path somewhere
(in LM386?) that much that I had strong distortion with volume poti
in round about the middle position and above.
But there are two other problems (maybe default bitx40 behaviour or
a broken part??):
1st: My RX signal is very weak.
I checked out several small speakers but I need to set volume to max
in any case. The bitx is then not as loud as a normal human voice
nearby you. Maybe a transistor in the RX path is a problem? I feed a
nf signal ~1kHz with some few mV into C116, C107 and C33. Everytime
I get a loud and strong signal. On C31 I did not get a good/strong
signal. Maybe in this stage is a problem? Is there a paper/wiki how
I could nail this problem down? First I thought about another NF
stage witha LM380. But after I get the loud signal with my
testsignal I guess this is not needed.
2nd: "White noise"/hiss in the NF signal:
I tried to power the PA independend with > 12V for more HF output.
This means: After the power plug I split the PWR IN with a LDO for
the main 12V circuit and another wire without the LDO into the PA
in. So fare, so good. The very interesting part is that I get high
freq hiss in the RX signal path as soon as the input voltage exceeds
the 12.0V out plus the drop voltage of the LDO. F.e. this means:
Clear RX signal up to 12.7V and high freq noise up from here. The
noise reaches its max volume about 13.0V. Is this a general problem
as soon as I drive the PA with higher volume or is there a change to
solve this issui with better groundings/shields..?
Best regards, 73 an thanks for help,
Stephan dc8lz
--
Liebe Gruesse, with best regards,
Stephan Lauffer

Telefon: +49 7661 905216
Mobile: +49 172 7145197
Ham Radio: DC8LZ, QTH JN37XX
Schulstr. 1c
79252 Stegen
Germany

Re: bitx40: low RF ower an dead part in RX path?

 

Your in out voltage is getting close to its lower limit + diode drop.

Raj

At 12-06-19, you wrote:

Yesterday I noticed an other "funny" thing: If the input power is lower than about 12.9V I can hear strong the tuning ticks. But I have no high freq hiss. If I increase the voltage the ticks went of and the hiss begings. (:

Re: bitx40: low RF ower an dead part in RX path?

Stephan Lauffer
 

Jerry,

Am 10.06.2019 um 04:43 schrieb Jerry Gaffke via Groups.Io:
[...]

If the Bitx40 is getting signals strong enough that you need the AGC circuit to prevent the audio from distorting,
that distortion is probably coming from too large of a signal into the Q12 audio pre-amp stage.
The LM386 audio amplifier should then give plenty of volume.
I suggest you triple check the way the volume control and speaker have been wired up,
perhaps try a larger speaker.
You mean Q16 not Q12, right?

At Q12 I changed R123 and R126 a bit to get a stronger MIC signal.

73, Stephan
--

Re: bitx40: low RF ower an dead part in RX path?

Stephan Lauffer
 

Hello Raj,

yes. I thought it shouldn't be a problem to work with some few volt below 12 (f.e. with 10V).

I found this fix https://www.youtube.com/watch?v=_7q7nG-awsc and it works very fine. :)

So now no more tuning ticks below 12V (12,9V). That's nice because I'd like to power it with 3S Lipo cells sometimes.

Am 12.06.2019 um 10:14 schrieb Raj vu2zap:
Your in out voltage is getting close to its lower limit + diode drop.
Raj
At 12-06-19, you wrote:

Yesterday I noticed an other "funny" thing: If the input power is lower than about 12.9V I can hear strong the tuning ticks. But I have no high freq hiss. If I increase the voltage the ticks went of and the hiss begings. (:
--
73, Stephan dc8lz

Re: bitx40: low RF ower an dead part in RX path?

Jerry Gaffke
 

You got it, I was wrong.
Q16 is the audio pre-amp.

Jerry


On Wed, Jun 12, 2019 at 01:43 AM, Stephan Lauffer wrote:
Jerry,

Am 10.06.2019 um 04:43 schrieb Jerry Gaffke via Groups.Io:
[...]

If the Bitx40 is getting signals strong enough that you need the AGC circuit to prevent the audio from distorting,
that distortion is probably coming from too large of a signal into the Q12 audio pre-amp stage.
The LM386 audio amplifier should then give plenty of volume.
I suggest you triple check the way the volume control and speaker have been wired up,
perhaps try a larger speaker.
You mean Q16 not Q12, right?

At Q12 I changed R123 and R126 a bit to get a stronger MIC signal.

73, Stephan
--

Re: Antuino and SWR

Michael Aiello
 

Hi Ashhar,

I do have a fixed and step attenuators, so I could use my KX3 as a signal source to get a signal down into the -10 to -40 dbm range. I have not attempted the frequency calibration. I was testing the SWR at 7.1 MHz.
I have done the return loss calibration - how do you perform the frequency calibration?

Thanks
Mike

Re: bitx40: low RF ower an dead part in RX path?

Jerry Gaffke
 

He has said previously that he understands that the regulator is out of regulation.

The tuning clicks are due to current surges into the ATMega328P on the Nano
causing drops on the  radio's 12v line due to no voltage regulation.
This can also be cured by adding a 25 ohm 1//2 Watt resistor in series with
the 12v supply wire into the Raduino, plus a 47uF cap from 12v to ground at the Raduino.

The LM2940 datasheet recommends a 0.47uF cap at the input to prevent oscillation,
which is a bit more than the 0.1uF that he reports.  That could be causing the hiss.
    https://www.ti.com/lit/ds/symlink/lm2940c.pdf

His 100uF at the output of the LM2940 should be plenty, if I were to add anything there to fix a his it would be a bunch of 0.1uF caps.
But I doubt that's the problem.

The LM2940 should provide protection from reversed power supply leads (an LM7812 does not!).
So he probably does not need the diode between the power supply and the LM2940, 
I power my Bitx40 IRF510 PA directly from the battery with no reverse protection, since reverse polarity there will
get shorted out by the IRF510's intrinsic diode from source to drain and blow my 3A fuse.
Buy you definitely want effective reverse protection of some sort for the main 12v lead into the radio.

Jerry



On Wed, Jun 12, 2019 at 01:14 AM, Raj vu2zap wrote:
Your in out voltage is getting close to its lower limit + diode drop.

Raj
Hide quoted text

 

At 12-06-19, you wrote:

Yesterday I noticed an other "funny" thing: If the input power is lower than about 12.9V I can hear strong the tuning ticks. But I have no high freq hiss. If I increase the voltage the ticks went of and the hiss begings. (:

Re: Antuino and SWR

Ashhar Farhan
 

Mike,
The procedure is documented on hfsignals.com. You hold down the tuning knob while switching on the unit, this puts it into calibration mode. Choose Frequency Calibration, and set the output (as measured on a receiver or freq counter) to exactly 10 mhz, tap the button once more to save it and restart the unit.
- f

On Wed 12 Jun, 2019, 4:47 PM Michael Aiello, <n2htt.mike@...> wrote:
Hi Ashhar,

I do have a fixed and step attenuators, so I could use my KX3 as a signal source to get a signal down into the -10 to -40 dbm range. I have not attempted the frequency calibration. I was testing the SWR at 7.1 MHz.
I have done the return loss calibration - how do you perform the frequency calibration?

Thanks
Mike

Re: Amateurradiokits Chassis and Grounding

_Dave_ K0MBT
 

It is just a coat of paint. A light sanding with 36-100grit would take about 5 minutes.

The real question is does it make a difference? Inquiring minds want to know.
Dave

Re: bitx40: low RF ower an dead part in RX path?

Stephan Lauffer
 

Hello!

Below a video just to get an impression about the noise I speak about.

Would be interesting to me if others have this, too.

https://drive.google.com/drive/folders/1o0NsVtNBXwDTpBLI22S1575aePq0BI_X

Maybe my LM2940 is not a good choice... hm... I have tried different caps on in and out of the lm24940 but right now this doesn't looks like to be the right way to fix the issue.

Am 12.06.2019 um 12:47 schrieb Stephan Lauffer:

Hello Raj,
yes. I thought it shouldn't be a problem to work with some few volt below 12 (f.e. with 10V).
I found this fix https://www.youtube.com/watch?v=_7q7nG-awsc and it works very fine. :)
So now no more tuning ticks below 12V (12,9V). That's nice because I'd like to power it with 3S Lipo cells sometimes.
Am 12.06.2019 um 10:14 schrieb Raj vu2zap:
Your in out voltage is getting close to its lower limit + diode drop.

Raj

At 12-06-19, you wrote:

Yesterday I noticed an other "funny" thing: If the input power is lower than about 12.9V I can hear strong the tuning ticks. But I have no high freq hiss. If I increase the voltage the ticks went of and the hiss begings. (:


--
73, Stephan dc8lz
--
Liebe Gruesse, with best regards,
Stephan Lauffer

Telefon: +49 7661 905216
Mobile: +49 172 7145197
Ham Radio: DC8LZ, QTH JN37XX
Schulstr. 1c
79252 Stegen
Germany

Re: Amateurradiokits Chassis and Grounding

Joe Puma
 

It’s really not that easy to scratch off, it’s definitely a task, Especially when your case is half built and you need to get to the holes on the inside. 

Does it work? You’ll have to ask Faraday himself or resort to any of his writings regarding a faraday cage. 

Faraday cage or Faraday shield is an enclosure used to block electromagnetic fields. A Faraday shield may be formed by a continuous covering of conductive material, or in the case of a Faraday cage, by a mesh of such materials.

Joe
Kd2nfc 


On Jun 12, 2019, at 9:17 AM, d balfour <davesters@...> wrote:

It is just a coat of paint. A light sanding with 36-100grit would take about 5 minutes.

The real question is does it make a difference? Inquiring minds want to know.
Dave



Re: bitx40: low RF ower an dead part in RX path?

Stephan Lauffer
 

Hi Jerry,

thanks for further ideas and help!

I put a bigger cap at input of the lm2940 but it does not seems to have any affect. In general the datasheet speaks about an optional cap at input if the power supply is far away.

Hm... I am measuring an testing...

Am 12.06.2019 um 13:22 schrieb Jerry Gaffke via Groups.Io:

He has said previously that he understands that the regulator is out of regulation.
The tuning clicks are due to current surges into the ATMega328P on the Nano
causing drops on the  radio's 12v line due to no voltage regulation.
This can also be cured by adding a 25 ohm 1//2 Watt resistor in series with
the 12v supply wire into the Raduino, plus a 47uF cap from 12v to ground at the Raduino.
The LM2940 datasheet recommends a 0.47uF cap at the input to prevent oscillation,
which is a bit more than the 0.1uF that he reports.  That could be causing the hiss.
https://www.ti.com/lit/ds/symlink/lm2940c.pdf
His 100uF at the output of the LM2940 should be plenty, if I were to add anything there to fix a his it would be a bunch of 0.1uF caps.
But I doubt that's the problem.
The LM2940 should provide protection from reversed power supply leads (an LM7812 does not!).
So he probably does not need the diode between the power supply and the LM2940,
I power my Bitx40 IRF510 PA directly from the battery with no reverse protection, since reverse polarity there will
get shorted out by the IRF510's intrinsic diode from source to drain and blow my 3A fuse.
Buy you definitely want effective reverse protection of some sort for the main 12v lead into the radio.
Jerry
On Wed, Jun 12, 2019 at 01:14 AM, Raj vu2zap wrote:
Your in out voltage is getting close to its lower limit + diode drop.
Raj
Hide quoted text <#quoted-69349553>
At 12-06-19, you wrote:
Yesterday I noticed an other "funny" thing: If the input power
is lower than about 12.9V I can hear strong the tuning ticks.
But I have no high freq hiss. If I increase the voltage the
ticks went of and the hiss begings. (:
--
Liebe Gruesse, with best regards,
Stephan Lauffer

Telefon: +49 7661 905216
Mobile: +49 172 7145197
Ham Radio: DC8LZ, QTH JN37XX
Schulstr. 1c
79252 Stegen
Germany

Re: Amateurradiokits Chassis and Grounding

Mike Yancey
 

I'd gotten the parts, but hadn't done this (YET!) but: I highly recommend it - I felt some tingly RF on a screw head on my mic and a couple of other points.
I used a two-battery power mechanism: 1 battery for the radio, 1 'stacked' (electrically) for 24-V on the PA. And at about 24-26 Watts, you can get a tingle!

Mike Yancey, KM5Z
Dallas, Texas, USA


On Tue, Jun 11, 2019 at 10:54 AM, Ravi Miranda wrote:

toggle quoted messageShow quoted text