Date   
Re: Help on parts and or repairs !

Timothy Fidler
 

Chuck I am sitting here on the side but this has happened before.
1. The uBitx as it comes from factory,  (you may have a Bitx40 you are not specific) is supposed to be biased correctly and the bias
instructions are supposed to be for set up a new pair of Mosfets. HOWEVER it would only take someone at the factory to be asleep and you could be where you are.
2. There have been a  vast number of IRF510 mafrs over years and they are not all born equal.  If you bought second tier components you may still have issues.
3. (the most useful one - possible GET OUT OF Jail ) . There are or used to be (Ashar Farhan does not ring me up to tell me every PCB rev) a number of top to bottom vias on the PCB around the IRFs.  If you look front to back and against the schema you will pick em up. Some are carring a lot of RF.  These have a rather sensitive plated through hole.  Clearly it is hard to test them with a DVM unless you have a known good PCB along side - ie a reading non Zero on ohms may still be acceptable.  However if fully toasted then putting through a bit of say Cat5e wire or a component lead and soldering both sides may just may get you out of jail. BUT at 30 Mhz the impedance of the fix will not be the same as a thin Cu PCB layer so you still may have a Princess board. 

Enough.

Re: Ubitx microphony

Bill Cromwell <wrcromwell@...>
 

Hi Alf,

It is entirely possible for the vibration from the speaker to rattle the microphonic parts on the board. Remove the speaker from that equation by using an external speaker at some distance. That will remove the speaker vibration induced microphonics and expose any remaining distortion from an overloaded amplifier that is probably clipping. If the speaker is causing some distortion on strong signals as you have described that would be in addition to clipping.

Turn the volume down to reduce the clipping. Use the external speaker to reduce the microphonics:)

73,

Bill KU8H

On 12/25/18 9:23 PM, Alf Baranda via Groups.Io wrote:
Ok Peter, the same thing happens to me but in my Bitx40.
When I gently touch the pcb and the components near the AF ic with a stick, I hear the friction on the loudspeaker as a result of microphony.
This occurs even when the Bitx40 receives perfectly.
When the signals coming out through the loudspeaker are loud they distort and I am beginning to think that it is because of this microphonic effect, which is fed back by the sound of the loudspeaker.
I replaced the Lm386 without a positive result.
Keep investigating.
--
bark less - wag more

Re: R60 mic bias

 

The 47uF would be charging via the 10K resistor and that would take a second or two.
Probably the cap was a little leaky.

Just a guess!


At 25-12-18, you wrote:

Solved! The blocking cap was too big! I added in series a 0.47uf electrolytic and the problem vanished. I chose that cap because it is a lower value than C60. I don't fully understand it but it works!!!



Il 25/dic/2018 14:21, "iz oos via Groups.Io" <and2oosiz2= gmail.com@groups.io> ha scritto:
>
> 47uF rated at 35v
>
>
> Il 25/dic/2018 13:59, "Raj vu2zap" < rajendrakumargg@...> ha scritto:
>>>
>>> electrolytic cap (the positive towards the ubitx)
>>
>> what is the value ?
>>
>> At 25-12-18, you wrote:
>>
>>> Actually when it becomes stuck if I wait let's say 20seconds then it works again.
>>>
>>> Il 25/dic/2018 12:42, "Raj vu2zap" < rajendrakumargg@...> ha scritto:
>>> Check voltages in audio stage and vogad when the audio is gone. That should tell you
>>> where to look!
>>>
>>>
>>> At 25-12-18, you wrote:
>>>
>>>> 12vdc from the battery, but after a resistor and the 7805 is 5vdc.
>>>>
>>>> Il 25/dic/2018 11:37, "Raj vu2zap" < rajendrakumargg@...> ha scritto:
>>>> What is the supply voltage for the VOGAD board ?
>>>> At 25-12-18, you wrote:
>>>> >Hi all, I have tested a mic compressor based on the VOGAD SL6270C (same schematics of its datasheet), and it works very well on the ILER QRPs. However when connected to the ubitx something weird happens. It works the first time I push to talk, I can talk also 5 minutes, and no problem, BUT when I release the PTT and then press again, it does not transmit anything. I did not remove R60 and put an electrolytic cap (the positive towards the ubitx) in the cable connecting the VOGAD and the ubitx. The VOGAD is always powered on via a battery or the same power supply and is DC isolated from the Ubitx. In fact the interconnecting cable also has an isolating transformer to avoid any possible ground loop. Should I really remove R60? Should I remove the DC power of the VOGAD each time I receive? Or should I simply add some polyester caps in parallel at the mic input?

Re: Bitx40 No display

Evan Hand
 

I would start with the simple and then go to more complex. 
Verify that you have the Raduino board plugged in correctly. I noted on my board that the socket on the Mac n board looks like the last pin connector has half of the plug left from when it was cut from the source strip. 

Next verify the 12v to the input of the 7805 regulator on the Radoino board. 

Fnally verify the tegulator output

the way the7805 is mounted in the Raduino board with the input closest to the main board, and output furthest away. 

Evan
AC9TU

Re: Bitx40 No display

Jack Purdum
 

I'm late to the disussion, but I'd load the Blink program to make sure the Nano is healthy, too.

Jack, W8TEE

On Tuesday, December 25, 2018, 10:11:21 PM EST, Evan Hand <elhandjr@...> wrote:


I would start with the simple and then go to more complex. 
Verify that you have the Raduino board plugged in correctly. I noted on my board that the socket on the Mac n board looks like the last pin connector has half of the plug left from when it was cut from the source strip. 

Next verify the 12v to the input of the 7805 regulator on the Radoino board. 

Fnally verify the tegulator output

the way the7805 is mounted in the Raduino board with the input closest to the main board, and output furthest away. 

Evan
AC9TU

Re: Bitx40 No display

Evan Hand
 

The 7805 regulator is not supplying power to the Raduino. When you plug in the USB connector, power is being supplied by the regulator on the nano board using power from the USB port.  

Re: Bitx40 No display

Curt
 

Make sure you adjust the pot that controls the backlight for the lcd. It goes from nothing to filling the screen. Careful adjustment is required to see anything.

Also check that the raduino isnt misaligned as mine has an extra partial row.

Curt

Re: Bitx40 No display

 

This is a BITX40 board!

At 26-12-18, you wrote:
I would start with the simple and then go to more complex.
Verify that you have the Raduino board plugged in correctly. I noted on my board that the socket on the Mac n board looks like the last pin connector has half of the plug left from when it was cut from the source strip.

Next verify the 12v to the input of the 7805 regulator on the Radoino board.

Fnally verify the tegulator output

the way the7805 is mounted in the Raduino board with the input closest to the main board, and output furthest away.

Evan
AC9TU

Re: Help on parts and or repairs !

chuckr@hostu.org
 

On Tue, December 25, 2018 8:14 pm, Curt via Groups.Io wrote:
Chuck


A new board can be ordered from hfsignals.com

I could only find link to complete kit, is their a link to just the parts
ie: main board as it comes in a kir ?

I did send an email a couple of weeks back to hfsignals but have heard
nothing back... Thanks






I am mystified by the finals, I wonder if you have a shorted pot or just
too much current.

I suggest getting it working in stock form before any mods, including
adding kd8cec firmware. Take small steps in your build.

Curt





Re: Bitx40 No display

Evan Hand
 

Sorry. Did it again. Did not read the title. 

Re: Tracing receive signal for low signal

jim
 

Possible, but unlikely ...As a first step tie the wire loop you wound thru the core to the input of your scope..measure the signal from tp2 to the scope across the bandwth you can sweep with your generator..look for any peaking/dropouts across the bandwidth ..

when I didn't have the SA/TG I now have, I made 2 identical RF probes ...Hooked one to one channel of scope, and one to the other ...Used one to monitor the input of a circuit and the other to monitor the output ...Sweep manually the frequency and looked for peaking/dropping/changes and why those occurred ...

I also constructed 2 identical RF attenuator boxes ..3db,6db,10db,20db,20db. with bnc connectors on each end (still use them)
to set levels and verify overload/distortion issues ..

Took HOURS to sweep/characterize circuit ..

Now it takes longer to hook up ths SA/TG than it takes to measure a circuit ..but its still doing the same thing

Its best to start at the "back end" of the circuit and work towards the front ..fixing one problem at a time

Virtually all the "gain" in this receiver is in the audio stages ...

Stage by stage ...Input low-pass ....Probably -3db loss
                            T1/T2 Mixer  .....Minimum 6db loss (probably more)
                            Q10/12 amp        15 Db gain Maybe ..
                            45 Mhz BPF       minimum 6 db loss (probably more)
                            T3/T4 Mixer ....Minimum 6db loss (probably more)
                            Q30/32 amp       15 Db gain Maybe
                            12 Mhz BPF    minimum 3db loss (Probably more)
                            T7 mixer .....Minimum 6db loss (probably more)

Add all those up ....Losses Minimum 30 Db ///Gains ...Maximum 30 Db ....

To get from 1 uV (microvolt) to 1 V (volt) you need 120 Db gain ..

All that has to happen somewhere between Q70 and whatever you are using for a speaker

Fix the audio   then (probably) most of these other issues will solve themselves

Jim

On Tuesday, December 25, 2018, 12:39:31 PM PST, Dave Space <davesspacebar@...> wrote:




Gave it a try same results 1900uv estimated at tp2 to get to .1p-p

9000uv estimated at tp1 to get .1p-p  (I think I reported my signal generator's input in my message last time and mentioned uv when it was really mv 900mv through a -40b attenuator so estimated at 9000 uv.)

with the wire wrapped through about 5 times (it was about as many as I could fit and it's even thinner magnet wire than they used on T2 itself.)

So perhaps that means its not matching that is the issue?

Re: Ubitx microphony

Alf Baranda
 

Ok Bill, I think that solution may be temporary but it does not end with the problem.
I have to continue investigating where the microfonics arises and how to solve it, because this effect is a failure of something that I have not yet located.
No circuit / componet must modulate the original signal by mechanical vibrations as it is in the case of the microfonismo that drives me crazy.
I also have to try to replace the electrolytic coupling ceramic capacitors to avoid the piezoelectric effect.
I will continue in the matter.
Thanks for your observations.

Re: Volume Limiting and Distortion Reduction for uBITX #ubitx

_Dave_ K0MBT
 

Wow clever adjusting the bias on the pin diode. I assume that the points connected to the volume control are added in parallel to existing wiring? Where do a1 b1 a2 b2 c1 and c2 go? Is that the existing k1 and 7805? up in the corner by the antenna input on the main board?

Thank you

Re: Help on parts and or repairs !

chuckr@hostu.org
 

I could only find link to complete kit, is their a link to just the parts
ie: main board as it comes in a kit ?

I did send an email a couple of weeks back to hfsignals but have heard
nothing back... Thanks

Re: Ubitx microphony

_Dave_ K0MBT
 

I had microphony that turned out to be coming from a poor fitting 8 pin audio cable.

Re: Volume Limiting and Distortion Reduction for uBITX #ubitx

Jerry Gaffke
 

There have been dozens of threads in this forum about adding AGC to the Bitx40 and uBitx.
Most get hacked in (both detection and attenuation) after the rx audio preamp,
to prevent ear damage on a sudden strong signal.
Then perhaps add a manual RF gain pot at the antenna port to avoid audio preamp overload.

Some used PIN diodes to attenuate the signal at RF (or IF) frequencies,
and thus get around the dynamic range limitations of that 2n3904 audio pre-amp stage.
Here's the earliest thread to identify the dynamic range issue of that Bitx/uBitx audio pre-amp stage:
:    https://groups.io/g/BITX20/topic/5945215#32066

Kees (K5BCQ) sold nearly 1000 kits of an AGC design from Don (ND6T).
This was audio detection with RF attenuation at the antenna port using 2n7002 FETs.
Nik (VK4PLN) was planning to sell a kit with audio detection and attenuation
after the audio preamp, I don't know what came of that.
    http://ubitx.net/category/hardware/agc-mod/
 

Sensing signal levels is probably best done after conversion to audio.
Must sense after the 12mhz crystal filter, or strong signals elsewhere in the band
will bring on the AGC action.  But if we sense between that 12mhz crystal filter
and the demodulator, then we will likely be seeing mostly the unshielded 12mhz bfo.

Attenuation could be anywhere between the antenna port and the input to the audio preamp.
Putting attenuation at the antenna port avoids overloading the mixers and IF amps,
but they generally have enough dynamic range that it doesn't really matter where we pot it.
Putting attenuation after the audio preamp works, but does not fix the dynamic range
issue of that preamp.

Various ways to implement attenuation at RF, here's a good one that 
tries to maintain a 50 ohm impedance match, and is quite cheap:
    https://www.nxp.com/docs/en/data-sheet/BAP64Q.pdf

Allison recommends using a 1n4007 as a pin diode to set the gain in one (or both)
of the bidi IF amps, many of us have a 1n4007 in the junk box:
  https://groups.io/g/BITX20/message/45984

Jerry, KE7ER

Re: Volume Limiting and Distortion Reduction for uBITX #ubitx

Jack Purdum
 

There are pros and cons to each approach, which is why JackAl has both RF and audio AGC. Indeed, the AGC section takes up a good portion of the JackAl's nanoacres. BTW, we just received the assembled Jack boards which has the SMD parts in place and looks like this:

Inline image

This is what QRP Guys will be selling after we spend a little more time testing everything. After adding the off-board parts (less than $13), the board looks like this:

Inline image

All of the yellow pins are test points to encourage experimentation. You also have about a dozen free I/O pins to experiment with.

Jack, W8TEE

On Wednesday, December 26, 2018, 11:26:29 AM EST, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:


There have been dozens of threads in this forum about adding AGC to the Bitx40 and uBitx.
Most get hacked in (both detection and attenuation) after the rx audio preamp,
to prevent ear damage on a sudden strong signal.
Then perhaps add a manual RF gain pot at the antenna port to avoid audio preamp overload.

Some used PIN diodes to attenuate the signal at RF (or IF) frequencies,
and thus get around the dynamic range limitations of that 2n3904 audio pre-amp stage.
Here's the earliest thread to identify the dynamic range issue of that Bitx/uBitx audio pre-amp stage:
:    https://groups.io/g/BITX20/topic/5945215#32066

Kees (K5BCQ) sold nearly 1000 kits of an AGC design from Don (ND6T).
This was audio detection with RF attenuation at the antenna port using 2n7002 FETs.
Nik (VK4PLN) was planning to sell a kit with audio detection and attenuation
after the audio preamp, I don't know what came of that.
    http://ubitx.net/category/hardware/agc-mod/
 

Sensing signal levels is probably best done after conversion to audio.
Must sense after the 12mhz crystal filter, or strong signals elsewhere in the band
will bring on the AGC action.  But if we sense between that 12mhz crystal filter
and the demodulator, then we will likely be seeing mostly the unshielded 12mhz bfo.

Attenuation could be anywhere between the antenna port and the input to the audio preamp.
Putting attenuation at the antenna port avoids overloading the mixers and IF amps,
but they generally have enough dynamic range that it doesn't really matter where we pot it.
Putting attenuation after the audio preamp works, but does not fix the dynamic range
issue of that preamp.

Various ways to implement attenuation at RF, here's a good one that 
tries to maintain a 50 ohm impedance match, and is quite cheap:
    https://www.nxp.com/docs/en/data-sheet/BAP64Q.pdf

Allison recommends using a 1n4007 as a pin diode to set the gain in one (or both)
of the bidi IF amps, many of us have a 1n4007 in the junk box:
  https://groups.io/g/BITX20/message/45984

Jerry, KE7ER

Re: Tracing receive signal for low signal

Dave Space
 

Interesting thanks that is a good map to work through will try to trace.

I noticed something interesting maybe it's expected trying to understand why though.  If I input a low signa from generatorl like 10mv 1khz one side of C50 I get a clear tone (the side away from the Q70 base) the other side towards Q70 base I hear nothing unless I increase the power to like 2v or more on the generator  (That could be due to the issue you found with collector voltage I guess... though I see similar behavior on the other transistors inputting to the base Q71, or  (72,73 - I see these in push pull config not sure if that correlates to needing more power at the base).

Re: Volume Limiting and Distortion Reduction for uBITX #ubitx

jpkellyburbank@...
 

Yes, points connected to volume control are in parallel with existing wiring.  The relay and regulator are new, not the existing uBITX ones.   Here is a photo of the mod that I made for mine.

Re: Tracing receive signal for low signal

jim
 

Check (with an ohm-meter) for resistance to ground on generator ...Likely it has 50 ohm to ground ..If you hook that directly across the base of the transistor, you've just mucked up the bias on that transistor ...If you want to random-probe circuits, you need a DC blocking capicitor on the generator lead

Jim


On Wednesday, December 26, 2018, 9:56:42 AM PST, Dave Space <davesspacebar@...> wrote:


Interesting thanks that is a good map to work through will try to trace.

I noticed something interesting maybe it's expected trying to understand why though.  If I input a low signa from generatorl like 10mv 1khz one side of C50 I get a clear tone (the side away from the Q70 base) the other side towards Q70 base I hear nothing unless I increase the power to like 2v or more on the generator  (That could be due to the issue you found with collector voltage I guess... though I see similar behavior on the other transistors inputting to the base Q71, or  (72,73 - I see these in push pull config not sure if that correlates to needing more power at the base).