Date   

Re: vfo trouble - bitx20a schematic.

Jim Kortge <jokortge@...>
 

cornhusker wrote:
HI!
I am having a similar problem. I am not getting any VFO output at all and R29 is warm along with Q8 and Q6. I redid T4, the trifilar toroid and checked C30 and C31 for shorts, but none there. The voltage on the base of Q8 is about .41V and the supply voltage to the VFO at the Zener is 5.6V . Where do I go next?
Joe,

I'm guessing that you have installed the 5.6 volt Zener who will go in the D1 spot on the PCB into the location meant for the 9.1 Zener which should be installed at the D8 location. As for the 0.41 volts on the base of Q8, it should be much higher than that, nearly 1/2 the supply voltage of 9.1 volts unless it is being loaded down by something downstream or the VFO is really oscillating and the reading device is getting confused by the presence of RF since both are present on the base of Q8. I guess that would go back and make sure that all of the other parts used in the VFO and its buffers are indeed the correct value. Some of the colors on resistors are a bit misleading. A "brown" for instance may well be "violet".

72 and kind regards,

Jim, K8IQY


Re: Low output level

david.g3ryp <david.g3ryp@...>
 

Alan

You don't have a problem! But you may have if the drive is excessive.

When you whistle into a microphone it only approximates a sine wave and you'll need, as you've found, to whistle hard to get full output. Unless you have a level sinewave to the mic input then your power meter cannot respond fast enough and hold long enough to show the full level being produced. When you talk you'll see even less power. But don't worry it's there!

To see what's really happening you'll need a peak reading power meter - I guess you'll find schematics on the web somewhere.

My BITX20A is working fine and I've made several contacts but no DX yet! Funny how it always works better when there's a contest on!

David


Re: Low output level

bugs5504
 

Hi

It may be worth connecting an AF signal generator (or the earpiece
output of a radio) to the Mic connections and see what output that
gives you. My BITX20a gives the full 10W out ,but looking at my cheap
wattmeter you have to whistle hard to get anywhere near that reading.
Using the signal generator I can get 10W out. I'm building an extra
stage of Mic. amplification plus a diode clipper circuit to boost the
average power out.

Alan


Low output level

lsasmazel
 

Can any one tell what is minimum driving signal for Q3 to achive 10
Watts? I did all DC adjustments but I am not seeing even 1/2 watts of
output from BITX20 (actually I am seeing 1V PEP to the 50 ohm load 20
mW) . I have no problem with receive. I am using dynamic microphone
and R92 is not installed it this time. Whistling to the mike is
generating 10mV pep at the gate of Q20. If any body have signal
information at the major connection points?

Thanks,
Levent – WW2L


Re: vfo trouble - bitx20a schematic.

cornhusker
 

HI!
I am having a similar problem. I am not getting any VFO output at
all and R29 is warm along with Q8 and Q6. I redid T4, the trifilar
toroid and checked C30 and C31 for shorts, but none there. The
voltage on the base of Q8 is about .41V and the supply voltage to the
VFO at the Zener is 5.6V . Where do I go next?
73, Joe K0NEB



-- In BITX20@..., Arv Evans <arvid.evans@...> wrote:

Greg

Good information that you found and fixed the VFO problems.
Most of the BITX20 builders have found both the original VFO
version and
the later one in the BITX20A to be quite stable.
As to your question about reducing VFO output for your non-BITX20
application, I would probably look into designing a resistive Pi
type
attenuator for that purpose. This lets you match impedances as
needed,
does not change the waveform, and helps maintain a fixed load on
the VFO
output.

Arv
_._


Greg W:-) wrote:

Hi Arv .

I found out what my problem was , it was a short circuit --- in My
BRAIN.! hihihi

Actually there was a number of separate issues and I had mislead
myself a bit.

This is my explanation for what occurred with that VFO (weak
attempt
at self justification)

The time that I get to do my home-brewing is between 9 to 12 at
night.
So by the time I had finished the VFO it was about 11:30.(thats my
first problem)
My 100mhz CRO is too large to leave on my bench so I must lift it
up
when needed and let it stand on its back feet., meaning I must
peer
over the top (when sitting) to see the display tube.
So I started the VFO up and connected the CRO probe and I saw that
waveform that I described yesterday.
From where I was sitting the CRO settings looked right but they
were not.
The timebase knob was right around the other side.
Due to tiredness (or dumbness) and my sitting position I missread
the
knobs positions on my Philips CRO.
What I thought was a bombed out waveform that wasn't oscillating
was
actually only a portion of a cycle being shown.
In other words , the VFO first stage WAS working.(somewhat)

So thinking that there was no oscillation , now accompanied by the
smell of burning parts you can understand what I was guessing.

Before rebuilding the VFO last night I set out to try and find the
causes for this burn up.

Remember that I said that R26 was very hot , looking around the
area I
found that my toroid (twisted winding bifilar)* had shorted out.
This is unusual, and I can't be sure if it was shorted before or
after
I applied power.(from heat)
Perhaps exposed conductors of the windings were made when
twisting ?
(not likely)
A fair bit of current was going to ground through the toroid
heating
the R26., but still it was providing power to Q6 because it was
getting very warm too.

I can't work out why Q6 would have got so hot.(maybe my Q6 was
faulty
to begin with?)
I think other things were going on too , on a component level ,
but as
I had previously snipped them out and cant test them now.

In the rebuild I checked my remaining components and they looked
fine
, as did the newly installed ones.
The board art was fine with no solder bridges or other faults.

Anyway , I powered it up and the new one worked first time , and
at
about 3mhz it has 5V P-P output.(probably rite for diode ring
mixer app)

The output on the scope is better than all of my other VFO's at
3Mhz ,
but it still is not perfectly clean.(its probably good enough)

I will need to reduce this output to 1V P-P for my application.
Would you recommend achieving that with decoupling the stage
further
of by bias adjustments of the buffers.??

Oh yeah , and I need to get a tuning cap with more pF swing , the
150khz tuning range that I have now isn't enough for full phone
band
on 20 meters in region 1., OR I might have to revise some of the
other
caps in the circuit.

One thing that I did notice , and something I will have to
investigate
further is the LACK of frequency shift from hand capacitance.
I am using a inductor wound on a small plastic (nylon?) rod with
windings running up and then back on itself - 2 layers.
Only when my fingers are almost touching it do i see my frequency
counter change.,, and then , not a lot , (a few kc's only)

I will have to look into this further.

Anyway , Thanks for the reply.

Regards

gregW:-) OH2FFY

*this VFO is not for a bitx 20
======================================================================

--- In BITX20@... <mailto:BITX20%40yahoogroups.com>,
Arv
Evans <arvid.evans@> wrote:

Greg

Good. It sounds like you are well on the way to figuring out
what went
wrong. The fact that R-26 became hot is possibly key to
understanding
what happened. This would make a shorted C-30 as the first
suspect.
Following the circuit would also indicate that a short to
ground or
wiring error in the T-4 and T-5 area could also be a problem. A
shorted
C-31 could put Q-6 near it's maximum power rating and eventually
destroy
that device. If C-31 were OK but the transistor Q-6 was bad, I
would
expect R-29 to be destroyed also. C-32 isolates the 2nd VFO
buffer
from
the 1st VFO buffer so I would not expect something that burned
up R-26
to cause problems for circuitry prior to C-32.

The BITX20A VFO was designed the way it is in order to insure
that the
output was as clean as possible, while still maintaining good
stability. There are a number of small changes that were made
to the
BITX20A design in order to minimize spurious content in the
output
signal. Some were made necessary by close component spacing
involved in
the PCB layout, while others were made possible by having a
standardized
kit of components available for the build. C-25 and L-10 were
necessary
to minimize VFO energy, unwanted mixer products, and possible
harmonics
that might get into the transmitted signal. The largest change
of
course is in the kit having push-pull power output and driver
stages.
This specifically reduces 2nd harmonic content in the output.

Good luck on your VFO debugging, and please let us know what
you find,
as this information may help some other BITX20 builder with
similar
problems.

Arv
_._
--
======================================
Web: http://K7HKL.homelinux.net
http://bitx20a.livejournal.com
http://home.earthlink.net/~arvevans/
http://www.geocities.com/k7hkl_arv/
======================================






Re: vfo trouble - bitx20a schematic.

Allison Parent <kb1gmx@...>
 

--- In BITX20@..., "sg2112" <SG2112@...> wrote:

I think you missed the point

The point was that Jim was able to get a stable, repeatable VFO using
a varactor instead of an air variable which is hard to do without a
PLL or huff puff circuit stablizing it

What is similar between the two VFOs is using a bipolar transistor
instead of the FETs we usually see in VFOs and taking the output off
the tank instead of the transistor

JR
Actually the topology and device used (assuming it's used and biased
correctly) makes little difference. It's contruction, attention to
parts quality (getting COG caps that really are) and if you take the
time a bit of compensation. The result can be a stellar quality VFO.
Varactor over air capacitor does make for some drift but it's
predictable and correctable. Crappy parts, long floppy leads,
parts that aren't well secured, transistors or fets incorrectly
biased and unregulated or poorly regulated DC and control votages
means drifty VFO.

Finally stage isolation or better a consistant and unchanging load
will enhance stability.

The basic Farhan design was pretty decent and I found it
acceptably stable as I assembled it using the FAR circuits
board. Mine ran at 4.6mhz (9.6mhhz IF) for 20M.

Allison







--- In BITX20@..., "Greg W:-)" <onegammyleg@> wrote:

Hi JR ..I looked at the schematics for the 2N2 radios and the VFO in
them look like conventional Colpitts designs , not the same as used in
the Bitx20A.

Drift shouldn't be a huge problem if you use an air spaced variable
capacitor for tuning (silver plated not alluminium) , an air core
inductor (not ferrite core) NP0 or C0G capacitors throughout and + or
- caps used for temperature correction.
Any trim caps used also should be of the highest quality.
Mechanical construction should also be very good.
Single sided boards only.
Fully shielded (including tune cap) with feedthough caps for supply
voltage.
No varactor tuning.
Use the lowest voltage possible to power the VFO to limit heating of
the parts internally.
Use at least 2 buffer stages.

Theses are the rules that I follow and my vfo's don't drift apart from
the initial drift which cant be helped.

Regards

gregW:-) OH2FFY

=====================================================================


--- In BITX20@..., "sg2112" <SG2112@> wrote:

Is the VFO a K8IQY design? It looks similar to some of Jim's 2N2-xx
transceivers VFO's .... They are without a doubt the most stable
varactor tuned VFO's I've ever built .... every other one I built
before that drifted like an old cowboy ....

JR


RX Voltages

Charlie <charlie@...>
 

Here are some volatge measurements taken on recieve using my DVM.
There is a 50 ohm dummy load on the input, the supply voltage is
12.7 and the current with no signal is 127 milliamps. I'm using a 4
ohm loadspeaker. I will put these and other measurements onto a
circuit diagram.

Measurement Point Voltage

Cathode D18 12.40

Base Q25 0.63
Collector Q25 5.50
Junction R79/C80 11.80
Emitter Q16 4.85

Emitter Q13 5.85
Emitter Q14 6.00
Collector Q13/14 11.20

Base Q8 4.40
Emitter Q8 5.60
Base Q7 4.30
Emitter Q7 3.65
Collector Q6 8.50
Base Q6 4.10
Emitter Q6 3.45

Collector Q11 4.60
Base Q11 6.65
Collector Q17 10.65

Collector Q9 8.15
Base Q9 2.50
Emitter Q9 1.85

Collector Q5 8.15
Base Q5 2.50
Emitter 1.85

I have rounded to the nearest 50 millivolts.

I have awful plasma TVI here so will have to get up early on the
weekend to set up the but it's certainly picking up that TVI!


Charlie.


Re: vfo trouble - bitx20a schematic.

Arv Evans
 

Greg

Good information that you found and fixed the VFO problems.
Most of the BITX20 builders have found both the original VFO version and
the later one in the BITX20A to be quite stable.
As to your question about reducing VFO output for your non-BITX20
application, I would probably look into designing a resistive Pi type
attenuator for that purpose. This lets you match impedances as needed,
does not change the waveform, and helps maintain a fixed load on the VFO
output.

Arv
_._


Greg W:-) wrote:


Hi Arv .

I found out what my problem was , it was a short circuit --- in My
BRAIN.! hihihi

Actually there was a number of separate issues and I had mislead
myself a bit.

This is my explanation for what occurred with that VFO (weak attempt
at self justification)

The time that I get to do my home-brewing is between 9 to 12 at night.
So by the time I had finished the VFO it was about 11:30.(thats my
first problem)
My 100mhz CRO is too large to leave on my bench so I must lift it up
when needed and let it stand on its back feet., meaning I must peer
over the top (when sitting) to see the display tube.
So I started the VFO up and connected the CRO probe and I saw that
waveform that I described yesterday.
From where I was sitting the CRO settings looked right but they were not.
The timebase knob was right around the other side.
Due to tiredness (or dumbness) and my sitting position I missread the
knobs positions on my Philips CRO.
What I thought was a bombed out waveform that wasn't oscillating was
actually only a portion of a cycle being shown.
In other words , the VFO first stage WAS working.(somewhat)

So thinking that there was no oscillation , now accompanied by the
smell of burning parts you can understand what I was guessing.

Before rebuilding the VFO last night I set out to try and find the
causes for this burn up.

Remember that I said that R26 was very hot , looking around the area I
found that my toroid (twisted winding bifilar)* had shorted out.
This is unusual, and I can't be sure if it was shorted before or after
I applied power.(from heat)
Perhaps exposed conductors of the windings were made when twisting ?
(not likely)
A fair bit of current was going to ground through the toroid heating
the R26., but still it was providing power to Q6 because it was
getting very warm too.

I can't work out why Q6 would have got so hot.(maybe my Q6 was faulty
to begin with?)
I think other things were going on too , on a component level , but as
I had previously snipped them out and cant test them now.

In the rebuild I checked my remaining components and they looked fine
, as did the newly installed ones.
The board art was fine with no solder bridges or other faults.

Anyway , I powered it up and the new one worked first time , and at
about 3mhz it has 5V P-P output.(probably rite for diode ring mixer app)

The output on the scope is better than all of my other VFO's at 3Mhz ,
but it still is not perfectly clean.(its probably good enough)

I will need to reduce this output to 1V P-P for my application.
Would you recommend achieving that with decoupling the stage further
of by bias adjustments of the buffers.??

Oh yeah , and I need to get a tuning cap with more pF swing , the
150khz tuning range that I have now isn't enough for full phone band
on 20 meters in region 1., OR I might have to revise some of the other
caps in the circuit.

One thing that I did notice , and something I will have to investigate
further is the LACK of frequency shift from hand capacitance.
I am using a inductor wound on a small plastic (nylon?) rod with
windings running up and then back on itself - 2 layers.
Only when my fingers are almost touching it do i see my frequency
counter change.,, and then , not a lot , (a few kc's only)

I will have to look into this further.

Anyway , Thanks for the reply.

Regards

gregW:-) OH2FFY

*this VFO is not for a bitx 20
======================================================================

--- In BITX20@... <mailto:BITX20%40yahoogroups.com>, Arv
Evans <arvid.evans@...> wrote:

Greg

Good. It sounds like you are well on the way to figuring out what went
wrong. The fact that R-26 became hot is possibly key to understanding
what happened. This would make a shorted C-30 as the first suspect.
Following the circuit would also indicate that a short to ground or
wiring error in the T-4 and T-5 area could also be a problem. A
shorted
C-31 could put Q-6 near it's maximum power rating and eventually
destroy
that device. If C-31 were OK but the transistor Q-6 was bad, I would
expect R-29 to be destroyed also. C-32 isolates the 2nd VFO buffer
from
the 1st VFO buffer so I would not expect something that burned up R-26
to cause problems for circuitry prior to C-32.

The BITX20A VFO was designed the way it is in order to insure that the
output was as clean as possible, while still maintaining good
stability. There are a number of small changes that were made to the
BITX20A design in order to minimize spurious content in the output
signal. Some were made necessary by close component spacing involved in
the PCB layout, while others were made possible by having a
standardized
kit of components available for the build. C-25 and L-10 were
necessary
to minimize VFO energy, unwanted mixer products, and possible
harmonics
that might get into the transmitted signal. The largest change of
course is in the kit having push-pull power output and driver stages.
This specifically reduces 2nd harmonic content in the output.

Good luck on your VFO debugging, and please let us know what you find,
as this information may help some other BITX20 builder with similar
problems.

Arv
_._
--
======================================
Web: http://K7HKL.homelinux.net
http://bitx20a.livejournal.com
http://home.earthlink.net/~arvevans/
http://www.geocities.com/k7hkl_arv/
======================================


Re: vfo trouble - bitx20a schematic.

sg2112 <SG2112@...>
 

I think you missed the point

The point was that Jim was able to get a stable, repeatable VFO using
a varactor instead of an air variable which is hard to do without a
PLL or huff puff circuit stablizing it

What is similar between the two VFOs is using a bipolar transistor
instead of the FETs we usually see in VFOs and taking the output off
the tank instead of the transistor

JR

--- In BITX20@..., "Greg W:-)" <onegammyleg@...> wrote:

Hi JR ..I looked at the schematics for the 2N2 radios and the VFO in
them look like conventional Colpitts designs , not the same as used in
the Bitx20A.

Drift shouldn't be a huge problem if you use an air spaced variable
capacitor for tuning (silver plated not alluminium) , an air core
inductor (not ferrite core) NP0 or C0G capacitors throughout and + or
- caps used for temperature correction.
Any trim caps used also should be of the highest quality.
Mechanical construction should also be very good.
Single sided boards only.
Fully shielded (including tune cap) with feedthough caps for supply
voltage.
No varactor tuning.
Use the lowest voltage possible to power the VFO to limit heating of
the parts internally.
Use at least 2 buffer stages.

Theses are the rules that I follow and my vfo's don't drift apart from
the initial drift which cant be helped.

Regards

gregW:-) OH2FFY

=====================================================================


--- In BITX20@..., "sg2112" <SG2112@> wrote:

Is the VFO a K8IQY design? It looks similar to some of Jim's 2N2-xx
transceivers VFO's .... They are without a doubt the most stable
varactor tuned VFO's I've ever built .... every other one I built
before that drifted like an old cowboy ....

JR


Re: vfo trouble - bitx20a schematic.

Greg W:-) <onegammyleg@...>
 

Hi Arv .

I found out what my problem was , it was a short circuit --- in My
BRAIN.! hihihi

Actually there was a number of separate issues and I had mislead
myself a bit.

This is my explanation for what occurred with that VFO (weak attempt
at self justification)

The time that I get to do my home-brewing is between 9 to 12 at night.
So by the time I had finished the VFO it was about 11:30.(thats my
first problem)
My 100mhz CRO is too large to leave on my bench so I must lift it up
when needed and let it stand on its back feet., meaning I must peer
over the top (when sitting) to see the display tube.
So I started the VFO up and connected the CRO probe and I saw that
waveform that I described yesterday.
From where I was sitting the CRO settings looked right but they were not.
The timebase knob was right around the other side.
Due to tiredness (or dumbness) and my sitting position I missread the
knobs positions on my Philips CRO.
What I thought was a bombed out waveform that wasn't oscillating was
actually only a portion of a cycle being shown.
In other words , the VFO first stage WAS working.(somewhat)

So thinking that there was no oscillation , now accompanied by the
smell of burning parts you can understand what I was guessing.


Before rebuilding the VFO last night I set out to try and find the
causes for this burn up.

Remember that I said that R26 was very hot , looking around the area I
found that my toroid (twisted winding bifilar)* had shorted out.
This is unusual, and I can't be sure if it was shorted before or after
I applied power.(from heat)
Perhaps exposed conductors of the windings were made when twisting ?
(not likely)
A fair bit of current was going to ground through the toroid heating
the R26., but still it was providing power to Q6 because it was
getting very warm too.

I can't work out why Q6 would have got so hot.(maybe my Q6 was faulty
to begin with?)
I think other things were going on too , on a component level , but as
I had previously snipped them out and cant test them now.

In the rebuild I checked my remaining components and they looked fine
, as did the newly installed ones.
The board art was fine with no solder bridges or other faults.

Anyway , I powered it up and the new one worked first time , and at
about 3mhz it has 5V P-P output.(probably rite for diode ring mixer app)

The output on the scope is better than all of my other VFO's at 3Mhz ,
but it still is not perfectly clean.(its probably good enough)

I will need to reduce this output to 1V P-P for my application.
Would you recommend achieving that with decoupling the stage further
of by bias adjustments of the buffers.??

Oh yeah , and I need to get a tuning cap with more pF swing , the
150khz tuning range that I have now isn't enough for full phone band
on 20 meters in region 1., OR I might have to revise some of the other
caps in the circuit.

One thing that I did notice , and something I will have to investigate
further is the LACK of frequency shift from hand capacitance.
I am using a inductor wound on a small plastic (nylon?) rod with
windings running up and then back on itself - 2 layers.
Only when my fingers are almost touching it do i see my frequency
counter change.,, and then , not a lot , (a few kc's only)

I will have to look into this further.

Anyway , Thanks for the reply.

Regards

gregW:-) OH2FFY



*this VFO is not for a bitx 20
======================================================================

--- In BITX20@..., Arv Evans <arvid.evans@...> wrote:

Greg

Good. It sounds like you are well on the way to figuring out what went
wrong. The fact that R-26 became hot is possibly key to understanding
what happened. This would make a shorted C-30 as the first suspect.
Following the circuit would also indicate that a short to ground or
wiring error in the T-4 and T-5 area could also be a problem. A
shorted
C-31 could put Q-6 near it's maximum power rating and eventually
destroy
that device. If C-31 were OK but the transistor Q-6 was bad, I would
expect R-29 to be destroyed also. C-32 isolates the 2nd VFO buffer
from
the 1st VFO buffer so I would not expect something that burned up R-26
to cause problems for circuitry prior to C-32.

The BITX20A VFO was designed the way it is in order to insure that the
output was as clean as possible, while still maintaining good
stability. There are a number of small changes that were made to the
BITX20A design in order to minimize spurious content in the output
signal. Some were made necessary by close component spacing involved in
the PCB layout, while others were made possible by having a
standardized
kit of components available for the build. C-25 and L-10 were
necessary
to minimize VFO energy, unwanted mixer products, and possible
harmonics
that might get into the transmitted signal. The largest change of
course is in the kit having push-pull power output and driver stages.
This specifically reduces 2nd harmonic content in the output.

Good luck on your VFO debugging, and please let us know what you find,
as this information may help some other BITX20 builder with similar
problems.

Arv
_._


Re: vfo trouble - bitx20a schematic.

Greg W:-) <onegammyleg@...>
 

Hi JR ..I looked at the schematics for the 2N2 radios and the VFO in
them look like conventional Colpitts designs , not the same as used in
the Bitx20A.

Drift shouldn't be a huge problem if you use an air spaced variable
capacitor for tuning (silver plated not alluminium) , an air core
inductor (not ferrite core) NP0 or C0G capacitors throughout and + or
- caps used for temperature correction.
Any trim caps used also should be of the highest quality.
Mechanical construction should also be very good.
Single sided boards only.
Fully shielded (including tune cap) with feedthough caps for supply
voltage.
No varactor tuning.
Use the lowest voltage possible to power the VFO to limit heating of
the parts internally.
Use at least 2 buffer stages.

Theses are the rules that I follow and my vfo's don't drift apart from
the initial drift which cant be helped.

Regards

gregW:-) OH2FFY

=====================================================================

--- In BITX20@..., "sg2112" <SG2112@...> wrote:

Is the VFO a K8IQY design? It looks similar to some of Jim's 2N2-xx
transceivers VFO's .... They are without a doubt the most stable
varactor tuned VFO's I've ever built .... every other one I built
before that drifted like an old cowboy ....

JR


Re: vfo trouble - bitx20a schematic.

sg2112 <SG2112@...>
 

Is the VFO a K8IQY design? It looks similar to some of Jim's 2N2-xx
transceivers VFO's .... They are without a doubt the most stable
varactor tuned VFO's I've ever built .... every other one I built
before that drifted like an old cowboy ....

JR


--- In BITX20@..., Arv Evans <arvid.evans@...> wrote:

Greg

Interesting observation, but not quite correct. The first buffer
shares
the bias resistors with the oscillator transistor itself. This holds
the emitter on that buffer at approximately 1/2 Vcc from that pair of
10K dividers (R-33 and R-34). The DC path for this bias is off the
junction of these two resistors, through L7 and R-32 to the base of
Q-7. Drive for the 1st buffer is taken from the VFO tank circuit, not
from the VFO emitter. This is a little different from some popular VFO
designs, but it does insure that output from this buffer is clean and
does not get driven into saturation or shut-off at any point in the
cycle.

<snip>


Re: VFO Drift

kwroberson
 

Charlie : OK , Tnx fer info , however the vfo is not stable
enough for the digi modes , so i am working on DDS fer vfo.
tnx agn 73 Ken K5DNL

-- In BITX20@..., Management <charlie@...> wrote:

kwroberson wrote:
Hello All,
Im at the point where Book said i cud test fer
signal with freq counter or rx , I did both and
the VFO has a lot of drift , lef>t it on fer abt
1 Hour , still drift.
I waved my hand over osc and freq went down abt
400 HZ and slowly drift back up , its all over the
place , is this the best it gets or is something
wrong with mine ???

Tnx agn Ken K5DNL


Ken,

It's hardly surprising that the oscillator drifts if you wave your
hand over it! Mine does too but if I leave it sitting there on the
bench and tune it in on my IC703 then it is incredibly stable
considering it's open to the air moving around the coil, etc.

I have to take some turns off the coil as I'm tuning below 14 MHz
but when I have done that I will do some checks on the stability.
(Just working on the RX not txing!)



Charlie.

--
M0WYM
www.radiowymsey.org


Re: VFO Drift

Management <charlie@...>
 

kwroberson wrote:
Hello All,
Im at the point where Book said i cud test fer
signal with freq counter or rx , I did both and
the VFO has a lot of drift , lef>t it on fer abt
1 Hour , still drift.
I waved my hand over osc and freq went down abt
400 HZ and slowly drift back up , its all over the
place , is this the best it gets or is something
wrong with mine ???

Tnx agn Ken K5DNL


Ken,

It's hardly surprising that the oscillator drifts if you wave your
hand over it! Mine does too but if I leave it sitting there on the
bench and tune it in on my IC703 then it is incredibly stable
considering it's open to the air moving around the coil, etc.

I have to take some turns off the coil as I'm tuning below 14 MHz
but when I have done that I will do some checks on the stability.
(Just working on the RX not txing!)



Charlie.

--
M0WYM
www.radiowymsey.org


Re: vfo trouble - bitx20a schematic.

billingsleysam <billingsleysam@...>
 

Arv,

I would appreciate a little more information on the VFO and BFO.

I am going to use a DDS module rather than the on board VFO oscillator. Can you give me the P-P voltage across C91 (i.e. input into the base of Q7?

I'm building a CW BFO to bypass the existing stuff and balanced mixer Iif you whistled into the Microphone during TX what would be the P-P voltage across R64 (i.e. into the Q12).

I know I can experiment when I get to that stage of building but just wanted the experience of someone that already had built and tested a kit. These values would help me insure that I have the proper levels in both areas.

Thanks for you help.

Sam AE4GX

----- Original Message -----
From: Arv Evans
To: BITX20@...
Sent: Wednesday, November 21, 2007 12:31 PM
Subject: Re: [BITX20] Re: vfo trouble - bitx20a schematic.


Greg

Good. It sounds like you are well on the way to figuring out what went
wrong. The fact that R-26 became hot is possibly key to understanding
what happened. This would make a shorted C-30 as the first suspect.
Following the circuit would also indicate that a short to ground or
wiring error in the T-4 and T-5 area could also be a problem. A shorted
C-31 could put Q-6 near it's maximum power rating and eventually destroy
that device. If C-31 were OK but the transistor Q-6 was bad, I would
expect R-29 to be destroyed also. C-32 isolates the 2nd VFO buffer from
the 1st VFO buffer so I would not expect something that burned up R-26
to cause problems for circuitry prior to C-32.

The BITX20A VFO was designed the way it is in order to insure that the
output was as clean as possible, while still maintaining good
stability. There are a number of small changes that were made to the
BITX20A design in order to minimize spurious content in the output
signal. Some were made necessary by close component spacing involved in
the PCB layout, while others were made possible by having a standardized
kit of components available for the build. C-25 and L-10 were necessary
to minimize VFO energy, unwanted mixer products, and possible harmonics
that might get into the transmitted signal. The largest change of
course is in the kit having push-pull power output and driver stages.
This specifically reduces 2nd harmonic content in the output.

Good luck on your VFO debugging, and please let us know what you find,
as this information may help some other BITX20 builder with similar
problems.

Arv
_._

Greg W:-) wrote:
>
> Hi Arv
>
> Ok then.
> So we have here a series tuned colpitts , which makes it a clapp.
> I haven't seen that arrangement of taking the output from the tank
> before, so I took it as a drawing fault.
>
> Quickly when you look at the drawing it looks like the base of Q7 is
> grounded but its not ,,even if it was grounded it wouldn't burn up my
> parts.
> Q7 - Q6 and R26 got hot enough to smell.
> My board is tiny so it is difficult to see exactly which parts were
> hot using the burnt finger tip method.
> I scoped the output and it showed a voltage swing + and then - but it
> didn't return to complete the oscillation.
>
> Assuming the transistors were now fried in at least the buffers I
> snipped them out (disabling that part of the circuit) , and cro'ing at
> the vfo output showed this same waveform.
>
> I have checked my board and it seems in line with the schematic and my
> active parts are installed correctly , I can only assume now that
> these Chinese resistors and caps I used had way off values , but even
> that is hard to imagine.
> Normally I measure my parts values before installing them but I didn't
> this time ,, perhaps the 10k resistors were misslabled 1 k's or whatever??
> But again that wouldn't easily explain the faults across the different
> sections.
>
> I have made many vfo's and this is the first one that didn't work
> straight off.
> I am in search of a clean and stable vfo at 3Mhz , most designs work ,
> but aren't very clean.
>
> If you know of any good source material for VFO's ide appreciate the
> link or whatever.
> Theres not much reliable info around on this subject , even in
> Experimental Methods it gave 1 paragraph devoted to the FET Hartley
> VFO.-- which isnt really a lot to go on., especially as LC oscillators
> don't follow all the rules as they should.
>
> I will build it up again tonight stage by stage and check things
> thoroughly and see where it went wrong.
>
> Regards
>
> gregW:-) OH2FFY
>
> =====================================================================
>
> --- In BITX20@... <mailto:BITX20%40yahoogroups.com>, Arv
> Evans <arvid.evans@...> wrote:
> >
> > Greg
> >
> > Interesting observation, but not quite correct. The first buffer
> shares
> > the bias resistors with the oscillator transistor itself. This holds
> > the emitter on that buffer at approximately 1/2 Vcc from that pair of
> > 10K dividers (R-33 and R-34). The DC path for this bias is off the
> > junction of these two resistors, through L7 and R-32 to the base of
> > Q-7. Drive for the 1st buffer is taken from the VFO tank circuit, not
> > from the VFO emitter. This is a little different from some popular VFO
> > designs, but it does insure that output from this buffer is clean and
> > does not get driven into saturation or shut-off at any point in the
> cycle.
> >
> > Not sure why or how you burned up some parts. My BITX20A uses the same
> > circuit and it works just fine. A number of other builders are using
> > the same circuit and they are reporting contacts, which makes me think
> > that their circuits must be working OK.
> >
> > I wonder which specific parts burned up? From that you might be
> able to
> > work backwards to determine the failure mode and it's cause.
> >
> > With 1K in the emitter of Q-7 it cannot draw enough current to destroy
> > itself (12V / 1K = 0.012A) or 144 mw, which is well within the rating
> > for that device. The 2.2K in the VFO emitter limits it's collector
> > current to (12V / 2200 = 0.0054A) or 65 mw, again well within the power
> > handling capabilities of that device.
> >
> > Arv
> > _._
> >
> >
> > Greg W:-) wrote:
> > >
> > > Hi all
> > >
> > > Just a little point I thought I'de bring up.
> > >
> > > If anyone is making a radio from the bitx20a schematic . Don't , it
> > > wont work.
> > >
> > > I have been waiting for someone else to notice it before but the
> > > schematic is fatally flawed in the VFO area.
> > >
> > > The first buffers base should go to the oscillator emitter but it
> doesn't.
> > >
> > > I built it up to test what I found ---
> > > The Result , a bunch of smoked parts and no vfo'ing.
> > >
> > > Follow THAT schematic with care.!!
> > >
> > > Regards
> > >
> > > gregW:-) OH2FFY
> > >
> > >
> >
> >
> >
> >
>
>

--
======================================
Web: http://K7HKL.homelinux.net
http://bitx20a.livejournal.com
http://home.earthlink.net/~arvevans/
http://www.geocities.com/k7hkl_arv/
======================================


Re: vfo trouble - bitx20a schematic.

Arv Evans
 

Greg

Good. It sounds like you are well on the way to figuring out what went
wrong. The fact that R-26 became hot is possibly key to understanding
what happened. This would make a shorted C-30 as the first suspect.
Following the circuit would also indicate that a short to ground or
wiring error in the T-4 and T-5 area could also be a problem. A shorted
C-31 could put Q-6 near it's maximum power rating and eventually destroy
that device. If C-31 were OK but the transistor Q-6 was bad, I would
expect R-29 to be destroyed also. C-32 isolates the 2nd VFO buffer from
the 1st VFO buffer so I would not expect something that burned up R-26
to cause problems for circuitry prior to C-32.

The BITX20A VFO was designed the way it is in order to insure that the
output was as clean as possible, while still maintaining good
stability. There are a number of small changes that were made to the
BITX20A design in order to minimize spurious content in the output
signal. Some were made necessary by close component spacing involved in
the PCB layout, while others were made possible by having a standardized
kit of components available for the build. C-25 and L-10 were necessary
to minimize VFO energy, unwanted mixer products, and possible harmonics
that might get into the transmitted signal. The largest change of
course is in the kit having push-pull power output and driver stages.
This specifically reduces 2nd harmonic content in the output.

Good luck on your VFO debugging, and please let us know what you find,
as this information may help some other BITX20 builder with similar
problems.

Arv
_._



Greg W:-) wrote:


Hi Arv

Ok then.
So we have here a series tuned colpitts , which makes it a clapp.
I haven't seen that arrangement of taking the output from the tank
before, so I took it as a drawing fault.

Quickly when you look at the drawing it looks like the base of Q7 is
grounded but its not ,,even if it was grounded it wouldn't burn up my
parts.
Q7 - Q6 and R26 got hot enough to smell.
My board is tiny so it is difficult to see exactly which parts were
hot using the burnt finger tip method.
I scoped the output and it showed a voltage swing + and then - but it
didn't return to complete the oscillation.

Assuming the transistors were now fried in at least the buffers I
snipped them out (disabling that part of the circuit) , and cro'ing at
the vfo output showed this same waveform.

I have checked my board and it seems in line with the schematic and my
active parts are installed correctly , I can only assume now that
these Chinese resistors and caps I used had way off values , but even
that is hard to imagine.
Normally I measure my parts values before installing them but I didn't
this time ,, perhaps the 10k resistors were misslabled 1 k's or whatever??
But again that wouldn't easily explain the faults across the different
sections.

I have made many vfo's and this is the first one that didn't work
straight off.
I am in search of a clean and stable vfo at 3Mhz , most designs work ,
but aren't very clean.

If you know of any good source material for VFO's ide appreciate the
link or whatever.
Theres not much reliable info around on this subject , even in
Experimental Methods it gave 1 paragraph devoted to the FET Hartley
VFO.-- which isnt really a lot to go on., especially as LC oscillators
don't follow all the rules as they should.

I will build it up again tonight stage by stage and check things
thoroughly and see where it went wrong.

Regards

gregW:-) OH2FFY

=====================================================================

--- In BITX20@... <mailto:BITX20%40yahoogroups.com>, Arv
Evans <arvid.evans@...> wrote:

Greg

Interesting observation, but not quite correct. The first buffer
shares
the bias resistors with the oscillator transistor itself. This holds
the emitter on that buffer at approximately 1/2 Vcc from that pair of
10K dividers (R-33 and R-34). The DC path for this bias is off the
junction of these two resistors, through L7 and R-32 to the base of
Q-7. Drive for the 1st buffer is taken from the VFO tank circuit, not
from the VFO emitter. This is a little different from some popular VFO
designs, but it does insure that output from this buffer is clean and
does not get driven into saturation or shut-off at any point in the
cycle.

Not sure why or how you burned up some parts. My BITX20A uses the same
circuit and it works just fine. A number of other builders are using
the same circuit and they are reporting contacts, which makes me think
that their circuits must be working OK.

I wonder which specific parts burned up? From that you might be
able to
work backwards to determine the failure mode and it's cause.

With 1K in the emitter of Q-7 it cannot draw enough current to destroy
itself (12V / 1K = 0.012A) or 144 mw, which is well within the rating
for that device. The 2.2K in the VFO emitter limits it's collector
current to (12V / 2200 = 0.0054A) or 65 mw, again well within the power
handling capabilities of that device.

Arv
_._


Greg W:-) wrote:

Hi all

Just a little point I thought I'de bring up.

If anyone is making a radio from the bitx20a schematic . Don't , it
wont work.

I have been waiting for someone else to notice it before but the
schematic is fatally flawed in the VFO area.

The first buffers base should go to the oscillator emitter but it
doesn't.

I built it up to test what I found ---
The Result , a bunch of smoked parts and no vfo'ing.

Follow THAT schematic with care.!!

Regards

gregW:-) OH2FFY



--
======================================
Web: http://K7HKL.homelinux.net
http://bitx20a.livejournal.com
http://home.earthlink.net/~arvevans/
http://www.geocities.com/k7hkl_arv/
======================================


Re: vfo trouble - bitx20a schematic.

kwroberson
 

Hello GregW, I am also building the BitX20 Kit , I have the
RX working , and the VFO works ok for what it was designed.
I am going to use the transciver for digi modes ( PSK31 , JT65A,
JT2 , JT4A , and others.
The VFO is not stable enough for those modes , so I am going
to use a NorCal FCC-1 for freq read out and Norcal FCC-2 digi
VFO , I Have the freq read out working and have 10 digi can read
freq down to 1 HZ. very nice .
Today I am working on the Digi VFO.
Also I am homebrewing the digi interface , computer to radio.
All in one box . Right now I have changed the local osc to xtal
control until I get the digi vfo working.
the only xtal that i had in my junk box was 3023 khz, That put
me in the cw part of the band . very stable , drift up abt
20 hz in abt an hour , then stable. Hope the digi vfo is that
stable , right now I am copy cw station while working on
digi vfo.
That's all I know .
73 Ken K5DNL Oklahoma


--- In BITX20@..., "Greg W:-)" <onegammyleg@...> wrote:

Hi all

Just a little point I thought I'de bring up.

If anyone is making a radio from the bitx20a schematic . Don't , it
wont work.

I have been waiting for someone else to notice it before but the
schematic is fatally flawed in the VFO area.

The first buffers base should go to the oscillator emitter but it
doesn't.

I built it up to test what I found ---
The Result , a bunch of smoked parts and no vfo'ing.

Follow THAT schematic with care.!!

Regards

gregW:-) OH2FFY


Re: vfo trouble - bitx20a schematic.

Greg W:-) <onegammyleg@...>
 

Hi Arv

Ok then.
So we have here a series tuned colpitts , which makes it a clapp.
I haven't seen that arrangement of taking the output from the tank
before, so I took it as a drawing fault.

Quickly when you look at the drawing it looks like the base of Q7 is
grounded but its not ,,even if it was grounded it wouldn't burn up my
parts.
Q7 - Q6 and R26 got hot enough to smell.
My board is tiny so it is difficult to see exactly which parts were
hot using the burnt finger tip method.
I scoped the output and it showed a voltage swing + and then - but it
didn't return to complete the oscillation.

Assuming the transistors were now fried in at least the buffers I
snipped them out (disabling that part of the circuit) , and cro'ing at
the vfo output showed this same waveform.

I have checked my board and it seems in line with the schematic and my
active parts are installed correctly , I can only assume now that
these Chinese resistors and caps I used had way off values , but even
that is hard to imagine.
Normally I measure my parts values before installing them but I didn't
this time ,, perhaps the 10k resistors were misslabled 1 k's or whatever??
But again that wouldn't easily explain the faults across the different
sections.

I have made many vfo's and this is the first one that didn't work
straight off.
I am in search of a clean and stable vfo at 3Mhz , most designs work ,
but aren't very clean.

If you know of any good source material for VFO's ide appreciate the
link or whatever.
Theres not much reliable info around on this subject , even in
Experimental Methods it gave 1 paragraph devoted to the FET Hartley
VFO.-- which isnt really a lot to go on., especially as LC oscillators
don't follow all the rules as they should.

I will build it up again tonight stage by stage and check things
thoroughly and see where it went wrong.


Regards

gregW:-) OH2FFY

=====================================================================




--- In BITX20@..., Arv Evans <arvid.evans@...> wrote:

Greg

Interesting observation, but not quite correct. The first buffer
shares
the bias resistors with the oscillator transistor itself. This holds
the emitter on that buffer at approximately 1/2 Vcc from that pair of
10K dividers (R-33 and R-34). The DC path for this bias is off the
junction of these two resistors, through L7 and R-32 to the base of
Q-7. Drive for the 1st buffer is taken from the VFO tank circuit, not
from the VFO emitter. This is a little different from some popular VFO
designs, but it does insure that output from this buffer is clean and
does not get driven into saturation or shut-off at any point in the
cycle.

Not sure why or how you burned up some parts. My BITX20A uses the same
circuit and it works just fine. A number of other builders are using
the same circuit and they are reporting contacts, which makes me think
that their circuits must be working OK.

I wonder which specific parts burned up? From that you might be
able to
work backwards to determine the failure mode and it's cause.

With 1K in the emitter of Q-7 it cannot draw enough current to destroy
itself (12V / 1K = 0.012A) or 144 mw, which is well within the rating
for that device. The 2.2K in the VFO emitter limits it's collector
current to (12V / 2200 = 0.0054A) or 65 mw, again well within the power
handling capabilities of that device.

Arv
_._


Greg W:-) wrote:

Hi all

Just a little point I thought I'de bring up.

If anyone is making a radio from the bitx20a schematic . Don't , it
wont work.

I have been waiting for someone else to notice it before but the
schematic is fatally flawed in the VFO area.

The first buffers base should go to the oscillator emitter but it
doesn't.

I built it up to test what I found ---
The Result , a bunch of smoked parts and no vfo'ing.

Follow THAT schematic with care.!!

Regards

gregW:-) OH2FFY


[Non-text portions of this message have been removed]


Special event operation - Birth Anniversary of Acharya Jagadish Chandra Bose.

Bharat Balsavar, VU2BDX <vu2bdx@...>
 

Hi All,

Sir Jagadish Chandra Bose is considered the father of Radio Science. More
details: http://en.wikipedia.org/wiki/Jagdish_Chandra_Bose

To mark his 150th birth anniversary, a few hams from India are licensed to
operate special call-sign stations. Below mail on the subject is self
explanatory.
Those interested in special event QSL cards, or otherwise are welcome to
establish contacts from the world over.

Please spread the word to your fellow hams.

73,
VU2BDX, Bharat


---------- Forwarded message ----------
From: ARASU MANOHAR <manohar_arasu@...>
Date: Nov 21, 2007 10:43 AM
Subject: Special event operation-Birth Anniversary of Acharya Jagadish
Chandra Bose.


Special permission of the Ministry of Communications and Information
Technology, Department of Communications ,Government of India, has been
accorded vide letter no. L-14011/640/2007-AMT dated 19.09.2007, to following
group of Amateur Radio Operator's licenses to use special call signs (as
mentioned below against each participant) to operate during the Birth
Anniversary of India's great scientist and inventor Shri. Jagadish Chandra
Bose, (which falls on Nov. 30th 2007) from 25th Nov 2007 to 02nd Dec 2007,
from their existing licenced location mentioned in the Radio Amateur
Licenses

1. VU2SMN AU7JCB
2. VU2DCT AT0JCB
3. VU2DSI AU2JCB
4. VU2SDF AU8JCB
5. VU2HFR AU4JCB
6. VU2UR AU1JCB
7. VU2SMS AU9JCB

In addition, some more applications are under process for the special call
signs, all of which have common Suffix " JCB" with varying prefixes from AT1

to AT0, and AU1 to AU0. This is the invitation to all amateurs world wide,
who are Prefix hunters, Special QSL hunters, etc, to avail the finest
opportunity , to work and get QSOs, and later on QSLs from the very special
prefix series AU1 to AU0.

The stations will be QRV on the following frequencies:

SSB:
40M: 7.030 MHz
20M: 14.155 MHz, 14.190 MHz - 14.240 MHz
18M: 18.105 MHz - 18.150 MHz
15M: 21.180 MHz - 21.240 MHz & 21.310 MHz
12M: 24.935 MHz - 24.975 MHz
10M: 28.485 MHz - 28.535 MHz

CW:
40M: 7.007 MHz & 7.017 MHz
20M: 14.030 MHz & 14.035 MHz
18M: 18.080 MHz & 18.085 MHz
15M: 21.030 MHz & 21.035 MHz
12M: 24.895 MHz & 24.900 MHz
10M: 28.030 MHz & 28.035 MHz

These frequencies are subject to QRM suffered and there could be a variation
of +/- 5 KHz. All DX stations are requested to send " QSL via VU2SMN
direct only" and , with 2 IRCs of the latest version only, which expires on
31.12.2009. All VU stations are likewise requested to QSL with SASE for
QSLs. No QSLs are handled via any bureau.
For more information on the operation please visit the web page
http://au9jcb.angelfire.com/
<http://www.rediffmail.com/cgi-bin/red.cgi?red=http%3A%2F%2Fau9jcb%2Eangelfire%2Ecom%2F>and
for detailed information on Sir. J. C. Bose
and his work please visit the following wonderful links:

http://www.tuc.nrao.edu/~demerson/bose/bose.html<http://www.rediffmail.com/cgi-bin/red.cgi?red=http%3A%2F%2Fwww%2Etuc%2Enrao%2Eedu%2F%7Edemerson%2Fbose%2Fbose%2Ehtml>
http://www.qsl.net/vu2msy/JCBOSE.htm<http://www.rediffmail.com/cgi-bin/red.cgi?red=http%3A%2F%2Fwww%2Eqsl%2Enet%2Fvu2msy%2FJCBOSE%2Ehtm>

This operation is in preparation of the 150th birth anniversary of this
great scientist and inventor when a large scale operation is planned.


Re: vfo trouble - bitx20a schematic.

Arv Evans
 

Greg

Interesting observation, but not quite correct. The first buffer shares
the bias resistors with the oscillator transistor itself. This holds
the emitter on that buffer at approximately 1/2 Vcc from that pair of
10K dividers (R-33 and R-34). The DC path for this bias is off the
junction of these two resistors, through L7 and R-32 to the base of
Q-7. Drive for the 1st buffer is taken from the VFO tank circuit, not
from the VFO emitter. This is a little different from some popular VFO
designs, but it does insure that output from this buffer is clean and
does not get driven into saturation or shut-off at any point in the cycle.

Not sure why or how you burned up some parts. My BITX20A uses the same
circuit and it works just fine. A number of other builders are using
the same circuit and they are reporting contacts, which makes me think
that their circuits must be working OK.

I wonder which specific parts burned up? From that you might be able to
work backwards to determine the failure mode and it's cause.

With 1K in the emitter of Q-7 it cannot draw enough current to destroy
itself (12V / 1K = 0.012A) or 144 mw, which is well within the rating
for that device. The 2.2K in the VFO emitter limits it's collector
current to (12V / 2200 = 0.0054A) or 65 mw, again well within the power
handling capabilities of that device.

Arv
_._


Greg W:-) wrote:


Hi all

Just a little point I thought I'de bring up.

If anyone is making a radio from the bitx20a schematic . Don't , it
wont work.

I have been waiting for someone else to notice it before but the
schematic is fatally flawed in the VFO area.

The first buffers base should go to the oscillator emitter but it doesn't.

I built it up to test what I found ---
The Result , a bunch of smoked parts and no vfo'ing.

Follow THAT schematic with care.!!

Regards

gregW:-) OH2FFY