|
This fix reduced the spurs by up to 10 db? and requires ONLY ONE
part to be added.
There is big change above 10MHz in the board. There is some improvement
below also.
The way I did it, CW may not work anymore will
need some more mods for CW:
1. T2 - desolder the transformer wires that go to pin 3 and 5. Pin 1
has a square pad.
2. Bring out the two wires above board and join them together and
solder.
3. Take a 45Mhz filter- 45M15 or? similar 2 pole - one xtal only.
Solder one end of filter
to the wires of T2 pulled out. The center filter wire to ground at one
end of R26. You will
see a ground via there.
4. Solder the third wire of filter to C10/R27 junction.
Thats it! This prevents the leaked TX signal that gets amplified by the
1st BiDi from getting into
the first mixer and creating havoc.
Farhan method of the same..much simpler and CW will work.
1. Remove R27
2. Solder the 45Mhz filter two extreme ends to the pads of the
resistor.
3. Solder the center lead of the filter to the nearest ground. R13 is
very near with a ground via.
The first method the extra filter will work in RX mode also and may help!
In the second the
filter is only in the TX path..
Folks with DSA815 or better please share your feed back. The filter may
work better properly
terminated etc.
Have fun!
--
Raj, vu2zap
Bengaluru, South India.
|
Would that be a good solution to make the IF amplifier tuned? Like this? Also, change the transistors to BFS17P, this is more suited to RF.
73s de HA5OGL
This fix reduced the spurs by up to 10 db? and requires ONLY ONE
part to be added.
There is big change above 10MHz in the board. There is some improvement
below also.
The way I did it, CW may not work anymore will
need some more mods for CW:
1. T2 - desolder the transformer wires that go to pin 3 and 5. Pin 1
has a square pad.
2. Bring out the two wires above board and join them together and
solder.
3. Take a 45Mhz filter- 45M15 or? similar 2 pole - one xtal only.
Solder one end of filter
to the wires of T2 pulled out. The center filter wire to ground at one
end of R26. You will
see a ground via there.
4. Solder the third wire of filter to C10/R27 junction.
Thats it! This prevents the leaked TX signal that gets amplified by the
1st BiDi from getting into
the first mixer and creating havoc.
Farhan method of the same..much simpler and CW will work.
1. Remove R27
2. Solder the 45Mhz filter two extreme ends to the pads of the
resistor.
3. Solder the center lead of the filter to the nearest ground. R13 is
very near with a ground via.
The first method the extra filter will work in RX mode also and may help!
In the second the
filter is only in the TX path..
Folks with DSA815 or better please share your feed back. The filter may
work better properly
terminated etc.
Have fun!
--
Raj, vu2zap
Bengaluru, South India.
|
I have tried the spur-zap fix. It really works. We need a big shout out to Raj, VU2ZAP. He has endlessly measured, tabulated but never given up on hunting this spur down. I have tried it this morning too. Here are my results. I took out the R27, it is the 47 ohm series resistor that connects the tx side IF p to the front end mixer. In its place, i soldered the two ends of a spare 45 mhz filter. The ground pin of the filter was soldered to the ground end of C11.
73, f.?
Would that be a good solution to make the IF amplifier tuned? Like this? Also, change the transistors to BFS17P, this is more suited to RF.
73s de HA5OGL
This fix reduced the spurs by up to 10 db? and requires ONLY ONE
part to be added.
There is big change above 10MHz in the board. There is some improvement
below also.
The way I did it, CW may not work anymore will
need some more mods for CW:
1. T2 - desolder the transformer wires that go to pin 3 and 5. Pin 1
has a square pad.
2. Bring out the two wires above board and join them together and
solder.
3. Take a 45Mhz filter- 45M15 or? similar 2 pole - one xtal only.
Solder one end of filter
to the wires of T2 pulled out. The center filter wire to ground at one
end of R26. You will
see a ground via there.
4. Solder the third wire of filter to C10/R27 junction.
Thats it! This prevents the leaked TX signal that gets amplified by the
1st BiDi from getting into
the first mixer and creating havoc.
Farhan method of the same..much simpler and CW will work.
1. Remove R27
2. Solder the 45Mhz filter two extreme ends to the pads of the
resistor.
3. Solder the center lead of the filter to the nearest ground. R13 is
very near with a ground via.
The first method the extra filter will work in RX mode also and may help!
In the second the
filter is only in the TX path..
Folks with DSA815 or better please share your feed back. The filter may
work better properly
terminated etc.
Have fun!
--
Raj, vu2zap
Bengaluru, South India.
|
Raj,
Your mod verifies my suspicion: apart form the mixing products
within the mixer harmonics of the TX Bidi amp in front of the
mixer also contribute to the problem, i.e. the first harmonic of
the BiDI amp (2*45 MHz = 90 MHz!!!).
Placing an xtal filter directly into the path without any
impedance transformation is a bad idea, the filter itself wants to
see a higher impedance than 50 ohms. If this filter is not
terminated correctly its insertion loss and passband ripple will
be "ugly".
In addition: the connection from R27 to the transformer T2 will
produce a source impedance close to 50 ohms. The output of the
emitter follower Q21 is low impedance. PLUS: any complex load
(especially capacitive) can cause Q21 to oscillate! A coure would
then be a series resistor ( e.g. 100 ohms or so) to the base of
Q21 .???
As the bidiamp produces harmoncis it would be easier to place a
low pass filter (corner freq. a bit larger than 45 Mhz but "good"???
attenaution at 90 MHz). A small pcb with good grounding should
do--??? please test this small pcb for real attenuation @90 MHz or
if available a "commercial low pass filter e.g. from Mini Circuits
could also do the trick for just a test.
A" fast design" using RFSIM99 for a 50 MHz five pole low pass
filter (chebychev, 0.1 dB ripple, 50 ohm impedance)??? C-L-C-L-C
gives the following component values: 73 pF 218 nH 125 pF 218 nH
73 pf. The simulated attenuation at 90 MHz is 30 dB.???
73
Henning Weddig
DK5LV???
Am 05.09.2018 um 10:46 schrieb Raj
vu2zap:
toggle quoted message
Show quoted text
This fix reduced the spurs by up to 10 db??? and requires ONLY ONE
part to be added.
There is big change above 10MHz in the board. There is some
improvement
below also.
The way I did it, CW may not work
anymore will
need some more mods for CW:
1. T2 - desolder the transformer wires that go to pin 3 and 5.
Pin 1
has a square pad.
2. Bring out the two wires above board and join them together and
solder.
3. Take a 45Mhz filter- 45M15 or??? similar 2 pole - one xtal only.
Solder one end of filter
to the wires of T2 pulled out. The center filter wire to ground at
one
end of R26. You will
see a ground via there.
4. Solder the third wire of filter to C10/R27 junction.
Thats it! This prevents the leaked TX signal that gets amplified
by the
1st BiDi from getting into
the first mixer and creating havoc.
Farhan method of the same..much simpler and CW will work.
1. Remove R27
2. Solder the 45Mhz filter two extreme ends to the pads of the
resistor.
3. Solder the center lead of the filter to the nearest ground. R13
is
very near with a ground via.
The first method the extra filter will work in RX mode also and
may help!
In the second the
filter is only in the TX path..
Folks with DSA815 or better please share your feed back. The
filter may
work better properly
terminated etc.
Have fun!
--
Raj, vu2zap
Bengaluru, South India.
|
Hi Henning,
I did try a filter but did not help much, I guess this issue needed a
filter with greater end stop.
Allison said she tried a filter and found improvement.
I originally visualized a pad with LC matching with xtal conditioning
filter. The pad would keep
the mixer peaceful and the BiDi will be happy with LC. Have to try this
in the next days.
What I felt is that the BiDi was amping the TX signal that it picked up
and sending to the
first mixer. When I lowered th power the spurs came down much more..
The spurs were moving together and apart in 3x 4x and 5x of the change in
VFO freq.
They came together every 2.5 Mhz and were worst behaved at 15MHz and
22.5MHz
Raj
At 05-09-18, you wrote:
toggle quoted message
Show quoted text
Raj,
Your mod verifies my suspicion: apart form the mixing products within the
mixer harmonics of the TX Bidi amp in front of the mixer also contribute
to the problem, i.e. the first harmonic of the BiDI amp (2*45 MHz = 90
MHz!!!).
Placing an xtal filter directly into the path without any impedance
transformation is a bad idea, the filter itself wants to see a higher
impedance than 50 ohms. If this filter is not terminated correctly its
insertion loss and passband ripple will be "ugly".
In addition: the connection from R27 to the transformer T2 will produce a
source impedance close to 50 ohms. The output of the emitter follower Q21
is low impedance. PLUS: any complex load (especially capacitive) can
cause Q21 to oscillate! A coure would then be a series resistor ( e.g.
100 ohms or so) to the base of Q21 .???
As the bidiamp produces harmoncis it would be easier to place a low pass
filter (corner freq. a bit larger than 45 Mhz but "good"???
attenaution at 90 MHz). A small pcb with good grounding should do--???
please test this small pcb for real attenuation @90 MHz or if available a
"commercial low pass filter e.g. from Mini Circuits could also do
the trick for just a test.
A" fast design" using RFSIM99 for a 50 MHz five pole low pass
filter (chebychev, 0.1 dB ripple, 50 ohm impedance)??? C-L-C-L-C gives
the following component values: 73 pF 218 nH 125 pF 218 nH 73 pf. The
simulated attenuation at 90 MHz is 30 dB.???
73
Henning Weddig
DK5LV???
Am 05.09.2018 um 10:46 schrieb Raj vu2zap:
This fix reduced the spurs by up to 10 db??? and requires ONLY ONE part
to be added.
There is big change above 10MHz in the board. There is some improvement
below also.
The way I did it, CW may not work anymore will
need some more mods for CW:
1. T2 - desolder the transformer wires that go to pin 3 and 5. Pin 1
has a square pad.
2. Bring out the two wires above board and join them together and
solder.
3. Take a 45Mhz filter- 45M15 or??? similar 2 pole - one xtal only.
Solder one end of filter
to the wires of T2 pulled out. The center filter wire to ground at one
end of R26. You will
see a ground via there.
4. Solder the third wire of filter to C10/R27 junction.
Thats it! This prevents the leaked TX signal that gets amplified by the
1st BiDi from getting into
the first mixer and creating havoc.
Farhan method of the same..much simpler and CW will work.
1. Remove R27
2. Solder the 45Mhz filter two extreme ends to the pads of the
resistor.
3. Solder the center lead of the filter to the nearest ground. R13 is
very near with a ground via.
The first method the extra filter will work in RX mode also and may help!
In the second the
filter is only in the TX path..
Folks with DSA815 or better please share your feed back. The filter may
work better properly
terminated etc.
Have fun!
--
Raj, vu2zap
Bengaluru, South India.
|
It is a idea to try Lev.. will give it a thought.
Raj
At 05-09-18, you wrote:
toggle quoted message
Show quoted text
Would that be a good solution to
make the IF amplifier tuned? Like this? Also, change the transistors to
BFS17P, this is more suited to RF.
73s de HA5OGL
On Wed, Sep 5, 2018 at 10:46 AM Raj vu2zap
<
rajendrakumargg@...> wrote:
- This fix reduced the spurs by up to 10 db?? and requires ONLY
ONE part to be added.
- There is big change above 10MHz in the board. There is some
improvement below also.
- The way I did it, CW may not work anymore will
need some more mods for CW:
- 1. T2 - desolder the transformer wires that go to pin 3 and 5. Pin 1
has a square pad.
- 2. Bring out the two wires above board and join them together and
solder.
- 3. Take a 45Mhz filter- 45M15 or?? similar 2 pole - one xtal
only. Solder one end of filter
- to the wires of T2 pulled out. The center filter wire to ground at
one end of R26. You will
- see a ground via there.
- 4. Solder the third wire of filter to C10/R27 junction.
- Thats it! This prevents the leaked TX signal that gets amplified by
the 1st BiDi from getting into
- the first mixer and creating havoc.
- Farhan method of the same..much simpler and CW will work.
- 1. Remove R27
- 2. Solder the 45Mhz filter two extreme ends to the pads of the
resistor.
- 3. Solder the center lead of the filter to the nearest ground. R13 is
very near with a ground via.
- The first method the extra filter will work in RX mode also and may
help! In the second the
- filter is only in the TX path..
- Folks with DSA815 or better please share your feed back. The filter
may work better properly
- terminated etc.
- Have fun!
- --
- Raj, vu2zap
- Bengaluru, South India.
Content-Type: application/pdf; name="if_amp-if_amp.pdf"
Content-Disposition: attachment;
filename="if_amp-if_amp.pdf"
Content-ID: <f_jlowtrh20>
X-Attachment-Id: f_jlowtrh20
|
A a big thanks to Farhan, Allison and earlier to Jerry!
Cheers
Raj
At 05-09-18, you wrote:
toggle quoted message
Show quoted text
I have tried the spur-zap fix.
It really works. We need a big shout out to Raj, VU2ZAP. He has endlessly
measured, tabulated but never given up on hunting this spur down.
I have tried it this morning too. Here are my results. I took out the
R27, it is the 47 ohm series resistor that connects the tx side IF p to
the front end mixer. In its place, i soldered the two ends of a spare 45
mhz filter. The ground pin of the filter was soldered to the ground end
of C11.
73, f.?
On Wed, 5 Sep 2018, 14:28 Lev,
<leventelist@...>
wrote:
- Would that be a good solution to make the IF amplifier tuned? Like
this? Also, change the transistors to BFS17P, this is more suited to
RF.
- 73s de HA5OGL
- On Wed, Sep 5, 2018 at 10:46 AM Raj vu2zap
<
rajendrakumargg@...> wrote:
- This fix reduced the spurs by up to 10 db?? and requires ONLY
ONE part to be added.
- There is big change above 10MHz in the board. There is some
improvement below also.
- The way I did it, CW may not work anymore will
need some more mods for CW:
- 1. T2 - desolder the transformer wires that go to pin 3 and 5. Pin 1
has a square pad.
- 2. Bring out the two wires above board and join them together and
solder.
- 3. Take a 45Mhz filter- 45M15 or?? similar 2 pole - one xtal
only. Solder one end of filter
- to the wires of T2 pulled out. The center filter wire to ground at
one end of R26. You will
- see a ground via there.
- 4. Solder the third wire of filter to C10/R27 junction.
- Thats it! This prevents the leaked TX signal that gets amplified by
the 1st BiDi from getting into
- the first mixer and creating havoc.
- Farhan method of the same..much simpler and CW will work.
- 1. Remove R27
- 2. Solder the 45Mhz filter two extreme ends to the pads of the
resistor.
- 3. Solder the center lead of the filter to the nearest ground. R13 is
very near with a ground via.
- The first method the extra filter will work in RX mode also and may
help! In the second the
- filter is only in the TX path..
- Folks with DSA815 or better please share your feed back. The filter
may work better properly
- terminated etc.
- Have fun!
- --
- Raj, vu2zap
- Bengaluru, South India.
|
Further experimentation with Farhan's method,
Instead of removing R27 47Ohms and putting the filter there. I removed
C22
and soldered the filter there.
The spurs on 20 dropped even lower @5W the spurs were -55 to -60dbm!
With proper termination the results may be better!
Raj
At 05-09-18, you wrote:
toggle quoted message
Show quoted text
This fix reduced the spurs by up
to 10 db? and requires ONLY ONE part to be added.
There is big change above 10MHz in the board. There is some improvement
below also.
Farhan method of the same..much simpler and CW will work.
1. Remove R27
2. Solder the 45Mhz filter two extreme ends to the pads of the
resistor.
3. Solder the center lead of the filter to the nearest ground. R13 is
very near with a ground via.
|
Filters suitable (I believe) for this mod are available here for $5.99 for a pair:?
If this solves the spur problem then it is also a very positive step toward solving the overall PA filter issue. Absent the spurs, and with the board layout problems addressed, the existing four filters should be adequate. I am about to receive a prototype 4 filter board that can accept the existing components for testing.?
Very nice work!
WA8TOD
|
This guy is cheaper (N2CBU ?) but shipping to India is
expensive..
Raj
At 05-09-18, you wrote:
toggle quoted message
Show quoted text
Filters suitable (I believe) for
this mod are available here for $5.99 for a pair:
If this solves the spur problem then it is also a very positive step
toward solving the overall PA filter issue. Absent the spurs, and with
the board layout problems addressed, the existing four filters should be
adequate. I am about to receive a prototype 4 filter board that can
accept the existing components for testing.
Very nice work!
WA8TOD
|
?I ordered the pair.? ?Interesting and exciting development.
gordon
toggle quoted message
Show quoted text
Filters suitable (I believe) for this mod are available here for $5.99 for a pair:?
If this solves the spur problem then it is also a very positive step toward solving the overall PA filter issue. Absent the spurs, and with the board layout problems addressed, the existing four filters should be adequate. I am about to receive a prototype
4 filter board that can accept the existing components for testing.?
Very nice work!
WA8TOD
|
If you guys want to try out the mod, i can have some spares shipped out. - f
On Wed, 5 Sep 2018, 19:06 Gordon Gibby, < ggibby@...> wrote:
?I ordered the pair.? ?Interesting and exciting development.
gordon
Filters suitable (I believe) for this mod are available here for $5.99 for a pair:?
If this solves the spur problem then it is also a very positive step toward solving the overall PA filter issue. Absent the spurs, and with the board layout problems addressed, the existing four filters should be adequate. I am about to receive a prototype
4 filter board that can accept the existing components for testing.?
Very nice work!
WA8TOD
|
Farhans method...
1. Remove R27
2. Solder the 45Mhz filter two extreme ends to the pads of the resistor.
3. Solder the center lead of the filter to the nearest ground. R13 is very near with a ground via.
Sounds like something that may seriously help. I tried a low pass filter there and it
did help but not enough.? Time and other pressing things never got back to try a
band pass filter.
One I'd liked to have tried is just moving the filter to the other end of the amp.
What is the impact on RX performance?
Allison
|
Raj,
Very cool that you found such an easy and cheap solution!
Though not so sure I was a part of it in any way.
So that 2.5mhz thing had nothing to do with the si5351, was caused by feedback from the power amp?
Very curious.? I have no idea how that 2.5mhz factor came about.
The extra 45mhz filter would solve the power amp feedback issue.
That was probably all the low frequency rumble in Warren's plots of a few weeks ago.
This would not be fixed by a LPF.
I had assumed that the 45mhz-DialFreq spur was generated inside the mixer at D1,D2.
But apparently the IF amp at Q20,21,22 was generating enough of a second harmonic?
that the resultant 90mhz energy minus the clk2 VFO was going straight on through
the mixer in the expected manner.? As Henning has stated previously.
I'm sure termination impedances around the new filter could be an issue somehow.
But if it works, I'm ok with that!
Passband ripple might not be much of an issue, as the filter is much wider than what we actually use.
Extra insertion loss may not be much of an issue either, especially with the crystal only in
the TX path since we have gain to burn there.? Less TX signal into the D1,D2 mixer is a good thing.
Good job!
Jerry, KE7ER
toggle quoted message
Show quoted text
On Wed, Sep 5, 2018 at 04:11 AM, Raj vu2zap wrote:
A a big thanks to Farhan, Allison and earlier to Jerry!
|
On Wednesday, September 5, 2018, 6:49:10 AM PDT, Ashhar Farhan <farhanbox@...> wrote:
If you guys want to try out the mod, i can have some spares shipped out. - f I'd like one if there are enough to go around
Jim (ab7vf)
|
Allison,
the filter will be only in the TX path, the roofing filter should also be in RX path.
why amplify all the mixes from the first mixer. A good change in the architecture of
uBitx.
Raj
toggle quoted message
Show quoted text
At 05-09-18, you wrote: Farhans method...
1. Remove R27
2. Solder the 45Mhz filter two extreme ends to the pads of the resistor.
3. Solder the center lead of the filter to the nearest ground. R13 is very near with a ground via.
Sounds like something that may seriously help. I tried a low pass filter there and it
did help but not enough. Time and other pressing things never got back to try a
band pass filter.
One I'd liked to have tried is just moving the filter to the other end of the amp.
What is the impact on RX performance?
Allison
|
How could I obtain one of the mods?
Thanks
Roxie -- K1AUS
|
The cheaper ebay guy says he has 62 of them left plus postage. Someone could make him a deal for all and reship them to uBITX owners for a $0.72 stamp on an envelope.
73 Kees K5BCQ
|
Farhan, Mine is a mess due to other work. >>If you guys want to try out the mod, i can have some spares shipped out.
However I have a few friends around me I can help using this mod and also a relay fix
already posted.
Allison
|
Raj,?
With the new filter placed in both the TX and RX paths as you originally proposed,
should be able to restore CW operation by lifting the bottom end of R105, tie it to T2 pins 3,5
I suspect that's already occurred to you, and it's a matter of finding the time to try it.
If we can have a clean all-of-HF transmitter without adding switchable bandpass filters?
in front of the first mixer, this is a significant advance to the art.
Jerry, KE7ER
toggle quoted message
Show quoted text
On Wed, Sep 5, 2018 at 08:05 AM, Raj vu2zap wrote:
the filter will be only in the TX path, the roofing filter should also be in RX path.
why amplify all the mixes from the first mixer. A good change in the architecture of
uBitx.
|
Raj vu2zap
