|
The radio went together fairly easily, though I'm at
a loss to figure out why an experimenter's radio is
jammed onto such a small board. This might be OK for
a production rig, but some room would be nice to
experiment.
That said, the radio works except there is no image
rejection and the DSP image rejection controls do
nothing. The instructions say, "If the image cannot
be nulled at least 50 db, then a problem exists..."
Well, some guidance would have been helpful.
Especially, given my opening criticism.
I am reluctant to tear into this think quite yet as
there is not a lot of room to work. I originally
thought it may be a transformer mis-wiring on my part.
Again, we're talking an experimenter's radio on 40
meters where things are relatively less critical than
other bands, so a little larger toroid with more room
to make changes would make it a lot easier.
I'm hoping when I fix the image problem that all
that 7.056 +/- 5 khz energy is going to at least be
diminished. 7.056 is S5. 7.051/7.061 are S3.
Anyway, I have no doubt the problem is my error. I
just want a little direction so that I can minimize
stress on the board.
Eric
KE6US
www.ke6us.com
|
Hi Eric,
Not being able to null the image has usually been associated with the I and
Q signals being crossed or one missing. Check to make sure the stereo cable
is connected to the board with the stereo connector tip to C18, the via
nearest the corner board mounting hole. Check with a meter to make sure
there is nothing to short out one of the I or Q signals. Also, if the QSD
is not getting one of the clock phases, open at a IC pin or short between
pins, it can result is such an unbalance between the I and Q signals such
that one can not get a null. Solder bridges between IC pins can sometimes
be hard to see without looking with good lighting and magnification.
Please let me know what you find or if you still have the problem. I may be
able to suggest other things to look at.
Good luch with the debug.
73,
Tony KB9YIG
toggle quoted message
Show quoted text
----- Original Message ----- From: "Eric" <eric_ke6us@...> To: <softrock40@...> Sent: Tuesday, September 20, 2005 8:10 PM Subject: [softrock40] DSP Image Rejection problem and some thoughts The radio went together fairly easily, though I'm at
a loss to figure out why an experimenter's radio is
jammed onto such a small board. This might be OK for
a production rig, but some room would be nice to
experiment.
That said, the radio works except there is no image
rejection and the DSP image rejection controls do
nothing. The instructions say, "If the image cannot
be nulled at least 50 db, then a problem exists..."
Well, some guidance would have been helpful.
Especially, given my opening criticism.
I am reluctant to tear into this think quite yet as
there is not a lot of room to work. I originally
thought it may be a transformer mis-wiring on my part.
Again, we're talking an experimenter's radio on 40
meters where things are relatively less critical than
other bands, so a little larger toroid with more room
to make changes would make it a lot easier.
I'm hoping when I fix the image problem that all
that 7.056 +/- 5 khz energy is going to at least be
diminished. 7.056 is S5. 7.051/7.061 are S3.
Anyway, I have no doubt the problem is my error. I
just want a little direction so that I can minimize
stress on the board.
Eric
KE6US
www.ke6us.com
Yahoo! Groups Links
|
Eric- I think you may be confused regarding image rejection. What is
meant is when you inject a signal at say, 7.042, which is about
14Khz BELOW the center freq of 7.056- The image that you are trying
to null will appear at about 7.060, or about 14Khz ABOVE the center
freq. The nulling process will not have any effect on the junk
around 7.056. My understanding is that the stuff you see there are
artifacts created by very low frequency noise within the the sound
card, as well as other factors relating to this low-cost design. A
high-end sound card may reduce this, but I would like to hear from
others using the SR40 with something like the M-Audio delta 44, or
other high-end cards. Hope this explaination helps.
73, Bruce N1RX
toggle quoted message
Show quoted text
--- In softrock40@..., "Eric" <eric_ke6us@y...> wrote: The radio went together fairly easily, though I'm at
a loss to figure out why an experimenter's radio is
jammed onto such a small board. This might be OK for
a production rig, but some room would be nice to
experiment.
That said, the radio works except there is no image
rejection and the DSP image rejection controls do
nothing. The instructions say, "If the image cannot
be nulled at least 50 db, then a problem exists..."
Well, some guidance would have been helpful.
Especially, given my opening criticism.
I am reluctant to tear into this think quite yet as
there is not a lot of room to work. I originally
thought it may be a transformer mis-wiring on my part.
Again, we're talking an experimenter's radio on 40
meters where things are relatively less critical than
other bands, so a little larger toroid with more room
to make changes would make it a lot easier.
I'm hoping when I fix the image problem that all
that 7.056 +/- 5 khz energy is going to at least be
diminished. 7.056 is S5. 7.051/7.061 are S3.
Anyway, I have no doubt the problem is my error. I
just want a little direction so that I can minimize
stress on the board.
Eric
KE6US
www.ke6us.com
|
Those were actually two different thoughts. When I inject a signal with my KX1 at 7.040, I get an image at 7.072 which is just about as strong. When I go to the DSP image rejection sliders, they have no effect on the 7.072 signal. I also see images of QSOs on the other side of the center frequency and can't reduce them. I mentioned, hope against hope, that fixing the image rejection problem might have some effect on the artifacts you mentioned which I realize are something inherent in the design and can't be eliminated. Thanks for the note, Bruce. I'm going to stick this thing on a scope later tonight with just power and an antenna and see what I can see. I don't have a computer in the shop or hamshack, both upstairs, so it is a little inconvenient working on the radio since the only computer I can use is in the dining room which is downstairs. Keeps me fit, though. Eric KE6US www.ke6us.com --- Bruce Beford <bruce.beford@...> wrote: Eric- I think you may be confused regarding image
rejection. What is
meant is when you inject a signal at say, 7.042,
which is about
14Khz BELOW the center freq of 7.056- The image that
you are trying
to null will appear at about 7.060, or about 14Khz
ABOVE the center
freq. The nulling process will not have any effect
on the junk
around 7.056. My understanding is that the stuff you
see there are
artifacts created by very low frequency noise within
the the sound
card, as well as other factors relating to this
low-cost design. A
high-end sound card may reduce this, but I would
like to hear from
others using the SR40 with something like the
M-Audio delta 44, or
other high-end cards. Hope this explaination helps.
73, Bruce N1RX
--- In softrock40@..., "Eric"
<eric_ke6us@y...> wrote:
The radio went together fairly easily, though I'm at
a loss to figure out why an experimenter's radio is
jammed onto such a small board. This might be OK for
a production rig, but some room would be nice to
experiment.
That said, the radio works except there is no image
rejection and the DSP image rejection controls do
nothing. The instructions say, "If the image cannot
be nulled at least 50 db, then a problem exists..."
Well, some guidance would have been helpful.
Especially, given my opening criticism.
I am reluctant to tear into this think quite yet as
there is not a lot of room to work. I originally
thought it may be a transformer mis-wiring on my part.
Again, we're talking an experimenter's radio on 40
meters where things are relatively less critical
than
other bands, so a little larger toroid with more room
to make changes would make it a lot easier.
I'm hoping when I fix the image problem that all
that 7.056 +/- 5 khz energy is going to at least be
diminished. 7.056 is S5. 7.051/7.061 are S3.
Anyway, I have no doubt the problem is my error. I
just want a little direction so that I can minimize
stress on the board.
Eric
KE6US
www.ke6us.com
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|
Ahh the small board -- good question as to why is it so dang small -- I think one of Tony's original goals for the gizmo was more of a demonstration vehicle than an experimenter vehicle. I for one wish it had more working room, but I will say the experience has vastly improved my soldering and rework in small places.
The central hump you're seeing around 7.056 is normal. The gunk you're seeing around this is a consequence of the software architecture. What is happening is that the hardware takes the swath of RF centered and 7.056 and downconverts it such that 7.056 is essentially at DC. Also down there near DC is noise and 60 hz (and its harmonics) hum. When one tries to tune down near 7.056, the local software oscillator will be down in the 100's of hz's. The output of this will be Software LO +/- 60 Hz (and harmonics). Things will always be a bit messy near the center frequency -- quieter less hummy sound cards can help, but I don't believe there's any practical way to get rid of all the gunk in the middle.
If you want to check out the hardware sans computer, and have a signal generator and a scope you can put in a -30 dbm signal at 7.050 or so into the antenna. Look at the audio output on the I and Q channels -- it should be about 6 khz (7.056 - 7.060) and on the order of about 0.8 Vpp or so (don't take my nums as precision numbers, they are all from memory). The thing to look at is if both the I and Q channels are comparable in magnitude -- if one is half the other something is not quite right in the hardware. You can also take a look at the phase relationship -- it should be about 90 degrees between teh two channels. While you've got the scope out check the clocking signals to the FST3126. If you've got a generator and no scope, you might be able to compare the two channels with a good RMS voltmeter.
One last thing to check -- make sure you're using a sound card with a stereo input. Using a mono mic in input would give the symptom of not being able to null the image.
Hope this helps.
Regards,
Bill (kd5tfd)
|
Thanks so much, Bill. I'm still going to play with the scope tonight, but I'd be willing to bet the input is to a mono mic input. I had to reach back in the dark with a flashlight and a mirror and probably did it wrong. I'll pull the computer out tonight and check it. Some day computers will be designed to be useful with a front panel instead of pretty with everything on the rear. I, and I'm sure others, appreciate your knowledge and patience getting us up to speed. Eric KE6US www.ke6us.com --- Bill Tracey <kd5tfd@...> wrote: Ahh the small board -- good question as to why is it
so dang small -- I
think one of Tony's original goals for the gizmo was
more of a
demonstration vehicle than an experimenter vehicle.
I for one wish it had
more working room, but I will say the experience has
vastly improved my
soldering and rework in small places.
The central hump you're seeing around 7.056 is
normal. The gunk you're
seeing around this is a consequence of the software
architecture. What is
happening is that the hardware takes the swath of RF
centered and 7.056 and
downconverts it such that 7.056 is essentially at
DC. Also down there
near DC is noise and 60 hz (and its harmonics) hum.
When one tries to tune
down near 7.056, the local software oscillator will
be down in the 100's of
hz's. The output of this will be Software LO +/- 60
Hz (and
harmonics). Things will always be a bit messy
near the center frequency
-- quieter less hummy sound cards can help, but I
don't believe there's any
practical way to get rid of all the gunk in the
middle.
If you want to check out the hardware sans computer,
and have a signal
generator and a scope you can put in a -30 dbm
signal at 7.050 or so into
the antenna. Look at the audio output on the I and
Q channels -- it should
be about 6 khz (7.056 - 7.060) and on the order of
about 0.8 Vpp or so
(don't take my nums as precision numbers, they are
all from memory). The
thing to look at is if both the I and Q channels are
comparable in
magnitude -- if one is half the other something is
not quite right in the
hardware. You can also take a look at the phase
relationship -- it should
be about 90 degrees between teh two channels. While
you've got the scope
out check the clocking signals to the FST3126. If
you've got a generator
and no scope, you might be able to compare the two
channels with a good RMS
voltmeter.
One last thing to check -- make sure you're using a
sound card with a
stereo input. Using a mono mic in input would
give the symptom of not
being able to null the image.
Hope this helps.
Regards,
Bill (kd5tfd)
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|
Possible ground loops? Feed the power to the device from an independent floating power supply and see if the gunk in the center of the band goes down. Should not be too hard to try out, I would do it myself but I have not received my order yet. Better yet supply the power from a set of batteries.
toggle quoted message
Show quoted text
Ahh the small board -- good question as to why is it so dang small -- I
think one of Tony's original goals for the gizmo was more of a
demonstration vehicle than an experimenter vehicle. I for one wish it had
more working room, but I will say the experience has vastly improved my
soldering and rework in small places.
The central hump you're seeing around 7.056 is normal. The gunk you're
seeing around this is a consequence of the software architecture. What is
happening is that the hardware takes the swath of RF centered and 7.056 and
downconverts it such that 7.056 is essentially at DC. Also down there
near DC is noise and 60 hz (and its harmonics) hum. When one tries to tune
down near 7.056, the local software oscillator will be down in the 100's of
hz's. The output of this will be Software LO +/- 60 Hz (and
harmonics). Things will always be a bit messy near the center frequency
-- quieter less hummy sound cards can help, but I don't believe there's any
practical way to get rid of all the gunk in the middle.
If you want to check out the hardware sans computer, and have a signal
generator and a scope you can put in a -30 dbm signal at 7.050 or so into
the antenna. Look at the audio output on the I and Q channels -- it should
be about 6 khz (7.056 - 7.060) and on the order of about 0.8 Vpp or so
(don't take my nums as precision numbers, they are all from memory). The
thing to look at is if both the I and Q channels are comparable in
magnitude -- if one is half the other something is not quite right in the
hardware. You can also take a look at the phase relationship -- it should
be about 90 degrees between teh two channels. While you've got the scope
out check the clocking signals to the FST3126. If you've got a generator
and no scope, you might be able to compare the two channels with a good RMS
voltmeter.
One last thing to check -- make sure you're using a sound card with a
stereo input. Using a mono mic in input would give the symptom of not
being able to null the image.
Hope this helps.
Regards,
Bill (kd5tfd)
Yahoo! Groups Links
--
Cecil
KD5NWA
<www.qrpradio.com>
I fail to see why doing the same thing over and over and getting the same results every time is insanity: I've almost proved it isn't; only a few more tests now and I'm sure results will differ this time ...
|
I had also a strong signal at 0Hz.
After powering the SR40 with a 5V supply away from
the computer and removing the earth connection (only one wire 14m antena), there
is only a very small puls left.
?
I'm using a Delta 44 at 96KHz sample, own test
software
?
73, PE0FKO
Fred
?
toggle quoted message
Show quoted text
----- Original Message -----
Sent: Wednesday, September 21, 2005 6:18
AM
Subject: Re: [softrock40] Re: DSP Image
Rejection problem and some thoughts
Possible ground loops? Feed the power to the device from an
independent floating power supply and see if the gunk in the center
of
the band goes down. Should not be too hard to try out, I would do
it
myself but I have not received my order yet. Better yet supply the
power
from a set of batteries.
>Ahh the small board -- good question as to
why is it so dang small -- I
>think one of Tony's original goals for the
gizmo was more of a
>demonstration vehicle than an experimenter
vehicle.?? I for one wish it had
>more working room, but I
will say the experience has vastly improved my
>soldering and rework in
small places.
>
>The central hump you're seeing around 7.056 is
normal.? The gunk you're
>seeing around this is a consequence of
the software architecture.? What is
>happening is that the hardware
takes the swath of RF centered and 7.056 and
>downconverts? it such
that 7.056 is essentially at DC.? Also down there
>near DC is noise
and 60 hz (and its harmonics) hum.? When one tries to tune
>down
near 7.056, the local software oscillator will be down in the 100's
of
>hz's.? The output of this will be Software LO +/- 60 Hz
(and
>harmonics).???? Things will always be a bit
messy near the center frequency
>-- quieter less hummy sound cards can
help, but I don't believe there's any
>practical way to get rid of all
the gunk in the middle.
>
>If you want to check out the hardware
sans computer, and have a signal
>generator and a scope you can put in a
-30 dbm signal at 7.050 or so into
>the antenna.? Look at the audio
output on the I and Q channels -- it should
>be about 6 khz (7.056 -
7.060) and on the order of about 0.8 Vpp or so
>(don't take my nums as
precision numbers, they are all from memory).? The
>thing to look
at is if both the I and Q channels are comparable in
>magnitude -- if
one is half the other something is not quite right in
the
>hardware.? You can also take a look at the phase relationship
-- it should
>be about 90 degrees between teh two channels.? While
you've got the scope
>out check the clocking signals to the
FST3126.? If you've got a generator
>and no scope, you might be
able to compare the two channels with a good
RMS
>voltmeter.
>
>One last thing to check -- make sure
you're using a sound card with a
>stereo input.????
Using a mono mic in input would give the symptom of not
>being able to
null the image.
>
>Hope this
helps.
>
>Regards,
>
>Bill
(kd5tfd)
>
>
>
>
>
>
>Yahoo! Groups
Links
>
>
>
>
--
Cecil
KD5NWA
I fail to see why doing
the same thing over and over and getting the
same results every time is
insanity: I've almost proved it isn't;
only a few more tests now and I'm
sure results will differ this time
...
|
Good, makes sense.
The card is trying to read micro-volt signals, the ground used for power in a PC is horrible as far as noise is concerned. To make matters worse the power supply ground is connected to earth ground so there and lots of ways to get ground loops. The only way on a PC to eliminate a lot of that is to have the device not be powered by the filthy dirty signals of the PC.
You should have one ground connection between the SR-40 and the PC, using the signal cable(power should not be flowing), and the power of the two units should be totally separate. That will cut down 60 Hz hum and it's harmonics.
toggle quoted message
Show quoted text
I had also a strong signal at 0Hz.
After powering the SR40 with a 5V supply away from the computer and removing the earth connection (only one wire 14m antena), there is only a very small puls left.
I'm using a Delta 44 at 96KHz sample, own test software <>
73, PE0FKO
Fred
----- Original Message -----
From: <mailto:KD5NWA@...>kd5nwa
To: <mailto:softrock40@...>softrock40@...
Sent: Wednesday, September 21, 2005 6:18 AM
Subject: Re: [softrock40] Re: DSP Image Rejection problem and some thoughts
Possible ground loops? Feed the power to the device from an
independent floating power supply and see if the gunk in the center
of the band goes down. Should not be too hard to try out, I would do
it myself but I have not received my order yet. Better yet supply the
power from a set of batteries.
Ahh the small board -- good question as to why is it so dang small -- I
think one of Tony's original goals for the gizmo was more of a
demonstration vehicle than an experimenter vehicle. I for one wish it had
more working room, but I will say the experience has vastly improved my
soldering and rework in small places.
The central hump you're seeing around 7.056 is normal. The gunk you're
seeing around this is a consequence of the software architecture. What is
happening is that the hardware takes the swath of RF centered and 7.056 and
downconverts it such that 7.056 is essentially at DC. Also down there
near DC is noise and 60 hz (and its harmonics) hum. When one tries to tune
down near 7.056, the local software oscillator will be down in the 100's of
hz's. The output of this will be Software LO +/- 60 Hz (and
harmonics). Things will always be a bit messy near the center frequency
-- quieter less hummy sound cards can help, but I don't believe there's any
practical way to get rid of all the gunk in the middle.
If you want to check out the hardware sans computer, and have a signal
generator and a scope you can put in a -30 dbm signal at 7.050 or so into
the antenna. Look at the audio output on the I and Q channels -- it should
be about 6 khz (7.056 - 7.060) and on the order of about 0.8 Vpp or so
(don't take my nums as precision numbers, they are all from memory). The
thing to look at is if both the I and Q channels are comparable in
magnitude -- if one is half the other something is not quite right in the
hardware. You can also take a look at the phase relationship -- it should
be about 90 degrees between teh two channels. While you've got the scope
out check the clocking signals to the FST3126. If you've got a generator
and no scope, you might be able to compare the two channels with a good RMS
voltmeter.
One last thing to check -- make sure you're using a sound card with a
stereo input. Using a mono mic in input would give the symptom of not
being able to null the image.
Hope this helps.
Regards,
Bill (kd5tfd)
Yahoo! Groups Links
--
Cecil
KD5NWA
<www.qrpradio.com>
I fail to see why doing the same thing over and over and getting the
same results every time is insanity: I've almost proved it isn't;
only a few more tests now and I'm sure results will differ this time
...
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Cecil
KD5NWA
<www.qrpradio.com>
I fail to see why doing the same thing over and over and getting the same results every time is insanity: I've almost proved it isn't; only a few more tests now and I'm sure results will differ this time ...
|
Eric,
There may be a small difference in the Softrock40 I and Q amplitude
that is out of range of the DSP gain/phase adjustments. I would
suggest opening your computer's Recording Control window and adjust
the Line Input Balance Control and see if that allows you null the
image. You will probably have to back to DSP Image Reject adjustment
to realize a greater than 50 dB null.
I hope this helps.
73,
Gene W3PM GM4YRE
toggle quoted message
Show quoted text
--- In softrock40@..., "Eric" <eric_ke6us@y...> wrote: The radio went together fairly easily, though I'm at
a loss to figure out why an experimenter's radio is
jammed onto such a small board. This might be OK for
a production rig, but some room would be nice to
experiment.
That said, the radio works except there is no image
rejection and the DSP image rejection controls do
nothing. The instructions say, "If the image cannot
be nulled at least 50 db, then a problem exists..."
Well, some guidance would have been helpful.
Especially, given my opening criticism.
I am reluctant to tear into this think quite yet as
there is not a lot of room to work. I originally
thought it may be a transformer mis-wiring on my part.
Again, we're talking an experimenter's radio on 40
meters where things are relatively less critical than
other bands, so a little larger toroid with more room
to make changes would make it a lot easier.
I'm hoping when I fix the image problem that all
that 7.056 +/- 5 khz energy is going to at least be
diminished. 7.056 is S5. 7.051/7.061 are S3.
Anyway, I have no doubt the problem is my error. I
just want a little direction so that I can minimize
stress on the board.
Eric
KE6US
www.ke6us.com
|
I'll give it a try. I put a scope on I and Q earlier in the day and discovered more than a small difference between the two. More like a 50% difference. That seems excessive, and might suggest something wrong with U6. Components are all correct value in correct position. Thanks, Gene. Eric KE6US www.ke6us.com --- gene_scot <gmarcus@...> wrote: Eric,
There may be a small difference in the Softrock40 I
and Q amplitude
that is out of range of the DSP gain/phase
adjustments. I would
suggest opening your computer's Recording Control
window and adjust
the Line Input Balance Control and see if that
allows you null the
image. You will probably have to back to DSP Image
Reject adjustment
to realize a greater than 50 dB null.
I hope this helps.
73,
Gene W3PM GM4YRE
--- In softrock40@..., "Eric"
<eric_ke6us@y...> wrote:
The radio went together fairly easily, though I'm at
a loss to figure out why an experimenter's radio is
jammed onto such a small board. This might be OK for
a production rig, but some room would be nice to
experiment.
That said, the radio works except there is no image
rejection and the DSP image rejection controls do
nothing. The instructions say, "If the image cannot
be nulled at least 50 db, then a problem exists..."
Well, some guidance would have been helpful.
Especially, given my opening criticism.
I am reluctant to tear into this think quite yet as
there is not a lot of room to work. I originally
thought it may be a transformer mis-wiring on my part.
Again, we're talking an experimenter's radio on 40
meters where things are relatively less critical
than
other bands, so a little larger toroid with more room
to make changes would make it a lot easier.
I'm hoping when I fix the image problem that all
that 7.056 +/- 5 khz energy is going to at least be
diminished. 7.056 is S5. 7.051/7.061 are S3.
Anyway, I have no doubt the problem is my error. I
just want a little direction so that I can minimize
stress on the board.
Eric
KE6US
www.ke6us.com
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--------------------~-->
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Yahoo! your home page
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__________________________________ Yahoo! Mail - PC Magazine Editors' Choice 2005
|
Double check the 4 signals controling U5. Also double check the component values and placement around U6.. You said you did that, but another check wouldn't hurt. c12 AND c13 of different values could cause the problem as well as anything around U6. Good luck! 73, Marsh, NC7V --- In softrock40@..., EricJ <eric_ke6us@y...> wrote: I'll give it a try. I put a scope on I and Q earlier
in the day and discovered more than a small difference
between the two. More like a 50% difference. That
seems excessive, and might suggest something wrong
with U6. Components are all correct value in correct
position.
Thanks, Gene.
Eric
KE6US
www.ke6us.com
--- gene_scot <gmarcus@k...> wrote:
Eric,
There may be a small difference in the Softrock40 I
and Q amplitude
that is out of range of the DSP gain/phase
adjustments. I would
suggest opening your computer's Recording Control
window and adjust
the Line Input Balance Control and see if that
allows you null the
image. You will probably have to back to DSP Image
Reject adjustment
to realize a greater than 50 dB null.
I hope this helps.
73,
Gene W3PM GM4YRE
--- In softrock40@..., "Eric"
<eric_ke6us@y...> wrote:
The radio went together fairly easily, though I'm at
a loss to figure out why an experimenter's radio is
jammed onto such a small board. This might be OK for
a production rig, but some room would be nice to
experiment.
That said, the radio works except there is no image
rejection and the DSP image rejection controls do
nothing. The instructions say, "If the image cannot
be nulled at least 50 db, then a problem exists..."
Well, some guidance would have been helpful.
Especially, given my opening criticism.
I am reluctant to tear into this think quite yet as
there is not a lot of room to work. I originally
thought it may be a transformer mis-wiring on my part.
Again, we're talking an experimenter's radio on 40
meters where things are relatively less critical
than
other bands, so a little larger toroid with more room
to make changes would make it a lot easier.
I'm hoping when I fix the image problem that all
that 7.056 +/- 5 khz energy is going to at least be
diminished. 7.056 is S5. 7.051/7.061 are S3.
Anyway, I have no doubt the problem is my error. I
just want a little direction so that I can minimize
stress on the board.
Eric
KE6US
www.ke6us.com
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Hi Eric,
I/Q outputs from U6 should be better than +/- 20% of each other. If one of the control signals to U5 (pins 1, 4, 10 or 13) is missing then the balance would be out by 50%. Please check carefully for opens at all IC pins and for solder bridges between pins.
73,
Tony KB9YIG
toggle quoted message
Show quoted text
----- Original Message ----- From: "EricJ" <eric_ke6us@...> To: <softrock40@...> Sent: Wednesday, September 21, 2005 6:34 PM Subject: Re: [softrock40] Re: DSP Image Rejection problem and some thoughts I'll give it a try. I put a scope on I and Q earlier
in the day and discovered more than a small difference
between the two. More like a 50% difference. That
seems excessive, and might suggest something wrong
with U6. Components are all correct value in correct
position.
Thanks, Gene.
Eric
KE6US
www.ke6us.com
--- gene_scot <gmarcus@...> wrote:
Eric,
There may be a small difference in the Softrock40 I
and Q amplitude
that is out of range of the DSP gain/phase
adjustments. I would
suggest opening your computer's Recording Control
window and adjust
the Line Input Balance Control and see if that
allows you null the
image. You will probably have to back to DSP Image
Reject adjustment
to realize a greater than 50 dB null.
I hope this helps.
73,
Gene W3PM GM4YRE
--- In softrock40@..., "Eric"
<eric_ke6us@y...> wrote:
The radio went together fairly easily, though I'm at
a loss to figure out why an experimenter's radio is
jammed onto such a small board. This might be OK for
a production rig, but some room would be nice to
experiment.
That said, the radio works except there is no image
rejection and the DSP image rejection controls do
nothing. The instructions say, "If the image cannot
be nulled at least 50 db, then a problem exists..."
Well, some guidance would have been helpful.
Especially, given my opening criticism.
I am reluctant to tear into this think quite yet as
there is not a lot of room to work. I originally
thought it may be a transformer mis-wiring on my part.
Again, we're talking an experimenter's radio on 40
meters where things are relatively less critical
than
other bands, so a little larger toroid with more room
to make changes would make it a lot easier.
I'm hoping when I fix the image problem that all
that 7.056 +/- 5 khz energy is going to at least be
diminished. 7.056 is S5. 7.051/7.061 are S3.
Anyway, I have no doubt the problem is my error. I
just want a little direction so that I can minimize
stress on the board.
Eric
KE6US
www.ke6us.com
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Yahoo! Groups Links
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