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Today I received the developers edition of the Bbitx.
I was pleased by the packaging quality.
Opening the package I was impressed with the actual radios packaging?
as it is quite substantial.? The box represents? good quality metal work
and reveals a decently sized heat sink on the rear.
What is not obvious from the HFsignals page is that this is a substantial
radio on both size and weight.?
As my usual I tend to inspect and confirm things that might shake loose
in shipping. before power up more to come.
Allison
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Something to pay attention to:
While examining the unit I noted that there was poor to no DC resistance
between case sections.? This happens with painted cases but it also
means assumed grounded items like heatsink or front panel are floating
for RF.? ?This can be a potential cause of unwanted receiver noises or even
transmitter instability.
Before I power it up I will clean the affected areas of paint so the
screws can do their job in ensuring all section are grounded.
Allison
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A useful and timely reminder, Allison. Good to see you aboard the sBITX train, also the Daylight express. I have missed your comments over the past year or so.
73 Bill VK7MX
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Allison, Thanks?for the reminder. My suggestion to everyone is to scrap the paint off around the countersink holes of the screws of the box panels.? The power coating is preventing the ground connectivity. It is most critical between the back panel and the bottom panel. - f
A useful and timely reminder, Allison. Good to see you aboard the sBITX train, also the Daylight express. I have missed your comments over the past year or so.
73 Bill VK7MX
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First light...
After cleaning all the mating surfaces, attaching a pigtail for PowerPole?
connectors (lab standard here) adding a fuse on the rear, and a stout
reverse polarity diode plus heatsink grease I started making basic
checks on current limited supply.?
I powered up to the sbitx software.? After playing some and making
measurements. things noted.
Power measured with BIRD wattmeter 50H slug in use (50W FS),
monitored on station RX and with SA.
Power out and dashboard setting have limited correlation.? When
set to 6W I would see anywhere from 15W (10M) to as much as
45W on 80m.? The other is that it wanted to push far more than
50W at 20M set to 40.? The actual after fetching the 100H slug
was 63W, way over.
Since the apparent power setting is based on drive? there is
considerable variation in power chain gain without any alc or
other direct measure of output.? Meter your output or risk frying
finals. It was very easy to both over drive and run the power
well past 40W into the dummy load.??
If not over driven the SA says its clean.? I haven't checked for spurs
or harmonics yet but it sounds right.?
The other is no audio key down TX 1.5A, I have to check bias
for drivers and finals.? While I had it apart a dab of heastsink
grease was applied to the finals.? Also insure the final are flat
to the heat sink for best cooling.
The touch screen need a longer timer as its very easy to touch
it and go off to odd places.? The screen timout (screen saver)
was a momentary upset before I realized rasipian nominally
has it set on.
This one also has the WIfi Zzzip buzz.? Not a surprise as the Wfi
chip on the RPi is maybe an inch from the audio board.
The upside is while running my main radio (FT8 on 10M) I used?
the Sbitx to decode my tx (not on antenna) and it did.? Good sign.
It will take much more digging into the radio. and like software.
More work ahead.
Allison
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One item noticed and causing concern is a very high current spike at startup.
How high?? Over 5A.? I noted this with mine as i added a fuse to protect it
and?on power up the 6A fuse blows, not a good thing.
I believe something is driving the power amp to full power momentarily and?
may have something to do with final getting blown up.? This is being
investigated and a solution should result.
While working with the radio use a current? regulated supply (set to 5-6A)
or fuse supply lead.? This may prevent disasters.
Allison
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Allison,
thanks for the feedback..I've had some issues, and I am sorting through them now..blew R403 and it burned the pad off on the Coil side...
as well as I think the T/R relay is welded to RX..more digging necessary.
a good BOM would be nice..(or maybe I haven't found one yet)
Vince
N2AIE
Sbitx S/N 0096
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Are you suggesting removing the paint on the exposed side of the panel with the countersink, or would it be sufficient to do it on the inside side, so you don¡¯t mar the appearance? I did a quick VOM check, and it looks like the connectors that the screws go into don¡¯t have good continuity on the surface (probably due to the anodized coating.
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Vince three things I'd like to have...
BOM,
Board etch diagrams
some coils have no data.
Fortunately I'm used to doing forensic engineering made a career out of it.
There are issues in the transmitter switching and I'm digging into that.
FYI throwing new parts at it do not solve that, it only brings you back to go.
When I power up the only thing that keeps it from running off is the
current limited supply.? But at startup it sucks down a lot of current?
(many amps!) when I'd thing far less be normal.
I cleaned out the countersunk surfaces and where each of the corner
blocks anodized their mating surfaces.? ?Hint don't drop screws they
are M4 metric.? Keep metal dust and flakes out of the radio.
Allison/0165
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Allison,
Just checked #163
Starts at 300-400mA and goes to 600mA and rises to 750mA when sBitx
starts running. No surge.
Raj, vu2zap
toggle quoted message
Show quoted text
On 29/09/2022 10:39 PM, ajparent1/kb1gmx wrote: One item noticed and causing concern is a very high current spike at startup.
How high?? Over 5A.? I noted this with mine as i added a fuse to protect it
and?on power up the 6A fuse blows, not a good thing.
I believe something is driving the power amp to full power momentarily and
may have something to do with final getting blown up.? This is being
investigated and a solution should result.
While working with the radio use a current? regulated supply (set to 5-6A)
or fuse supply lead.? This may prevent disasters.
Allison
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Raj,
I suspect its has to do with the startup state of the Rpi and the peripherals
it talks to.? By nature its undefined in many cases.
If I arrange power to the Rpi and front panel separate from main board
I do not see the current spike on startup (powering the main board).
So it appears something wants to start in an undefined state at
power up and causes a current spike.? Its likely the IO that drives Q10
(TX enable power).
Next thing I'll try is disable TX command line to the main board and see
if it starts up without current pulse.
Systems I've done in the past have a generated signal called
Delayed-power-good that is used to inhibit anything that can
do unacceptable actions until the MPU or whatever is stable
and takes command.? Its usually a very trivial circuit like a RC
and? gate as a schmitt trigger with a time less than 1 second.
Allison
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Allison,
Farhan discovered this spike on his sBitx. The wave goes down and
rises rapidly
and very high before settling down quickly. Enough to blow the
finals.
Disconnect C14 and see if that cures it.. the charging and
discharging during RX/TX
changeover is? an issue.
My first sBitx #9 was connected to the 20A shack PS after I
smoked something in RX.
Due to some unfortunate accident and vertigo could not fix it.
The next one #163 I connected to 2.5A PS just to be safe !!
This one sometimes starts and everything displays fine except it
doesnt show
any signals and a reboot cures everything, I can live with that
but a delay in
start may fix it.
73, Raj vu2zap
On 30/09/2022 6:08 PM, ajparent1/kb1gmx
wrote:
toggle quoted message
Show quoted text
Raj,
I suspect its has to do with the startup state of the Rpi and the
peripherals
it talks to.? By nature its undefined in many cases.
If I arrange power to the Rpi and front panel separate from main
board
I do not see the current spike on startup (powering the main
board).
So it appears something wants to start in an undefined state at
power up and causes a current spike.? Its likely the IO that
drives Q10
(TX enable power).
Next thing I'll try is disable TX command line to the main board
and see
if it starts up without current pulse.
Systems I've done in the past have a generated signal called
Delayed-power-good that is used to inhibit anything that can
do unacceptable actions until the MPU or whatever is stable
and takes command.? Its usually a very trivial circuit like a RC
and? gate as a schmitt trigger with a time less than 1 second.
Allison
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Raj,
I am aware of Farhan's C14 test, have looked and tested.?
The question is why is that happening.? ?I have ideas that?
?have been shared.? ?And doing my own investigation.
Due to reading everything I was aware the finals issue so initial
startup was very carefully conducted.? Now I'm into hunting
down a fix.
Allison
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Raj,
That C14 tests suggest that K9 relay is either in NC state at the wrong times
along with U3 or enough leakage though to make a big high power oscillator.
Do we know if any of the relay coils have diodes across them??
Allison
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Allison, As we are using the ULN2003, it has built-in diodes between the Vcc and the driver outputs. I have confirmed with scope that the reverse diodes work. - f
On Fri, Sep 30, 2022, 11:49 PM ajparent1/kb1gmx < kb1gmx@...> wrote: Raj,
That C14 tests suggest that K9 relay is either in NC state at the wrong times
along with U3 or enough leakage though to make a big high power oscillator.
Do we know if any of the relay coils have diodes across them??
Allison
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I dont think these have a diode across the coil. Enclosed is a data sheet.
Raj
toggle quoted message
Show quoted text
On 30/09/2022 11:49 PM, ajparent1/kb1gmx wrote: Raj,
That C14 tests suggest that K9 relay is either in NC state at the wrong times
along with U3 or enough leakage though to make a big high power oscillator.
Do we know if any of the relay coils have diodes across them??
Allison
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Raj,
the relays do not have a diode across the coils. The I2C coil driver chip does.?
73
Evan
AC9TU
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Evan,
Yes I know that. I am not the one who asked the question!
Raj
toggle quoted message
Show quoted text
On 01/10/2022 11:34 AM, Evan Hand wrote:
Raj,
the relays do not have a diode across the coils. The I2C coil driver chip does.
73
Evan
AC9TU
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Raj,
Several things:??
The contacts are rated .25A, at more than that you can safely bet they will stick.
If that happens that causes havoc.? .25A at 50 ohms is only 3.125W!
I tend to keep reed relays of that size for very very low power use as
sticking has been a source of pain in my engineering life.? Those
contacts are very close so isolation tends to be marginal.
Having seen that data sheet my immediate plan is to replace that relay
with a sugar cube that has at least 1A contacts and add a diode across
the coil. The relay DPDT will be wired to switch the LPF filter between
RX and TX and the second set of contact will switch RX in (C14) to?
ground during TX and into the filter on RX.
Allison
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Te problem with relays is activation speed,? the one used for the LPF section
typically need about 30-40mS to operate often too slow for CW and acoustically
noisy as well.
The alternate is a much larger reed relay like Tentec used decades back but
they are large.? The one in the Sbitx is way too small to handle RF like that.
The other alternative is PIN diode switching and that is more involved but
offers extremely high speed switching.? There are designs using the 1n4007
diode which for the last 40 years is also known as the poor mans pin diode.
The 1A part will easily handle 50W without strain and I've used them at over
100W without failures.
Back to the drawing board.
Allison
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Vince N2AIE
Mark Erbaugh
Raj vu2zap