Re: ubitx audio amp problem discovered
Thanks for the analysis. There are two other significanr issues with the current mic amplifier. 1. The output impedance is 1000 ohms, the modulator needs a 50 ohms drive. 2. The gain is not less but too much. The electrer mic produces about 50mV of audio, the modulatoe needs less than 150mv drive. A gain of two or three is more than sufficient. The apparent loss is due to the mismatch between the 1000 ohm output and the needed 50 ohms drive. These can be solved by adding an emitter follower with a 47 ohms resistor in series with the output of the emitter follower and removing the emitter bypass of the original mic amplifier. - f
I've been working on the uBitx audio circuit for a while now and I think I've discovered a problem that I've never seen anyone mention before. If anyone has experience with this circuit, please review and let me know if I've missed anything. Here are my notes:
?Audio Amp notes.
The uBitx has always
had challenges with the audio amp. It has insufficient gain for the
condenser mic that is provided. Solutions include:
a. Use a mic with an
amplifier built in.
b. Add an additional
amplification stage such as the SSM2167.
c. Increase the mic
circuit gain.
Mic amplifier
circuit with suggested modifications. Also showing the load of the
following stage.
SEE ATTACHED FILE
Analysis:
Given that the
receive transistor Q70 is connected directly to the output of the
microphone amplifier, the output of the mic amp must be less than
0.6v. We¡¯ll say 550 mV to give us a bit of safety margin.
The input drive
required to achieve 550mV out of the mic amp is 200mV. Most have
claimed that the mic amp has a gain of around 20 due to the collector
resistance of 1k divided by the emitter resistance of 47 ohms. This
simple analysis is incorrect because it neglects the load impedance
of the mixer circuit. Spice analysis and actual observation shows the
actual gain to be about 2x or 3x.
A big problem with
this mic amplifier is that it is incorrectly biased. With the
originally specified bias resistor R61 set at 2.2k, the transistor
runs out of emitter current at about 160mV of output voltage. In addition to limiting output, this causes distortion of the audio waveform. By increasing R61 to 10k,
the circuit can easily output the 550 mV (1.1V P-P) originally
suggested.
In my own uBitx, I
have chosen to use the SSM2167 as a preamp in order to enjoy some
voice compression. However, the simplest solution is to decrease R63
to 10 to 22 ohms. I¡¯d advise not to go lower than 10 ohms, since
that circuit should fully drive the mixer with a mic output of only
40 mV. But before doing anything else, increase R61 to 10K.
|
ubitx audio amp problem discovered
I've been working on the uBitx audio circuit for a while now and I think I've discovered a problem that I've never seen anyone mention before. If anyone has experience with this circuit, please review and let me know if I've missed anything. Here are my notes:
?Audio Amp notes.
The uBitx has always
had challenges with the audio amp. It has insufficient gain for the
condenser mic that is provided. Solutions include:
a. Use a mic with an
amplifier built in.
b. Add an additional
amplification stage such as the SSM2167.
c. Increase the mic
circuit gain.
Mic amplifier
circuit with suggested modifications. Also showing the load of the
following stage.
SEE ATTACHED FILE
Analysis:
Given that the
receive transistor Q70 is connected directly to the output of the
microphone amplifier, the output of the mic amp must be less than
0.6v. We¡¯ll say 550 mV to give us a bit of safety margin.
The input drive
required to achieve 550mV out of the mic amp is 200mV. Most have
claimed that the mic amp has a gain of around 20 due to the collector
resistance of 1k divided by the emitter resistance of 47 ohms. This
simple analysis is incorrect because it neglects the load impedance
of the mixer circuit. Spice analysis and actual observation shows the
actual gain to be about 2x or 3x.
A big problem with
this mic amplifier is that it is incorrectly biased. With the
originally specified bias resistor R61 set at 2.2k, the transistor
runs out of emitter current at about 160mV of output voltage. In addition to limiting output, this causes distortion of the audio waveform. By increasing R61 to 10k,
the circuit can easily output the 550 mV (1.1V P-P) originally
suggested.
In my own uBitx, I
have chosen to use the SSM2167 as a preamp in order to enjoy some
voice compression. However, the simplest solution is to decrease R63
to 10 to 22 ohms. I¡¯d advise not to go lower than 10 ohms, since
that circuit should fully drive the mixer with a mic output of only
40 mV. But before doing anything else, increase R61 to 10K.
|
Re: possible loss or change to ham bands
Its impact is to anyone under the PART-90? umbrella like commercial radio
and shortwave stations.
It leaves us alone.
--
Allison
------------------
Please use the forum, offline and private will go to bit bucket.
|
Re: sBitx DE finals and heat sink temperature plots
David,
Your entitled to the opinion...
After 50+ years of engineering and design, what do I know?
Besides designing with 2n6084s in the '70s.
--
Allison
------------------
Please use the forum, offline and private will go to bit bucket.
|
Re: sBitx DE finals and heat sink temperature plots
MadRadioModder,
Love your wiggly icon you have on your posting!!!!!.
Jack and Al really have built a beautiful transceiver too. they took several years to develop it and they have a great book with all the info..
They truly have a special project with very efficient design.Im planning to buy one when its listed for sale.
73
David
ac9xh
|
possible loss or change to ham bands
hello,
read this on the 4sqrp group. this needs to be read and passed around. possible interferance or loss of bands is possble . once the big money pockets get near our bands, they wont stop. 2-25mhz is the bandwidth they are eyeing.
73
David
ac9xh
""Hi all,
Just watched this video where Jim thinks a proposed change to frequencies near 20M would make them unusable.....
?
His video:
?
Link to FCC info:
?
FCC Petition:
?
This has good info and comments:
?
I recently lost my internet for about 2 weeks (Tekfinity)(it's a wireless, over the air system). They had some trouble getting it back up. The last time they came out, they had told me they were about out of options.
Turns out, there is some new transmitter that is on 5Ghz, that is close enough that it knocked me completely off the air. They have it back (had to switch to an old radio on a different frequency!). But, I understand better now how interference causes problems!
?
Why can't the FCC just do a test install of this new, 'great' system and simply monitor interference...... If it's too much, simply deny them!
?
Hope this is something we can work on.""
|
Re: sBitx spurious emissions
Evan I built the tap you described  and I also have a stepped attenuator., and also a 50 watt 30db attenuator/dummy load should get here in 3 days. I'm charging up my tinySA which I'll be using for the first time. Do you know of any links or resources that give a quick rundown of how it would be used for tracking down spurs? Also, I put in a small iFlight filter right after the 5.4V regulator for the DE that came with mod #1 but I still see spurs less than 1-200 kHz on both sides of my carrier.?This is checking with the scope on my IC7600. I'm assuming that's from some unwanted modulation of the carrier that leads to a jumbled look on my oscilloscope rather than the nice sine wave I get with my 7600. I also got a much larger, about 1 inch long DKARDU EMI suppressor that I could use instead of the iFlight but I was wondering first whether you or others had success with one of those before squeezing it in. To be clear I'm not looking currently at possible spurs at odd harmonics of the carrier frequency but of sideband spurs at multiples of 25 kHz or so off next to the carrier. Also I have a 680 uF electrolytic on the input side of that regulator. I have a 3300 uf unit that I could swap out but it's so much larger that I would like to avoid changing out the 680 uF capacitor. Any suggestions? Jack, N6LN
|
Re: sBitx DE finals and heat sink temperature plots
hello, this transgress all topics here. i would post to another topic but alot of member have been reading this thread. will post a new topic.
His video:
?
Link to FCC info:
?
FCC Petition:
?
This has good info and comments:
this possibly has the chance to change our bands forever
73
David
ac9xh
|
Re: sBitx DE finals and heat sink temperature plots
Or maybe try out that design that the T41 boys are using.? The new PA being sold to complement the radio is magnificent.? There is no reason to use anything else on a QRP radio.? End of transmission. ?
toggle quoted message
Show quoted text
From: [email protected] < [email protected]> On Behalf Of Terry VK5TM Sent: Saturday, July 15, 2023 12:18 AM To: [email protected]Subject: Re: [BITX20] sBitx DE finals and heat sink temperature plots ? There is another failure mechanism to MOSFETs that is not being mentioned here, that of too low a gate to source voltage, this does result in thermal runaway.
Whether that is part of the problem of them dying prematurely in these rigs, maybe someone might care to investigate the possibility (I don't currently have any workbench facilities).
The failure mechanism is explained in the attached pdf from Onsemi.
--
-- ¡_. _._
|
Re: sBitx DE finals and heat sink temperature plots
oh and the pic of the amplifier isnt the mrf455, its a different amp i forgot to mention, i use it for my 6 meter gear.
Sorry for any confusion.
73
David
ac9xh
|
Re: sBitx DE finals and heat sink temperature plots
forgot the rf amplifier that has the semiconductor grounded to case and heatsink, i built this one from scratch using mrf455s.
Never had a failure, and pumps out great rf power with switchable filters for each band.I built this for some of my QRP gear. for the ten tec argonaut 509, hw-8 and a few other transceivers i stll own.
Anyway May the SBITX live forever!!!!!! A beautiful design.
73
David
ac9xh
|
Re: sBitx DE finals and heat sink temperature plots
Allison,
respect your experience and views but i totally disagree with anyone saying that there is no thermally stable fet or power transistor.Whether they are an engineer or not.
just my own opinon.and work experience. I would take a lower gain component over a fried component every day. Hope u all get ur fried finals problems figured out.Truthfully, Ashhar designed a beautiful transceiver.When shipping from overseas, things happen stuff comes loose.
For $499 I wouldnt expect any? problems like fried finals .especially if its the second version with improvements.Someone is doing something wrong. like tinkering where they shouldnt, not setting biasing correctly, or adding stuff that doesnt belong, or not truelynot matching the unit to the antenna correctly.
I have bought many units off Ashhar, bitx40,ubitx3,ubitx6, several times. never had any problesm with any of them except when i tinkered with them to "upgrade the software, and or display and such".
been building my own rf power amps for over 20 years.And if i experienced this with mine, i would be going a different route.
But again, Allison, no offense,. just my own opinon.and not of staff and management.HI HI.
73
David
ac9xh
|
Re: sBitx DE finals and heat sink temperature plots
G Todd,
Simple solution do like I do for the over 100W stuff MRF151, MRFE101, BLF184, BLF188
The only down side is the need for 50V power.? All of them required thermal stabilized bias.
MRF255, 100W push pull and good cooling flange mount 13V part.? Theremal stabilized
bias as well.
Or 8 IRF510s on 6M putting out 220w at 28V.? ?Oh, that can't work they?
are not flange ground.? SiO/SiN insulators do well.
There are no such thing as "?more thermal stable fet", going bipolar?
is really nuts as most bipolar are 10-11DB max gain where even the lowly
IRF510 is 13-16Db gain.
THere there is the QRPL 10W amp two stage amp with 36DB of stable gain
good from 1.8 to 10 and useful at 6M (gain is 4db don but full power).? Not
bad for a nominal 12V amp.
--
Allison
------------------
Please use the forum, offline and private will go to bit bucket.
|
Stuart,
HFSignals does sell the v6 Raduino board separately here:
It is 1/4 of the cost of the uBitx full kit.
73
Evan
AC9TU
|
Re: sBitx DE finals and heat sink temperature plots
conductivity of heat is the most important thing for power amplifiers, but also im my own opion is a design that allows the finals to be mechanically bolted to heatsinks and transceiver casings WITHOUT the insulating material. Meaning the designers design the transceiver or Amplifier with the finals with common? connections without the need for insulating wafers like mica or anything. conductive grease helps alot,but if the finals can actually be physically connected to the heatsinks without ANY insulating material, it will solve alot of problems. I own 3 RF power amplifiers and only 1 of the uses this practice. its an older amplifier of about 25 years.
comparing it to the new ones, it seems to me the design is simpler and the heatsink plus the transceiver casing adds to the control of heat . NO worries if you are fully insulating the semiconductor with separating wafers of mica or whatever, This particular amp has a heatsink that also clamps onto the front of the finals to help dissipate heat plus the conductive grease. Its also a genric Amp.
Maybe someone needs to go a different path to seek out a more thermal stable fet? or maybe a small board allowing POWER TRANSISTORS? I mean if all these fets are burning up, then a new WHEEL needs to be created.have the option to wire into the finals an experimental board that allows different fets or power transistors.might have to use a converter to raise the voltage to allow a different thermally stable semiconductor?Plenty of different parts on the market.like the mrf422,mrf486,or the mrf455 which is bipolar transistor,2-30 mhz, 60 watts, 12 votls. these and other rf power semiconductors might cost more, but you are installing parts proven in the field many times over.
just my take of all your problems.
73 David ac9xh
On Saturday, July 15, 2023 at 09:54:11 AM EDT, Gordon Gibby <docvacuumtubes@...> wrote:
got the aluminum nitride insulators ordered via aliexpress hope they get here sometime!! Gordon
On Sat, Jul 15, 2023 at 9:29?AM Gordon Gibby via <docvacuumtubes= [email protected]> wrote: Thanks, Allison!? ?Great recommendation.? ?I think I'll try to find some of the?aluminum nitride insulators.
Another SCARE this morning with the radio.? Just starting a QSO on 40 meter CW and suddenly dropping dits and loss?of power.? Lots of stuff going wrong all at once.? ?Then basically zero power.? And of course, in my befuddlement I hit the SPLIT somewhere also.....to add insult to injury.
An hour later I finally figured it out -- the Drain solder joint of the RIGHT IRFZ24N had quit.? ?Basically zero DC and zero AC on the drain.? ?Left hand side working perfectly.? This exact same thing happened to the LEFT side months ago!? ?There wasn't much solder on those connections; instead of being convex?surface they were indented down into the hole....? ? Got the soldering iron -- I'm in the vacation home, less equipment ...of course a solder bridge, finally got it all soldered and cleaned up. and POWER AGAIN!!?
I'm guessing the expansion/contraction driven by the hot temperatures of the final tend to work poor soldering joints loose, to have this happen to BOTH of the final mosfets over time?? ?And, I had this apart again working on things 2 weeks ago which put torque on those connections, also...? ?Anyway, something to watch for.? ?my? QTH is in a terrible valley beween?mountains and my end-fed antenna is sad here also, but managed a cw qso with a POTA volunteer to prove it was working right.? ?
If I get some aluminum nitride insulators, I'll wait for a good time and pull this apart and check the surface of the heatsink also and get this done right.? ??
Ashhar has really made some good improvements.? ?The experience of cw qsos (once I got the relay mess cleaned out) is getting to be really really good.? ?Very little click/thump.? ?The semi-full break in is SO SO SO SO MUCH BETTER than my 7300.? ??
Gordon kx4z
On Sat, Jul 15, 2023 at 9:13?AM ajparent1/kb1gmx < kb1gmx@...> wrote: Some notes:
BEO dust is toxic!? Just don't!
I have used?Aluminum Nitride as its not toxic and works well...
One place personally used it the OZ1PIF amp and I found the thermal
conductivity excellent.
I was never a fan of the mica used for the DE, also they were used DRY
without thermal conductive paste.? Add to that a heatsink with terrible
surface quality (rough) and bad stuff happens.
--
Allison
------------------
Please use the forum, offline and private will go to bit bucket.
|
Re: sBitx DE finals and heat sink temperature plots
got the aluminum nitride insulators ordered via aliexpress hope they get here sometime!! Gordon
On Sat, Jul 15, 2023 at 9:29?AM Gordon Gibby via <docvacuumtubes= [email protected]> wrote: Thanks, Allison!? ?Great recommendation.? ?I think I'll try to find some of the?aluminum nitride insulators.
Another SCARE this morning with the radio.? Just starting a QSO on 40 meter CW and suddenly dropping dits and loss?of power.? Lots of stuff going wrong all at once.? ?Then basically zero power.? And of course, in my befuddlement I hit the SPLIT somewhere also.....to add insult to injury.
An hour later I finally figured it out -- the Drain solder joint of the RIGHT IRFZ24N had quit.? ?Basically zero DC and zero AC on the drain.? ?Left hand side working perfectly.? This exact same thing happened to the LEFT side months ago!? ?There wasn't much solder on those connections; instead of being convex?surface they were indented down into the hole....? ? Got the soldering iron -- I'm in the vacation home, less equipment ...of course a solder bridge, finally got it all soldered and cleaned up. and POWER AGAIN!!?
I'm guessing the expansion/contraction driven by the hot temperatures of the final tend to work poor soldering joints loose, to have this happen to BOTH of the final mosfets over time?? ?And, I had this apart again working on things 2 weeks ago which put torque on those connections, also...? ?Anyway, something to watch for.? ?my? QTH is in a terrible valley beween?mountains and my end-fed antenna is sad here also, but managed a cw qso with a POTA volunteer to prove it was working right.? ?
If I get some aluminum nitride insulators, I'll wait for a good time and pull this apart and check the surface of the heatsink also and get this done right.? ??
Ashhar has really made some good improvements.? ?The experience of cw qsos (once I got the relay mess cleaned out) is getting to be really really good.? ?Very little click/thump.? ?The semi-full break in is SO SO SO SO MUCH BETTER than my 7300.? ??
Gordon kx4z
On Sat, Jul 15, 2023 at 9:13?AM ajparent1/kb1gmx < kb1gmx@...> wrote: Some notes:
BEO dust is toxic!? Just don't!
I have used?Aluminum Nitride as its not toxic and works well...
One place personally used it the OZ1PIF amp and I found the thermal
conductivity excellent.
I was never a fan of the mica used for the DE, also they were used DRY
without thermal conductive paste.? Add to that a heatsink with terrible
surface quality (rough) and bad stuff happens.
--
Allison
------------------
Please use the forum, offline and private will go to bit bucket.
|
Re: sBitx DE finals and heat sink temperature plots
Thanks, Allison!? ?Great recommendation.? ?I think I'll try to find some of the?aluminum nitride insulators.
Another SCARE this morning with the radio.? Just starting a QSO on 40 meter CW and suddenly dropping dits and loss?of power.? Lots of stuff going wrong all at once.? ?Then basically zero power.? And of course, in my befuddlement I hit the SPLIT somewhere also.....to add insult to injury.
An hour later I finally figured it out -- the Drain solder joint of the RIGHT IRFZ24N had quit.? ?Basically zero DC and zero AC on the drain.? ?Left hand side working perfectly.? This exact same thing happened to the LEFT side months ago!? ?There wasn't much solder on those connections; instead of being convex?surface they were indented down into the hole....? ? Got the soldering iron -- I'm in the vacation home, less equipment ...of course a solder bridge, finally got it all soldered and cleaned up. and POWER AGAIN!!?
I'm guessing the expansion/contraction driven by the hot temperatures of the final tend to work poor soldering joints loose, to have this happen to BOTH of the final mosfets over time?? ?And, I had this apart again working on things 2 weeks ago which put torque on those connections, also...? ?Anyway, something to watch for.? ?my? QTH is in a terrible valley beween?mountains and my end-fed antenna is sad here also, but managed a cw qso with a POTA volunteer to prove it was working right.? ?
If I get some aluminum nitride insulators, I'll wait for a good time and pull this apart and check the surface of the heatsink also and get this done right.? ??
Ashhar has really made some good improvements.? ?The experience of cw qsos (once I got the relay mess cleaned out) is getting to be really really good.? ?Very little click/thump.? ?The semi-full break in is SO SO SO SO MUCH BETTER than my 7300.? ??
Gordon kx4z
On Sat, Jul 15, 2023 at 9:13?AM ajparent1/kb1gmx < kb1gmx@...> wrote: Some notes:
BEO dust is toxic!? Just don't!
I have used?Aluminum Nitride as its not toxic and works well...
One place personally used it the OZ1PIF amp and I found the thermal
conductivity excellent.
I was never a fan of the mica used for the DE, also they were used DRY
without thermal conductive paste.? Add to that a heatsink with terrible
surface quality (rough) and bad stuff happens.
--
Allison
------------------
Please use the forum, offline and private will go to bit bucket.
|
Re: sBitx DE finals and heat sink temperature plots
Some notes:
BEO dust is toxic!? Just don't!
I have used?Aluminum Nitride as its not toxic and works well...
One place personally used it the OZ1PIF amp and I found the thermal
conductivity excellent.
I was never a fan of the mica used for the DE, also they were used DRY
without thermal conductive paste.? Add to that a heatsink with terrible
surface quality (rough) and bad stuff happens.
--
Allison
------------------
Please use the forum, offline and private will go to bit bucket.
|
Re: SBitx V2 things I would like to see
As I recall in March or April, when I saw the device on video and there was no mechanical size anywhere. Then I saved a picture from the video and measured it with a screen meter. Good old days :-) -- Gyula HA3HZ 
|
Re: sBitx DE finals and heat sink temperature plots
Both of you guys are amazing.??
The curves that John produced appear valid.? ?His temperature rise of the heatsink is about the same in both experiments, indicating validity of his measurements.
The time for the DIE to hit its temperature limit is much, much longer when he used the BeO insulator.
I hunted for such an insulator and only found very very expensive items.
I ran some calculations for Aluminum oxide insulators and came up with a disappointing 0.8 degC/W for an available product of 1.78 mm thickness, and TO-220 physical dimensions (had to break out the AP Physics equations to run that calculation with thermal conductivity).?
The data for Aluminum Nitride that Gyula presents appears much more exciting, with conductivity similar to BeO and hopefully less toxic and cheaper.
The only suppliers I could find for TO-220 type aluminum nitride insulators were chinese (alibaba, and a couple of other firms) -- but this is very very interesting.
Switching to a much more highly conductive insulator would appear to dramatically increase the safety of the design for key-down time @ 30W output or so.
I looked at the paper on the inflection point in temperature properties -- VERY interesting.? ?Looking at our usage, there is a reasonable chance that we are in the "good" side of the inflection point at higher powers on the sBitx, although at lower powers we may be on the unfavorable side of temperature properties, but it won't matter as much there because the temperatures/dissipation are so much lower.
Since the development edition uses a BAR to press the devices, it makes it much easier to try some of these much more interestng insulators.
I think the next step would be to acquire some of them.
Great work, guys!
Gordon KX4Z
|
John Terrell, N6LN
MadRadioModder
HA3HZ