Date   
Re: Farhan's new PA for ubitx

atouk
 

Is there a best and final solution yet or are we still waiting for Allison's final comments on changes?


On 5/29/2018 9:45 PM, ajparent1/KB1GMX wrote:
those are .1 uf caps, pass rf block dc.  Says so in small print on the schematic.

That is the negativefeed back to keep the mosfets tame at low hf.  Without the cap its full
on forward bias likely will not hurt them but it will suck down many amps as under that
condition the mosfets look like s short to ground

Chaning R97/98 to 220 ohm is going the wrong way and not advised. 

Allison

Re: Farhan's new PA for ubitx

Jerry Gaffke
 

A bit ambiguous, but I believe Allison is suggesting you might want to leave
those 0.1uF caps at C261 and C262 in place, as they were originally.
And while you're at it, she suggests leaving those resistors at R97,R97 as they were with 47ohms.

I suggest you sit on your hands for a few days or weeks till this shakes out a bit further,
and we have some consensus as to what is the best way(s) to upgrade the uBitx final.

Unless you have a fair understanding of what's going on here and the instruments to see it. 
Or at least a nice stock of spare IRF510's on hand.



On Tue, May 29, 2018 at 06:52 pm, Jerry Gaffke wrote:
That's a cap, so the zero means 0pf.  
Be sure to place the two PCB pads infinitely far apart.  ;-)

Farhan is disabling the negative feedback around the IRF510's.

Re: Farhan's new PA for ubitx

Jerry Gaffke
 

Final could be weeks, still waiting for Allison's intermediate comments on changes.
I suggest you leave the rig stock unless you are keen to do your own development.

First thing I would experiment with is Farhan's suggestion of adjusting the value
of C81 and R83 near Q90 to 470pf and 2.2 ohms as per his new v4 schematics.
Should even out the power across the various bands somewhat.
Then re-adjust RV1 for no distortion on any band after doing any mods.

What should be changed around the IRF510's is still open for debate.


On Tue, May 29, 2018 at 07:17 pm, atouk wrote:

Is there a best and final solution yet or are we still waiting for Allison's final comments on changes?

Re: Farhan's new PA for ubitx

Jerry Gaffke
 

Separate universes.


On Tue, May 29, 2018 at 07:03 pm, Vince Vielhaber wrote:
Yes, it's recommended you put the two pads in separate rooms.

Re: Farhan's new PA for ubitx

Jerry Gaffke
 

It's really tough to make a 0pf cap (or 0 ohm resistor) that is accurate to within 1%
Or 100%.



On Tue, May 29, 2018 at 07:26 pm, Jerry Gaffke wrote:
Separate universes.
. . .

 


On Tue, May 29, 2018 at 07:03 pm, Vince Vielhaber wrote:
Yes, it's recommended you put the two pads in separate rooms

Re: Farhan's new PA for ubitx

Ashhar Farhan
 

0 pf is 'no pf', that is, it is open. Take out the capacitor. It has been placed on the circuit to be used if needed with PA transistors with higher gain like the RD16HHF1s, etc.

- f

On Wed, 30 May 2018, 08:06 Jerry Gaffke via Groups.Io, <jgaffke=yahoo.com@groups.io> wrote:
It's really tough to make a 0pf cap (or 0 ohm resistor) that is accurate to within 1%
Or 100%.



On Tue, May 29, 2018 at 07:26 pm, Jerry Gaffke wrote:
Separate universes.
. . .

 


On Tue, May 29, 2018 at 07:03 pm, Vince Vielhaber wrote:
Yes, it's recommended you put the two pads in separate rooms

Re: Ideas for AM, NB FM Demod and CW filter board

Ashhar Farhan
 

I once played with an AOR7030 on AM at Anil's QTH. It blew my mind. Synchronous AM detection is certainly something.
- f

On Wed, 30 May 2018, 07:10 ajparent1/KB1GMX, <kb1gmx@...> wrote:
My favorite AM radio is my Hallicrafters SX100 or the highly modded S120
of for just being odd ball my really old (1953) RCA am potable AC/DC/battery
using tubes.  ;)

I still wish I had the old RBO II shipboard AM RX.   It was heavy enough to
hold down a truck.


Allison

Re: Oscillation problems Bitx20a

Fokko PH0KKO
 

Nice job Allison. My PA print is about the same size, 2.5 by 5 inches and that includes one corner 1.5 by 1.5 " cut out to leave access to the BFO/AF mixer below and also 2 reasonably big heatsinks of about 1.5 by 1.2" each placed horizontally on but isolated from the board. Next to the heat sinks I placed a vertical PCB strip for shielding and behind that was just enough room for the LPF band filter. So you actually have very little space left to place all the components. It does required some planning ahead but you can fit it all on there easily, I even managed to position each coil in another direction. But I doubt they will influence each other's field much, it's just to be on the safe side.

That is why I am hesitant on replacing the T50-6 toroid coils and make new ones using T50-2. I glued them in and it is a tight squeeze there, I don't want to damage anything surrounding it when taking them out. The T50-2 would result in a better Q for these coils but do I really need that? My IF is 10 MHz and I left the BFO a little below that, so the upper side band passes through the crystal filter. The DDS works from 17.0 to 17.3 MHz so I get 27 and 7 MHz mixed before the BPF. The BPF only lets the 7 MHz part through and turns USB into LSB and vise versa. Worst case scenario there may be some unwanted 27 (17+10) and 14 (7x2) MHz signals. They are much higher in frequency than the desired 7 MHz so I wonder: do I really need better coils with a higher Q and thus steeper slope? To me it seems impossible it will ever interfere in the 20 meter or CB band. 

Maybe, when everything else is finished and I want to use some more power, I could consider adding a new bandfilter and simply bypassing the old one. 

Re: Farhan's new PA for ubitx

Skip Davis
 

Tim, Farhan’s suggestion was to remove C261 and C262 not short them out which will remove the feedback on the IRF510’s.


Skip Davis, NC9O 

On May 29, 2018, at 22:25, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:

Final could be weeks, still waiting for Allison's intermediate comments on changes.
I suggest you leave the rig stock unless you are keen to do your own development.

First thing I would experiment with is Farhan's suggestion of adjusting the value
of C81 and R83 near Q90 to 470pf and 2.2 ohms as per his new v4 schematics.
Should even out the power across the various bands somewhat.
Then re-adjust RV1 for no distortion on any band after doing any mods.

What should be changed around the IRF510's is still open for debate.


On Tue, May 29, 2018 at 07:17 pm, atouk wrote:

Is there a best and final solution yet or are we still waiting for Allison's final comments on changes?

Re: Farhan's new PA for ubitx

Tim Gorman
 

Thank you!

So R261 and R262 aren't used either, right? They could also be removed?

tim ab0wr

On Wed, 30 May 2018 08:15:30 +0530
"Ashhar Farhan" <farhanbox@...> wrote:

0 pf is 'no pf', that is, it is open. Take out the capacitor. It has
been placed on the circuit to be used if needed with PA transistors
with higher gain like the RD16HHF1s, etc.

- f

On Wed, 30 May 2018, 08:06 Jerry Gaffke via Groups.Io, <jgaffke=
yahoo.com@groups.io> wrote:

It's really tough to make a 0pf cap (or 0 ohm resistor) that is
accurate to within 1%
Or 100%.



On Tue, May 29, 2018 at 07:26 pm, Jerry Gaffke wrote:

Separate universes.
. . . <#m_4917506501796616938_quoted-43406361>



On Tue, May 29, 2018 at 07:03 pm, Vince Vielhaber wrote:

Yes, it's recommended you put the two pads in separate rooms


Re: Farhan's new PA for ubitx

VE7CWS WRSeiler <waltrseiler@...>
 

If the process is flawed then surely the outcome will most certainly be flawed!

Re: Farhan's new PA for ubitx

ajparent1/KB1GMX <kb1gmx@...>
 

Actually the IRF510s have higher gain that the RD16s.  At least at lower frequencies.
though the difference is generally within 3db. Read the spec sheet and not run with 
myth and lore.  The RD16HHF is a fine device but limited to 12V systems and 
has a slightly better IMD, it is not a panacea.  Most of the issues with IRF510s
is people trying to get a lot of power but putting little in or from unstable sources
then wondering why its flakey and oscillates.    

Keeping the feedback lowers the gain and keeps them stable at lower
frequencies with reactive loads.  I'd rather see the driver make a bit more power. 
As the low power out has not been an IRF510 issue its a drive to them that is
being worked. Example I was getting 1.6W but the drive was barely 70 milliwatts.
The IRF510 was doing very well at 10M knowing that.  the problem was why
only 70mW of drive and worse from 4 devices pulling 100ma idleing?

Generally to make a stable amplifier chain you don't run devices wide open
if possible. Lower gain and more devices to make it generally is safer as
your not forcing power by forcing gain especially in high power stages.

Right now speculating on intermediate work I've done is not in ones best
interests as you might have to take it all out.  The mods around q90 help some
and its the only for certain mod I've done is to put a BFR106 there for more
even gain plus the peaking mods suggested by Farhan.  It also insure that
at 28 mhz it can produce the design gain.  The 2n3904 could not do that
though it was doing better than the book and theory claims.


Allison




Re: Farhan's new PA for ubitx

 

Being a symbol of a capacitor, it would mean ZERO pF or open circuit.

If you put 0 ohms then you surely will blow the finals or fuse!

Raj

At 30/05/2018, you wrote:

Is that 0 capacitor for C261 and C262 *not* a 0ohm jumper? From drain to
ground I get about 220ohms which is what I would expect from the two
220ohm resistors R98 and R261 in series paralleled with R97 and R262 in
series.

Any comments, suggestions, ideas?

How to reduce uBITX output power?

vick.perry@...
 

Hi, 

I have had success with the WSPR beacon mode using Dr. Lee's uBITX firmware. On each WSPR band, I matched my antenna for low SWR as best as I could. On some bands, the finals get VERY HOT so I would kill power to the uBITX hopefully before I destroyed the finals. I do realize that digital transmission modes are high duty cycle loads. 

In an attempt to reduce output the uBITX RF power, I turned RV1 clockwise 1/8 turn to reduce output power on the finals - that helped prevent overheating. 

Is adjusting RV1 the best way to reduce output power with a stock uBITX build?

Regards,

Vick KG7UNJ

Re: How to reduce uBITX output power?

Tom, wb6b
 

I have a small mains powered fan. Placing that near the heatsinks keeps them cool. Right now I just turn it on when needed. I'l use a 12v fan when I finally put the uBITX in a case. Rather than add the extra complexity of temperature control, I'll just hook the fan to the 12v from the uBITX transmit relay contact.

Tom, wb6b

Re: Need help understanding a line of code in ubitx_si5351.cpp (msxp2 = ...) #radiuno

Terry Morris
 

Jerry,

I can't say that I completely understand everything that you just described but I do have a better understanding. It is Elmer's like you that make this hobby so inaugurating. I thank you for taking the time to explain this to me. I still have a lot to learn. Your explanation was not more than I want to hear. It was perfect.


Terry - KB8AMZ


On Tue, May 29, 2018 at 5:35 PM, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:
OK, a few more words about what's going on inside the si5351.
Perhaps more than you really want to hear.

Assume you are tuned into a CW station at 7.1mhz.
We have a  single conversion superhet such as the Bitx40, the VFO is 7.1 mhz above
our 12mhz intermediate frequency, so 19.1mhz.  The Si5351 is providing that VFO.

But the Si5351 only has an 875mhz reference oscillator, it has to do some sophisticated math inside
to create that 19.1mhz VFO.  And that math sometimes has rounding errors.
Most of the time the VFO is right at 19.1mhz, but it does occasionally jump around a little bit, 
in extreme cases by a kilohertz or more.  So in addition to letting you hear that 7.1 mhz station,
your radio might also be letting through bits and pieces of other stations at 7.099 or 7.101 mhz, if only 
for a millionth of a second or so.  Those bits and pieces add up, they sound like noise. 
Specifically, phase noise.

To reduce that phase noise requires better computations inside the si5351, and that requires more power.
 


Here's a brief example of the sort of math that goes on inside the Si5351:
Assume we have a 875mhz reference, and want to generate a 19.1mhz signal.
We an get close by dividing by 46, giving 19.0217 mhz out.
We can divide by 45, to get 19.4444 mhz.
If we mostly divide by 46, and sometimes divide by 45, it can average out to exactly 19.1 mhz,
but if you look close you can still tell that it is just jumping between 19.0217 and 19.4444 mhz out.
Some serious phase noise.
This is called a fractional divider, because it is dividing by something between the integers 45 and 46.

That's what SiLabs does, except they also add a programmable delay line to the output pin.
They delay the rising and falling clock edges a few picoseconds, differently for each clock edge,
doing calculations with each clock edge to determine how much delay is needed to make the output
look like a 19.1mhz square wave.  Those calculations aren't perfect, nor is the delay line. 
So we still get some residual phase noise.

The Si5351 operates in two stages, first stage brings the 25mhz crystal oscillator up to around 875mhz.
This involves a second fractional divider much like the one described above.
In this case, 875/25 = 35.0 exactly, but that figure of 875 could have been anything between 600 and 900 mhz.

Jerry._,_._,_


Re: Instruction Manual needs revision #ubitx

Terry Morris
 

I am interested Jon.​

Terry KB8AMZ

Re: Instruction Manual needs revision #ubitx

W7PEA
 

Yeah K5KDT, I hear you, the wiki on Groups.io is pretty lame and managing the files, pictures, linking them etc is really time consuming. 

If people we're interested, we could move that stuff to github and use a github.io free hosting for the docs. Or some other approach. But unless there are several people willing to contribute content this site is fine too. I'm personally open to any approach that is open to the group to own and manage and not linked to one person or owner.

What do you all think?
W7PEA

Re: How to reduce uBITX output power?

Jerry Gaffke
 

Adjusting RV1 is the best way to reduce power.
You might also go to a bigger heatsink someday, but note that the IRF510 tabs are at 12 volts
so be careful you don't ground them.  Tom's fan is also a good idea.
You do not want the IRF510's getting so hot you can't hold your finger on them.


On Tue, May 29, 2018 at 08:51 pm, <vick.perry@...> wrote:
Is adjusting RV1 the best way to reduce output power with a stock uBITX build?

Re: The new uBITX boards are here

Terry Morris
 

I still have my slide rule and books with the logrithms Allison.

Terry KB8AMZ


The magic is that I can remember the logs of 10 for integers at age 65 but, not what day it is. ;-)
Hint I grew up with and still have a slide rule.  The calc in the iphone is decent in scientific mode
(turn it landscape).

Allison