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Re: the cause for the spurs, found!

 

Interesting, I had built the uBITX bi-amp stage only, on a small pcb some time ago.

I just measured the 2nd and 3rd harmonics as shown below, with -30, -20 and -10dBm input from an HP8640B sig gen and monitored the output on an SA.

The other 'grass' is local fm stations and shack stuff but the 2nd and 3rd harmonics have markers 2 and 3 on them. 45MHz is marker 1.








neg30dBm_input.jpg
neg20dBM_input.jpg
neg10dbm input.jpg
neg30dBm_input.jpg

Re: the cause for the spurs, found!

 

Which corner frequency for the LPF solution should be used, 50Mhz?


Il 03/nov/2018 08:19, "iz oos" <and2oosiz2@...> ha scritto:

Excellent finding! Adding a low pass filter seems the easiest solution. At which impedance should be designed? 50ohm, 500ohm? Where exactly place it, considering the schematics of ver. 3 and ver. 4. I hope it doesn't involve cutting traces on the board.


Il 03/nov/2018 03:39, "Ashhar Farhan" <farhanbox@...> ha scritto:
the 45 mhz if amplifier is distorting and producing a second harmonic at 90 mhz. this mixes with the local oscillator to produce a spur at 90 mhz - local oscillator.

here is how it happens :

the spur moves down as you tune up.
when the radio is tuned to 28 mhz, the spur is at 17 mhz. when the ubitx is tuned to 28.150 mhz, the spur is on 16.850 mhz.?
at 28 mhz, the local oscillator? is at 73 mhz.
there is a signal X such that :
X - local oscillator = 17 mhz
local oscillator is 73Mhz.
X - 73 = 17, X must be 90 MHz.

after checking the spur on a number of frequencies between 15 MHz and 30 MHz, it was confirmed that the above formula works consistently to predict the spur.?

what is th cure?
there are three solutions
1. decrease the distortion of the if amp by modifying or replacing the IF amp (the tx side at least)
2. add a low pass or bandpass filter between the final mixer and the if amp.
3. move to 60 mhz or 70 mhz IF insteead of 45 mhz. a double or triple bandpass should do it.

this is a result of joint investigation between Raj and I.

- f
Re: the cause for the spurs, found!

 

Excellent finding! Adding a low pass filter seems the easiest solution. At which impedance should be designed? 50ohm, 500ohm? Where exactly place it, considering the schematics of ver. 3 and ver. 4. I hope it doesn't involve cutting traces on the board.


Il 03/nov/2018 03:39, "Ashhar Farhan" <farhanbox@...> ha scritto:
the 45 mhz if amplifier is distorting and producing a second harmonic at 90 mhz. this mixes with the local oscillator to produce a spur at 90 mhz - local oscillator.

here is how it happens :

the spur moves down as you tune up.
when the radio is tuned to 28 mhz, the spur is at 17 mhz. when the ubitx is tuned to 28.150 mhz, the spur is on 16.850 mhz.?
at 28 mhz, the local oscillator? is at 73 mhz.
there is a signal X such that :
X - local oscillator = 17 mhz
local oscillator is 73Mhz.
X - 73 = 17, X must be 90 MHz.

after checking the spur on a number of frequencies between 15 MHz and 30 MHz, it was confirmed that the above formula works consistently to predict the spur.?

what is th cure?
there are three solutions
1. decrease the distortion of the if amp by modifying or replacing the IF amp (the tx side at least)
2. add a low pass or bandpass filter between the final mixer and the if amp.
3. move to 60 mhz or 70 mhz IF insteead of 45 mhz. a double or triple bandpass should do it.

this is a result of joint investigation between Raj and I.

- f
Re: Harmonics and Relay Replacement

 

I tried EPCOS TDK and it works as well as one marked S+M



This one has it marked R68K , tried and works well.

Raj

At 02-11-18, you wrote:
Hi all.
I was looking for the specs of the L5 and L7 replacement. I cannot find the exact yellow ones on the internet. The NLT on comkey are not there. They have NLV type. Is this a typo??
Please your source for me and some other builders in my club. We found the relays.But are looking for this parts.
Rob PA0RBL
Re: Harmonics and Relay Replacement

 

The SMDs I used are marked S+M and yellow in color. Smaller ones did not help.

Just do the relay mod for now.. don't use sockets for them.

Raj

At 02-11-18, you wrote:
Hi all.
I was looking for the specs of the L5 and L7 replacement. I cannot find the exact yellow ones on the internet. The NLT on comkey are not there. They have NLV type. Is this a typo??
Please your source for me and some other builders in my club. We found the relays.But are looking for this parts.
Rob PA0RBL
Re: Si5351 correction question

 

Mark wrote:
> CLK2 is the only one used on xmit and then it should be the dial freq +- 800 Hz depending on sideband selection.

When transmitting, the display should show the frequency of the carrier in the case of CW,
and should show the frequency of the suppressed carrier in the case of SSB.
If your firmware does otherwise, that's a bug.
The only funny stuff is during receive of CW, the receiver must tune to one side of the
incoming carrier so you can hear a beat note between that signal and your BFO.

When transmitting SSB, all three clocks are used in double conversion,?
the process is the same as during receive except reversed.
All three clocks remain the same when switching from receive to SSB transmit.
When transmitting CW, clk0 and clk1 are shut down, the mixer at D1,D2 is unbalanced,
and clk2 is set to the operating frequency.

I'd recommend the?algorithm of post???/g/BITX20/message/54501?for calibration.
Tune the rig following the algorithm of post??/g/BITX20/message/44278
The funny offset for CW receive is not included in that tuning algorithm, an exercise for the reader.
I have no idea what the various firmware releases are doing these days
except that none of them seem to be doing it right.

Jerry, KE7ER



On Fri, Nov 2, 2018 at 10:11 PM, Mark M wrote:
What firmware are you running??

Mine seems to be OK on xmit but several hundred Hz off on rcv. I'm thinking it might be the constants used in the firmware for the USB & LSB offsets. They're used by the firmware to calculate the freqs for CLK1 for a given dial freq. The BFO freq (CLK0) also will affect the actual tuned freq. AFAIK, the only way to change those CLK1 constants is editing the firmware source.

CLK2 is the only one used on xmit and then it should be the dial freq +- 800 Hz depending on sideband selection.

At least that's how I understand it from wading thru the firmware source (I'm running the CEC v1.11 firmware).

Mine also seems to change slightly as it warms up and it also does not seem to track linearly...if I get it spot on for, say, 14 Mhz, it's off at 7 Mhz and vice versa.
Re: Si5351 correction question

Mark M
 

What firmware are you running??

Mine seems to be OK on xmit but several hundred Hz off on rcv. I'm thinking it might be the constants used in the firmware for the USB & LSB offsets. They're used by the firmware to calculate the freqs for CLK1 for a given dial freq. The BFO freq (CLK0) also will affect the actual tuned freq. AFAIK, the only way to change those CLK1 constants is editing the firmware source.

CLK2 is the only one used on xmit and then it should be the dial freq +- 800 Hz depending on sideband selection.

At least that's how I understand it from wading thru the firmware source (I'm running the CEC v1.11 firmware).

Mine also seems to change slightly as it warms up and it also does not seem to track linearly...if I get it spot on for, say, 14 Mhz, it's off at 7 Mhz and vice versa.
Re: K5BCQ agc

 

Thank you 73¡¯s
the cause for the spurs, found!

 

the 45 mhz if amplifier is distorting and producing a second harmonic at 90 mhz. this mixes with the local oscillator to produce a spur at 90 mhz - local oscillator.

here is how it happens :

the spur moves down as you tune up.
when the radio is tuned to 28 mhz, the spur is at 17 mhz. when the ubitx is tuned to 28.150 mhz, the spur is on 16.850 mhz.?
at 28 mhz, the local oscillator? is at 73 mhz.
there is a signal X such that :
X - local oscillator = 17 mhz
local oscillator is 73Mhz.
X - 73 = 17, X must be 90 MHz.

after checking the spur on a number of frequencies between 15 MHz and 30 MHz, it was confirmed that the above formula works consistently to predict the spur.?

what is th cure?
there are three solutions
1. decrease the distortion of the if amp by modifying or replacing the IF amp (the tx side at least)
2. add a low pass or bandpass filter between the final mixer and the if amp.
3. move to 60 mhz or 70 mhz IF insteead of 45 mhz. a double or triple bandpass should do it.

this is a result of joint investigation between Raj and I.

- f
Re: Ubitx5 ?

Timothy Fidler
 

Roger I got put on moderation by Wicked Witch of the West or perhaps it was the Tin Man.? Bit like being stuck in Mt Eden Gaol for a few weeks without any playthings except the local Tribesmen.. . don't risk it.
Re: Tone on Nextion LCD Dimming

 

Evan It's almost certain the dimming is done by PWM, ie chopping the LED supply.?? Did you try adding some series inductance to the display supply along with your extra capacitors.?
vk3pe
Tone on Nextion LCD Dimming

 

A relative and I have both purchased the uBitx boards and upgraded to the CED firmware with a Nextion diplay (he has a 3.5" enhanced and I have a 2.4" enhanced).? Both exhibit a tone when the LCD is dimmed below 92.? We have tried adding capacitors to the 5v line to the Nextion display, as well as on the 12v general supply.? Nothing seems to remove the tone.

Testing on the audio output at the high end of the volume control reveals aprox 300 hertz signal that goes away when fully dimmed or full bright.? I have tried probing the 5vdc line to the display, and cannot find any signal there.

The only thing that has worked so far has been to use a separate 5 vdc supply for the display.

Any thoughts on what could be causing the tone?? Our current guess is that the dimming is done by chopping the supply to the LED back light.? But if this were the cause the filtering on the supply line should at least reduce the sound.

?Seems like over kill to add another regulator to solve the tone issue.

Thanks for any suggestion that you might provide.

Evan
AC9TU
Re: Ubitx5 ?

 

Tim....some one has to tell the truth. There much BS talked here.....


On Sat, 3 Nov 2018 2:08 pm Timothy Fidler <engstr@... wrote:
Watch it Roger, they will ban you from the site and then you won't get to hear about Rev 5 and the 50 percent off coupon that AF is going to give out to disgruntled purchasers of V3 and V4 boards. !!!? I heard that from a reliable source I can't name....

Axicom relay switching #ubitx #filters

 

This might have been posted before, so forgive me if doubled up, but an interesting web page on how to use Axicom rf type relays.



vk3pe
Re: Ubitx5 ?

Timothy Fidler
 

Watch it Roger, they will ban you from the site and then you won't get to hear about Rev 5 and the 50 percent off coupon that AF is going to give out to disgruntled purchasers of V3 and V4 boards. !!!? I heard that from a reliable source I can't name....
Re: Ubitx5 ?

 

I don't agree.....this rig will work to some extent and I have used it for QSOs on 80-40- and 20 metres in CW SSB FT8? and WSPR.?
But the software calibration to get it working correctly is an impossible mission unless you are prepared to tolerate always being off frequency.
The drive must be kept very low unless you want to radiate spurious RF. I reckon it is good for about 3 watts.
There is just not enough information from the factory.?

I have wasted too many hours on this. It may be relatively inexpensive, but I did expect it to live up to the statements about what it could deliver.

I certainly wouldn't recommend it to a friend, an enemy maybe.
73 Roger ZL2RX
Re: Si5351 correction question

 

Hi Bill.

Did you run in upper sideband and the other in lower sideband?
I think that would make a difference. The instructions I have
specify doing that calibration with the radio in upper sideband.
This is a bare Si5351 board being controlled by an Arduino. This
is the environment in which the calibration sketch expects to
execute.

If I set the correction constant, I get the correct frequency
at the Si5351 CLK2 for the ubitx. I'm just surprised I had to
use two different values. I wonder if it could be related to
how long the board had been powered on.

73

- Mark N1VQW
Re: Cursed?

 

I don't know how much this helps, but your description of when it died reminded me very strongly of a problem I found years ago.? A customer had equipment that kept going crazy and failing and couldn't figure it out.? I went in and fixed the machine (component fried).? An employee started using it while I was talking with the owner.? While he was working, another employee plugged in a hand plasma cutter to the same outlet that the machine was plugged into, and as soon as he fired it off, the machine went crazy again.? They couldn't understand it, until I was able to show them that it was putting over a thousand volts of noise into the control - eventually scrambling the computer (it was random when it failed).? They hadn't told me about the plasma before... indeed, it was put away until they decided to use it and didn't realize their plasma needed to be on a completely different circuit.

Strong RF fields near pins can do just as you described, especially pins that aren't terminated or shielded, on computers (including Arduino units)? - even fry them.? I wonder if you've got a situation where some portion of your TX circuitry is loosing the ground connection, or a rf voltage-based short (yes, I've seen them - a low voltage signal wouldn't short, but as soon as higher voltage hit the component - shorted out, then cleared as the voltage went down).? Those could cause the high current but low RF out.? There are other things that also can do that - parasitic loops and so on.

Anyway, good luck with it, if you decide to pound on it a little more!? (GRIN!)

Bob

N4FBZ

On 10/31/18 5:17 PM, Woody wrote:
Original thread was "RX Trouble". ? Sort of a rant here...

I am not superstitious but beginning to believe my uBITX (both factory & CEC firmware) is cursed. Have had issues since first power-up, but now I think the problems are fatal.? Have a lot of time & money in it (Axicom relays, trouble shooting, etc.) but think I might call it quits.? Never had problems with my scratch built rigs.? Had a problem with my K2 build, but fixed that when I discovered a copper whisker (under the coating, I took optical micrographs !) shorting a pair of runs on the control board.
However, the uBITX has been a relative nightmare.

Original issues, to name a few:
Not on frequency, low audio, poor RF sensitivity, pinched audio response (narrow - filter issue?),? very narrow tuning for understandable audio, etc.

I fixed the too low for headphones audio with an off board amplifier.? But, the distortion was even worse from the speaker. I found a power/signal driven oscillation in the external amp and fixed that.? Afterward, the volume was OK and the distortion was somewhat lower - but still not great audio.? The other problems remained.

Observation:
There was (I think, maybe) something oscillating on the board. There was a low level (~700) Hz tone on the audio coming from the board.? Found that with a 'scope, but did not find the source. Also, the 12 MHz crystal filter was rather microphonic - With no received signals lightly tapping crystals produced audio output. Normal?? Not normal?

The TX power was inconsistent with measurements by others.? Got 10 +- watts out on higher bands, dropping a bit as frequency increased.? But, for 40M and below, the power dropped to about 1.5 watts while the supply current was much higher (almost by 1 amp). ? Frustrated with the RX problems, decided to look at the TX power issue using 'scope on TPs in the TX amp stages.
-- The following is when the patient died. No brain activity ;) --
CW keyed the TX for testing but I didn't get far before the fatal problem occurred. After a few short dummy load TX sessions, it stopped keying.?? Immediately noticed a display issue.? The top row was all solid fill characters, nothing on the bottom row. Clocks 0, 1, 2 not there.? The 7805 on the Radiuno is supplying 5 v.? This is a bit subjective, but is does not seem to get quite as hot as initially? -? likely not supplying as much current as before?.
Hoping the cause was somehow corrupt firmware, tried reloading. Xloader appeared to connect and tried to upload, but never left the "uploading" mode - Failed to reload firmware.? The display stayed the same - solid top row, empty bottom row.
Tried uBITX Manager to read.? It appeared to connect, but when "Read from uBITX" was attempted, returned this:? "[8:30 PM] Error Receive Length = 0/1027".
OTOH,? uBITX Manager did report success when told to upload the .btx backup file I created earlier (Load from File).? BUT - it again failed the "Read from uBITX" command.? Display never changed.? I get the impression the Arduino died...

Ready to take it outside and shoot it? ;) , but probably will put this project away for now.? A big question is, if a version 5 is released to fix some of the original issues like spur/harmonic levels, do I try again ????????

Better luck to everyone else!
73,? Woody?? KZ4AK
Re: Ubitx5 ?

 

Dennis

If you already have a ubitx, its issues can be addressed. Honestly my K2 has more mods than this ubitx needs. The spurs can be fixed. I would rather see an affordable mod kit to service the vast number of ops who already have a ubitx versus a rush to a new version. As for transmit audio, mine exceeds expectation in making contacts.

The QSX mentioned will be an alternate multiband rig from qrplabs. Not open source but thus far firmware upgrades have been free on existing products. Its a traditional kit requiring board assembly. The ham community around the world is well served by these rigs.

Based upon measurements of my v4 ubitx the spurs are much more significant on upper HF. I clearly don't recommend running a Tx amplifier with an uncorrected ubitx. It does make sense to work toward fixing the rig.

73 curt
Re: Si5351 correction question

 

Hi,

Did you run in upper sideband and the other in lower sideband? I think that would make a difference. The instructions I have specify doing that calibration with the radio in upper sideband.

73,

Bill KU8H

On 11/02/2018 05:45 PM, Mark Pilant wrote:
I have finally got my "Franken" uBitx to the point where it is receiving
signals; at least from my HP 8642A signal generator. But, there is
something
strange going on, and I am wondering if anyone else has seen the same
strangeness.

When I originally ran the si5351 calibration program, everything looked
great and I have up with a correction number of 15380. The 10 MHz was
measured by my HP 53131A counter referenced to a GPSDO.

Fast forward to a little more testing, and I discovered signals I had been
receiving were no longer where they once were.

Running the calibration program again, with the same Adafruit Si5351 board,
I arrived at a correction number of 14210.

So my question is: has anyone else seen the same Si5351 use different
correction factors to generate the same output frequency?

Really scratching my head over this one.

73

- Mark N1VQW



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