Re: the cause for the spurs, found!
Raj
The input VSWR with that mod increased the input VSWR to around 7:1.? (measured 0-30MHz, my current setup)
I didn't check before the mod but assume its closer to 1:1.
glenn
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Re: the cause for the spurs, found!
Not much change really Raj, I used 39k.
At -10dBm input, there is a slight improvement by maybe 2-3dB
At -20 & -30dBm in, virtually same result.
I wonder if a notch could be added for the 2nd Harmonic..... Did you do any sums on the 3rd harmonic? It may also contribute.
glenn
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Re: the cause for the spurs, found!
Ashar,
I always had a lot of doubts that the first mixer should be the
culprit but suspected taht the first BiDi amp must be the reason
in producing harmonics. But now You and Raj confirmed my
suspicion. This findings also explain why putting another xtal
filter between the output of the BiDI amp (in TX direction) and
mixer.
My proposal: first of all put a diplexer on the IF output of the
mixer and the following stage. THen use two 90 deg hybrids and in
between tho identical xtal fitlers, i.e. split the 45 MHz IF
signal into two path, filter them within two identicla filters
(gain and phase) and combine. Both dipexer and 90 deg hybrids with
the xtal filters will attenuate harmonics.
I am also thinking of another diplexer (LP - Hp ) at the
RF-In/Out of the mixer, the high frequency path be treminated into
50 ohms. In TX mode the image (LO+IF) will then be terminated and
not be reflected into the mixer.?
In addition do a good leveling of all stages in the TX path, but
keep in mind that the balanced modulator has a limited LO
suppression, so the carrier suppression (and image band) must be
taken into account.
Henning Weddig
DK5LV? ?
Am 03.11.2018 um 03:39 schrieb Ashhar
Farhan:
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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
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Re: uBitxr4 audio distortion fix
Sundar,
It should be best sound around half. Just check if final audio tr's are too hot!
Raj
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At 03-11-18, you wrote: Dear Raj,
I added one 100 ohms preset (not trimmer) in between the diode d15 and D16 (after cut the track) the audio is ok and volume is increased.
Good result.
vu2nsk
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Re: the cause for the spurs, found!
Glenn,
Please try a mod..
Remove first transistor's base bias resistors uBitx = 1K and
2.2K
Connect a 39K or 47K resistor from first base to last emitter.? The
emitter voltage will be around 5-7v.
I used 44K and voltage was 6.8 half of my supply.
repeat the test below. I want to see if the feedback improves the
distortion in any way.
Cheers & Thanks
Raj
At 03-11-18, you wrote:
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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.
![[]](/g/BITX20/attachment/61266/)
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Re: uBitxr4 audio distortion fix
Dear Raj,
I? added one 100 ohms preset (not trimmer) in between the diode d15 and D16 (after cut the track) the audio is ok and volume is increased.
Good result.
vu2nsk?
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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.   
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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.
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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
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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
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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
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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
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Show quoted text
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
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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/44278The 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.
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Re: Si5351 correction question
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.
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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
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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.
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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
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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
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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....
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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
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Raj vu2zap
