Sorry for the above message. The audio is there its just very low. I should have checked
the info on the web site re this problem. and? Shall? have to get an amplifier to boost the audio
A Redface Regards
Fred Aunger (G6FJA)
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Re: the cause for the spurs, found!
Correction:
After seeing your results I feel the stage is OK for upto -5 dbm
input output where as the actual input
is -30 to -40 dbm. The output of the stage is max -10 dbm and so
the input will be 15 -20dbm
less (i.e. gain of stage) So your Bidi amp is good to go.
At 03-11-18, you wrote:
toggle quoted message
Show quoted text
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!
Thats a given. The stage becomes a high impedance input.
Try a 470 Ohms parallel with input to compensate the resistors
removed.
We did discuss the notch but I have not tried.
After seeing your results I feel the stage is OK for upto -5 dbm
input where as the actual input
is -30 to -40 dbm. The output of the stage is max -10 dbm and so
the input will be 15 -20dbm
less (i.e. gain of stage) So your Bidi amp is good to go.
So where is the offender, it is the strong harmonics of the final that is
getting coupled from
the relay contact loops and into the input of the Bidi amp which is
getting overloaded !
This unholy mix of signals is causing spurs.
Replacing the stock top contact relays with bottom contact AXICOM of Mike
Doty relays reduces
the loop size and so the coupling to L5. I noticed if the stock 45MHz
filter is mounted high by 3mm
then the spurs increase, it needs to be close to the board. That gave me
the clue!
The harmonics are also getting picked up by L1/2/3/4 !
1: Change the relays and you will see major relief. DO NOT mount in
sockets, they add to the loop.
additionally but may not be needed for your board.
2: Change L5/7 will make a small change only if the relay is
changed.
3: Change L1/2/3/4, one of my boards became unstable if any wires or
finger was near.
4: Add another 45MHz filter at the Bidi out to clean up after the Bidi
but with a big power loss.
5: Do't over drive on higher bands. Drive settting that gives 10W on 40M
is fine on all bands
with only relay change. We need a audio clipper / hard limiter for the
next board.
Raj
At 03-11-18, you wrote:
toggle quoted message
Show quoted text
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!
Glenn,
pleas keep in mind to check the output of Your signal generator,
mostly the ahrmonics are in the same range i.e. about -30 dBc to
the main cyarrier. So to make sure You do not make false
measurements, place a low pass fitler between the output of Your
sig gen and DUT.
Henning
Am 03.11.2018 um 10:33 schrieb Glenn:
toggle quoted message
Show quoted text
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: uBitxr4 audio distortion fix
Dear Raj, No heat in the final Audio Transistor , It is cool including my self?
Thanks & regards sudanthiram vu2nsk
Sundar,
It should be best sound around half. Just check if final audio tr's are too hot!
Raj
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: Tone on Nextion LCD Dimming
Thank-you for the reply.? I did try wrapping the 5 v lead through a toroid I? had, though at 300 hz, even if a square wave, I would not expect much attenuation.? I will try a larger inductance.
On Fri, Nov 2, 2018 at 8:47 PM Glenn < glennp@...> wrote: 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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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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Show quoted text
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
toggle quoted message
Show quoted text
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:
toggle quoted message
Show quoted text
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/)
![[]](/g/BITX20/attachment/61266/1)
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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?
|
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
toggle quoted message
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: 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
toggle quoted message
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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Raj vu2zap
