SP9BSL
positron
alter Hase
 Offline
Posts: 443
 
|
 |
Re:UHSDR TX Carrier shift instead Audio Shift
« Reply #15 on: 14. June 2018, 22:35:06 »
|
|
Hi,
some measurements of xlate on/off. I think can confirm your observations with spurs, ony last spur is visible because of my spectrum analyzer RBW limit. After weekend will test on 10Hz R&S one. Anyway, some other interesting wideband observation inside the pdf.
|
73 Slawek
|
|
|
|
|
SP9BSL
positron
alter Hase
Offline
Posts: 443
|
|
Re:UHSDR TX Carrier shift instead Audio Shift
« Reply #17 on: 15. June 2018, 06:32:14 »
|
|
Hi Andreas
i suppose that ~3kHz is one of the spurs (leftmost showed by Paolo) that is visible out of the resolution filter limit in sprectrum analyzer. I will do furher investigation with N2PK like 150MHz VNA today. In some circumstances it can work as a spectrum analyzer with very narrow resolution filter. Unfortunatelly i do not have Zeus like SDR used by Paolo.
|
|
 Logged
|
73 Slawek
|
|
|
SP9BSL
positron
alter Hase
Offline
Posts: 443
|
|
Re:UHSDR TX Carrier shift instead Audio Shift
« Reply #18 on: 15. June 2018, 16:56:38 »
|
|
Hi,
Some more measurements with N2PK VNA used as spectrum analyzer. This exactly confirms Paolo measurements.
|
73 Slawek
|
|
|
|
|
SP9BSL
positron
alter Hase
Offline
Posts: 443
|
|
Re:UHSDR TX Carrier shift instead Audio Shift
« Reply #20 on: 15. June 2018, 18:34:44 »
|
|
Yes, it can by software setting (see pdf). I choose the 10m band to better show the problem because spurs are bigest. On 80m it looks better. I didn't touch the opamp bias voltage (still on 2.5V). We have spurs also in translated mode but are wider spreaded (look at my yesterday's measurements with 1MHz span).
I have to look at the dac output with soundcard and fft.
|
73 Slawek
|
|
|
SP9BSL
positron
alter Hase
Offline
Posts: 443
|
|
Re:UHSDR TX Carrier shift instead Audio Shift
« Reply #21 on: 15. June 2018, 21:35:24 »
|
|
Hmmm, changed the components to proposed by Paolo (except the opamp) and have not noticeable profit of it, carrier stays at exactly the same level. Seems that probably precision of opamp does the job here.
|
|
Logged
|
73 Slawek
|
|
|
|
|
SP9BSL
positron
alter Hase
Offline
Posts: 443
|
|
Re:UHSDR TX Carrier shift instead Audio Shift
« Reply #23 on: 16. June 2018, 07:11:26 »
|
|
Hi Andreas,
as the mod is not working i went back with the rest of the mod, soldered the coupling capacitors and have the mixer connected like in first schematic of 0.4 from Chris. I did it because i suspected input offset amplification on output of the opamp (my words about precision of opamp). The result: nothing changed. So the problem lies around the FST3253. The carrier suppression changes wit frequency, with increasing it, the carrier attenuation is worse. It points to conclusion that there is capacitive couplig across the mixer.
I think all the rest of spurs is due to AM modulation by presence of carrier. In translated mode the modulation is wider and in non translated mode it is narrow.
|
| « Last Edit: 16. June 2018, 07:12:25 by SP9BSL » |
Logged
|
73 Slawek
|
|
|
IZ6MAF
Neuling
Offline
Posts: 23
Ich liebe dieses Forum!
|
|
Re:UHSDR TX Carrier shift instead Audio Shift
« Reply #24 on: 16. June 2018, 08:41:13 »
|
|
As Andreas said, the problem is very complex because so many variables are involved.
To better analyze the QSE mixer I started a new series of tests: I disconnected the R84 R85 resistors from the IN I and IN Q signals, and connected them to the bias in order to make measurements / modifications on the mixer that are not influenced by the UI board.
Too bad that LTC 5598/99 of Linear Technology can only be used from 5 mhz up, if we could have used it would have solved all the problems.
look at that very interesting tube https://www.youtube.com/watch?v=SUyNyIYcl6U
vy '73 Paolo
|
|
Logged
|
|
|
|
SP9BSL
positron
alter Hase
Offline
Posts: 443
|
|
Re:UHSDR TX Carrier shift instead Audio Shift
« Reply #25 on: 16. June 2018, 09:14:20 »
|
|
Hi Paolo,
using of integrated specialized IQ modulator involves new pcb design. Let's wait for OVI40 RF board, you will be suprised...
|
|
Logged
|
73 Slawek
|
|
|
IZ6MAF
Neuling
Offline
Posts: 23
Ich liebe dieses Forum!
|
|
Re:UHSDR TX Carrier shift instead Audio Shift
« Reply #26 on: 18. June 2018, 18:50:43 »
|
|
Hi Slawek
With the R84 and R85 resistors disconnected and connected to the bias voltage of the OPA 4192 (1,65V), only the carrier signal appears, which after changing the sn74AC74 with a PO74G74 powered by an LP2985 / 330 has an increase of 32 db when i move from 80 m to the 10 m (before was 40 db) and of course it is independent of all settings.
If I change the voltage across the resistors the signal changes in frequency and amplitude, but remains clean.
I begin to think that the spurs can come from channels I and Q coming out of WM 8731 that are not properly filtered as specified on page 13 point 3 of the data sheet.
I am very satisfied as the L.O. leakage now in 10 m is lower than 50 db of Tune single tone 750 hz transmission signal at a power of 5 w.
I look forward to the RF OVI40 card that will surely be even better.
Please could you compare my results with your tests?
vy '73 Paolo
|
|
|
|
IZ6MAF
Neuling
Offline
Posts: 23
Ich liebe dieses Forum!
|
|
Re:UHSDR TX Carrier shift instead Audio Shift
« Reply #27 on: 18. June 2018, 18:57:05 »
|
|
Hi Andreas
Why the text that I write in English (see attached) when I send the post is changed?
vy '73 Paolo
|
|
|
|
|
SP9BSL
positron
alter Hase
Offline
Posts: 443
|
|
Re:UHSDR TX Carrier shift instead Audio Shift
« Reply #28 on: 18. June 2018, 20:40:32 »
|
|
Hi Paolo,
changing the 74AC74 to Potato shows that there is also a kind of phase issue. Unfortunatelly I do not have both the Potato chip and the OPA4192 here. Yes for this moment 50dB looks good, i'm afraid that this is all what can be done with mcHF RF. The problem lies in TX mixer chip which have high leakage caused by internal capacitance. I planned to check output of the dac (i mentioned that already speaking about checking dac output by fft) will try to connect an analyzer to this week.
And speaking about English - it is Google translation. Sometimes when i do not understand, simply move cursor on text, and the original is showed. I think it is due to English->German and then back to English.
|
| « Last Edit: 18. June 2018, 20:43:00 by SP9BSL » |
Logged
|
73 Slawek
|
|
|
Author
RF_0.4_Xlate_on_off_measurements.pdf
