IZ6MAF
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UHSDR TX Carrier shift instead Audio Shift
« on: 26. May 2018, 08:25:44 »
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The UHSDR firmware now has a good TX image rejection setting, but it can not improve carrier suppression that depends on the hardware and is of about -30/-35 db.
Of course we could add a hardware balance as it is in the Eagle TRX, but its calibration is valid for one frequency only and does not solve the problem
To avoid transmitting unwanted signals in the band away from the carrier frequency, it is possible to adapt the UHSDR firmware to switch from a TX audio shift approach to a carrier shift approach as better described in the HB9DRI article (http://www.linkrf.ch/IQ+XT.html)?
’73 Paolo IZ6MAF
EDIT:
corrected link
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| « Last Edit: 26. May 2018, 09:05:20 by DF8OE » |
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IZ6MAF
Neuling
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Re:UHSDR TX Carrier shift instead Audio Shift
« Reply #2 on: 13. June 2018, 20:28:25 »
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Hello Andreas, I am attaching a brief summary of the tests I have done to improve the TX Carrier suppression on my mcHF/Eagle and what I hope you can do even better by optimizing the firmware
vy 73 Paolo IZ6MAF
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SP9BSL
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Re:UHSDR TX Carrier shift instead Audio Shift
« Reply #4 on: 14. June 2018, 08:28:51 »
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Hi,
first of all, thank you Paolo for your work! All the mods you've done are pushing old mcHF project much forward.
We can do option in menu for test (Debug menu) and have some tests against problems. Will look into the code.
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73 Slawek
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SP9BSL
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Re:UHSDR TX Carrier shift instead Audio Shift
« Reply #6 on: 14. June 2018, 09:10:56 »
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Yes, ofcourse Paolo can test this idea with Xlate off without firmware change, and then we decide to add it or not to menu, ok?
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| « Last Edit: 14. June 2018, 09:11:18 by SP9BSL » |
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73 Slawek
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SP9BSL
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alter Hase
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Re:UHSDR TX Carrier shift instead Audio Shift
« Reply #8 on: 14. June 2018, 09:59:23 »
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I will also test this with spectrum analyzer, and publish some pictures here at evening.
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73 Slawek
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SP9BSL
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Re:UHSDR TX Carrier shift instead Audio Shift
« Reply #10 on: 14. June 2018, 10:32:37 »
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I already have almost all modifications described by Paolo, but without voltage bias decrease for TLV2464 and thus FST3252. I played some with potentiometers but as Paolo described - it works but only for one band.
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73 Slawek
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IZ6MAF
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Re:UHSDR TX Carrier shift instead Audio Shift
« Reply #12 on: 14. June 2018, 11:19:15 »
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I quickly repeated the measurements at 3500 and 28500 khz with and without Xlate and as you can see from the images without Xlate there is a considerable production of spurious. What will they be due to?
'73 Paolo
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IZ6MAF
Neuling
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Re:UHSDR TX Carrier shift instead Audio Shift
« Reply #14 on: 14. June 2018, 17:05:53 »
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I am using tune, single tone, 750 hz.
It would be very useful if others could repeat the tests I performed to make a comparison.
vy 73
Paolo
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Author
Carrier_suppression_improvements.pdf
