Title: mcHF 0.7 STM32F7 2048kb: Phantom signals 24khz above real frequency
Post by: DL4SM on 12. November 2018, 09:35:27
Hello there,
as I have done quiet a lot of tests to my new mcHF during the weekend I am a little confused about some functions and features.
1. I am experiencing always (setting Xlate -12kHz) phantom signals which are located 24kHz above the real signal on the other side band and you can hear it there.
2. The waterfall also shows this phantom signal, but instead of being displayed above the real signal it is displayed 24kHz below the real signal and you can not hear it there.
Here you can see/hear the real signal on 14267kHz USB and can see the "just" displayed phantom signal on 14243kHz LSB:
https://filehorst.de/d/cifoJlCd
Here you can see/hear the phantom signal on 14291kHz LSB
https://filehorst.de/d/cIaFDcuq
I have tried various things without success:
a) Install older firmware (back to 2.9.15)
b) clear all settings F1/F3/F5
c) IQ Calibration of RX Phase / RX Balance
The only way how the phantom signals disappear is to either turn off the RX/TX Freq Xlate or to switch the RX IQ Auto correction to "ON"
If the IQ Auto correction is switched to "ON" the AGC is disabled and the RX is very low in sensitivity / turns deaf.
I really can´t imagine that I am the only one having these problems. I am quiet happy with the TRX, but those issues I would like to fix.
Any help / idea would be appreciated
Vy 73, Sascha
DL4SM
PS: I have posted this on the yahoo mcHF board as well as there are probably different readers then here
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Title: Re:mcHF 0.7 STM32F7 2048kb: Phantom signals 24khz above real frequency
Post by: DF8OE on 12. November 2018, 10:10:41
If you do not use "IQ auto correction" (strongly recommended!!!) you must do RX IQ calibration like described in WIKI. But this manual correction does not work as good as auto correction, so my hint: turn it on!
It has absolutely nothing to do with AGC and does not impact speed of UHSDR.
EDIT:
But of course you have to adjust AGC corresponding to WIKI. If you do malsetting to AGC your RX can become deaf, of course.
vy 73
Andreas |
Title: Re:mcHF 0.7 STM32F7 2048kb: Phantom signals 24khz above real frequency
Post by: peter_77 on 12. November 2018, 16:19:33
Fully agree !
Its mandatory to switch on IQ autocorrection ! And if you correctly tune RX gain and also the AGC and AGC settings everything works just fine. The RX is even more sensitive as an IC 7300.
That can be proofed either on mcHF as well as I40 and SParrow !!
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Title: Re:mcHF 0.7 STM32F7 2048kb: Phantom signals 24khz above real frequency
Post by: DL4SM on 13. November 2018, 22:51:04
Hi again,
if I want to use the manual setting of RX Phase and RX Balance it doesn't seem to have any effect on the signals.
When I use the IQ auto correction the signal levels drop by approx 30dB, but the noise level also drops by about that amount. So the signal stays as clear and loud as before
Not using the manual settings just confuses me, but if only the auto correction for the RX works, I probably have to live with that.
The Phase and Balance settings for the TX works though.
vy 73
Sascha
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Title: Re:mcHF 0.7 STM32F7 2048kb: Phantom signals 24khz above real frequency
Post by: DF8OE on 14. November 2018, 06:56:45
You are doing definitely something wrong.
RX IQ manual setting works like a charme if you follow *exactly* the WIKI. Of course it is only some dB better than auto-IQ at exact the two reference frequencies at 80m and 10m and much worse at all other frequencies - it is just an iteration there ::)
Auto-IQ does not touch my noise floor at all. It does not change the noise floor in any way.
EDIT:
The phantom signal 24KHz above working frequency (@Xlate -12KHz) is the result of a bad RX IQ setting. It's exactly the math which clarifies it. You can suppress it perfectly by auto-IQ (strongly recommended) or via manual settings on 80m and 10m. All other bands are just fixed linear approaches so do not reach auto IQ which works dynamically.
EDITEDIT:
If auto-IQ has impact on your noise floor but not at suppression of unwanted mirror and manual IQ does not work, too there is a hardware issue in IQ chain. Begin with verifying if both LO signals are present on the mixer, then follow each path from the secondary winding of T1 up to the correspondent output to the header to UI board.
vy 73
Andreas |
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