LIME MINI USB testing TX on HF Bands

[IK2NBU]

Hi Guys,

I'm a long time radio builder, and I'm planning a hybrid analog/digital RTX.

I am testing RF output with a spettrum analyzer using SDR Consolle with LIME MINI USB on the HF band TX (setting 3 MHZ Hf-TX)

In some bands, even if they are very rich in harmonics, the problem will be overcomed with a good filtering before RF amp.

But on some HF bands it is not possible to remove a spurious signal at only 500 KHz separation from the transmission frequency, you can see 2 attach images in the 7 MHz band.

Even setting everything to minimum like SW drive and TX doesn't change anything, the spurious frequencies remain the same.

Suggestion please ?

73 Arnaldo www.ik2nbu.com

[Simon G4ELI]

Hi,

Look at the available Lime options. I can't see them without connecting a Lime, I'm busy elsewhere atm.

Maybe show me the options you've selected?

I seem to remember there's a TX calibration somewhere.

[IK2NBU]

Dear Simon,

my normal setup on LimeMini USB:

Bandwidth = 3 MHZ (HF-TX)
Drive Level = Minimun - 40 db / Max - 10 db level
Mode TX Half Duplex
Antenna: auto for both
Calibrate RX and TX passed
TX streaming : 0 ms
Test and measurements with TX in AM 50% carrier

I'll post the screenshots tomorrow.

I repeated with various levels of RF drive, the spurs are always there, only 2 bands, the 1.8 Mhz and 18 Mhz bands are saved which are clean (see 2 images).
All the other HF bands they have spurs very close typically to 500 Khz, and there is always a fixed spur at 30 MHz.

73 www.ik2nbu.com

[IK2NBU]

Complete LIME screenshot,

the only error is the TX calibration, even with the maximum output drive level (0 db) it gives me a low drive signal message.

73 Arnaldo www.ik2nbu.com

[IK2NBU]

I found the way!

I did the TX calibration at 70 MHz and then I went back to HF. The spectrum result is completely different, and I can operate in HF with good mandatory low pass filters. There is no trace of spurious frequencies near the HF carrier. The trick was to do the calibration in VHF.