100KHz~30MHz

#1

Hello, I used EasyFix1 and EasyFix2 methods according to LimeSDR HF Performance, and the GQRX CDR was used for testing, which can only measure 5MHZ at the minimum. May I ask if it is ok to change the software and hardware like this?There is still need how to set or change, I want to test the short and medium frequency.

#2

in LMS7_Device::SetFrequency of lms7_device.cpp

There is some code that changes the NCO when you tune the frequency bellow 30 MHz. Looks like the code has been there for a few years, so it might have been broken for some of that time.

When I look at the transmit on the spectrum analyzer when tuned bellow 30 MHz, I see a >30 dBm spike at 30 MHz.

#3

30MHz spike is LO leak and can be eliminate using tx dc gain I and Q values.

#4

I did the matching circuit with EasyFix2 and changed the NCO value, but the test value was still not ideal.Given a 1M HZ signal with a signal source and limesdr the signal attenuates a lot.Do you need to adjust balun’s match?

#5

i believe @yt7pwr better able to answer those questions. I have not made those fixes to my boards yet.

#6

If I understand correctly 1MHz is minimum for your board but with high attenuation? What software are u using? What about settings for RX sample rate and RX LPF?
My board is not modified.

#7

@liang12,

I can actually weigh-in on this. If you do the Easy Fixes per the documentation that exists on the MyriadRF forum and website, you can tune down to 100 kHz, but don’t expect the receive sensitivity to be very good because the baluns are rated at 2.0 MHz to 2.4 GHz (or so). Further matching with external capacitors and/or inductors to the baluns was performed to optimize for the original use of the LimeSDR - - Cellular and WiFi - - but it was found later that if the capacitors and/or inductors were removed that the LimeSDR was perfectly capable of receiving into the HF range (2 - 30 MHz) without much extra modifications.

If you expect to spend a lot of time working in the 100kHz to 1 MHz range it’s going to force you to remove the baluns from the receive channel (RXH, RXL, WB) you want to experiment with and ‘roll your own’ 50 Ohm impedance matching network for that lower frequency and apply it to that receive channel. I will caution you that you have to be careful of those receive channels entering the LMS7002 RF ASIC - - they are super sensitive to ESD and you CAN permanently disable them if you do anything wrong while making a major modification - - so please use caution when making a large mod to your board.

Given all that - have fun with it.

73 de Marty, KN0CK

#8

Minicircuits has better baluns for lower frequencies in the same form factor. Something like 100 KHz to 500 MHz, if I remember right. Just look up the part numbers on Minicircuit’s website & find the right series.

Ed

#9

Thank you very much for your help. I will try my best!