I just check AM at 9840. Hermes board -46 dBm. LimeSDR -96 dBm. I did find the LNA_H port was about 8-10 dB better than the other two RX ports.
Guys, be careful how you compare different receivers. Do not compare absolute signal levels (dBm) because (1) it needs calibration and (2) even calibrated, different hardware can have different absolute levels.
I know many SDRs display ādBmā but itās mostly nonsense unless the device really has been calibrated across the its frequency range. Try to measure the signal to noise ratio instead using similar bandwidth and FFT settings.
@csete Alex, which ever way you view it, the signals are in the mud compared to any sdr, even an rtl/upconverter combo is better on HFā¦ And the difference on the 1.2 to 1.4 boards is clearly down, see @martywittrockās samplesā¦
Yeah, I had similar experience when I tried some time ago with my v1.2 board.
@nn4f_radio as stated elsewhere, a comparison of a v1.2 to a v1.4 board at this stage is not conclusive, since we have not ruled out possibility of firmware/software changes. Improvements have previously been made after discovering transceiver configuration/programming errors and correcting these.
Hi Andrew,
Iām not sure if I understand you correctly. Are you saying that the v1.4 board needs to be looked at, firmware and/or software wise, to bring performance in the 100 kHz to 30 MHz up to standards? And will this action be taken?
Waiting here for my LimeSDR and I canāt say that I am happy with the news on performance in the 0.1 to 30 MHz frequencies so far.
Alex,
You are 100% right. So I went back to my Hermes and set it for 3 x 384k stitched receivers. 1.1 MHz BW. FFT set at ~ 11 Hz
On my Lime, 2.5 MHz BW was the lowest I could select in SDRConsole. FFT showed 9.5 Hz
On 9.505 MHz, strong religious broadcaster, Hermes showed peaks at 70 dB above the noise. Lime showed 45 dB.
Not 100% scientificā¦ But this is typical of what Iām seeing.
Mike
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Thanks for the update Mike.
Alex,
Just so we have balance here (and Iām in the HF camp and always have been), what has your experience been as far as performance of the LimeSDR running it on the Weather Satellite frequencies as compared with other SDRs youāve used? I just want to know if itās better or worse. Let us know your opinion for 100 MHz and greater (frequency) performance.
73 de Marty, KN0CK
I check schematics , the input circuit is designed for > 700MHz only , so If you need low frequency you must modify input circuit. The spec. of LM70002M is 100KHz-3.8GHz but I donāt know why Lime design team designed input circuit very bad, there is no input filter as RTLSDR or SDRPLAY. There is no way to improve HF by software , you need to mod input circuit for using with HF.
@martywittrock It worked well and I have posted my results while the crowdfunding was running. I have not done any side by side comparisons to other SDRs.
At this point there is so much confusion between hardware/firmware/driver versions, theoretical specs vs. practical experiences that I think I will stay quiet until I have my device in my hands and can do more tests.
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There is no hardware mod to improve the low frequency sensitivity.
I did some measurements and found there is a small internal capacitor in series in front of the LNA. It results in a high input impedance with - even more important - a high Q at low frequencies. Such a network can not be matched at a wide bandwidth.
Lime seems to be aware of it. Or why do they specify the input parameters only down to 100 MHz?
I was using SDR Console for tests above 6m and posted a few picks here. These are NOT lab tests but I work on the theory that with the exception of a few WSJT modes that I can SEE a signal long before I can HEAR a signal on VHF SDR. I know nothing about HF but on 6 and 2 the Lime, when viewing the beacons I can see, looks about as good as a TS2K. I know that is not what most of you want to hear but even a TS2K can be made very usable on 6/2. As with the TS2K it needs a LNA to bring it up to the standard of a FCD+. But remember the FCD+ on VHF is a better RX than most of the older rigs such as a 756 or 746pro. I think from my own experience the only one of the rigs from that era that comes close to the FCD+ is the 706MK11. I am happy at what I am seeing on VHF. I will wait for the Lab Rats to give the noise floor and all the other dBm readings but to me it is proberbly the best 2m and up TX/RX SDR rig out thereā¦
My EME tower and antennas are out on loan so I will have to wait until the snow melts to get them back and test the Lime on EME RX.
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Is there a schematic of this that supports this ?
I would tend to believe you, but id like more information ā¦
What is the characteristics of the first LNA ?
The parameters you ask for can be deembedded from the given S-parameters. At low frequencies the circuit can be described as a resistor (kOhm) in parallel with a small capacitor (some few pF) and the DC blocking capacitor in series in front of it.
There has been a discussion on this subject at Facebook/LimeSDR.
Im on Facebook/LimeSDR ā¦ perhaps there are more than 1 ā¦
Iām on it - as an Admin, tooā¦ 
I didint see a discussion about signal loss on low HF ā¦
and i dont think im seeing 80db on 80M attenuation ā¦ more like 15db compared to my UHFSDR ā¦
I need to put an attenuator on the crystal calibrator to see if UHFSDR/LimeSDR show the same signal reduction ā then the claim of 15db should be accurate. My UHFSDR uses a SPF5043 for its LNA.
I cant work out the expected gain/freq sweep from the S-parameters. I donāt have a program to use them.
Though a -J300K in parallel with a 5K resistor ā¦ is basically 5K.
Dear Marty,
Please could you give me your e-mail address.
Here is mine: malet-bernard@orange.fr
Best regards
Bernard