For that frequency you really don’t need an LNA. You don’t even need an RF transistor. Most general purpose amplifiers will work fine. A good antenna would be the first step. But, yeah, I get nothing at the LW frequencies with any of my HF antennas.
@sboyce - Sid,
Lance is correct - right now your tuner is set to 20.802MHz (where you’re actually tuned) and you’ll have to have NCO turned on and the DC button activated to remove the DC spike in the spectra. Sampling rate is set too low, too, as it’s at 500 kHz ans should be set to something like 6.000.000 or 7.000.000. If you make those adjustments (NCO, DC, and set sampling rate to 7.000.000) then you should be able to tune into the LW band at 198 kHz. Give it a try and report back. If I don’t answer immediately, I’m working on a large home renovation project that is an all-day task and I’m checking the forum at night here - so do bear with me. Either I or Lance will get you going.
73 de Marty, KN0CK
You have the Lo antenna selected. It is for low cellular, 700-900MHz. Try the Wi, Wide band. It is still too high for 198 KHz but does pick up some signal. Lo is pretty deaf at that frequency. Otherwise you are almost there.
I asked for the HF mod but got mine with MN18 still installed so I removed it and the antenna is connected to the SMA connector above T3 (RX1_L).
Selecting Antenna Wi instead of Lo everything is quiet unless I turn off squelch which then just brings up wideband noise but no signal.
What about FIR setting?
Ah, yes. Turn that off. I think that is around the center frequency, not the NCO frequency. I will do a test. I was just listening to some 20 meter.
Edit: No, I am wrong. It works around the NCO frequency.
Further: Using the same settings as you I got the same result. Bumping up the sample rate to 17,000,000, H at 4, S at 32, everything else the same as yours, and I am able to barely copy a tone at 198. It may be just a birdy but the spectrum looked good. Definitely a birdy. I can’t go below 12M on the sample rate without loosing the signal to a blanket of noise.
No luck on 198KHz.
Tried 20m but only one French station seen on 14.126 on my HiQSDR with the 2-el Quad - Q5 S3, nothing on the LimeSDR with the 40m sloper.
I’ll swap antennas later.
I noticed a strange effect. As I change the sample rate images of far away frequencies would appear across my waterfall. When I zoomed out the software sample rate I could see these images marching across the display as if they are wrapping around the ends as the sample spectrum widens or narrows. At one point I had some CW and SSB from 20 meter that was as clear at LW as it was at 14MHz. There seems to be a need for strong image rejection here.
Are you using band preselector filters?
These are must with SDR.
Only a 30MHz lowpass. I thought that would be enough. I works good at 10 and 20 meters but at LW for sure.
That’ll kill the FM images but SDR is basically a wide open front end so any big signals from anywhere in it’s gigantic passband will create images, so in your case you are blocking the top 30Mhz of the front end while allowing everything below 30 to be processed all at once.
What you need is a band specific preselector to remove everything except what is in the band you want to listen to before it hits the front end for processing.
Sv1afn has one that I am using and it works great.
Image rejection is really a quality of analogue front ends, this is all direct digital down conversion here so digital rejection filters on a 60MHz front end will only get you so far.
I’m curious which BPF you are using and how you are finding it… he has a few different ones.
I’m using his HF Bands Preselector, it is a long red board…
The design is good and the component choices give a good filter cut off profile, the pass bands are decent with pretty low attenuation.
My only complaint is the board choice, it is rather thin so that centre mount hole really does need a stand off under it as well for anything portable.
Performance wise it does the job, out of band images are knocked down effectively and the noise floor drops bringing the signals I want out of the mud.
I was thinking of giving some of his other designs a go as well, they aren’t expensive and can be used in front of my tube rigs if they aren’t up to SDR standards.
I use the preselector in an Atlas350xl … its variable freq and about 40khz wide
I looked over the circuit diagram and found RX1_W and I presume that’s what you refer to.
In that case should I remove inductor MN26?
Here using LNA4HF with 30 MHz low pass combined with FC-707 and/or PRC320 front end
antenna tuners. Some times also tunable ferite antenna.
73
Dj
Whichever chip inductor that is between the rf transformer and radio IC … ill send you a pic of my lime in a bit
@sboyce - Sid,
I’m using a 30 MHz Low Pass Filter that’s made by Kenwood (LF-30A) that’s been effective in removing anything above 30 MHz for the LimeSDR, but practically any good lowpass filter will work that has a ‘knee’ at 30 MHz or even up to 6m (50 - 54 MHz). You only need it for receive to remove the FM images that the Lime will pick up because of the response of its own front end filtering, but it would also help on transmit to remove any spurs above 30 MHz/50 MHz prior to amplifying the Lime’s output, too.
73 de Marty, KN0CK
@sboyce - Sid,
Here’s a link to an article I posted back in February (if my crumbling memory recalls right) pertaining to the location of the capacitors that need to be removed for the Lowband and Wideband ports on the LimeSDR:
There are other threads that follow it, including the Lime Microsystems post on the matter, that describe the ‘Easy-Fix’ and the more involved fix with replacement parts - - All I’ve ever used is the ‘Easy Fix’ for receive and it works fine.
Let me know if you have any questions or comments on this -
73 de Marty, KN0CK