Hello Radek,
Thanks for looking.
I also feel mislead if this is the case.
Let’s hope that it is only a software issue.
Someone else try to transmit below 30 MHz?
Regards Ben
Nils,
I understand…The EU is nothing to mess with - that’s why we ‘Yanks’ get our ducks in a row when we have to work with EU Members, too. You’re doing the right thing…
73 de Marty, KN0CK
I did some rough simulations for the Tx_L in LTSpice, the 100 nF coupling caps should present a dead short even at those frequencies so the output filters should be capable of transmitting until ~ 1 MHz.
I think what you’re seeing should be a software bug on GnuRadios side, masking a silent exception. I checked the source code on GitHub, and without checking whether the registers themselves even support tuning in the LMS7, the tuning code won’t support going lower than 29.687 MHz (3800 MHz / 2^7). Relevant lines are 40, 1245 and 1261-1271. https://github.com/myriadrf/LimeSuite/blob/2c63118350587785ab0ec8b25ea758ab1ce537a5/src/lms7002m/LMS7002M.cpp
^ Just verified the above with LimeSuiteGui, It will let me do 30 MHz but throws an error when trying 29, mentioning the lower 3800 MHz limit on one of the VCO’s. I think to actually go lower in GnuRadio, you’ll need to set the frequency to 30 MHz and then use some additonal programming features (?) to set the TxTSP NCO module separately to get what you want.
I’ll try hooking it up to my scope tomorrow and seeing what kind of response I can get both at 30 MHz output, and using the NCO’s to tune lower. I need to go dig through my crap and find my SMA-BNC adapters.
Slightly relevant note, I think the next version of software needs to expose more of that NCO tuning ability to get that, or provide some combined analog+digital frequency selection capability.
NCO relate to digital IF and using to reduce the frequency of digital IF (base band) . If you want to transmit at frequency lower 30MHz it is more complicate .
You need to make a proper transmit IQ IF signal (by software ) and mix it with TXPLL frequency , at output you will have signal that frequency is different of IF frequency and TXPLL . Control IQ waveform of IF you will have low frequency signal you want .
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@pe2ben, @Mrkva, @Kryan92, @sdr_research
It is possible to transmit below 30 MHz with the LimeSDR. I used LimeSuite (which at the time was called LMS7Suite) to downconvert from 30 MHz to transmit from 29 MHz to 1 MHz. I’ve done it, it’s possible. Here is an excerpt from an email back in April of 2016 to the Lime Team discussing it and a video that proves it:
Pull down the video and see for yourself the work I did a year ago on this so you can learn from it. Take this information and play with it in LimeSuiteGUI - - it’s totally doable in LimeSuiteGUI and in future software apps.
73 de Marty, KN0CK
@Mrkva What you refer to is in Table 5: Synthesizer specification! This means, it is the Output Frequency Range of the Synthesizer, not the hole system!
73 de Sabine, OE1YVW
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Looking at the schematics again at Tx1_1 … id say that for HF and who knows for vhf/shf … MN8 and MN5 should be 100pF>(MN8/5)>1pf … the last capacitor in that chain is a 100pF(C6)
Nice video. Did you do the tuning and config from the LMS GUI with RF sample data coming from some other program?
@sdr_research, the LMS7 chip has a built-in complex mixer with a programmable NCO, so you don’t need to do anything baseband or program side besides programming the correct tuning settings (and possible interp/filtering settings, haven’t touched those yet).
@Kc7noa, that last cap might actually be a typo in the schematic (or worse, a bug with the hardware). The 1v4 schematics show Tx1_1 C6 AC-coupling cap is 100 picofarads. While on the next page, the Tx2_1 C26 AC-coupling cap is 100 nanofards, which is inline with what I’d expect for a low frequency cutoff.
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using foo_limesdr plugin ,I can send FM signal on 15Mhz
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Seems my limeSDR went through customs and will be delivered sometime next week. As mentioned before I joinend the campaign looking for a radio going all the way from 100 kHz up. After some back and forth we were presented with a a whole bundle of solutions to achieve this.
In terms of functionality the best option seems to be to modify the broadband input, because it does not hamper the performance in the other band plus it gives the smoothest response.
Unfortunately I will not be able to implement the more complex of these, because there is no way for me to replace SMD parts, nor do I have a source for the replacement parts.
I would highly appreciate if Lime Microsystem would provide a service to do the modifications. neccesary. If this is not possible they should provide the parts needed, so I can try to find a local to do the modification.
Any thoughts on this?
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@pe2ben, @Mrkva, @Kryan92, @sdr_research,
I wanted to pass along some more information on how I did transmit in the HF band and I found this nugget from almost a year ago…Uses LMS7Suite (which is now LimeSuiteGUI) to get a CW carrier into the HF band where the reference frequency to mix is at 30.72 MHz. Here is a snapshot of the email I had with Ricardas on this nearly a year ago:
Use this information, along with the video I posted last night to get this working.
@Kryan92: No other app was in place - I just used the (then) LMS7Suite (now LimeSuiteGUI) application straight to generate the CW carrier to get into the HF Band, but I’m sure I/Q can be applied to the Lime to modulate it - @jocover has done it in an FM sense.
Hope this recent information coupled with my efforts nearly a year ago help your efforts now. If you have any questions on any of this, please feel free to ping me on it - If I don’t have the answer, I’ll find it for you.
73 de Marty, KN0CK
First off, I have to tell you that your foo_limesdr application is REMARKABLE…! I love it…!! But can I be a little selfish and ask that other modes be added to it - specifically, LSB, USB and CW in your app? One other request if I can make it…Instead of the file playing, can you attach the audio to a live microphone stream in your app, too…? Both of those additions would be GREATLY WELCOMED by A LOT of Lime users for transmit.
Continue your great work, @jocover,
73 de Marty, KN0CK
Ok … yea, Tx1_1 and Tx2_1 do not match … probably populated with 100nF
It looks like the C6 on my board is a 100nF one, so this is probably just an issue with schematics.
Anyways, I managed to transmit with Gnuradio to dummy load and noticed sharp drop of performance at 25-30MHz:
50MHz 0.8Vpp (voltage across the 50Ohm dummy load)
30MHz 1Vpp (also the signal starts to look quite not-sine)
25Mhz 0.8Vpp
20Mhz 0.2Vpp
Going to try the LimeSuiteGUI next.
Your using Tx1_1(Tx2_1) i assume …
Yes, I don’t think TX1_2 and TX2_2 would work for these frequencies at all.
Hi @Nils please note that the LimeSDR is not CE certified, since it is provided for use as a development board and a component that is part of a larger system.
dang … thats quite the drop off … wonder if its related to a gain stage. At least trying to keep a sinosoidial waveform …
25Mhz 0.8Vpp
20Mhz 0.2Vpp …
That’s 0.1v per 1Mhz with a transformer that’s rated for .18db insertion loss @ 4.5Mhz (unless you look at the other PDF’s charting that says 1db loss)…
MN7 impedance at 20Mhz would be about 4K – not enough to show that kind of drop.
MN6 should not be populated …
What is the response of the coax your using? does it have a low end specification? – kinda doubt this is an issue , but never hurts to verify.
Opss , was thinking db and not volts …
That drop is about — what, 1.2db … not too bad … but id like to have a flatter response till the 4.5Mhz point is reached …
… thanks, Andrew- so it cannot get lost of the CE certification by modification … 
At least in Germany, as such the board must be used (not sold to - but that’s another story …) legally only by hams with a valid amateur radio licence plus some professionals exclusively on their job within their institutes. This excludes the by far bigger scene of just listeners, makers and hackers. As customs and law enforcement agencies usually don’t know about these exemption in the R&TTE Directive of EU, some people already had run into serious trouble even when importing such devices. Thus, you should make clear this point to your customers.
My other question still persists: Will these boards which hadn’t been delivered after the 100-kHz-topic had been discovered (as mine), delivered with the modification made by the producer or not? I would rather prefer that they should be delivered to their specifications, even if there will be some delay.
I am very curious how LimeSDR will perform on HF, as I will publish a story in Germany’s largest magazine about that.
Best regards: Nils
12dB when calculating power level, or 2.4dB/MHz, if I calculate this right.