LimeSDR mini HF mixer on 40Mhz clock out

For Listening to HF I first used the TX port to generate a sine into a ADE-6 Mixer. The drawback are: this takes up the TX port and there is no easy way to use gqrx for listening and generating the sine output at the same time.

Not long after that i realized that the mini has a 40 Mhz clock out, Although its a squire wave when measured on my scope the Vrms is 601mV into 50 Ohm. This would be between 8~9 dBm for a 600mV Sine wave according to this table

Connected up this the result:

Now i got some questions:

What is the power level of the 40Mhz clock output?
The Mixer is designed for +7dBm as sine measured into 50 only i’m feeding it a squire wave.

Can this clock be split up?
Next up is trying to TX at HF using the same mixer, so clock out connected to 2 mixers.
Can this be done without damaging the Mini?

Hello colleague!

I see a simple engineering solution to your question.
Output CLK it is necessary to load on 1-geytovuyu buffering logic of type 74LVC1G00 (04). After the buffer put the bandpass filter 40MHz of the 3rd order of the type “Ecliptic”. It can be simpler, such as a low-pass filter of the 5th order. After the filter, put the buffer amplifier type EPA-xx and the usual resistive splitter for 2 loads. If the levels are greater than + 7dBm, then we add attenuators.

Please describe which software are you using to receive and transmit?

Hi Alex,

Have to look into that idea, wonder if filtering of the squirewave is necessary because the mixer uses diodes.

The first test with the mixer on the TX port was done with gnuradio
For Listening on the clock output i use gqrx (see picture). With LNB LO set to: -40,000000 MHz
Have not tested transmit yet, although this could be done in gnuradio as well as in SDRangel.

Hello Pauluze

Now there are 2 types of mixers.
1 type: these are ADE mixers. In them, the LO signal participates in the mixing process. If we feed a rectangular signal to the input of the ADE chip, then on the output we get a very very dirty signal spectrum.
On the diode mixer it is better to feed a pure sine signal, then at the output we will have only the mathematics of signal multiplication.
2 type: it is a mixer on controllable logical keys (multiplexer). Such as 74LVC1G3157 or of similar ones. In such mixers, the LO signal is not involved in the process of signal mixing.

If you want to use the ADE mixer in your design, then it is better to clean the rectangular signal. In the worst case, it will be difficult for you to clean the output spectrum of the signal after the mixer. At the output of the mixer there will be a lot of false signals and digital processing NOT will help you.

If you want to use a rectangular signal from the CLK-out of mini-Lime, then use the mixer on the logical controllable keys (multiplexer). And be sure to use the buffer on the logical element. If you make 2 mixers (RX and TX), then use 2 independent buffers.

PS: This is the right engineering solution. In reality, you can do things differently much easier.

Thanks, seems like some more thought has to go into this in the future.
Might be nice to use a clock buffer with 3 or 4 outputs so 2 can be used for the mixers and the rest can be brought out to keep the external reference as well.

Would be some kind of upconverter with a rf bypass switch on RX and TX switched from the EGPIO pins. These pins are the only ones I and probably most user would be comfortable with soldering headers to.

Only i have seen no examples / docs for using the EGPIO’s yet. Also haven’t found drivers for this as well. Might be that this needs some fpga work first? With some clever work this could also drive some shift register or i2c and we could switch multiple switches and pre-selectors of these 2 pins.

I only recently received my mini-lime, and now I am deeply studying all the threads of our forum.
From the reading I realized that the task of external control of the transmission and external switching of the BPF was not solved yet. In one of the streams dedicated to the hamradio Marti wrote that he was interested in this issue, but I never saw the solution.

I would like to ask a question to Andrew or Zak.
For what reason in the Mini-Lime was the frequency of the card below 10 MHz restricted? The Lime-USB chip is exactly the same as the Mini-Lime, but for some reason the range of received frequencies is limited. Why?

As an example: I have an SDR Adalm-Pluto. Originally from the store, it was positioned from 300 MHz. But, a little shamanism on the command line allowed him to work from 70 MHz.

Is it possible to unlock the mini-lime access to frequencies below 10 MHz and get access to the full HF frequency section?
This action eliminates the need for the up-transverter to use the HF band.

If i’m correct it has to do with the LimeSdr mini’s design.
Also the LimeSDR USB doesn’t perform at its best at lower freq’s, even after HF Mod
For the LimeSDR USB there is some info couldn’t find it for the mini.

So not even up-converting with their own clocks (32.72 or 40.00 MHZ) brings us in optimal range.
On the LimeSDR usb you could use the second TX port to drive the mixer to a better range. The Mini on the other hand you only got one which would mean no more TX possibilities.

Hence me using the clock output, plus its synced to the lime. An other possible way would be to have to the fpga drive a clock on a gpio pin. That would require some fpga work above my knowledge, and takes up pins we would like to use for switching.

Still assuming most users only are comfortable with soldering the 0.1" EGPIO pins on the mini or the 4 user LED pins on the Limesdr USB, or even pogo-pins could be used without the need for soldering and warranty issues later.

Also seeing multiple user wanting to use GPIO pins for switching still needs a solution:

For the LimeSDR_USB there is the GPIO board (only 8 switches)
One could bit bang a shift register over the user LED on the MCU
Or Bitbang a shift register over the user LED on the FPGA

For the Mini haven’t found anything yet
There is the grove starterkit bundle, only that connects to a raspberry pi and not to the Mini

Both seem to have a I2C master in their fpga and i.e the temperature sensor can be read out from LimeSuiteGui. If something like I2C or RS232 etc could also be routed to the EGPIO / USER_LED pins, we still need drivers to access this from soapy, gr-limesuite etc. Last Software like SDRangel, GQRX etc need to support this as well.

So before pinging a lot of people i think should be involved let’s see what @andrewback thinks we should ask to help us.

Just to visualize

Alex_RK6AJE, your topic offering RF design help would be appreciated a lot for this, if there is a working interface.

Due to the different matching networks.

Hi Andrew!

I understood the idea. It’s not about software and digital limitations?
In Lime-USB we have several inputs and several separate matching circuits. We can modify one of the sites, as did Marty.
In Mini-Lime, there is only one matching circuit, which already works in ultra-wideband mode.

I propose the idea for Lime-micro: It is programmatic to make the entire available range of 0.1-3800MHz on the Lime-Mini, but to make a reservation about that below 10MHz and above 3500MHz, the performance of Mini-Lime is falling. Those who are well acquainted with RF-design, without problems, will be able to correct the matching circuits for good performance/matching at frequencies below 30 MHz. We will get an excellent all-band radio for advanced and novice radio amateurs!

I guess that more than 50% of people buying mini-lime are radio amateurs and they are most interested in the frequency range 0.1-1300 / 2000 / 2600MHz. So maybe they should give this opportunity? Even with a reservation about performance.

Now you have few competitors on the SDR market. Full-scale broadband cheap transceivers no one produces.

Hi Pauluzs.
An interesting good structural scheme. Give me some time, I’ll think about the circuitry part.

No, there are two each for Tx and Rx. See:

Hi Andrew.
I carefully studied the Mini-Lime scheme and the datasheet on the LMS7002 chip. Obviously, in datasheet there are no restrictions on 3 different inputs at a lower frequency.
On page 3 of the lms7002 datasheet in Table 2 “General RF Specifications” it is indicated that the lower frequency for all 3 inputs is 0.1 MHz.

In this regard, I would like to ask you to consider the issue of a special test firmware for me with a lower frequency of up to 0.1 MHz. I have measuring instruments and special equipment for mounting SMD parts. I can make measurements, perform research work and, possibly, based on the results of measurements, I could optimize the input circuits for HF band.
In the scheme of input matching circuits I do not see any difficulties, the scheme is clear and simple.

How hard is it to fix or make a new firmware with a start range of 0.1MHz?

I think this is probably a question for @Zack.