RF product - moRFeus - frequency converter and signal generator


#1

Hi Forum!
We’re launching a new RF product soon. It’s not a core Outernet product, but a spin-off from technologies the team ended up developing for other reasons. We’d like to get your feedback on the pre-launch page on Crowd Supply and, in particular, find out what questions you have (or think other people may have) about the product. We’re building out FAQs and want to know what to address. It’s for hackers/hams/RF tinkerers/etc. We also have it on the Outernet website here. There’s a data sheet and user guide on the website. Any feedback would be appreciated!
Thanks
Kara


#2

Kara,
This is really the basis to a lot of projects I wanted to do after Outernet. I’m assuming it’s a double-balanced mixer and a synthesizer for the LO.

Ideas: Basis for a home-brew microwave transverter for 1.2, 3.3 or 5 GHz ham bands.

Questions/comments:

  1. On Features, LO Step size … the superscript does not seem to render on Chrome.

  2. On the second gif, there is a setting for Bias Tee on/off. What is the voltage range you can supply on that? It’s not in your specs.

  3. Can the LO be swept? Is that something you’ve considered?

  4. What is your conversion loss, assuming that your RF signal is at an optimum level?

  5. Can it the LO be switched? Eg. can it switch between transmit and receive to accommodate a split?

–Konrad, WA4OSH


#3

Tagging @zoltan on this.


#4

Hi Konrad,

Answers:

The mixer is a wideband, double-balanced Gilbert cell type.

  1. LO step size:" Step size is frequency-dependent. Lower step sizes (1-2Hz) are characteristic of lower frequency domains and higher step sizes (2-3Hz) of higher domains."
    https://cdn.shopify.com/s/files/1/0770/0935/files/moRFeus_Data_Sheet_v1.6.pdf?7851427270568564511

  2. Bias Tee voltage is 5V (minus some loss on the FET switch) its fed by USB voltage.

  3. From USB-HID (now only Linux environment) users can control everything. I think it’s pretty quick to make a script realizing the LO sweep.

In standalone operation from FW this is not realized now. Altough this could be a clever milestone for upcoming revisions. Thank you for such feedback!

  1. Conversion gain (loss) is in page 2 of the datasheet shared above.

  2. Switchable LO is again a very good idea! This is not in the FW yet but we can put it to the list I think. From the USB-HID command line this could be also realized remotely.

Please mind that the input and output ports are not interchangeable in this particular mixer configuration. So for full duplex operation one might use 2 moRFeus or RF switch networks (we also have ideas to add switch network to the roadmap).

What do you see a good idea for TX/RX switch? Possibly a single digital input pin is good for that?

Thanks,
Zoltan


#5

Zoltan,
How would you build a half-duplex analog or DVB-T transceiver with this as a basic building block? Yes, possibly a single digital input pin.

How would you select between two LO frequencies for a repeater offset or for a satellite up/downlink selection, etc.? Yes, a separate digital input pin.

Don’t tie these two together and it gives you more options.

Eg., this could be the basis for a LoRa terrestrial radio on 1.2, 3.3 and 5.9 GHz using the SX1280 chip, which you already know how to use (or buy on E-bay). Now the frequency offset is not a duplex offset selector tied with the TX/RX line, but maybe an in-band frequency select.

–Konrad, WA4OSH


#6

I missed the datasheet entirely.

Mixer performance … 4000 MHz twice? Is that a typo? Did you mean 6000 MHz?

–Konrad, WA4OSH


#7

Zoltan,
Did I miss this? Maybe there should be an RF ON/OFF key or blanking line to prevent moRFeus from generating RF when output is not needed.

–Konrad


#8

What is the biggest differentiator from using commodity parts and, say, a HackRF One knock-off from China ($170) or something like this?

The “Freq and Tx power” graph on the datasheet needs its axes labeled and maybe some clue on how this was measured?


#9

HackRF has a Software Defined Radio in it, this does not.

Think of this as a down or up converter.

–Konrad, WA4OSH


#10

I recently have been shopping for a signal generator. The Seeed rf explorer was at the
price point I was looking at.

This moRFeus seems to match my needs with the additional mixer capabilities. I do find the
phase noise to be very favorable. But is it really step size of 1 , 2 or 3 Hz. ? I think you mean
kilohertz. The 2.5ppm precision is fine for my needs.

Update: to clarify: RF Explorer Signal Generator (RFE6GEN) is what I almost purchased:
see link:


#11

Yeah, so you could use the HackRF as a signal generator in this case and hook it to an external (cheap) mixer board…


#12

72-12865 - RF Explorer Model WSUB1G Handheld Digital Spectrum Analyzer

RF Explorer claims to be a Spec-An, not a Sig-Gen.

On E-bay there are a couple of Sig-Gens:
140MHz~4.4GHz Radio frequency signal generator band scanning function
54M-13.6GHZ RF ADF5355 Phase-locked Loop Frequency Synthesizer Board PLL VCO

Neither one have a mixer or LO though.

–Konrad, WA4OSH


#13

This is the signal generator I think that @ac8dg was referring to.

I got one of these mixers for $25 and have used it on a number of projects… up to 4 GHz. So the moRFeus has this as an advantage. So is the only real advantage that this is an all-in-one?


#14

Need to unplug micro USB


#15

Hi Konrad,

first row is “LO freq” set in morfeus
third row is " Input Freq " this is driven from a signal generator to the morfeus input port.
check " Output Freq " those are corresponding to that: 3000 and 1400 MHz

So no, that not a typo, but the LO was fixed, while the input test signal was changed.


#16

RF Explorer is a nice tool, of course you can build your own “morfeus” using some double sided tape and kitchen box and some flexible coax.

Possibly the biggest difference that RF explorer has 1000 Hz resolution while morfeus has 1.5…3 Hz


#17

no typo, it’s Hz!

actual LO settings swept manually by lowest decimal value (Hz). The FW allows (rounds to) only the select able values which was 3 Hz in this case:


#18

OK. I see that now. I glanced at the spec sheet during morning break. I think you meant columns instead of rows; I got it.

The conversion losses seem pretty typical - a little painful, but worth the conversion.

Do you know where its “sweet spot” is for RF in? This will let me know how much bandpass filtering and gain stages need to be put in front of the mixer.

-===-

Will that be Linux Mint, Unbuntu, Debian compatible?

–Konrad, WA4OSH


#19

Yeah columns, sorry my mistake.

Yeah, there are more ideal conversion gain mixers out there, but most of them much more narrow band, and / or more expensive, bigger etc. As always this is a compromise of a compact unit, what I think still practical.


#20

Konrad, what I know for sure that for USB programming a 64-bit linux machine needed.

Perhaps Linux distribution is not important, but @Abhishek can answer this who created the Linux tool for morfeus .

Zoltan