Low cost Software Defined Radio (SDR) Panorama

Here is a new and promising RX/TX SDR project for all platforms... (!)

Development is ongoing (V1.1.0 at current time) but it will evolve for sure.

The particularity is the full integration of digital modes beyond the FFT/Signal processing/Classical interface.

Can be used locally or remotely.

I'm absolutely convinced we will hear about it in the following years.

Not yet installed in my lab... But it won't be long now, believe me !

Will keep you updated on my experience...

Github : https://github.com/dividebysandwich/sdroxide/

Manual : https://github.com/dividebysandwich/sdroxide/blob/main/docs/USER_MANUAL.md

Let's restart a series of "ultra simple SDR" !

Yes, you can build extremely simple but still efficient SDR with basic discrete components (transistors, diodes...)

Remember my posts on "Tiny SDR" or on "QSD/QSE HF transceivers by Tasić Siniša-Tasa"...

Those 2 first examples of this new series are presented by an Australian HAM (VK5TM) inspired by another well-known Australian HAM (VK3YE)

They are not "I/Q" designs, but simple down-mixers... Thus you will have a folding of upper and lower side bands on the same baseband... But for reception of narrowband signals (as seen on HF typically) it is not mandatorily a tremendous issue :

• You degrade NF by 3 dB, but frankly not a problem for HF
• More important however, you might have signals from both upper and lower sidebands "falling" on the same baseband region and thus interfering. But from a "statistical stand point", with narrowband signals, this do not happen so much ... And for the price, do not complain   ;oD

14 years ago, I published a scoop on the growing MATCHSTIQ family from EPIQ   Take a look at the complete catalog here : https://epiqsolutions.com/product/sdr/overview 

The MATCHSTIQ family has now expanded significantly, with products incorporating 1 to 4 RX, 1 to 4 TX, having 50 to 2000 MHz instantaneous BW, tuning 6 to 18 GHz of max RF frequency, and presenting digital dynamics from 60 to 75 dB...

...And new families have appeared, like the SIDEKIQ family.

The today's article is on the smallest form factor "Z2" for portable or drone's application for instance, and probably the less expansive product of the family (still in thousands of $ however)

Datasheet is there : https://epiqsolutions.com/hubfs/Epiq/Epiq%20-%20Datasheets/Epiq%20-%20datasheet%20-%20Sidekiq%E2%84%A2%20Z2.pdf?hsLang=en 

As you can see, it is based on a well known combination now : an AD9364 RX/TX direct conversion frontend + ZYNQ FPGA !

With its 8 grams, it is intended for systems where consumption matters, but still consumes 2 to 10 Watts, much more than a conventional "specialised receiver" with much narrower band capabilities... This is price of flexibility with SDR !

Among the lowest price SDR's, the RTL-SDR family is well known (see my old posts)

Based on TV/DVBT chips, most of them cover from low VHF to about 1.5/1.8 GHz because of this primary usage. Limited to 8 bits, you get what you get for the (very low) price. But it is OK for an amateur usage or for quick lab experimentations (I know some experienced radio pro using it.... Much less heavy than an HP or R&S machine on your desk   ;o)

Some people have extended their coverage down to HF, either via an HF upconverter, either through direct sampling for last versions of RTL's BaseBand-ADC/USB interface.

The RTL-SDR V4 from RTL-SDR.com was from this last category ... But we just learned it is no longer available...

It seems RTL-SDR.com is preparing a "new V4"...

RX888 family is a 16 bit / 32-64 MHz BW commercial SDR receiver inspired by BBRF103 SDR open design of Oscar Steila (IK1XPV -- You can find all data at this address : https://github.com/ik1xpv/BBRF103)

It is based on the LTC2208 ADC and a CYUSB3014 for USB3 handling.

One of the rare large bandwidth SDR not using an FPGA and directly connectable to a PC.

I had bought a "Mark1" in 2020 which is very close to the "MarkII" available today (differences are on the RF input probably a little bit more linear on MarkII)

HF (1K to 64 MHz) is direct sampling, V-UHF (64-1800 MHz) is down-converted to a 10 MHz I/Q baseband by a RD828D (vs a R820 on Mark1)

My experience is :

• USB3 is mandatory
• You need a relatively strong PC to benefit from 32+ MHz band
• It works well with HDSDR (my preferred) or SDR console
• RX only, no TX
• 16 bit --> relatively good dynamic
• Relatively good sensitivity (probably better on MarkII)
• For top sensitivities and purity, filtered LNA's needed in V-UHF
• (but like for majority of wideband SDR, no miracles)
• Not equivalent to a top ultrahigh resolution SDR (24 equivalent bit or more) or top classic receiver based on filters... Or combination of both ... But still a solid performance !
• And this for less than 200$...

Indeed, as for every SDR or superhet/SDR, you could increase dynamic by constructive decimation - 1 additional bit per 4x BW reduction with proper hardware filter on baseband --> 20 bits if BW reduced down to 250 KHz for instance... But you must insert a BB filter and I do not know any public software providing decimation, other than the one we are doing by ourselves ... Unless somebody know some, and I'm then interested !

Few other links on RX888 :

https://elekitsorparts.com/some-truths-about-rx-888-mk2-sdr/

Link on Mark1 : https://sdr-prototypes.blogspot.com/2020/10/rx888.html

Initial BBRF103 design : https://github.com/ik1xpv/ExtIO_sddc/blob/master/hardware/BBRF103/BBRF103_posts_2017_2020.pdf

Techmind review of MarkII : https://www.rtl-sdr.com/techminds-reviewing-the-rx888-mk2-software-defined-radio/

A review in French : https://on5vl.org/rx888-mkii/ 

Some SW supporting RX888 : https://rx-888.com/rx/guide/clients.html

I said I "was back", partly because of the recent availability of medium to high bandwidth SDR at (relatively !) low cost ... This site, exhibiting multiple "crowdfunded" SDR projects, is a good illustration of the trend I mentioned.

Browse it, you will find many designs, their funding status, their commercial availability, and, most importantly, technical details.

Here is another interesting one, because of :

• Its price (around 190€)
• Its RF coverage 24-1800 MHz
• Its instantaneous BW : 10 Msps --> 9 MHz
• Its ext clock input (like few other)
• Its robust packaging and robust USBC
• Its ease of installation
• Its "3 radios / 3 USB in a box" version
• Its architecture ("kind of" RTLSDR but at 12bits vs 8bits, and with a triple core LPC4370 MCU instead of RTL chip- No FPGA)

It is very close to Airspy R2, the difference being that it uses a Rafael R828D tuner chip, instead of the Rafael R820T2.

Last but not least : Everything is open source : https://github.com/hydrasdr

Can operate on PC, phones, tablets, under Windows, LINUX, MAC, Android, with many SDR SW .... But in particular SDR++ ( https://www.sdrpp.org/   Will maybe come back on this one later...)

Datasheet link : https://hydrasdr.com/downloads/HydraSDR_RFOne_Datasheet.pdf

The WEB-888 is somehow a "cousin" of the RX-888. And as its name mention it, it has been designed to ease its connexion to ethernet/internet.

It covers few KHz to around 60 MHz on "HF" port and 115 to roughly 150 MHz on VHF port (thus aviation band that you can "see" in its (almost) integrality and 2m amateur band)

You can use it on local machines connected to your network, or remotely through internet (privately or publicly)

It is fully compatible with the Kiwi-SDR environment, and, BTW, considered as being better than the original Kiwi-SDR radio... Well, 16 bits versus 14 bits, thus for sure, at least 90/95 dB global dynamic versus 80/84 dB.

Once again, let's keep in mind that if 16 bits over 60 MHz BW is definitely acceptable for an amateur or a radio installation under "low stress", there is no way it would work correctly for a "radio transmission center" type of installation, with TX transmitting not far from RX, or other "highly stressed" situations. For those kind of environments, you would mandatorily need higher resolution SDR, and/or more conventional receivers with well positioned protection filters (superheterodyne before A2D for instance), and/or, generally speaking, proper RF filters for specific sub-bands of focus ... Life is a perpetual tradeoff, right ?

This being said, for the price (below 270/300 $) you have a serious perf/cost ratio, than you would have not been able to find even only 5 to 6 years ago !

Another example of today's "MHz instantaneous bandwidth" SDR. This is an experimentation platform from Analog Device to expose their AD936x I/Q transceiver family. And you can buy it for as low as 225 $...

Now, let's keep in mind that :

• It is a 12 bits platform - Dynamic won't be exceptional
• AD936x is largely integrated, with a "certain success"... Be careful with procurement for medium/large volume
• Large integration is nice, but increases your dependency to the supplier....

And let's restart with "KiwiSDR". It appeared few years ago now, providing a direct sampling (with 14 bits resolution) of a roughly 40 MHz bandwidth. It is based on a LTC2248 ADC and an ARTIX7 FPGA for processing and transfer (of whole/partial spectrum representation + chosen radio channels)

It quickly had success as a remote SDR for VLF/LF/HF which led to a well developed global receiver network (Map here for instance : http://rx.linkfanel.net/   an addition to the WebSDR network I presented many years ago !)

You can indeed precede Kiwi board with a V/U/SHF converter for higher operation, using Kiwi as an IF. But very few can be seen connected on the web.

KiwiSDR, mostly intended for HAM radio enthusiasts or educational purposes, has been also founding professional applications. It is very easy to set up on the web as a remote receiver.

With 14 bits, do not expect to compete with a conventional high grade HF receiver in terms of dynamic, blocking and other saturation. But it is largely good enough in most of the situations, even with a big antenna (0 to 31.5 dB attenuator by 0.5 dB steps integrated @ input) particularly if you notch the MW band at input which induce pretty large signals in some countries/locations.

In any case, a very interesting performance for the price...