Tagged: dru-244

XMass_offer_ill_2_ver_on

SDR Radio equipment – It is time for a cool Christmas gift

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A smart Xmas gift? SDR radio Equipment!

Jingle waves, jingle waves, jingle all the way, oh what fun it is to not get socks this Holiday! Your children get the cutest vampire barbies, the latest Star Wars figures, and all the flying, beeping gadgets they asked for. Your wife is happy with her new shinny earrings because her friends and colleagues will be green with envy after Christmas. But what about you? Socks and ties again? No!

This Xmas should be different! Play safe and shop smart. Forget the huge watches and drones. You need something cool. What about an SDR Radio Equipment?

Top 3 ideas if you are interested in Ham Radio:

Beginner level – It is a beginning of a beautiful friendship with the waves. Check and buy Get on the Air with Hf digital Guide to know all what you need for becoming a Ham Radio.

Get_onDigital

Advanced level – Somebody dreaming of white Christmas. Who cares about snow? All you need is a really good HF antenna, get it here.

HF_antenna_illustration

Black belt Ham Radio fan level - Would you like to develop your Ham Radio station? Why don’t you enter the 21th century with an SDR platform like Quadrus SDR!

DRU-244A-1028bb

Have you ever heard about Black Friday? It is the day when the Christmas Shopping Season (your wife’s/girlfriends kind of madness) begins in the USA. In the last couple years, this day became known globally, so these days most everyone can make good bargains in November.

Our special offer Quadrus SDR Christmas Pack is available this Christmas only, from November 25th to December 14th.

The offer includes:

  • A DRU-244A card, which can be found in our webshop
  • 3 hours of VIP customer support from one of our seniors consultants – only available in this offer
  • Free shipping to anywhere on the globe

Hurry up, because the stock is limited, and if you order until December 6th, you are also getting a bonus:

http://spectrafold.com/quadrus/radio-software/application-testing/must-have-book-for-sdr-funs/

So, do you want the socks again? Or something really smart?

 

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cw

Performance testing of Software Defined Radios

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Performance testing of Software Defined Radios

Do SDRs perform better than conventional Superhet architecture radios? A big problem is that many of the traditionally used tests, which compare radios on league tables and in reviews, are not very relevant to SDRs due to fundamental differences in technology.
A very good article on this topic by Andrew Barron ZL3DW
Performance testing of Software Defined Radios

We already published a post on the sensitivity of the Quadrus SDR here:
http://spectrafold.com/quadrus/digitizer-hardware/sdr-receiver-sensitivity-test/

The published results are:
SSB -111 dBm at 10 dB S+N/N with 2.1 kHz bandwidth
CW  -119 dBm at 10 dB S+N/N with 400 Hz bandwidth

According to Andrew:

MDS (Minimum Discernible Signal)

MDS is a measurement of how sensitive the receiver is. It represents the weakest signal you can hear. You need it to be good if you want to hear very weak signals on a quiet band, for example when sunspots are poor or the band is closing. If the band is noisy the noise level coming in the antenna port will often be higher than the MDS so sensitivity is not as relevant.

In the test a signal is input to the receiver and the MDS is the input signal level when it shows as 3dB above the receiver noise floor. The MDS is better if the bandwidth of the receiver is reduced because a narrow bandwidth allows less noise in. So it is usually measured using a typical CW bandwidth of 500Hz and using a typical SSB bandwidth of 2.4kHz. It is normally checked on several bands as well. In most SDR receivers especially direct sampling (digital down conversion DDC) receivers you would expect the same performance on all bands. When you compare results relating to different radios, check that no attenuators or preamplifiers are in use. Most SDR receivers have an MDS better than -125dBm in 500Hz bandwidth and better than -115dBm in 2.4kHz bandwidth. Excellent receivers can achieve an MDS better than -130dBm in 500Hz bandwidth and better than    -120dBm in 2.4kHz bandwidth. SDRs with 8bit analog to digital conversion (ADC) will probably not be able to achieve that level of performance because of limited dynamic range.

It is not easy to compare the results, because we’ve measured in 400 Hz / 2.1 kHz bandwidth instead of 500 Hz / 2.4 kHz, and we’ve measured a 10 dB signal above the noise floor instead of 3 dB. However, we can do a very simple calculation of adding 7 dB to the 3/10 dB measurement level difference.

So our performance testing comparable to this reference article is:
SSB -118 dBm at 3 dB S+N/N with 2.1 kHz bandwidth
CW  -126 dBm at 3 dB S+N/N with 400 Hz bandwidth

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SDR pre-selector filter | Direct digital SDR

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What is direct digital SDR?

Software-Defined Radio (SDR) is a type of radio, where the analog signal is converted into the digital domain, and functionality is implemented in the digital domain employing signal processing algorithms. Conversion technology is limited in terms of bandwidth and frequency range, thus the right point for conversion has to be carefully chosen. Conversion can take place at the baseband, Intermediate Frequency (IF), or directly at the Radio Frequency (RF). In case conversion happens at the operating RF (likely after the pre-selector), we can talk about direct digital SDR.

Domain converter frequency parameters

Analog-to-Digital Converters (ADCs) and Digital-to-Analog Converters (DACs) are employed to bridge the analog and digital domains on the radio hardware platform. Converter parameters determine how we can use them in the radio implementations.

Instantaneous bandwidth

One of the most important parameters is the real-time bandwidth or instantaneous bandwidth. It is determined by the sampling frequency of the converter, and according to the Nyquist law, it is equal to the half of the sampling frequency.

Frequency range

The other very important parameter is bandwidth or frequency range of the converter itself. Usually, this is determined by the circuits involved: it starts with the analog components, and includes circuitry within the converter, like the sample-and-hold stage. The Nyquist criteria states that the bandwidth should be equal to the half of the sampling rate in order for a perfect reconstruction in both time and frequency domains. Hence, there is a possibility to generate and sample higher frequency signals too, if we keep the bandwidth inside half of the sampling rate. In other words, we can use upper half bands, called Nyquist bands. If we have a wider spectrum, we have to be sure not to alias or fold from higher Nyquist bands to the baseband. The anti-aliasing filter or SDR pre-selector is used for that propose. If we are talking about ADCs and receivers, the latter terminology is employed.

Frequency parameters of the DRU-244A SDR hardware

We’ve used 80 MHz as sampling frequency for our hardware platform, so, the instantaneous bandwidth is 40 MHz. We can tune to radio channels within this band using on-board hardware DDCs. The input bandwidth of the ADC itself is 650 MHz. This is the -3 dB point of the input stage, and it has no brick wall slope.

bandwidth response

This means that we can use not only the 0-40 MHz first Nyquist band, but upper bands, like 160-180 MHz, too using an SDR per-selector filter. However, the bandwidth is degraded, because we have to use some other input analog circuits, like input low-noise preamplifiers and leveling attenuators. Still, it is possible to receive with good results up to 500 MHz. See this post about satellite signal reception at 435 MHz:
http://spectrafold.com/quadrus/digitizer-hardware/direct-digital-uhf-sdr-radio-receiver-dru-244/
http://spectrafold.com/quadrus/radio-software/direct-digital-sdr-receiver/
For more information, please see AN-835 application note from Analog Devices:
http://www.analog.com/static/imported-files/application_notes/AN-835.pdf

Designing SDR pre-selector filter

You can find a lot of different filter design tool kits on the net, which will approximate your requirements, and determine the right components for different realizations. I think, the best practice, – which I’ve used in the last decades – is to cascade a separate high-pass and  a low-pass filter if the relative bandwidth is high. On the other hand, the band-pass approach will work for narrow band (<10%) filters. I always like to use standard components. E12 or E24 1% components will do good job for anti-aliasing and pre-selection filter implementations. Usually, the capacitors are the easier part, inductors may have to be manually wound and tuned.

Bandpass filter for VHF bands

Using the Dyonusos filter design software, I’ve designed a band-pass SDR pre-selector filters utilizing the capacitive coupled resonator structure, which is my favorite. The relative bandwidth is higher than 10%. During the approximation phase, I like to see ~40 dB attenuation at the Nyquist band corner. However, only 30 dB could be achieved by the high-pass filter at the lower band edge frequency if the insertion bandwidth was kept at 20 MHz. You can see the calculated filter response, the filter values, and the measured response after having very careful fine tuned the inductors in the circuits. Seems easy enough, but you need some practice to reach such results with a 5th order resonator filter. For beginners interested in designing and implementing filters, let me suggest to start with 3rd order structures and standard complements as close as possible to the calculated component values.

Approximation:

SDR pre-selector BPF 160-200 SDR pre-selector BPF 120-160

Elements:

SDR pre-selector BPF 120-160 SDR pre-selector BPF 160-200

Realization:

SDR pre-selector BPF 160-200 SDR pre-selector BPF 160-200

Measurements:

SDR pre-selector BPF 160-200 SDR pre-selector BPF 120-160

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dru-nb01

Using Quadrus SDR with a laptop

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Why a laptop?

Even until fairly recently, the resources offered by an average laptop were insufficient to run wide-band, multi-channel SDR applications. Thus, the original SDR hardware was designed with more capable desktop computers in mind. However, with increasing laptop performances, it is now finally possible to run even the more challenging applications. The obvious advantages are flexibility and mobility, and by now they are omnipresent in our everyday lives.

Connecting Quadrus SDR to a laptop

The Quadrus SDR platform’s phase-coherent SDR hardware digitizer board is a standard PCI slot card. This form factor does not allow us to connect it directly to a laptop. Fortunately, we have the possibility to use an external PCI slot extender, and place the DRU-244A card into one of the external slots. There are several products in the market, they differ mainly in the number of slots and connections. One of the most well known suppliers is Magma, who offers different solutions, like the one slot PCI extension. They also offer products with different interfaces to the laptop: ExpressCard 34mm and 54mm versions, and CardBus/PCMCIA card with 1 m or 1.5 m cable length.

1slotB_xl_0 1SlotPCI_connection

Beyond this well known and proven supplier, we’ve just found another very cost-effective external PCI solution. Polotek offers a solution based on the ExpressCard interface. It essentially contains one PCIe and one USB interface. Their idea is very simple: use the PCIe connection with a high-speed extender cable and add a PCIe-PCI brige chip on the external slot card. Their other approach is to use a standard USB3 cable manufactured in high volume. However, the connection itself is not following the USB3 protocol, they simply utilize the high-speed differential wire pair within the cable to connect the PCIe slot to the extender card, which has the PCIe-PCI bridge.

polotek2 polotek

Testing the DRU-244A phase-cohernet SDR hardware digitizer with a laptop

You can place low volume orders at several places:
http://www.aliexpress.com/item/It-go-notebook-pci-slot-laptop-pci-express-external-sound-card-graphics-card/1487192711.html
http://www.aliexpress.com/store/product/Free-shipping-Laptop-ExpressCard-34-to-2-PCI-express-16x-slot-Riser-Card-Compatible-with-PCI/1452034_2055140423.html
http://www.aliexpress.com/store/product/Free-shipping-ExpressCard-To-2-PCIe-slots-adapter-Laptop-Express-Card-to-dual-PCI-e-16x/211886_32242097031.html
I’ve ordered from Aliexpress, and received the package with the components as shown on the web.

dru ext1 dru ext2

Setting up the hardware and installing the DRU driver was trivial. The single issue, I’ve noticed, is that the Plug-and-Play functionality is somehow not working properly in all cases. Sometimes I’ve lost connection to the card after some sleep or screen saving actions. In these cases, I just removed and reconnected the ExpressCard and re-initiated the Plug-and-Play cycle. I had no chance to test it with any other computer than my Dell power notebook with an i7 processor.

dru driver machine

driver1 driver2 driver3

 

 

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SDR hardware manufacturing batch arrived

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Design and preparation of manufacturing

The DRU-244A digitizer SDR hardware went trough some design polishing and preparation for mass production without close interaction with the original design team.

DRU-244A-design

Verification and testing

Before releasing the SDR hardware, the manufacturing plant is responsible for the full verification and testing of all functionality. They need to program the clock chip that provides the different sampling clocks and other miscellaneous clocks of the architecture as well. After that, the initial EEPROM content of the PCI interface should be loaded. If the card is working fine with external power supply at this point, it can be placed into a PC for further testing using its test software. In this phase, the RF parameters are tested.

dru-sample-app dru-sample-fequ

Beta testing with selected users

After all the cards were tested in the factory, we’ve immediately shipped some of them to our beta testers. They have the latest version of the SRM-3000 receiver SDR software available to use with the card. We are looking for the initial responses from them, and appreciate any suggestions for further improvements.

14100+-100KHz-20140316-111835-0984

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RF input response for a -120dBm input signal level

Direct digital UHF SDR radio receiver with DRU-244

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Direct digital receiver

A direct digital receiver has the Analog-to-Digital Converter (ADC) directly connected to the incoming RF signal without any frequency translation. This is contrary to the superheterodyne or direct conversion methods, which translate the RF signal to an Intermediate Frequency (IF) or the BaseBand (BB) respectively before digitizing. The direct digital receiver concept can be regarded as an example of the ultimate software defined radio.

Instantaneous versus input bandwidth

Instantaneous bandwidth is the frequency band that is continuously processable by the digitizer device. This bandwidth is determined by the sampling frequency; half of the sampling frequency is often called the Nyquist-frequency. The maximum bandwidth of the processable signal should be less than this Nyquist-frequency in accordance with the Nyquist-Shannon sampling theory. However, the input bandwidth is determined mainly by the the analog front-end and the sample-and-hold circuit in the ADC. If the limit imposed by these circuits is higher than the Nyquist-frequency, we have a chance to sample higher frequency signals as well. This is usually called under sampling or sub-Nyuist sampling.

Input bandwidth of the DRU-244

I have an older version of the DRU-244 digitizer board. The input bandwidth was not specified, but it should be up to a few hundred MHz. Maybe even as high as 144 MHz or 432 MHz. I’ve connected the 432 MHz output of the signal generator to the input of the SRM SDR radio receiver, and I’ve tuned to the same frequency to get a good look at the signal. I’ve observed that the level is more than 20 dB less than in the HF band. So, I need at least 20 dB preamplification to maintain the sensitivity in the UHF band.

Sensitivity testing in the 432 MHz (70 cm) band

First, I’ve checked the sensitivity with my FT-897 transceiver. I’ve connected a signal with a -120 dBm output power, which had a well audible sound level employing the Singel SideBand (SSB) demodulator.

sig

Next, I’ve connected two MiniCircuits ZX60-6013E amplifiers in cascade providing 30 dB amplification with a reasonable noise figure.

preamp

I’ve checked the input noise level of the receiver without the connected preamp.

selfnoise

Then, I’ve checked again with the preamp. The noise floor increased by a couple dBs.

preampnoise

This was a good indication that the system sensitivity was determined by the preamp as opposed to the digitizer in the receiver.

I’ve connect the -120 dBm signal to the input, which was unfortunately less audible after the SSB demodulation then with the FT-897.

sig01

The Signal-to-Noise Ratio (SNR) at AF level was not sufficient.

sig02

437 MHz falls into the 11th Nyquist band of the converter. My idea was that all of the preamp output noise ended up getting aliased into the baseband, and consequently reduced the SNR. So, I’ve tried a Band-Pass Filter (BPF) at the preamp output, before the digitizer input. It helped a lot, and the SNR increased substantially.

sig01a

I had a really good, clear audio signal without any noise. The next picture shows the audio output spectrum of the direct digital SDR radio receiver with DRU-244 running the SRM radio receiver software for the -120 dBm input signal at 437 MHz.

sig02a

 

Conclusion

Usually, modern ADCs have significant input bandwidth, and allow sampling in higher Nyquist bands. This way direct digital VHF/UHF radio receivers can be built with simple architectures. However, input signal degradation should be mitigated with input preamplifiers. Although, we loose some dynamic range, this is an acceptable price for a very simple receiver architecture.

PS: Why 437-450MHz? This is the down-link of the MASAT-1 satellite. So, I guess, now you know my next plan… :-)

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