g31ddc-review-radiouser.pdf

review

■ The latest software defined radio from WiNRADiO reviewed by Mike Richards

Mike Richards has been

WiNRADiO Excalibur

testing the very latest model

from WiNRADiO, a company

E xcalibur is the latest in a

that is well established in the

pedigree line of digital radio

receivers and it is bristling with

new features and more power than

ever. The incoming RF spectrum (up to

50MHz wide) is converted to digital right

at the front end and then decimated down

to 2MHz chunks for ﬁ nal processing in

the PC. Digitising the signal very early in

the receiver completely eliminates any

analogue tuning and everything can be

controlled digitally. The ﬁ ltering options

are a joy and you can process up to three

different receive channels simultaneously

within the selected 2MHz chunk.

world of software defined

radio.

Digital Receiver

I’ll start with a basic primer on Direct

Sampling and Digital Down Conversion

because they are at the heart of

the Excalibur. The key to this type

of receiver is the availability of fast

Analogue to Digital converters (ADC)

and Field Programmable Gate Arrays

(FPGAs). Because the Excalibur covers

a frequency range from 9kHz to 50MHz,

it requires an ADC that can sample at

twice the rate of the highest frequency

you want to be able to receive – that’s

100 million samples per second. To help

explain what an ADC does, you can think

of it as being rather like a programmable

digital voltmeter. It monitors the input

signal and takes/stores voltage readings

at a rate of 100 million every second.

In the case of the Excalibur, the voltage

is measured to 16 bit accuracy. That

means each time the signal is sampled,

the voltage can be any one of a possible

65,536 different voltage steps.

Once this stage is complete, the output

is a high-speed stream of data with a

100 million new, 16 bit, values appearing

every second.

In order to give the user lots of

configuration options, the data stream

is sent to the PC for the final part of

the signal processing. However, with

such a high sample rate, the data rate

on the link to the PC would need to be

at least 1.6Gb/s, a lot faster than any

of the common interfaces or PCs can

manage. The solution is to use a process

called Digital Down Conversion (DDC) or

decimation to select a segment of the full

bandwidth and send just that to the PC.

This conversion is handled by Excalibur’s

high speed FPGA, which uses thousands

of logic blocks that are interconnected

to create sophisticated digital filters and

re-samplers to extract a segment of the

spectrum (up to 2MHz wide). DDC is

the digital equivalent of a conventional

mixer where the incoming RF signal

is converted to a more manageable

The Excalibur.

Attenuator

MW Filter

(switchable)

Amplifier

& Filter

Analogue

to digital

conversion

Digital down

conversion

Antenna

ADC

DDC

USB

Excalibur block diagram.

August 2010 radiouser

intermediate frequency. In the Excalibur,

DDC reduces the data rate to about

64Mb/s, which is well within the capacity

of a standard USB 2.0 link.

Once the 2MHz data stream is in the

PC, the WiNRADiO software takes over

and provides all manner of goodies. The

Excalibur implements this technique

seamlessly and despite the underlying

use of 2MHz chunks, you can freely

move around the entire 50MHz spectrum

without having to pre-select the chunk

you want – the software does all that for

you.

Excalibur monitoring the 11MHz broadcast band.

Getting Started

As with all WiNRADiO receivers,

installation is very simple. You load the

CD-ROM first because this installs the

receiver software and the vital drivers

so that the Excalibur hardware will be

recognised when you plug it in. System

requirements were reasonably modest

with a 2GHz dual-core Pentium and 1GB

RAM as the starting point.

The receiver itself is housed in a

solid die-cast case that is enclosed in a

translucent plastic cage and connections

are simple, with all the necessary leads

provided in the box. The antenna uses a

miniature 50Ω SMA connector but a BNC

adaptor is included in the box, which

is very thoughtful. The USB lead has a

bespoke WiNRADiO connector at the

receiver end and a standard USB plug at

the other. Power is supplied via a linear

external power unit, which avoids the RF

interference problems often associated

with some switch-mode power units.

That’s it for connections but the receiver

case also has a push-button power on/off

switch and a blue LED indicator that can

be used for power/status indication.

Once the installation is complete, the

Excalibur receiver unit can be tucked

away out of sight because all the

functionality is controlled from within the

software.

A waterfall display of a CW

signal.

Excalibur receiving Hamburg Met.

bottom of the screen can be set to show

the entire receiver bandwidth from 9kHz

to either 30MHz or 49.95MHz. For most,

30MHz will be the best bet and provides

clearer analysis of the spectrum but the

full 50MHz is available if you want it.

However, the performance declines close

to 50MHz due to the use of anti-alias

filters to improve ADC performance.

A grey vertical bar on the display

shows the size and location of the DDC

chunk that’s being passed to the other

sections of the receiver. This can be

placed anywhere in the spectrum by a

simple mouse click and you can alter its

size simply by stretching the sides with

the mouse! This was an incredibly quick

and easy way to get around the bands

and look for activity. By looking at the

entire spectrum, you can quickly assess

band conditions and jump straight

to an interesting section. I found this

particularly useful for keeping an eye

on the higher frequencies as conditions

are extremely variable currently. When a

band becomes active, you see the noise

floor rise and an increasing number of

active peaks popping up and down.

In addition to providing a general

overview of band activity, the spectrum

display has a vertical marker that follows

the mouse pointer and shows the precise

frequency and signal level at any point in

the spectrum.

Immediately above this full spectrum

display are a number of controls

that can be used to fine tune the

performance. The RBW control sets the

bandwidth of each measurement point

on the spectrum display and ranges from

1.5kHz through to 98kHz. At the 1.5kHz

end you will get a very fine resolution,

spiky, display whilst at 98kHz the display

is smoothed right out. In practice, the fine

resolution is great for spotting individual

station activity whilst the higher settings

allow you to view the levels of an entire

sub-band more easily.

The next adjustment is for the

minimum level that will be displayed. This

effectively moves the trace up or down

on the display and the default setting of

-135dBm is likely to suit most situations.

To help make some signals more visible,

it’s worth making use of the Averaging

control. This specifies the period over

which the signal is averaged for display

and it has the effect of smoothing out

the display and makes rapidly varying

signals more visible. A good example

is a RTTY signal as with no averaging

it’s difficult to spot the classic two-peak

shape of the signal. However, if you bring

the averaging up to 0.3 or 0.4 seconds

all becomes clear.

If you want a better view of a section

of the spectrum, you can use the zoom

control and there’s even a snapshot

button so you can save a screenshot of

the spectrum to disk as a bitmap.

If you prefer waterfall displays to

conventional spectrums because they

Spectrum Analysis

When the software starts, you are

presented with a busy screen. There’s

a full-width spectrum display at the

bottom, another top left, a third top right

and general receiver controls at the

top. This might seems a bit daunting

but the displays are easy to master and

do provide a very comprehensive view

of the entire spectrum. Having visibility

of the entire 0-30MHz or 0-50MHz

spectrum changes the way you operate.

The large spectrum display at the

radiouser August 2010

are very effective for spotting continuous

signals, you have that option with the

waterfall button.

At the bottom of the main spectrum

are a few additional controls that provide

adjustment of the main signal path. First

is the attenuator that provides adjustment

from 3 to 21dB in 3dB increments. This

can be set manually or by pressing the

auto button, which causes the attenuator

to switch in automatically if any signal

exceeds 0dBm.

Dithering is a method of reducing

minor ADC artefacts but these are very

low in the Excalibur so this probably

won’t get much use.

Finally, there is the MW filter that

switches in an attenuator for all

frequencies below 1.8MHz, which should

reduce the risk of overload from strong

medium wave signals.

Excalibur’s Filter length control panel.

Filter Length

Digital filtering is an iterative process

and the longer the cycle of repeats, the

better the filter becomes – think of it like

cascading conventional filters one after

another but without the insertion loss.

Excalibur includes an option to

determine the length of the filter chain,

which can be between 10 and 5000 taps.

At the lower end, the filters are very soft

with gentle rolling curves whilst at 5000

taps, the filters are so sharp you could

cut yourself!

The reason for not fixing the setting

to 5000 is resorces because running

the Excalibur with a 2MHz DDC and

a filter setting of 5000 requires a lot of

processing. The recommendation is that

you set the filter length as high as you

can whilst keeping the processor load

below 30% – there’s even a processor

load meter in the setting panel. However,

I was pleasantly surprised to find that my

Intel Q8300 quad core processor PC was

fine and could easily handle 2MHz DDC

and a 5000 filter setting with a processor

load of only 20%.

Scheduler for unattended recording.

DDC Spectrum

This display is located at the top left and

provides analysis of the DDC segment of

the overall spectrum. This can be set to

any value between 20kHz and 2MHz by

using the DDC bandwidth control on this

display.

As with the main display, there are

controls for the display bandwidth,

averaging, waterfall and zoom. However,

this display provides finer analysis of the

spectrum because it only has to deal with

the 2MHz DDC section. In fact, this display

is so fine that on full zoom you can see the

dots and dashes of a CW signal!

This display also includes a grey shaded

section that shows the demodulator

bandwidth that’s set up in the next section.

The main factor in determining what

DDC bandwidth to use is how many of

the three receive channels you are using

and what frequency span they have to

cover. If you are using three channels

to monitor or record three stations in the

same broadcast band, then 500kHz would

probably be fine. However, I suspect

most listeners will only be using one

receive channel at a time in which case a

20-50kHz DDC bandwidth would be fine.

Another little gem in this section is the

record option that lets you record the

entire DDC data to disk for replay later.

This is great for signal analysis as you

can capture a chunk of spectrum and

repeatedly examine it. The replay includes

a pause and loop control to help with this

process.

Demodulator Spectrum

Finally, we come to the demodulator

spectrum that provides a view of the

signal we’re monitoring. There’s no

waterfall option but instead there’s

the choice between the audio and RF

demodulator spectrums along with

similar display bandwidth and averaging

controls.

A new addition is the demodulator

bandwidth, which can be adjusted in

100Hz steps from 10Hz through to

62.4kHz wide!

The quality of the filtering is excellent

and is primarily determined by the filter

length setting. Having fine control of

such good quality filters means you can

really pluck your wanted signal out of

the noise. This worked superbly well for

me during the review and made utility

monitoring so much easier.

As with the DDC section, the

demodulator also includes a data

recorder so you can capture and replay

the demodulator spectrum!

Tuning

Tuning has been made very simple with

several different methods available. If

you know the frequency you want, then

the best way is to tap it into the numeric

keypad. You can also use the mouse

with the spectrum displays to click on

the approximate frequency that you

want.

For general tuning around you can

use the mouse wheel, up/down keys or

put your mouse over the tuning knob.

For all these options, the default tuning

rate is 1kHz per click but that can be

reduced to 100Hz, 10Hz or 1Hz. You

can also hover the mouse over the

frequency display, press shift and then

spin the numbers with the mouse.

All the tuning options are live all the

time, so you can mix and match as you

please. With such a comprehensive

range of options, tuning was very easy.

Three Receivers in One

Excalibur has three separate receive

systems that can process any frequency

Excalibur’s main receiver controls.

August 2010 radiouser

summary

within the selected DDC band. Although

the receivers are created in software,

they are completely independent

with their own analysis windows and

demodulators. You can record the output

from each one and there is even the

facility to mix the demodulated audio

between the left and right channels so

you could listen to all three at once!

Whilst simultaneous operation of all

three receivers is only possible within the

limits of the DDC band, you can tune any

of the three receivers to any frequency

in the 50MHz spectrum and use it as a

preset – just click on the receiver and

everything changes over to the new

frequency.

This is great receiver that will

change the way you monitor the

HF bands. Being able to see the

entire spectrum on one display

and jump to any point with the

click of a mouse is a very powerful

tool. The receiver performance is

extremely good and it’s helped by

the filters, which were magnificent.

The Excalibur cost £649.95 and

my thanks to WiNRADiO for the

loan of the review unit.

Scheduler

Unattended recording of signals is

supported using a scheduler that has

access to all the important demodulator

functions and it can make digital

recordings to your hard drive. You can

set file size limits to make sure you don’t

use up all your free space.

Masterstroke

The masterstroke is that WiNRADiO

have done a brilliant job with the

Excalibur user interface and this receiver

is an absolute breeze to use once you’ve

spent a bit of time finding your way

around it. Whilst it may sound as though

you have to carefully set the DDC width

and so on, in practice, you can point and

click your way around the bands in a

flash. It really does change the way you

operate because the entire spectrum is

at your fingertips and available at the

click of a mouse.

with additional controls covering tuning,

audio, notch filter, squelch, gain/AGC

and a noise blanker.

Within the audio section is an excellent

audio filter that you can use to optimise

the audio bandwidth.

Excalibur also comes with a

comprehensive memory system where

you can store all your favourite stations

along with detailed receiver settings.

Demodulation

Excalibur can demodulate AM,

Synchronous AM, LSB, USB, CW, FM,

DRM and FSK signals. There’s even

a User Defined Mode where you can

make up your own receive settings. Also

in this section are a set of seven tabs

●

Specifications

Receiver type: Direct-sampling, digitally down-converting software-defined receiver

Frequency range: 9kHz to 49.995MHz

Tuning resolution 1Hz

Mode AM, AMS, LSB, USB, CW, FMN, FSK, UDM, DRM mode optional

Image rejection 90dB typ.

IP3 +31dBm min.

Attenuator 0 - 21dB, adjustable in 3dB steps

SFDR 107dB min.

Noise figure 14dB

MDS -130dBm @ 10MHz, 500Hz BW

Phase noise -145 dBc/Hz @ 10kHz

RSSI accuracy 2dB typ.

RSSI sensitivity -140dBm

Processing and recording bandwidth (DDC bandwidth) 20kHz - 2MHz (selectable in 21 steps)

Demodulation bandwidth 10Hz - 62.5kHz (continuously variable in 1Hz steps)

Spectrum analyzers Input spectrum/waterfall 30 or 50MHz wide, 1.5kHz resolution bandwidth

DDC spectrum/waterfall

max 2MHz wide, 1Hz resolution bandwidth

Channel spectrum

max 62.5kHz wide, 1Hz resolution bandwidth

Demodulated audio

16kHz wide, 1Hz resolution bandwidth

ADC

16 bit, 100 MSPS

Sensitivity (@ 10 MHz)

AM -101dBm (2.00μV) @ 10dB S+N/N, 30% modulation

SSB -116dBm (0.35μV) @ 10dB S+N/N, 2.1kHz BW

CW -123dBm (0.16μV) @ 10dB S+N/N, 500Hz BW

FM -112dBm (0.56μV) @ 12dB SINAD, 3kHz deviation, 12kHz BW

Tuning accuracy

0.5 ppm @ 25°C Tuning stability 2.5 ppm (0 to 50°C)

MW filter Cut-off frequency

1.8MHz @ -3dB Attenuation 60dB min @ 0.5MHz

Antenna input

50Ω (SMA connector)

Output

24-bit digitized I&Q signal over USB 2.0 interface

Power supply

11-13 V DC @ 500mA typ.

Consumption

11-13V DC @ 45mA typ. (power save)

Operating temperature

0 to 50°C

radiouser August 2010

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