Situation Review: SDR Transceivers

HRW Present

Think Different II
To SDR or To Not SDR?
I4LEC - Claudio
September 22nd 2012

Seconda Convention Hamradioweb
Organizzata da Hamradioweb e dalla Sezione A.R.I. di Bologna
con il patrocinio del Comune di Sasso Marconi

Today's question mark

Should I still continue to use a “classic” radio....

Or move to the latest Software Defined ones....


Fundamentals: The three radio components

1. RF Part
2. Signal Processing
3. User Interfce

Courtesy of DH1TW

The RF component transforms high frequency signals into baseband
signals or vice versa. Parts of the RF component are filters, mixers,
amplifiers, oscillators, etc.
The baseband signal is processed / generated in the Signal Processing
component. In this component we will find functionality taking charge of
modulation, demodulation, filtering, noise reduction, etc.

The User Interface (UI) is the command and control unit of the radio. It’s
the frontend to the (human) operator. The user interface might consist of
buttons, knobs, LEDs or just a PC screen.


Main differences between the two

Classic Radio, all three
components are within
the same black box. With the
advent of digital technologies,
phisical dependecy increased
even more

Courtesy of DH1TW

SDR Radio, all three components
are independent and can be
combined based on specific
needs/architectures. No phisical
or logical independecy


SDR's modular design
The “radio” consists of two physical
components, the Quadrature Sampling Detector
(QSD) or Digital Down Converter (DDC) and a
desktop PC.
The only connection between the QSD and
the PC is a stereo audio signal.
There is no physical dependency. The QSD
could be exchanged (e.g. a softrock receiver
against a Genesis) without affecting the
signal processing or the user interface at all.

Courtesy of DH1TW

The user connects through the web browser
to the WEB server. The Web browser is
WebSDR
the User Interface. The user selects the
desired signal on the band with a single
mouse click. A few milliseconds later he can
hear the signal through his loudspeakers.
The user can be located everywhere in the
world.


In spite of the enhanced flexibility why SDR's radios do not
take off, specially among contesters ?
1. Lack of performances ? 2

2. Lack of features ? 3

3. Lack of reliability ? 11

4. Lack of station's devices integration ? 1

5. Lack of proper user interface (UI) ? 10
6. Pc dependence ? 10
7. More critical under heavy RF field ? 8
8. Others ? 5


Lack of performances ? I don't think so
IP3 2kHz
(dBm)

28,5
12,5/21,5
21

17,5
-14/4

-6

Overall dynamic receiver’s range IP3= (IMD x 1,5) + MDS Courtesy of Sherwood lab. sorted by close-in dynamic range (DR)

IP3 2kHz
(dBm)
12
-10
-9
-7,5
-13
-27,5/-18,5

The 3rd order intercept point (IP3): A Measure of Merit
• The ratio of the smallest usable signal to the largest tolerable signal.
• The amplitude range over which a mixer can operate without degradation of performance.
• Noise should determine the lower limit of a receiver’s dynamic range.
• However, the lower limit can be set by the MDS—a some what more qualitative measure.
• The upper limit is normally set by either noise or distortion.

The graph illustrates that the
3rd order intercept point is
defined by the intersection of
two hypothetical lines. Each
line is an extension of a linear
gain figure: first of the signal
of interest; and second, of
the 3rd order intermodulation
distortion product—from which
IP3 gets its name.

Courtesy of W4UOA

The larger the value of IP3, the less likely the receiver will be adversely affected by 3 rd order
intermodulation products


LO noise (Rec. Mix) & IMD figures

The LO noise is the upper limit, the aim is to fulfil the gap in the way that the IMD product values
at the given spacing get as close as possible to the LO noise values.
Flex’s figures based on claims data Courtesy of I4SBX


Real life performances based on the table
• Lower sensitivity!
Ran two years a side by side IC775 (-135dBm) and Flex 1500 (-115dBm), even with 20 dB delta,
on 10m never felt the lack of sensitivity, both radios operating with their pre-amps ON.
Very weak signals were barely readeble on boths radios, the 8 bands equalizer helped
readibility on the Flex. (CompareCW) (CompareSSB) (YJ0VK_UN)

• Slightly worst blocking!
Less than 10dB difference on average among the other radios, practically to saturate the Flex it
takes a signal of 0 dBm (S9+73dB), while the Elecraft can handle up to +10dBm (S9+83dB).
The little Flex 1500 blocks at -8dBm (S9+65dB), happened only once while beaming at IR4X.
Not really meaningful since IMD3 takes place much earlier.

• Noiser local oscillator!
Closer to the carrier dynamic range is highly desirable here. A low noise oscillator can mean
clean audio reproduction where a noisier carrier will mean more distortion inherent in the
recovered signal audio. Basically the radio limit, ideally IMD figures should tend to this limit.

• Better Dynamic Range!
Close spaced Dynamic Range: 75-80 dB or so is acceptable for most users, as per my IC 775,
higher here is better especially during contest/dx/serious cw work. Only the Yaesu is better,
Elecraft picks up with the ultra narrow 200Hz 5 poles roofing in. The Flex keeps the same figures
at any spacing. Did I ever feel the need of more dynamic, no on both radios, however on the 775 I
thought to place a narrower roofing, in the right place of the chain, for improving the DR.


Lack of features ? I don't think so
Binaural audio features make use of the human mind & ears ability to gain
intelligibility by the way of the head-related transfer function, an
improvement in reception available at this time only in the hamshack
other than through SDR. Being able to listen to the RX in a true binaural
mode by listening to the I and Q channels in separate ears.

Having built in diversity reception is otherwise presently only in few very high
end single transceivers (Flex 5000 plus opz. RX2).
Using multiple receivers connected to separate antennas for improving the
intelligibility of received signals by improving the signal to noise ratio and
mitigating signal fading and drop outs.

The transmitted voice processing, equalizer, compender, compression and
other tweaks is available in the hamshack in stand alone gear, though three
pieces of specialist kit would be needed.

Recording either the entire bandwidth (up to 192kHZ) or just the receiving
channel.

Accurate meter, with dBm & S unit reading, not altered by the pre-amps.
Pre-amps increase sensitivity, noise floor lowers accordingly .

Very sharp & narrow customized CW
filters, as narrow as 12Hz. My cascaded
250hz filters (IC 775) compared with12Hz
DSP filters, makes a theoretical difference
of 10log 250/12 =13.2 dBm.

Memory banks with related parameters.


Even the little Flex 1500 has all PowerSDR’s features, these are building up at every
new release, as per the latest one, with the Tracking Notch Filter(s) TNF add on

Lack of reliability ? Essentially SW related
Start up and shut down procedure to follow precisely
in order to avoid the need of data base reset, I had to do it
three or four times in two years time
Power SDR, not settled yet, new releases still on going, even
if at lower pace, not just to implement new features but also
to correct bugs.
Occasionally some audio pops, often related to the load
introduced by other applications, as Skype, Mozilla, etc.

Had to send the Flex 1500 to the European service once
for 40 m power alignment, exceeding 5W. Power Master
Watt meter deemed necessary.
Documentation still on draft version

Lack of station's devices integration ? The main strength
By means of virtual audio cable (VAC) and virtual serial cable (VSC)
PowerSDR integrates very well with third party SW, mostly freeware
No hardware device interfaces
required

Station components like rotor
control, antenna switching,
audio recording, Watt/SWR
Metering, Digital Mode, Amplifier,
Logging Programs, DX Spots, and
audio processing under control,
the SDR opportunity allows a
single shack interface through
the computer, no matter whether
Hardware or Software


Lack of proper user interface (UI) ? I think so
Human interface by means of a mouse drag, click, wheel turn on
PowerSDR application. It does very well but you ought to on
PowerSDR active window.
During quick running or contest environment, focus must be mainly on
Logging program, while you should still be able to operate the radio as
tuning both VFOs, filtering, band changing, etc

I do consider this the main flaw, recently Flex introduced an accessory
called flexcontrol, which some how met the target but at the expense of
a single knob and three programmable push buttons


Lack of proper user interface (UI) ? I think so

Here is what Tobias, DH1TW, has developed to fulfil the gap, a USB microcontroller device fully
programmable to your taste, the SW bridge is called PowerSDR-UI available in beta version…..
cons. you ought to wait for Tobias new releases

The 3rd way (my way)
Hybrid solution.....classic plus SDR



How to combine the two


In the contest with Win Test
All logging and Power SDR’s windows within the same screen, radio’s operation by means
of the DJ console, focus on the entry logging window

Operation experiences
Very easy and effective split operations…thanks to separate VFOs audio sources diverted
into right & left ear as well as the visual aid which allows an instant tune…… D64K

Personal experiences and tests
On the Flex 1500, single tone image down around 100dB, dual tone just a little over 70dB, during a CW
crowed contest, some images were detected/decoded below the lower band edge by the in-house
skimmer
Courtesy of I4SBX

Inserire immagini

Wide band white noise test (NPR) resulted in poorer Dynamic Range on QSD
SDR’s radio than the classic radios....……this due to the image rejection issue

Sorted by noise Power Ratio (NPR)

The NPR method emulates many signal by loading the receveirs with white
noise. In this way, all combinations of carrier frequency spacing are taken into
account, and a true worst-case measurement is made.
Courtesy of I4SBX, I2VGA


Noise Power Ratio test for an overal RX measurements, including input
filters, not just the Mixer.

Courtesy of I4SBX

An educational instrument
An S9+20dB signal perfectly within the filter bandwidth

Same signal strengh, what a difference, 8kHz wide bandwidth, poor
TX IMD….?

Yes….indeed

Courtesy of I4SBX

As per the here above case…..3rd order only down 25dB, we worry so much on RX IMD and almost
none on TX IMD. The DR3 number is important on CW. It is less important on SSB since the IMD
products of all transmitters, except very few cases, is worse than most radios. Thus the limit in how
close you can work a weak station next to a strong one is almost always the generated IMD products
of the strong undesired near by signal, not the dynamic range of the receiver.

Am I out of band? Yes
Where should I tune in order not to bother ? Right on the tuned Freq.

Best buy/performances (under test)

TS 590 IP3 = -14/4dBm

Flex 3000 IP3 = 12dBm

K3 IP3 = 12,5/21,5dBm

IP3 = Overall dynamic receiver’s range Courtesy of Sherwood lab. and I4SBX lab.

Then, SDR, Classic or………both ?

It seems like the old question beetwen Quad and Yagi, the Quad claims
better gain, lower take off angle, less subject to noise, better F/B.
How many of these Quads are used among the serious contesters?
……..subject for another session?

Thank you

Situation Review: SDR Transceivers

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