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SDR: Software Defined Radio

As I've learned from my web-hoster's statistics, most of my website vistors are hitting this particular 'SDR' page directly.
The topic seems to generate a lot of interest.

So, I will be trying to enrich this particular web page in the future. At least, as far as my knowledge and contribution
allows for. So stay 'tuned'. Anyway, I will put focus on any new 'insights' I've gained of the topic of 'SDR' and I will post
these right here.


> Preface
> My SDR history
> 2 small very low-cost mono-band SDR RX kits
> PMSDR HF allband low-cost RX kit
> Flex-Radio Flex-3000 transceiver
> FA-SDR transceiver: a low-cost kit offered by the German Ham Radio magazine "Funkamateur"

Pick the item directly or just read on and scroll down this page to cover all posts.


First of all, I would like to confess that I am a very strong "advocate" of SDR technology.
The main reason is: it brings back the spirit of "experimental radio" and the lessons learned out
of this experience into real-world projects and implementations.

Plus, this technology  makes use of contemporary developments in SW and HW and thus allows
for a "new" approach with respect to the implementation of ham radio equipment.

Pure "innovation". That's what we need in ham radio, always!

The fascinating thing about SDR equipment is that it is been developed and promoted more
and more by a community of independant hardware and software developers.

However, some of  the "big" names do play a significant role especially in providing the associated
Software on a GNU-based kind of license.

The Software plays a key part in SDR development. So, I consider "Software" as the main
building block for any SDR development. Most of that Software is there already, "for free"!

Plus, "Software" has the beauty of being enhanced without touching the Hardware at all (if the
overall HW/SW concept is done well). It's just a Program or Firmware Update.

However, there is still a lot of "playground" for the hardware developers in order to achieve the best
possible solution for the Hardware implementation. Various concepts compete with each other.

No matter what: exciting times, as far as SDR concepts is concerned. 

My view: this kind of technology will be the future of ham radio equipment within a very few years!

This is it!

Might be some real challenge for the big names in ham radio equipment as the name of the game
might change quite dramatically! I wonder how they will react to this kind of development.

My SDR History:

Back in 2005 I got my first SDR radio which was a Flex-Radio SDR-1000.
After some initial excitement I decided to put it on the shelf and get back to "normal" radios.
The main reason was this latency issue with the rig at those days back in 05/06, which made the rig
quite unuseful for me. My main mode of operation is CW. And this was where it sort of "struggled"
in transmit mode. Reception was excellent, though.

What also sort of annoyed me were the *many* cables that were necessary to be run between PC,
external sound card and the transceiver. Plus I was feeling not comfortable at all with those 3.5mm
Mini-Stereo-plugs! This relates to the consistency of a solid signal connection, which is elementary
when dealing with something like I and Q signals.

Starting over again:

Two small RX kits

Early this year I came across some very price attractive litte SDR receiver kits and gave them a try,
just for curiosity, to find out what kind of performance these little receivers would show-up with.
I must confess: I expected very little!

So I built a SoftRock Lite II for 40m and another kit from the German ham radio magazine "Funkamateur",
also covering 40m, in order to be able to make some comparison.
Both kits are using about the same design. However, SoftRock uses SMD parts, the other kit does not, it
uses standard THT (through-hole) parts.
This can be seen in a huge difference in physical size of the 2 kits.
To make this story short: on 40m both kits (to me and at my location and antenna) perform the same.

SR40 Lite 2 and FA kitpicture at left:

SoftRock 40 Lite II at the left side, the 40m SDR kit from the German
ham radio magazine "Funkamateur" at the right hand side.

SoftRock is based on SMD parts, the FA kit on conventional THT parts.

You can see the difference in size by looking at the kit's PCBs.
Quite some difference in size!

General Information on the SoftRock can be found here. Excellent step-by-step builder notes for
the Softrock Lite II can be found here.

Information on the SDR kits from "Funkamateur" magazine (German) can be found here.

I was really surprised to see how well these 2 little radios performed especially in face of the pretty
dense European 40m and 41m band.

As the radios were only single-band capable, I was looking for an all-band alternative.


pmsdr At some time when googleing the Internet on SDR kits I came across a post
somewhere referring to an SDR RX all-band kit from Italy, called "PMSDR".
I went to their shop website and ordered the kit plus a small ready-drilled
housing plus LCD display option. The cost was about 200 Euro, which seemed
quite reasonable to me. The whole thing went together in about an hour because
the PCB is already stuffed with the SMT components and only a few THT parts need to be soldered.

As far as the Software is concerned I downloaded Winrad (free), installed it on my PC and switched
the PMSDR on. I was amazed by the strength and clarity of signals this little RX produces. It's simply
fantastic, especially given the small price you pay.

PMSDR: added 06-Dec-2009:

Martin, IW3AUT, is continuously adding new features to the PMSDR receiver. This includes both Software
updates as well as Hardware add-ons.

The next Hardware add-on to come is a small PC board to be integrated into the PMSDR. It is a switch box
which allows the PMSDR to be used as the receiver in combination with an existing HF transceiver (100 watts).
The box switches the antenna connections between the PMSDR and the Transceiver (used as the TX) and at the
same time (when transmitting on the TRX) mutes the PMSDR RX.

This allows for fully integrating the PMSDR into one's other station set-up and utilizing the PMSDR's advanced

The switching can either be done by HF-VOX or PTT signal (ground for TX and certainly the preferred method
for switching between RX and TX mode). CAT control of the TX/TRX is or will (depending on the TRX brand)
also be possible and adds a lot for the conveniance of  the set-up. That looks like going to be a 'killer' application,
given the price you need to pay for a PMSDR kit.

For further details please check the according websites.

The IW3AUT homepage for PMSDR can be found here.

My builder notes (in German) can be found here.

My PMSDR picture gallery is here, or just click on the picture above.

Software (new 12-Nov-2009)

The above mentioned kits require a corresponding Software in order to make the whole SDR radio
'working'. There are various Software programs available in the web. Most of them are free of charge.

What is important re. the Software is, that it supports I and Q signal streams delivered by the hardware.

To name just two programs:

> 'PowerSDR-IQ' (a special I/Q version of the the Flex-Radio Software); a bit complex for the beginning
> 'Winrad', see here for full details

For Newcomers to SDR I would recommend starting with 'Winrad' first, as from my point of view it's
the easiest way of getting things working. Software configuration is quite easy.

Flex-3000 by Flex-Radio:

Flex3k frontSince Flex-Radio changed it's system design by integrating
the sound card into the radio and making the connection
between transceiver and PC a single-cable affair (Firewire, i.e.),
I was curious of trying one of their newer design radios.

With my Flex-1000 CW experience still in my head, I didn't go for
the Flex-5000 radio (about 3000 Euro) but ordered a Flex-3000 for
a little more than half the price (I mean there are many possible
ways of "burning" money, but I just didn't dare to go this risk a
second time ;-) . So I decided for the lower cost Flex-3000.
More on the Flex-3000 see here.

UPDATE 10-Jan-2010:

I've used the Flex-3000 today for the first time in a contest style of environment.

The contest was the DARC 10m Contest, lasting only 2 hours, mixed mode (CW and SSB).

I must say it's a totally different kind of operation. You need to get used to it. I mean I've used the
Flex3k quite often so far in a rag-chewing style of operation. But contesting with it is a different animal.

Especially if you are also logging your QSOs on a computer. It was sort of getting a bit "hectic state" as
far as the computer user interfaces is concerned, and if you are not much used to it. Takes a while until
it *works*.

In any case: I am very excited of the SDR capabilities in such an environment as far as the overview of
viewing on-screen  "what's going on where" is concerned and e.g. had no issues in finding a clear frequency
where I could call "CQ contest" myself!

The F3k performed exceptionally well in both CW and SSB mode during the contest.

With a little more training I'm quite convinced that this is the way to go. Both in CW as well as SSB.

UPDATE 06-Dec-2009:

I've bought a new Notebook with a fast 2-core CPU & Firewire400 interface and installed MS Windows 7 on it.
This was a 'fresh' install of Win 7, no upgrade from an earlier MS Windows version.

After the Win 7 install and the updates I installed the Flex-Radio drivers and PSDR. No issues. Runs like
a champ!

UPDATE, 21-October-2009:

As could be read on the Flex-Radio web-site, the Flex-3000 radios got an hardware and firmware update
for free mid of September 2009. For that reason I could not use my Flex3k during the 2009 IARU Region-1
SSB fieldday as my radio was in their labs for the update around this time-frame.

That definitely was a pity and I am still convinced that we would have scored at plus 50 QSOs minimum
with the SDR transceiver due to it's faster to operate user interface.

I had no chance so far to evaluate the hardware/software changes to the unit as band propagations on
17 to 10 m had been not too magificient during the past few weeks. I will post any new findings here as
soon as I have gained news.

Update August 17, 2009:

The Flex-3000 transceiver arrived on Friday, 14-Aug-2009.

You can find my German language "first impressions" review on my local ham radio club website here.

In English language here in brief:

What it is:

real great SDR radio for the price you pay; dual-RX/TX within RX-window (ca. 90 KHz);
much improved lantency, can now go much faster speed CW TX; clean sidetone;
built-in sound-card, no complex user adjustments (done by the factory);
single wire PC connection through FireWire-400;
excellent steep filters and good NB (in my case);
real "plug & play", if latest Microsoft patches have been installed on your PC/Notebook
plus Microsoft .NET components for running PowerSDR;

What it is not:

a full CW QSK-capable radio in a sense that you can hear between dots, dashes or characters;
not *very* quiet, as fans start working whenever you go TX;

What you need to take care about:

make sure you are not getting RF feedback (possibly over your coax feed line shield) into your radio.
especially important if you use a vertical antenna in close distance. I have experienced RF feedback
issues with my UK-manufactured "Sandpiper" Vertical on 40m with a poor radial system installed (my fault)
for 40m and no grounding on the TRX. This completely disappeared when I drove my 80/40/30m trapped
dipole on 40m with 100 watts.

'FA-SDR' - Transceiver

I/Q-based low-power and low-cost HF SDR transceiver kit published and provided
by the German 'Funkamateur' Ham Radio magazine

The German Ham Radio magazine 'Funkamateur' in it's editions October to December 2009 published
an I/Q HF allband transceiver design which, after some delays due to parts availability, is available as
a kit now (June 2010).

The design and kit looks quite 'inspiring' especially for those ham radio fellows who have never touched the
SDR grounds so far, however do have expertise in assembling kits and add-on building blocks themselves
and also can cope with the possible challenges of an SDR as far as PC/Software etc. know-how is concerned.

The kit and add-on blocks are provided at quite reasonable cost.

Click here in order to see more details/pictures of the kit's components.

Some "bad news" upfront for non-German speaking people:

As I've learned from a phone call with "Funkamateur" magazine today (28-Jan-2011) they do not have any
current plans to provide the kit with an English language kit builders' documentation!

The documentation is available in German language only. So, if you are not familiar with the German
language or don't have someone doing the translation for you, it will be pretty cumbersome to understand
a couple of the "specialties" of the kit which are elementary to get them done "right".

For those of you not familiar with German, I would rather recommend e.g. the "PM-SDR" kit from Italy (RX only!),
or the "Genesis G59" kit from Australia (a transceiver kit). Both kits are documented in English and there are
Yahoogroups in place where you can read things up or can ask for help in case of difficulties.
And there will most likely be difficulties, as "SDR" still is a work in process! And that's for sure!

Brief technical description:

In short, the kit consists of a 'mother' PCB where all SMD parts have been populated already by 'the factory'.
THT (through hole) devices still need to be soldered to the PCB.

The local oscillator is based on the Si570 chip (no AD DDS chip!), is a separate module and needs to be ordered
specifically ('FA-SY 1'). This oscillator as well as other functions of the TRX are controlled via USB from the
associated PC/Notebook.

The mixer architecture is based on the Tayloe Zero IF QSD principle which is quite popular e.g. from the
Flex-Radio SDR-1000 transceiver times.

On RX, the antenna signal goes through a manually tuned pre-selector. The pre-selector sports a post-amplifier
in the form of an SGA5289 chip. There are means of inserting a 0, 6 or 12db attenuator pad on RX.

On TX, the TX mixer signal goes through the same pre-selector and amplifier stages as on RX, with the exception
of the attenuator circuitry.

The TX signal then goes either directly to the RX/TX switch-over relay (some 10 mW of driver power), or goes to
the 1 watt linear amplifier module (if included). For this purpose 2 jumpers need to be set appropriately.
There are no additional Low Pass Filters included for the TX signal. Therefore appropriate LPF's may need to be
added by the user, certainly if an outboard amplifier is driven by the little SDR TRX.

The TRX motherboard has a row of interconnections for the optional plug-in 1 watt TX amplifier board.
The linear amplifier uses 2x RD00HHS1 MosFET devices in push-pull. BIAS voltage for the final transistors can be
adjusted individually.

Connecting lines to the PC/Notebook are done via USB and for the I/Q signals via line-in and line-out
of the sound card.


In order to get the little SDR TRX running, appropriate Software needs to be installed on the PC or Notebook.
The FA-SDR-TRX construction manual recommends "Rocky" or "PowerSDR" and gives examples for installation
and settings.

Language support of the docu:

To my knowledge, at present (June 2010) there is only a German language assembly manual available.
However, if there's some noticeable demand by foreign, non-German speaking users, I'd assume that the vendor may
possibly come up with an English language version of the assy manual. But please: don't take that as guaranteed!
It's just my guess!

Claimed performance data:

The claimed performance data look quite promising (source: 'Funkamateur' 10/2009):

Frequency range: 1.7 to 30 MHz

Additional ranges: 6m and 2m,  if appropriate RF pre-selection and amplification is added by the user

MDS 80m: -123 dbm (@ 500 Hz BW)
MDS 10m: -127 dbm (@ 500 Hz BW)

IP3: > +15 dbm

IMDR3: > 90db

Pout (with plugged-in optional amp): <= 1 watt

TX IMD(3) at 1 watt: -35 dbc
TX IMD(3) at 10 mW: -50 dbc

Spurious emissions at 1 watt CW output:

image: -60 dbc
carrier: -65 dbc
other spurious: -50 dbc

sideband surpression:

w/o software optimization:  - 35 db
with software optimization:  - 70 db

Summary: (update 13-Jan-2010)

As per it's specs this little kit plus add-ons is not going to be a "killer" Contest radio
or competitive alternative to e.g. a Flex5k or HPSDR etc.

That doesn't seem to be the target at all, as far as my understanding goes.

IMHO, the target is to provide a simple to build, low-cost (very affordable) basic I/Q SDR
transceiver platform in order to take the first steps (and more) in SDR-based technology
on all HF bands.

For more Details on the "FA-SDR-TRX":

Please see DH1TW's webpage here.


All quoted data as per 'Funkamateur' magazine, issue 10/2009, subject to changes.
No responsibility taken by DK3QN for typo errors etc.
Please check the 'Funkamateur' website for first hand information.

see here: 

... to be continued

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