Differences between ULRs and SDRs

Rick Robinson <w4dst@...>

The Si473X based ULR radios are not software designed radios, they are hardware based. The Si473X family use an external enbedded code microprocessor to send the commands to the Si chip to control frequency, bandwidth, etc. This is the same as any digital radio be it a CCrane SWP or an Eton E10. There is software, or firmware, in the microprocessor that gives the Si4734 its commands, but this is not "software designed radio".

A true SDR, see the Elektor SDR receiver or RFSpace receivers, have no RF components other than front end bandpass filters. All the functions of the Si4734 hardware are done in software with an SDR design. An SDR relies on the sound card of a computer along with special software to perform all the functions the Si4734 receivers perform with hardware. The DSP functions of the ULRs are performed with hardware designed into the IC while the DSP of an SDR is performed by the control software.

SDR receivers use what is called an I/Q mixer and output 2 signals, the I and Q outputs, to the sound card. The Si4734 based chips and no I/Q output. ULRs are "stand alone" receivers, SDRs are not. SDRs must have a sound card to operate and SDRs have no problem with AM, FM, CW, SSB, and multiple bandwidths since all of this is done with software. This is why the ULRs would have a problem with adding a BFO while SDRs have no problem with multiple modes.

For $1.80, you can download the Elektor article on the Elektor SDR radio. This is a very informative article on the basics of SDR radio. For about $160 including shipping to the US, you can buy an assemble and tested Elektor SDR and a nice selection of free SDR software to explore. My Elektor SDR is on the way and if anyone is interested, I'll post a report to the ULR list even though it is off topic.

Good DXing,

Rick W4DST

On 1/7/2011 8:27 AM, Gregory wrote:
The DSP radios are using what is called "Software Defined Radio".
Adding CW and SSB demodulation would be done in the software.
I think the big hurdle for these particular radios is the 1 KHz local
oscillator steps are too large. The frequency synthesis would have
to be redesigned for something like 50 Hz steps. It's possible
as my "Buzz Aldrin" radio has small step synthesis.

If you are interested in SDR radio check out the yahoo groups
soft_radio and sdr-iq. What these radios are capable of is
astonishing. The PL-380 and similar radios give you just a slight
taste of what they can do.

73 Greg

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