Homebrew SDR Receiver

[ka1tdq]

I found this article ( A Binaural I-Q Receiver)  http://p1k.arrl.org/pubs_archive/97523 in a 1999 issue of QST, page 44.  I was wondering if you could use this portion of the project shown in the picture to make a home-brew SDR receiver.  The I/Q outputs are shown coming off of the mixers and could that be used to feed the I/Q inputs to the sound card of SDR software?

A fundamental frequency sine wave input could be used rather than using a frequency/4 application that the SoftRocks use.  This would be perfect for my $16 Chinese DDS VFO that only goes to 8 MHz.  I could use this receiver on 40 meters.  Just put the VFO on the center of the 48 KHz segment of the band you want to use.

Jon
KA1TDQ

[W3RSW]

Go for it. Not sure of the dynamic range, overload from AM BC, rejection of adjacent QSO's , etc. compared to a a DDC SDR using say an LTC2208 (16 bit, or even a lesser 14 bit chip) but you'll have fun finding out.  Also what's the noise figure of your Chinese oscillator?

Guess it won't matter much for normal 40 meter receiving of the boys on 7200  and you probably will want to lash up a buffer stage on the IQ outputs on the way to your sound card.  A decent sound card might get you to 192kHz bandwidth.  LP-pan has recommended cards listed.

[ka1tdq]

I was wondering about the output of the mixers since the circuit isn't powered.  An amp at the outputs would be needed. 

And I'm not sure of the noise figure of the VFO.  I'm using a similar one to drive my CW transmitter.  I don't have a scope and such since those things are highly over-rated.   

My other option would be to get a SoftRock SDR for $21 and put a different crystal in it to get me to the AM window. 

Jon

[W3RSW]

This is probably a better way to go for you.

Proven, good entry level SDR, reasonable price and you still get the fun of building.  Yes, even winding a turn or two.

http://fivedash.com/index.php?main_page=product_info&cPath=1&products_id=16

SoftRock RX Ensemble III HF Receiver Kit
 
$68.00
   
The SoftRock RX Ensemble III HF Receiver Kit provides coverage for HF operation, 1.8 MHz through 30 MHz. It includes a 9.5dB pre-amplifier for the 16 MHz to 30 MHz range for improved, low-noise reception.

 The circuit board measures 4.5 inches by 2.0 inches.

[KF1Z]

OR

add a $30-35  "QPR2000"  vfo kit to the softrock LITE  and your SDR will go "anywhere".


From 1mhz to about 60mhz.

just remove any frequency sensitive parts from SRlite.

no crystals, no problems.

Plus the QRP2000 is compatible with most SDR software, so it's frequency as an LO can be controlled directly
from the SDR software.

And, if you get bored with that, you still have a handy RF generator that is useful past 200mhz.

[W4AMV]

"I found this article ( A Binaural I-Q Receiver)"

I built the binaural receiver several years ago and it is a fun unit too use particularly if you have a good set of audio stages in the I and Q amplifiers. That said, if you really want to get the full effect of the binaural response, particularly for CW, concentrate on a super fidelity set of audio strips. My Rx VFO and LO line up used the imaging IF concept, great for a DC receiver, so that one with one VFO and division by 2 and multiplication by 2 and 4 etc... you can cover 80,40 and 20 meters. With proper audio channels configured and decent fidelity speakers, signals appear to float in space. Turning your head one way or another will provide a form of single signal selectivity! Quite fun. I'll try to post a pix of the unit.

Alan

[ka1tdq]

I just got my VFO kit in the mail and put it together. It works, but...

It only seems to want to go to 60KHz. It has a high speed option at 1, 2, 4 and 8 MHz, but that's it. You can't vary off of those frequencies.

So much for $16.  It's just a good audio generator.

Jon