[hpsdr] Now this is what I call a real SDR - OT

[Scott Cowling]

Since it is kind of quiet, I'll risk a bit of Off Topic here...

I just read this on eHam at

http://www.eham.net/reviews/detail/3151

73,
Scotty WA2DFI

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I bought a vintage Drake 2-C, fixed few things and aligned it. Well, having 
a R8 I was not extremely impressed at first. This receiver is hybrid, tubes 
are used up to demodulation and solid state transistors are used for 
demodulation. It sounds pretty much like the Drake R8, the if filters are 
both at 50Khz and LC type and spaced similarly. It is a triple conversion 
with preselector. Well I prefer the double conversion and the front-end 
design of the R8, which I consider a better set.

HOWEVER I MODIFIED IT VERY EASILY TO DRAMATICALLY IMPROVE ITS PERFORMANCE 
AND GET UNSURPASSED PERFORMANCE.
1) First it is not a general coverage receiver but the preselector can tune 
from 3 to 30Mhz if crystals are provided. Well without using crystals I 
could tune continuosly from 3 to 19Mhz the receiver feeding the reciver 
with an external DDS oscillator controlled by a PC! I used the DDS60 
available at
http://www.amqrp.org/kits/dds60/index.html and a small impedance tranformer 
(50:400) between the DDS output and the external crystal socket. Not too 
bad for about 40USD!!! Moreover I used the DDS to align the receiver!!!

2) The 2nd IF is at 455Khz. Well I connected to the socket for the Noise 
blanker a third solid state mixer to convert it to 12Khz and connect it to 
the sound car of a pentium 4.
In a small shielded box I placed a Crystal mixer fo=462 KHz use for IF 
exact 450 kHz which I bought at http://www.sat-schneider.de/DRM/DRM.htm for 
other receivers.
Before the mixer I placed in series two wide Murata filters F-450K-P2 which 
match well the mixer and provide excellent analog filtering to the third 
external mixer.

3) I connected the mixer to the soundblaster of the laptop and used the 
DREAM software downloaded at http://www.sat-schneider.de/DRM/DRM.htm.

Well, performance is outstanding. I could get a very clean sound, perfect 
DSP filtering at IF, IF noise reduction, Digital AGC and DRM and even FM 
reception.

Basically what this OLD TUBE radio becomes after this modification is a 
TUBE SDR software defined radio!! Only the stages up to the second 
conversion are used in the receiver. The external mixer connects the Drake 
to the computer. Demodulation and audio is made by the computer.

The last but not the least, no hole was drilled in the receiver and it can 
be used as before the mod without any change. Just Full Coverage, IF-DSP 
FILTERING and CLEAN DIGITAL DEMODULATION have been added!!!

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