I've got an RFSpace, Inc. SDR-IQ Software Defined Radio, which is a
truly nifty gadget, but it stops at 30 MHz. I'd like to put together a
downconverter that I can drive with a DDS LO or my HP 8640B, to pull the
stuff above 30 MHz down into some part of the HF (or lower) spectrum. It
would be nice to be able to see a 190 KHz chunk of 6m or 2m or 70 cm., as
I can with the spectrum below 30 MHz.

At the moment, I'm looking at just plumbing together a MiniCircuits mixer
(probably +3dBm or so), some low-pass filtering, and maybe some front-end
gain so that I can be sure there's enough RF to drive the mixer.

Does anyone know of
COTS boxes to do this, or
designs in QEX or some other ham publication to do this, or
another ham who has done this or is working on it?

If someone here is doing or has done this, I'd love to know if I need a
gain block before the mixer. Other constructive comments will be welcome,
too.

73, de

--
Mike Andrews, W5EGO

Tired old sysadmin

Mike Andrews wrote:

I've got an RFSpace, Inc. SDR-IQ Software Defined Radio, which is a
truly nifty gadget, but it stops at 30 MHz. I'd like to put together a
downconverter that I can drive with a DDS LO or my HP 8640B, to pull the
stuff above 30 MHz down into some part of the HF (or lower) spectrum. It
would be nice to be able to see a 190 KHz chunk of 6m or 2m or 70 cm., as
I can with the spectrum below 30 MHz.


I have considered using subassemblies from C-band satellite receivers for
a similar task; the bandwidth may not be as great but certainly useful
for some tasks, and the tuning range is substantial (sorry I don't have
useful numbers while I am posting this).

Regards,

Michael

Mike Andrews wrote:
I've got an RFSpace, Inc. SDR-IQ Software Defined Radio, which is a
truly nifty gadget, but it stops at 30 MHz. I'd like to put together a
downconverter that I can drive with a DDS LO or my HP 8640B, to pull the
stuff above 30 MHz down into some part of the HF (or lower) spectrum. It
would be nice to be able to see a 190 KHz chunk of 6m or 2m or 70 cm., as
I can with the spectrum below 30 MHz.

At the moment, I'm looking at just plumbing together a MiniCircuits mixer
(probably +3dBm or so), some low-pass filtering, and maybe some front-end
gain so that I can be sure there's enough RF to drive the mixer.

Does anyone know of
COTS boxes to do this, or
designs in QEX or some other ham publication to do this, or
another ham who has done this or is working on it?

If someone here is doing or has done this, I'd love to know if I need a
gain block before the mixer. Other constructive comments will be welcome,
too.

73, de

Mike,

With what you describe, the COTS box would be a connectorized
MiniCircuits mixer. Just attach the antenna to the RF port, the signal
Generator to the LO, and the receiver to the IF ports. The noise figure
will be kind of high, but you should be able to see moderately strong
signals. A MiniCiruits amp in front would help sensitivity a bit, but
at the price of possible intermodulation from strong signals. Adding
additional RF and IF filtering would help as well.

Good luck and 73,
Erich N6FD