On Tue, 15 Mar 2005 12:49:01 -0500, "Netgeek"
wrote:

It's my understanding (and I
mean a fairly fuzzy understanding) that direct conversion has many
benefits but is limited to lower bands (unless you're the military with
a big budget)??? What are the trade-offs in doing a downconversion
followed by DDS-based conversion?

My suggestion of using a DDS for direct conversion in the 10-20 MHz
range is based on the assumption that DDS chips running with 50-60 MHz
clock frequency should be available at a quite a reasonable price,
compared to similar chips running at 400 - 500 MHz, which would be
required for direct synthesis in the VHF band.

However, translating the whole band down to HF requires a strong down
converter, especially due to the nearby strong signal broadcast band.
Some flimsy NE602 type converter will not survive very well in such
environment, but a high current preamplifier followed by a diode ring
mixer might be a better converter.

Paul OH3LWR

The Mini-Circuits SRA-2H comes to mind...............Level 17, which
requires 50mW of LO injection.

Pete

"Paul Keinanen" wrote in message
...
On Tue, 15 Mar 2005 12:49:01 -0500, "Netgeek"
wrote:

It's my understanding (and I
mean a fairly fuzzy understanding) that direct conversion has many
benefits but is limited to lower bands (unless you're the military with
a big budget)??? What are the trade-offs in doing a downconversion
followed by DDS-based conversion?

My suggestion of using a DDS for direct conversion in the 10-20 MHz
range is based on the assumption that DDS chips running with 50-60 MHz
clock frequency should be available at a quite a reasonable price,
compared to similar chips running at 400 - 500 MHz, which would be
required for direct synthesis in the VHF band.

However, translating the whole band down to HF requires a strong down
converter, especially due to the nearby strong signal broadcast band.
Some flimsy NE602 type converter will not survive very well in such
environment, but a high current preamplifier followed by a diode ring
mixer might be a better converter.

Paul OH3LWR