[minima] Re: for minima project

  • From: allison <ajp166@xxxxxxxxxxx>
  • To: minima@xxxxxxxxxxxxx
  • Date: Mon, 25 Jul 2016 12:44:43 -0400

On 7/25/16 11:36 AM, Mark Smith (Redacted sender smittyhalibut for DMARC) wrote:

Thank you Ben for that. I looked at the schematics and understand them. I've been a ham since 1991, but am just getting into RF electronics and circuit design. Schematics like that one make it so much easier to understand what's going on. Thank you!

One question, that's not specific to your design. I've never understood the benefit of more than two conversions, one IF. Why does the HF1 convert to 45MHz, loosely filter with LC, then convert again to 10MHz and filter with crystals? How is that better than converting to 45MHz, filtering with crystals, then converting directly to base band?

Continuous tuning from some low frequency like 1mhz to 30mhz without crossing the IF, or having image problems.
That's the advantage of having the IF higher than 30mhz. The pain is that you need to down covert from that IF to
something lower where selectivity using crystals is easier.

The down side is more gain stages but they are simple and fairly cheap. The other is more mixer and oscillators
to cause birdies.

The transmitter low pass filters are still required for harmonics.

In general a multiband rig is harder to do well than a monobander.

There are also a couple more amp stages in there, but those are probably just to make up for losses in the filters and conversions, and could be added anyway without the extra conversion.

There were two issues with Minima, RF from the LO making it to the antenna and IF getting to the antenna.
The filter requirements were hard to meet.

Allison/KB1GMX

To be clear: I'm not saying you're wrong, I'm totally ignorant and asking for education. :-)

Thanks!

-Mark

On Jul 25, 2016, at 7:23 AM, Ben Aupperlee <beninturkye@xxxxxxxxx <mailto:beninturkye@xxxxxxxxx>> wrote:

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