The Minima is still the best sounding receiver that I have brewed. There is
a little complicated way to do the transmission;
Use an NE612 mixer for transmit. It is doubly balanced with excellent
suppression of local oscillator. you could tap out the transmit IF after
the filter and feed it to the NE612/SA602 mixer and proceed with a separate
low pass filter.
the other, really impressive way out is to use narrow-band IF filters. I
know that i complicates the design. but really, it is the same doggone
circuit for each band. it is just a matter of wiring it all up, one band at
a time. but it will give you a robust, exceptionally well performing
transceiver.
- f
On Mon, Jul 25, 2016 at 10:14 PM, allison <ajp166@xxxxxxxxxxx> wrote:
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> wrote:
