Hello Mark
I am building my TRX based upon the idea of the si570 and si5351, just what you
typed. I extended the use of the 5351 by using the third oscillator to test and
tune the set with the help of extra software programs. I am currently writing
the manual as a form of a catalog of all the modules you could choose from , to
make it qrp or 50 watt, a one bander or 3 or all bander.
In case you are interested, i can send you a zip later.
Regards Ben (in Turkije)
-------- Origineel bericht --------
Van:"Mark Smith (Redacted sender "smittyhalibut" for DMARC)"
<dmarc-noreply@xxxxxxxxxxxxx>
Verzonden:Tue, 26 Jul 2016 08:34:52 +0300
Aan:minima@xxxxxxxxxxxxx
Onderwerp:[minima] Re: for minima project
Thank you, all three of you who gave a great answer to my question. The first
IF being high allows continuous tuning but crystal filters are rubbish up
there. So convert to the second IF where we can filter nice an narrow as
needed. Then, down to base band audio. That makes a lot of sense. I wasn't
aware of that limitation of crystal filters.
So, the KISS mixer from the minima was really a problem? The write-up made it
sound like it was better at rejecting the carrier than you all make it out to
be. Not as good as matched diodes like the HF1, then?
Next question: any reason that I couldn't use an Si5351 for at least two of
the LOs (since I can do two completely independent PLLs, but the third is
dependent on one of the other two), probably the VFO on the front end, and the
second IF mixer, so that I can just control the USB vs LSB in software at the
LO, and remove the whole complex oscillator? Why would that be a bad idea?
Add a third oscillator, and you could implement an IF Shift by moving both LOs
around the crystal filter up or down a bit.
-Mark
On Jul 25, 2016, at 9:44 AM, 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:
