Re: Stone Soup


On Wed, 5 Sep 2018 16:04:14 +0200
"Henning Weddig via Groups.Io" <> wrote:


I am also thinking heavily on a new design!

But what has t be done beforehand is to specify what we want!  I already
posted this requirement but only got minimal response. I know for EE´s
to write a spec is a task which is not welcome...
Yes... yes. Basically, I want to have a cheap radio, that have a reasonable good receiver, and its transmitter meets the FCC and European standards. I want to use the RIG mainly on digital modes, like PSK. It should be open source, and designed by KiCAD.

So some yo Your ideas stated below can be used as a first spec. I want
to include some more thoughts:

use diplexers especially on the IF port of mixers-- bandpass typ (sereis
resonator + parallel resonator) with a relative low loaded Q (about 3).

I know there is an old paper "reactive loads the big mixer meanace" 
published in the 70´s . Unfortunately I do not have this paper.

For the first mixer one more thought: in transmit mode the other
sideband (LO + 45 MHz) which has the same amplitude as the wanted
sideband is not terminated properly. So my idea is to put a lowpass -
high pass diplexer the hp side to be terminated into 50 ohms on the RF
port of the mixer.
So the diplexers are there to load the mixers equally at all frequencies? Why not then just load it with a resistor, and insert a follower? Sorry my RF knowledge ends here.

For the frist mixer: the configurattion should look like this:

RF port with LP- HP diplexer

IF port with BP diplexer but then a 90 deg hybrid with two xtal filter
branches summing up into a second 90 deg hybrid. In order to get a good
match both fitler branches should have equeal amplitude (S21) and
transmisson phase (Phi21) characteristics.
What do we gain by the hybrids? Sorry, I don't want to challenge you, I just simply want to understand your motivations.

Then a first bidi amp (low noise would preferrable) but our normal bidis
with 6 dB NF could also work. We do not need a super low overall NF! 
For these bidis we should use appropriiate high ft transistors as
Allison already stated!
Yes. I think this is the point where everybody agrees. We shell dump the 2N3904s. However, I'm thinking about not having bi directional amplifiers. What if we create separate TX and RX circuit? All we loose is two mixers and the XTAL filter. Also, why the transmitter shall be double conversion?

In order to avoid  the still existing problem of the spur genratoed
within the mixer I chose a IF of 70 MHz. XTAL filters were ordered.
Could you write the exact device you ordered?

So please have a look on my block diagrammes and total noise calc.

Before a new pcb is routed (preferrably 100 * 100 mm) the new sub
modules should be characterized. I do have a good equipped home lab with
spectrum analyser, signa l gerator VNA ---).
That's good. I only have Oscilloscope. So may I ask you to publish your test results if you have the thing up and running?

Thank you very much for your thoughts.

73s de HA5OGL

Levente Kovacs
Senior Electronic Engineer


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