[minima] Re: How to adjust the bias of the KISS mixer in the Minima - Video
- From: Joe Rocci <joe@xxxxxxxxxx>
- To: minima@xxxxxxxxxxxxx
- Date: Sun, 30 Mar 2014 07:06:05 -0400
I'm still not clear what the test hookup or goal is. Is this the normal mixing
process with the two input signals (LO & RF) connected to their usual points &
at their usual levels/frequencies? What are those levels/frequencies? Or is
this some sort of test of reverse isolation where the signals are hooked up
backwards? Please provide a thorough description of the test goals and
conditions.
Joe
Sent from my tablet
-------- Original message --------
From Thomas Sarlandie <thomas@xxxxxxxxxxxxx>
Date: 03/30/2014 6:13 AM (GMT-05:00)
To minima@xxxxxxxxxxxxx
Subject [minima] Re: How to adjust the bias of the KISS mixer in the Minima -
Video
Joe,
The red and yellow curve are the voltage (ac coupled) at the drains of the
JFETs (where they connect to the transformer). Note the little arrow on the
left for the reference (0V) of each of them.
The green curve is the sum (calculated by the scope) of them.
I think what I am seeing on the RF port is the sum of those two signals. If
they were perfectly phased out, the LO would be completely balanced out and
there would be no LO on the RF port. But because they are not absolutely
symmetric, the sum is not null and I am guessing this is why I have a strong
leak of the LO on the RF port.
This is just a theory. Does this make any sense?
thomas
On Sun, Mar 30, 2014 at 2:40 AM, Joe Rocci <joe@xxxxxxxxxx> wrote:
Thomas
I'm not sure what I'm looking at in ths picture. Can you elaborate?
Sent from my tablet
-------- Original message --------
From Thomas Sarlandie <thomas@xxxxxxxxxxxxx>
Date: 03/30/2014 1:12 AM (GMT-05:00)
To Thomas Sarlandie <thomas@xxxxxxxxxxxxx>
Cc minima@xxxxxxxxxxxxx
Subject [minima] Re: How to adjust the bias of the KISS mixer in the Minima -
Video
About my asymetry, if I inject just the LO on the IF port, it appears on the RF
port at -15dB. It's at -48dB on the IF port.
I have plugged my scope on the drains of both JFET and I have two signals that
are out of phase but if I sum them (the green curve) on the screen, I get a
very clean sine wave and intuitively I think that this is what I get on the RF
port.
If I unplug one of the drain, the LO goes down by 5dB.
I have shortened all the connections. And made sure I had the same length on
the transformers windings for the "symmetric" windings. I have also rewound the
transformer that had very small wires with AWG32. I still get that asymmetry.
Any idea?
73,
thomas
On Sat, Mar 29, 2014 at 8:35 PM, Thomas Sarlandie <thomas@xxxxxxxxxxxxx> wrote:
Mvs Sarma / Joe: I just tried driving it with a square wave but it makes very
little difference, maybe 1dB less on the LO leaked and on the mixing product.
Nothing amazing.
Joe: I can try your self-biasing setup. Could you refresh my memory on this one?
Joshua: I don't explain the asymetry either but I see it on both my mixer. I
will keep scratching my head a bit on this one.
I will also do some research on compression point measurement and IMD3
measurement. I have a vague understanding of the theory but it will be fun to
actually try to get the measurement.
73!
On Fri, Mar 28, 2014 at 5:48 AM, Joshua Blanton <jtblanton@xxxxxxxxx> wrote:
Hi Joe,
I do not currently have an (easily usable) IMD3 test setup, which is why I
measured P1dB. I will look at what I need to re-jigger to test IMD3 when I find
some more bench time.
Thanks,
Josh, KB8NYP
Sent from my phone - please excuse my brevity.
On Mar 27, 2014 12:04 PM, "Joe Rocci" <joe@xxxxxxxxxx> wrote:
>
> Hi Josh
>
> I'm interested in both the P1dB and IMD3. My rule-of-thumb for diode ring
> DBM's is that IMD3 is about 15 db above P1dB. I wanted to find out if the
> JFET mixer behaves the same. Intuitively, I'd expect the JFET's non-linearity
> to be 'softer' than a diode's, so maybe the IMD3 is even better.
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