OK, I found it.
It turns out I didn't build exactly Farhan's circuit that uses just a current
balun for a phase splitter, I designed my own transformer that was actually two
transformers on one core. The one driving the switches was a voltage
transformer and driving the primary of that was a current balun. I did that
because my LTSpice analysis indicated that the current balun's phase split
starts to deteriorate when both the primary as well as the load gets unbalanced
wrt ground, as it does in this circuit. On the other hand, voltage xfmrs have
other problems due to capacitive leakages if you ground-reference the primary.
What I did here is an old method I learned when I worked in Cable TV design.
The voltage xfmr does the phase splitting and the current balun keeps the VT's
primary balanced wrt ground, resulting in better overall match and performance.
Others posted plots of Farhan's exact design if I recall though.
Anyway, the circuit and plots of the performance in both directions are
attached.
Joe
----- Original Message -----
From: Joe Rocci
To: minima@xxxxxxxxxxxxx
Sent: Friday, December 12, 2014 2:37 PM
Subject: [minima] Re: A New Approach
"It works better with two voltage transformers."
-------------------
Not so true. If you look at the plots I did with Farhan's D-KISS (I'll have
to dig them out), you'll see that his actually does a little better on the
isolation of residuals. Some of that might be in the transformers. As I recall
though, I built his up using the same voltage transformers I use in my quad.
I'm not sure what the comparative IP3's would be, as no one's done that kind of
testing here (that I can recall). Let me see what I can find in the archives.
----- Original Message -----
From: allison
To: minima@xxxxxxxxxxxxx
Sent: Friday, December 12, 2014 2:31 PM
Subject: [minima] Re: A New Approach
On 12/12/2014 02:13 PM, Joe Rocci wrote:
Allison
Here's the quad-switch mixer I've been talking about, along with a plot
of the outputs in a Minima-like scenario. The LO was 34 mhz and the RF signal
was 14 mhz, with a desired output at 20 mhz. The plot shows desired sigs and
residuals. Conversion loss was 4.5db.
Yes, thats the same one I've been calling double balanced (least for RF and
IF). The conversion loss is
low too. It works better with two voltage transformers.
That with your IF is Minima V3.
Allison/KB1GMX
Also similar is Farhan's D-KISS which eliminates the output transformer,
allowing a DC coupled output. I like mine for the 'balanced' topology and
Farhan's for the ability to deliver output down to DC, useful in direct
conversion receivers or balanced modulators. Mine uses two voltage transformers
and Farhan's uses a single current balun for phase splitting. Both versions
performed similarly under the test conditions shown in my plot.
----- Original Message -----
From: Joe Rocci
To: minima@xxxxxxxxxxxxx
Sent: Friday, December 12, 2014 1:50 PM
Subject: [minima] Re: A New Approach
I have another amp that I developed and haven't seen anywhere else but
I'm sure it's been done. Instead of an emitter to emitter complimentary current
buffer, this one's a collector to collector complimentary circuit that delivers
voltage as well as current gain with an end result of almost 20 db gain, over
50 mw uncompressed output and only 20 ma current @ 12V. It's almost flat to
over 20 mhz and only uses 2 transistors (3994/3906). Good input/output match
too. I like it for its simplicity, but it doesn't have the AGC capability which
was so important to me. Might be another good candidate for a sub into the
Minima though, using bus switches for turnaround.
Joe
----- Original Message -----
From: allison
To: minima@xxxxxxxxxxxxx
Sent: Friday, December 12, 2014 1:30 PM
Subject: [minima] Re: A New Approach
On 12/12/2014 10:51 AM, Joe Rocci wrote:
Rev 1.1 of the previously referenced paper is attached, showing
Rx/Tx switching using a bus-switch.
----- Original Message -----
From: Joe Rocci
To: minima@xxxxxxxxxxxxx
Sent: Friday, December 12, 2014 8:47 AM
Subject: [minima] Re: A New Approach
For anyone who might like to try out my Buffered HyCas IF
amplifier (B-CAS), I wrote the attached paper that describes background, theory
and construction notes. I intend to post something additional describing the
switching to make it BiDi.
Â
Joe
Joe,
That is great work and documentation.
Add a suggestion. For those wishing higher gains the use of two
packages and paralleling the
switches gets one clear of the substrate coupling issue. It might
even make for a cleaner board
layout and is not cost prohibitive. Relays can be used as well but
the coil current are often a
battery penalty.
Some history and useful info attached.
An interesting detail on the Hayward/Damm HyCas is they documented it
and presented it for
a very useful and flexible IF.  Their work characterizing it was
valuable as the circuit was forgotten
save for a few oldsters like me. made for interesting Emails. I'd
been using it for the front end of
my Allied/RadioShack AX190 for two decades by then and in 2001 build
of frankenradio my first
6M SSB design (bidirectional IF, 8pole filter, fet/bipolar RF, agc
and alc).  That radio is still in use
now mobile with Le Junque Box brick (uses MRF247 for 60W with 4W
drive on 6M).
They had speculated on its origins and at the time I recognized it as
a variant of the circuit published
in the early 70s National (and Siliconix) in ap-notes.  I'd used
it in differential form (two stacks coupled)
as the solution for the video amps in my first solid state O'scope.Â
The solution was twofold Miller reduction
and getting past the modest voltage limits of then current FETs. Â
The Miller reduction gets both more stable
gain and bandwidth and at that time saved a FET as at that time they
were not as cheap or common
in my parts supply. I've attached the ap-note the reference circuit
is on page 7 top but there are
other useful ones.
Note the circuit on bottom right page 8 used with a buffer into a
diode doubler circuit makes a fair
AGC detector rectifier for either RF or Audio AGC. If the same
circuit is used again after the diodes
and RC time constant it can provide level shifting without opamps
with a few value adjustments.
Everything old is new again. ;)Â Â That and a lot of old ap-note are
being scanned and return to the 'net
with a lot of valuable info.
Allison/KB1GMX
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