[minima] Re: A New Approach
- From: allison <ajp166@xxxxxxxxxxx>
- To: minima@xxxxxxxxxxxxx
- Date: Fri, 12 Dec 2014 16:00:57 -0500
On 12/12/2014 02:55 PM, Joe Rocci wrote:
> 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.
>
Ok, compound transformers are not unusual to me and for the reasons
stated.
The biggest problem is transformers and their size are frequency
related aka phase.
Smaller is better but choking impedances are hard to attain without fine
wire to get
the needed turns. Then total length as well as path length is still a
factor. Too small
and then power related issues rear their head.
TLTs in both voltage and current form are still art. Despite all the
models I have a file
with papers and books by Sevick, Guanella, and Ruthroff et al together
for those
tough cases.
Yes, your FST3257 plot is cleaner. Proves that mixers is the sum of the
parts not just
the switch used.
Allison/KB1GMX
> Anyway, the circuit and plots of the performance in both directions
> are attached.
>
> Joe
>
> ----- Original Message -----
> *From:* Joe Rocci <mailto:joe@xxxxxxxxxx>
> *To:* minima@xxxxxxxxxxxxx <mailto: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 <mailto:ajp166@xxxxxxxxxxx>
> *To:* minima@xxxxxxxxxxxxx <mailto: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 <mailto:joe@xxxxxxxxxx>
>> *To:* minima@xxxxxxxxxxxxx <mailto: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 <mailto:ajp166@xxxxxxxxxxx>
>> *To:* minima@xxxxxxxxxxxxx <mailto: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 <mailto:joe@xxxxxxxxxx>
>>> *To:* minima@xxxxxxxxxxxxx
>>> <mailto: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. The solution was twofold Miller
>> reduction
>> and getting past the modest voltage limits of then
>> current FETs.  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.Â
>> 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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