EMRFD Message Archive 507

Message Date From Subject
507 2007-03-07 06:51:49 Giancarlo H-Mode Mixer as tested by PA3AKE
Hi All,

If you like to know more about D'MIXER that removed the mixer from
the most critical stages in a receiver see what Martein Bakker,
PA3AKE, has just published; a magnificent document regarding his
evaluation of Colin Horrabin's "H" mode mixer under various test
conditions and using many different transformers and active devices.
He spent thousands of Euros on proper test equipment, and as many
hours obtaining his published results. This is the real way we
should do measurement but certainly it requires a lot of investment
in $$$$ and working time and also knowledge. Martein's document has a
lot of pages with a lot of information and it is a good reading for
peoples that know what he is talking about and also for people that
want to learn. This is a sharing of information and knowledge that
sometimes is missing in our amateur radio environment. As Harold
Johnson, W4ZCB, stated: I commend the read to your attention, LOTS of
meat in the pages. You can get the document at:


I am sure you will see that Harold is right, there is a lot of meat
to chew and digest too. The comparison is not only associated to the
FST3125 switches but there is a very interesting comparison with
modern video switches.

A good friend of mine, Eraldo Sbarbati, I4SBX, has done a similar
work during 2005 winter. A lot of work. He has made tests on
commercial mixers and then on the H-Mode with the 3 transformers
(G3SBI original configuration, used in the CDG2000) and the 2
transformers (I7SWX simplified version, used in the STAR) using
various balun cores (size, material and turns configurations) using
homebrewed transformers. He has also checked where the mixers loose
the 1:3 ratio. I4SBX has started the publication of these reports in
the Italian Ham Magazine RKE, Radio Kit Elettronica, since this past
summer. The final two articles fully dedicated to the H-Mode Mixer,
with particular focus on the two transformers version, are expected
to be published in the March and April 2007.
Eraldo's tests include the divide by two (74AC74), and fundamental
squarers (using 74AC86 XOR and LVDS receivers). The comparison is
also referred to the super CDG2000 RTX, front end and post-mixer
roofing filter.

It will not be possible to make the translation from Italian into
English of all six issues due to copyright and the work required. I
will discuss with I4SBX any possibility of publishing a digest of his
work, including his tables and graphics produced using the N2PK VNA.
You will be kept posted … if …

G3SBI H-Mode Mixer invention has still a lot to give ... Thanks so
much Colin!

73 and enjoy PA3AKE's document.

508 2007-03-09 20:58:38 Mike Brainard Re: H-Mode Mixer as tested by PA3AKE
I just wanted to share the thought that it may not be strictly
necessary to divide the local oscillator frequency by 2 in order to use
those switches which require Q and !Q for control.

A SET-RESET flip flop could be driven in push-pull from a bifilar
secondary winding to implement a trigger circuit with Q and !Q outputs.

For those who missed the dawn of the digital era, a S-R flip flop can
be implemented with a pair of cross connected inverting gates.

509 2007-03-10 03:09:43 Joe Rocci Re: H-Mode Mixer as tested by PA3AKE
I don't think that will guarantee the duty-cycle symmetry that the divide-by-2 approach provides.
----- Original Message -----
510 2007-03-10 22:51:39 Mike Brainard Re: H-Mode Mixer as tested by PA3AKE
> I don't think that will guarantee the duty-cycle symmetry that the
divide-by-2 approach provides.

PA3AKE shows some results (FSA3157 switch + 74AC04 squarer circuit)
where the duty-cycle was tweaked for optimum mixer performance.
Performance parameters did not all optimize at the same duty-cycle
setting. It is certainly appealing to one's intuition that the duty-
cycle symmetry guaranteed by the divide-by-2 approach is optimum,
however this work suggests that the ability to adjust duty-cycle may be
useful. An S-R trigger could be made adjustable by providing separate
bias to the R and S inputs. The 74AC04 squarer circuit used by PA3AKE
provides an alternative to divide-by-2 for SPDT switches with a single
control input. I simply wanted to point out that an S-R trigger could
provide a similar alternative for SPST switches that require
complementary control inputs.
511 2007-03-11 09:30:39 Allison Parent Re: H-Mode Mixer as tested by PA3AKE
512 2007-03-11 09:35:21 Allison Parent Re: H-Mode Mixer as tested by PA3AKE
513 2007-03-11 09:57:00 Joe Rocci Re: H-Mode Mixer as tested by PA3AKE
The XOR doublers I've seen use an RC delay  (or sometimes a gate delay) in one input leg of the XOR. Doesn't this degrade the HF phase noise by introducing a tiny amount of jitter in the delayed path?. Every RC oscillator I'm familiar with certainly has this problem. Also, if the waveform that's driving the XOR doubler isn't symmetrical or if the XOR doesn't have matched prop delays, I believe the divided signal will still be asymetrical, no?
----- Original Message -----
514 2007-03-11 10:04:43 Allison Parent Re: H-Mode Mixer as tested by PA3AKE
516 2007-03-12 12:34:15 Giancarlo Re: H-Mode Mixer as tested by PA3AKE
Hi Allison et all,

it is not necessary to have a divide by two local oscillator to drive
the H-Mode Mixer.

I have poste, in FILE, one of my simplified H-Mode Mixers using two
transformers in place of the 3 as in the original G3SBI design. The
squarer is made of XOR 74AC86 and you have two XOR gates giving
complementary LO signal to the FST3125. You can see a simple balance
adjustment. This circuit is used in the G3XJP STAR transceiver. The
transformers are made using balun core #43-2403 or - 202. Do not be
scared by the "strange" 5 winding transformer.
Unless you are really looking for IP3 around +40dBm you may avoid the
balance adjustment.
You may look at some measurement data on both the 3T G3SBI and 2T
I7SWX H-Mode Mixers done by JA9TTT - See the "SW Funny translati