2T H-Mode Mixer by I7SWX (called MoMix)
for the Yaesu FT1000mkV & Field MP too * * *
HowTo transform a commercial receiver into a SUPER_RECEIVER (or quasi).
Simplyfied block diagrams.
Some time ago ...
surfing the WWW I stumbled upon a report for possible improvements of the FT1000MP receiver and consequently
also the newer series of the mkV-Field rigs.
That report was written by my friend Gian I7SWX.
What attracted my attention was the replacement of the 2nd IF mixer.
From a FULL_ANALOGIC classic stile to a DIGITAL ultra modern(n1) mixer and its superlative characteristics.
The very simplified schematics are shown above.
The above improvements simply "jump out" from a commercial equipment , making it a superlative receiver
(gain redistribution) from the 2nd IF roofing filter.
with the help of a STATE of the ART schematic.
The first reading of Gian's report was done in a very short time like a thirsty chap in the desert drinking his first glass of water.
Reading the report with more calm I tried to understand what Gian was talking about....digital mixers, diplexers,squarers,
signal buffers, impedances and signal levels.
As a natural reaction to all those technical explanations led me to think about many questions.
The easiest solution was to write to Gian. He was very kind and open to clarify all my requests.
Of course I passed many evenings to search&read on the WWW about the 2THmode mixer.
From the well known PA3AKE web site to the PIC-A-STAR receiver project, to Sergio IK4AUY and many others .
All the references retuned my readings to the Gian's optimum (and perhaps fantastic) mixer replacement .
Of course all those mods so well explained theorically on the paper MUST be transferred in the hardware world.
The hardware part will be explained below, first comes the long awaited test report.
First Test (semi-pro) and i m p r e s s i o n s.
After Gian's MoMix mixer replaced the original, the couriosity for feeling the performances of the new functionalities was big.
The receiver worked quite well and 2 winters of activity on the low bands specially the 160mt showed that the mod
was doing the job for which was developed.
Live comparisons, between an original FT1000MP and the modified FT1000-Field receivers, were made several times with different
bands conditions. Every time the MoMix-Field resulted a better performer specially in those bands where a lot of stations are close one to the other.
Of course the improvements of the Dynamic Range \ IP3 \ etc.strange numbers are not "audible-things",
but it was much much easier to listen to very weak stations even close to the strongest one.
As I have no specialized test equipments, I had to wait looong time for a visit of Gian I7SWX to my shack.
The tests has been done with a I7SWX homemade 10Mhz,10Khz spacings dual tone generator.
The above pics show Gian at my desk and the very clean spectrum of the homemade generator.
The spectrum analyzer is Gian's SignalHound portable SA and as RF attenuator a 140db semi-pro device.
As the time Gian stayed at my qth was too short, to make a deeper test session, this first experience showed
that the modified rig was reaching easily the more modern receivers.
We both were so suprised of the results, that we have quite forgotten to take any picture of the resulting signals,
for such documentation we MUST wait till next time.
Instead what we have done is to put on paper all the results of the measures.
The following table reproduced from FUNKAMATEUR magazine (n2) and the below pic show Numbers that can be compared to some
old and new receivers.
The above values are the minimum values Gian has suggested to write on the table.
We have repeated for every measurement two or three times and some tests went well and sure above the published numbers.
As there are some more THINGs to be added and modified in my receiver, we both have decided that in a next testing time
all the measures will be repeated to get the best performances and that pictures will be taken to demonstrate how a commercial
receiver can become a SUPER RECEIVER with the Gian's mods.
In my shack, opening (well...reopening) my main rig is quite simple as I had already done such task many times ,
Take a look at my howto for my other modifications.
The hardware part follows ASAP.
Note 1 = the proper description is : passive switched mixer using digital fast bus switches.
Note 2 = the table reproduced with permission of FUNKAMATEUR magazine , an article of Petermann B.,DJ1TO:
KW-/6-m-Transceiver Elecraft K3: vieles anders – und besser. FUNKAMATEUR 58 (2009) Nr. 4, p. 374–379