mixer: DBM or dual gate mosfet?
 

What is the IP3 of a typical dual gate MOSFET mixer?
One can also use HC4066 or 4053 as the switching element at lower
freqs.

JJ


I really do not know what is the IP3 of a DG Mosfet as I never have
seen any value reported. I hope some readers may have data on this.
Certainly we have to look at IIP3 and OIP3 as the DGM mixer may have
high conversion gain 15-20dB and is somewhat limited in dynamic range.
Maybe it could have an OIP3 around +5dBm equivalent to an IIP3 of -10
to -20dBm .... more or less similar to the NE602.
The DGM mixer was a common mixer in the first series of transistorized
RTX with valves PA (FT101Z, TS820 etc). The DGM has a good square law,
better than JFET.

74HC4066 is OK at low frequency conversion but it has a haigh
conversion loss, around 8-10dB and so associated noise figure.

Today the switched mixer should use fast bus switches like the FST3125
family when looking at high performance mixers. The examples are the
CDG 2000 and STAR (Pic-A-Star) projects with IP3 around +40dBm and
+36dBm, where the H-Mode Mixer with FST3125 is used.

73

Gian
I7SWX

mixer: DBM or dual gate mosfet?
 

Anyone remember the CA3028 singly balanced mixer?
It was just 2 transistors as difference amp and current source transistor.
What would the IP3 be for it?

JJ

mixer: DBM or dual gate mosfet?
 

mixer: DBM or dual gate mosfet?
 

Why use a AD831 if the noise figure is 10dB?

It has gain, high IP3 and 10db my mixer standard is not that bad.
A low gain RFamp with low noise figure will override mixer noise.
Of course the RFamp must have a good IP3 as well.

Allison
Ok, I like to try the AD831.
When is dual supply better than single ended?
There must be a socket to fit the package but is it all right to solder
tiny leads to it for prototyping?

JJ

mixer: DBM or dual gate mosfet?
 

Hi all,

Allison has given important information on mixers data.

His comments are very usefull.

I would like to underscore the last note:

All of that is good but unless the post mixer amp, IF and filters
following it are up to the task and well matched the results can be
very disappointing. When going to that level of performance one
needs to look at the recieving system and examine carefully.

It is right to relook at a receiver design when selecting a high
performance mixer. The limiting problems will show up in other stages
as the improuvements may not be very detectable.... amplifiers,
filters, l.o. phase noise...

Well one need to start from somewhere to improuve a receiver. If the
non mixer stages have a maximum IP3 of around +15dBm, certainly a
+35/40dBm mixer may not make much of a difference, unless it is
replacing a NE602. In this case you may use the I7SWX 1 transformer
double balanced mixer using the FST3125 (half of an H-Mode mixer) with
an IP3 of +25dBm.

As an example, I defined with afriend of mine a mod on the Elekraft K2.
The 1st mixer (TUF) was replaced by an I7SWX 2T H-Mode Mixer followed
by a 10kHz BW 2 xtal roofing filter . Two tones at 7.050 and 7.070 MHz

IP3 Results of the K2 we

Original mixer: +15dBm
with H-Mode Mixer: +27dBm

as you may see these are important differences. The actual limiting
stage is the original post mixer amplifier.

73

Gian
I7SWx

mixer: DBM or dual gate mosfet?
 

"Giancarlo Gian Moda, I7SWX" wrote in
ups.com:


Well one need to start from somewhere to improuve a receiver. If the
non mixer stages have a maximum IP3 of around +15dBm, certainly a
+35/40dBm mixer may not make much of a difference, unless it is
replacing a NE602. In this case you may use the I7SWX 1 transformer
double balanced mixer using the FST3125 (half of an H-Mode mixer) with
an IP3 of +25dBm.

Gian
I7SWx

That is a very interesting suggestion. Where can I find the 1 transformer
DBM using the FST3125?

JJ

mixer: DBM or dual gate mosfet?
 

Hi JJ,

the note on the 1T DBM was reported in RadCom, Technical Topics column,
June 2004.

I asked a friend to insert all mixer infos in my web page
www.qsl.net/i7swx but I do not know when he will be able to do it. In
my web page in homebrewing you my read the experiences and measuremnts
done by JA9TTT on both versions (3T & 2T) of the H-Mode Mixer. This is
a software package translation from japanese but it is understandable.
You will be able to see Spectrum Analyzer measurents too.

If you send me (callsignatyahoo.com) your e-mail address I can send you
the complete 1T DBM note in english (more stuff than in TT).

A NOTE for ALLISON ... I see you have been fiddling with DEC stuff.
Were you working for DEC or a customer? I was with DEC for a quarter of
a century ...hi

73

Gian
I7SWX

mixer: DBM or dual gate mosfet?
 

mixer: DBM or dual gate mosfet?
 

Hi Allison,

From '83 to '93. Had a 6digit number as I was part of CSSE and
central engineering for high end printing systems. I really liked the
Mill.

Ah..OK CSSE ... I sold a PDP11/10 with a card reader from CSS to the
Italian Goverment as a donation to a University in Peru'...the highest
PDP11 installation on the world at that time...hi


Ah, the plastics fire if memory serves. Never played with any of the
15bit hardware or the controls. Just PDP-8, 10, 11 and VAX.

OK. PDP9 and 15 wer 18bits .. I did some work on DEC10, 11 and when
the VAX came out I was in sales... I made some of the first sales in
Italy and most of my VAXes were linked in Decnet to PDP11/70 and 45.

Just finishing up a 85W brick for it now.

Nice power. On 6 meters I have an FT726 with the 50MHz converter (RX) supermodified ... the only original pieces are 1x Jfet and 2 IFTs ...hi.
I also have an FT920 a Xmas gift (a few years ago) from my good FRIEND
(with capital letters !!!) Art (and his wife)...hi

Just talked to him this weekend! He's about 30miles NE of me. Next
net I'll mention you name and say HI.. One of his project was to
restart the old AM nets, he's got maybe 6-8 regulars.

How nice... Too bad we did not get in touch during my business
quarterly trips in W1 (for confessions with my boss 2000 to 2003...hi).
I was usually at K1GBX house at weekends ... eating lobsters and other
good stuff...hi.When I took my wife and my daugther Luisa for her first
trip we even had a story in a local newspaper and picture...hi
I m sure when you will tell him we had this kbd chatting he will jump
on his chair and get crazy...hi For a jike tell him we had a QSO on 6
meter SSB... than you will tell him the true story...hi

Small world, smaller if we get some propagation.

Yes, amateur radio makes the world really small, some time ... hi

Sorry for this non Mixers conversation for our friends.... I will
comment on the following...

73

Gian
I7SWX


Allison
KB1GMX ,

mixer: DBM or dual gate mosfet?
 

The 602 is now replaced with the 612 but is still an old design.

If you design your mixer ( /doubler ) with AD8343 and use proper RF
transformers from CoilCraft, it just cannot go wrong... ( well, Murphy
et
al of course... )

Da / M0DFI

Hi Dan,

Yes the AD8343 is an interesting mixer... but for me it may be too
noisy (10dB). THe IP3 is certainly much better (+15dBm) than the
602/612 (-15dBm), but this one has a lower NF of 5dB.
If you build my 1 homebrew transformer (50c) FST2125 DBM you do get am
IP3 of +25dBm NF 5dB ... adding a post mixer 10dB LNA you probably get
a 3dB NF.
Certainly you have to select the most valid mixer for the specific
project as always we have to compromise and give priority to one of the
many parameters.

73

Gian
I7SWX