mixer: DBM or dual gate mosfet?
 

Chris Jones wrote:

wrote:

hello,

I'm building my first reciver. I can't choose what kind of mixers
should I use. I have read that diode ring mixers are far superior
compared to dual gate mosfet mixers.

Is this true for both - first (RF / VFO) and second (IF / BFO) stages?
Or is there any real difference at all?

thanks

I have recently bought the books from the RSGB which contain all of the
Technical Topics columns from RadCom for the last couple of decades or so.
It seems like they really like making mixers from FST3125 Bus Switch ICs,
and up to perhaps 50MHz these are supposed to be much better than the
average diode ring mixer. They call the configuration "H-mode" and the
guy who I believe is supposed to have come up with the idea is called
Colin
Horrabin. Here is an article randomly selected from a google search:
http://
xoomer.virgilio.it/sergiocartoceti/pdf%20files/IK4AUY_%20qex_07-2004.pdf
I don't like the way they generate the LO signals with XOR gates but apart
from that it is interesting.

Chris

One thing I forgot: I7SWX I believe is responsible for many of the H-mode
mixer circuits in the the Technical Topics column.
http://www.qsl.net/i7swx/index.htm

Chris

mixer: DBM or dual gate mosfet?
 

"Paul Keinanen" wrote in message
...

In Europe, there are several high power broadcasters starting at 7100
kHz, which would easily overload the 40 m receiver. Assuming loaded Q

OH2BT's comments about how much better things have gotten in Europe really
made me say hmmmm.... I only recently heard actual measurements, rather
than whining, and things are pretty horrible today - they must have been
intolerable decades ago.

Tight front ends and careful control of levels obviously are important with
any mixer, but especially something with the gain of a 602. Nevertheless, I
doubt there are many cases where a 602 would be even useable in Europe, let
alone "good".

...

mixer: DBM or dual gate mosfet?
 

On Thu, 2 Mar 2006 21:11:16 -0500, "xpyttl"
wrote:

"Paul Keinanen" wrote in message
.. .

In Europe, there are several high power broadcasters starting at 7100
kHz, which would easily overload the 40 m receiver. Assuming loaded Q

OH2BT's comments about how much better things have gotten in Europe really
made me say hmmmm.... I only recently heard actual measurements, rather
than whining, and things are pretty horrible today - they must have been
intolerable decades ago.

We had problems keeping Radio Moscow out of _audio_ equipment :-).

Guitar amplifiers were quite problematic with long cables and a top
capacitance (the guitar and the player) at the end, bringing quite
large RF voltages into the audio stages, causing rectification in
unfiltered input stages.

Paul OH3LWR

mixer: DBM or dual gate mosfet?
 

On Thu, 02 Mar 2006 22:06:10 GMT,
wrote:

The lowly SA/NE602 isn't so bad considering the power it uses and the
15-17db of gain it offers. Like any power power mixer care in use is
important.

Certainly usable for receiving strong international broadcasters, in
which case the input signals can be sufficiently attenuated, however,
trying to receive any weak signals with such an attenuator at the
front end, is not very productive :-)

Paul OH3LWR

mixer: DBM or dual gate mosfet?
 

The FET-switch mixers seem to be a really nice alternative, and
although they've gotten relatively little visibility in amateur-radio
applications they've become very popular in commercial use (e.g.
cell-phone handsets). I haven't yet had a chance to play with these
myself but they look like fun!

There was an article in the ARRL HB (1995 and probably others)
about using an SD5000 quad mosfet as a mixer. I bought a few
of these transistors a few years ago (now where did I put them,
got lost in the last move!). They are supposed to make
a very good mixer. The only disadvantage was the circuit
required injection at twice the lo frequency as it used a jk flip
flop to develop the required 180 degree injection. I suppose
a balum could do the same thing. In any case the AD9954 DDS I am
thinking of using can clock to 400mhz and develop output to
160mhz, so getting up to 80mhz (for use with a 9mhz if) would still
be no problem.

mixer: DBM or dual gate mosfet?
 

On Fri, 03 Mar 2006 22:20:28 -0500, Ken Scharf wrote:

There was an article in the ARRL HB (1995 and probably others) about using
an SD5000 quad mosfet as a mixer.

Also see N6NWP's article from QST June 1993. And the
H-mode mixer by G3SBI in RadCom and various other RSGB
publications.

I bought a few of these transistors a few years ago...
I see the SD5000 is still listed on Calogic's website
http://www.calogic.net/html/dmos.html Is the SD5000
still widely available? The search engines turn up a
lot of data but very few suppliers. Perhaps a ring of
discrete MOSFETs or a fast switch IC like the FST3125
might be a better choice.

73, Ed. EI9GQ.


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mixer: DBM or dual gate mosfet?
 

Ken Scharf wrote:

The FET-switch mixers seem to be a really nice alternative, and
although they've gotten relatively little visibility in amateur-radio
applications they've become very popular in commercial use (e.g.
cell-phone handsets). I haven't yet had a chance to play with these
myself but they look like fun!



There was an article in the ARRL HB (1995 and probably others)
about using an SD5000 quad mosfet as a mixer. I bought a few
of these transistors a few years ago (now where did I put them,
got lost in the last move!). They are supposed to make
a very good mixer. The only disadvantage was the circuit
required injection at twice the lo frequency as it used a jk flip
flop to develop the required 180 degree injection. I suppose
a balum could do the same thing. In any case the AD9954 DDS I am
thinking of using can clock to 400mhz and develop output to
160mhz, so getting up to 80mhz (for use with a 9mhz if) would still
be no problem.


Hi !

At the same time Signetics included to the same fet family a double fet
SD6000
It was planned for front end applications
Single fets were done under type numbers SD305 and SD306
All three were N-channel enhancement types. Positive bias only.
I wonder whether Signetics still exists. Signetics was bought by Philips
company.

I use those fets successfully in one of my conventional type homebrew
tranceivers.
The first if is having a 10.7 MHz xtal filter. That is mixed down to
455 kHz either with 10.245 MHz or 11.155 MHz xtal
Sideband selection is done with the selection of mixing direction.
455 kHz is using Collins mechanical filter having very good shape factor
and special skirt for lower sideband use.

73, Risto OH2BT

mixer: DBM or dual gate mosfet?
 

I see the SD5000 is still listed on Calogic's website
http://www.calogic.net/html/dmos.html Is the SD5000
still widely available? The search engines turn up a
lot of data but very few suppliers. Perhaps a ring of
discrete MOSFETs or a fast switch IC like the FST3125
might be a better choice.

73, Ed. EI9GQ.

GM Ed. Certainly a better choice when it comes to conversion loss. I've
built a half dozen SD5000 mixers and although at least one of them managed a
measured +50 dBm Ip3, (G3SBI measured it not me!) I never managed to get the
conversion loss below 9 dB and more often 10. Conversely, the 3125/ family
readily does 4.8 dB conversion loss thanks to the very respectable Rds on.
REALLY simplifies things in the front end department, to at least 30 MHz,
with attention paid to the front end filters, you can get away without an RF
amplifier.

Regards
W4ZCB

mixer: DBM or dual gate mosfet?
 

GM Ed. Certainly a better choice when it comes to conversion loss. I've
built a half dozen SD5000 mixers and although at least one of them managed a
measured +50 dBm Ip3, (G3SBI measured it not me!) I never managed to get the
conversion loss below 9 dB and more often 10. Conversely, the 3125/ family
readily does 4.8 dB conversion loss thanks to the very respectable Rds on.
REALLY simplifies things in the front end department, to at least 30 MHz,
with attention paid to the front end filters, you can get away without an RF
amplifier.

Regards
W4ZCB

Hi all,

Harold, W4ZCB, has given some "comments" on the H-Mode Mixer that are
REAL and TRUE.
G3SBI has removed the mixer from the stages that are critical on a
receiver and in the CDG2000 project it was demonstrated the IMD due to
passive components like core of coils. The FST3125 fast bus switch has
lowered the conversion loss of the H-Mode Mixer and made the RX front
end "hot", although not reaching the IP3 of +50dBm it still has plenty
of +dBm to give ...around +40dBm!You can permit yourself to add a xtal
filter behind the h-mode mixer and still getting high numbers on IP3.

If you are looking for a low consumption and simple mixer you may go OK
with the classic NE/SA602 and similar ones. BUT ... if you are looking
for high performance you need the H-Mode Mixer in the 3 transformer
G3SBI or the 2 transformer I7SWX configurations.
The H-Mode Mixer has been tested on downconversion (CDG2000, STAR
projects) and also on upconversion projects (I7SWX). For upconversion I
have devised a new squarer using LVDS and test it at IF of 35 to 70 MHz
(and 100MHz) with conversion loss around -5dbm and IP3 between +35 to
+40dBm (3.3V FST3125).
The H-Mode Mixer has been tested for RF input up to 50MHz in RX and
converter to 27-28MHz IF.
At 144MHz it performs like a standard diode db mixer having a conv loss
around -8dB. The input limit is due to the internal gates timing and
unbalancing as the FST3125 may have a bandwidth between 300 to 400MHz.
For those interested I may suggest a visit to JA9TTT web page where he
has reported measurement on both G3SBI and I7SWX versions using the
74AC86 squarer with balance adjustment. The comments are in japanese
but a translator is making the reading understandable :
ja9ttt.homedns.org/. I have posted a copy in my web page
www.qsl.net/i7swx in the subdirectory homebrewing. JA9TTT page permits
to enlarge the spectrum analyzer screen pictures.
I have also developed a 1 transformer double balance
mixer/demodulator/modulator using the FST3125 and 74AC/HC86 squarer
with an IP3 of around +25dBm.
Notes on the H-Mode Mixers and 1T DBM have been reported in RadCom,
G3VA's Technical Topics column.
For those interested on more detailed information I can make available
notes in English and Italian. Please write to my e-mail address:.

73

Gian
I7SWX
F5VGU
W1-I7SWX
G-QRP #10241
I QRP #571

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