In article ,
Risto Tiilikainen wrote:

If you think the situation in short waves today:
Russian and their previous satellite country jammers are quiet
Local broadcast is nearly completely in FM
Propaganda is no more effective to transmit in short waves
Commercial data is practically in Internet. and in satellites
Marine communication is in satellites.

All this means less cross modulation products in first mixer than some
sixteen years ago
Atmospheric noise in sw is much higher than the noise of modern front
and mixer stage
Advantage of diode mixer is marginal

There's a good discussion about the advantages and disadvantages of
various mixer types, for different applications, in "Experimental
Methods in Radio Frequency Design", a book I strongly recommend.

As others have pointed out, there's no one right solution. Even for
use in what seems like a simple, constant application (e.g. a CW
receiver for the 40-meter band), the choice of which is more
appropriate can swing one way or the other based on how you intend to
use the receiver.

As one example given in EMiRFD, if you're looking for a simple
receiver which is intended for QRP operation on backpacking trips,
then the low power consumption, and the mixer gain of an active mixer
such as a Gilbert cell (e.g. SA602 and similar) can make this the
ideal. Out in the woods, the RF levels will be low, and the
relatively low IP3 of these sorts of mixers isn't likely to be a
problem.

On the other hand, if you're planning to build a receiver which may
have to operate in a strong-adjacent-signal environment (e.g. for
Field Day or other contesting), then you may want to favor a
diode-ring double-balanced mixer operating at a high LO-injection
level, and the devil take the power consumption :-)

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!

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

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.

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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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

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

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

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

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