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

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

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

There are a lot of historical chips and solutions around on the market and
in the litterature. I use the Analog Devices AD8343 mixer, good for DC to
2.5GHz and with a IP3 of 16.5 dBm.

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... )

Cheers

Da / M0DFI

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

guys, bear in mind that the intercept point is primarily a function of
the operating quiescent poit. you cam make it high, really high and get
superlative mixers, even single ended. i designed one aroun the now
defunct VMP4 from Siliconix with an Id of 500mA!!! the damned thing had
nearly +50dB IP#. About the same went with the LNA. All in all 24W
power dissipated in the front end. How many of us can afford that or
need that for the matter?
drop it! what the guy needs is some reasonable value of dynamic range
and around 10-12 dB for IP3. he isn't going to build a radio telescope
receiver on his first attempt. Be reasonable!
with FET's the thing to ensure is that the operating point is
setablished with Vgs set at about half of the pinchoff voltage to
ensure maximum dynamic range. a noise figure under 10dB is adequate for
HF. it's not the galactic noise that limits your reception!
Saandy 4Z5KS

Hi Saandy,

I have some russian power FET similar to the VMP4 and probably better
but there is no sense to use them as they are no more in production and
diffcult to purchase in East Europe.

I believe a discussion on Mixers is important particularly for a
newcomer. He must know all the different kind of mixers than he will
have to decide.... it is like talking about small car or motobykes
because it is better run with a bicycle...one should not know about
racing car or motobykes.... he can putchase a byke tha add a little
mosquito engine or pss to a bigger motobyke or a small car later ...
but he will know what he has (he will have to push a lot with his legs
and then see to push less or not at all).... it is like for a portable
RTX were consumption is at premium... you cannot put (probably an
h-mode mixer has you will have to spend 30-50mA plus an amplifier with
other 20mA versus a NE612 that needs 3mA !!! To hell the IP3... one can
use his brain as a DSP...hi

73

Gian
I7SWX

go with the simplest one! something like a dual gate FET: that's going
to ease problems with the local oscillator.
But build it as a separate module on a small PCB, and wire it in. that
way you'll be able to experimwnt later on by replacing the module. that
way you can go from easy and simple to complex and high perfoemance.
for a first it hard to beat the method. i see you're getting too much
info, especially for a newcomer!
stay in touch, I'll try to help you to the limit of my abilities.
Saaandy 4Z5KS