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

On Wed, 01 Mar 2006 01:03:21 -0800, aadu.adok 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.

It depends on what you mean by superior. The mosfet mixer has gain
and usually has a lower noise figure. The diode mixer will have superior
strong signal handling (higher IP3), but will have about 7dB loss. The
diode mixer needs more local oscillator power. They both make excellent
mixers if they are applied properly.

To get the most bang for your buck, it is hard to beat a ring of
1N914 or 1N4148 diodes at a few cent each. The ferrite 'cups' from
scrap Toko IF transformers can be used as cores for the trifilar
wound transformers.

There are a few other options you should consider. High level IC mixers
like the AD831 are worth considering. Switching mixers using MOSFETs
are capable of very high performance. Search for info about the N6NWP
front-end from QST Feb 93 or the H-mode mixer used in several recent
homebrew designs.
http://uk.groups.yahoo.com/group/picastar/
http://xoomer.virgilio.it/sergiocartoceti/article_7.htm
http://www.warc.org.uk/cdg2000/introduction.htm

If you build the receive mixer as a separate module,
you can try them all and pick the one that works best for you.

73, Ed. EI9GQ.


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wrote in message
oups.com...
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.

"Superior" is something of a loaded word. Whether a particular parts is
superior or not depends on your design intent.

Probably the most popular mixer for simple HF receivers is the NE/SA
602/612. This is an active mixer. It has amazing amounts of gain, such
that an RF stage is almost never needed. It is extremely simple to deploy,
and it requires almost no power. Thus, in portable/battery powered circuits
it is almost always the mixer of choice. It has an absolutely horrid TOIP.
There are other, mostly older, even poorer, active mixers, but the 602 is a
very versatile part, so it seems to show up everywhere.

At the other extreme are diode ring mixers. These can have stellar TOIPs,
but take a lot of oscillator power. Further, they need lots of RF as well,
so some sort of RF stage is needed. All this adds up to a need for plenty
of power. The best diode ring mixers will use matched, Schottky diodes, but
good old 1N4148's do work, and quite well. Many designs use packaged diode
ring mixers such as those from Minicircuits.

The dual gate MOSFET falls kind of in the middle. It doesn't have the
horrible TOIP problems of an active mixer, but it's not as power hungry as a
diode ring. The MOSFET seems to have fallen out of favor lately, in spite
of being a "balanced" sort of solution. I suspect most designers are either
going for power consumption or performance, and really, quite good
performance can be had with the active mixers with careful design.

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

Careful design can manage what the second mixer sees more easily than than
the first. This can make the dynamic range problems of an active mixer less
of an issue. For that reason, balanced designs that tend toward management
of power consumption will sometimes use a diode ring for the first IF and an
active mixer for the second. But a superhet bent all out on power
conservation will almost always use a pair of 602's. Designers who want to
avoid ICs for whatever reason will use a pair of diode rings.

I shouldn't sound so down on the 602. A WELL-DESIGNED 602 receiver can
easily match the performance of the $1000 class rice box rigs. It cannot,
however, come close to the performance of an equally well-designed diode
ring rig. But the diode ring rig will probably consume three times the
power, meaning three times the heat to deal with and the associated
oscillator compensation issues.

So you picks your poison.

...

wrote in message
...

If you building a radio that runs on
batteries then using more power may be bad.

Also keep in mind that more power=more heat

If you are building a simple analog VFO, temperature compensating the VFO
can be the most tedious part of designing a receiver. Depending on how
tight your box is, the difference in heat could be an issue. Keeping the
oscillator stable while delivering more power also means more buffer stages
between the VFO and the mixer.

If you are designing with a DDS, of course, all this is pretty much moot.
With a typical DDS chip and a packaged clock oscillator at some high
frequency, the oscillator will draw so much current and generate so much
heat that what the mixer requires is invisible.

...

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

wrote:
On Wed, 1 Mar 2006 09:04:13 -0500, "xpyttl"
wrote:


wrote in message
. ..


If you building a radio that runs on
batteries then using more power may be bad.

Also keep in mind that more power=more heat

If you are building a simple analog VFO, temperature compensating the VFO
can be the most tedious part of designing a receiver. Depending on how
tight your box is, the difference in heat could be an issue. Keeping the
oscillator stable while delivering more power also means more buffer stages
between the VFO and the mixer.


Actually even without the heat issue you still have to compensate it
or ambient variation will drive you nuts. Granted a few transistors
delivering 5-10mW of power is not a great heat generator when you add
all the surrouding possible sources.


If you are designing with a DDS, of course, all this is pretty much moot.
With a typical DDS chip and a packaged clock oscillator at some high
frequency, the oscillator will draw so much current and generate so much
heat that what the mixer requires is invisible.


Since buffereing the VFO is a good idea anyway the buffer and later
statges can supply the 5 or more milliwatts needed for level 7 rings.
Since those stages can be "remote" the small heat generated is not a
big issue. However between a VFO, buffer and a buffer to deliver
power you can be hitting 30-50mA and on batteries thats a bigger
issue.

If you using DDS, likely power is not an issue and the combined DDS
and control plus display could be surprizingly high or at least has to
be managed.

However you approach the problem a little though to the overall
effects are important. After all what usually seperates a great
reciever from a passable one is attention to the little details.


Allison
Some of the modern DDS chips require little power. Analog Devices
has some DDS chips that draw less than 50ma at 5v, I think there is
one that takes but 15ma. True a vfo will draw even less, but we
are not talking about gobs of power in any case.

DDS vfo's have very low phase noise, and the ones that can be clocked
at 100mhz or higher can deliver quite low spurs. The AD9954 series
have a 14 bit DAC and can make a very good HFO for a single conversion
receiver with no PLL loop filter needed to clean up the output.

....a long explanation, but a needed one.
One of the most important characteristics of a mixer is its ability to
handle large input signals without overloading. if overloaded by an
unwanted signal, chances are that it will not be able to handle the
weak signal you're interested in. the physical mechanism involved is
not important, except for the fact that increasing current through an
active mixer (re FET or transistor, or the injection power in a DBM
tend to alleviate the problem in some measure. the nois figure of both
is more or less equal and adequate in the HF range. the main advantage
of the dual gate MOSFET is that it needs much less power from the local
oscillator and can save you an amplifying stage. Not really crushing,
but sometimes neeedful.
If you're talking about a simple first receive I'd go with the MOSFET
mixer. there are very good examples in the hand book. iI used them for
years with success and still using them in one form or another.
the problem is much less severe at the second mixer, because the IF
filters tend to defend it from large unwanted signals and the amplituse
variations are also smaller due to AGC action.
Soooo , KISS (keep it simple, stupid!!!), a very good adage. goood luck
with your first.
Saandy 4Z5KS

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



Hi

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
IGFET mixer is simple and advanced solution for DIY project.
IGFET mixer doesn't need any front amplifier stage.
A selective band filter in front of mixer is superior to broadband
transformers
I am using loosely coupled 3 stage band filter tuned by variable triplet
air capacitor
3 coils for low end of sw and 3 coils for upper end of sw.
Coils are DC selected by small reed relays
KISS

If you are constructing premixer then I recommend DBM to keep birdies
in low levell
For IF/BFO my recommendation is also DBM or "semi DBM"
For both of those DBM solutions I recommend you to Google a nice
advanced component MC1496.
In some Motorola handbooks and ARRL handbooks are examples for MC1496 as
DBM, product detector and balanced modulator.
It is mostly used in single ended circuits in RF meaning and balanced
for DC

73, Risto OH2BT

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!

On Wed, 1 Mar 2006 07:03:01 -0500, "xpyttl"
wrote:

Probably the most popular mixer for simple HF receivers is the NE/SA
602/612. This is an active mixer. It has amazing amounts of gain, such
that an RF stage is almost never needed. It is extremely simple to deploy,
and it requires almost no power. Thus, in portable/battery powered circuits
it is almost always the mixer of choice. It has an absolutely horrid TOIP.
There are other, mostly older, even poorer, active mixers, but the 602 is a
very versatile part, so it seems to show up everywhere.

If you really intend to use mixers with such horrible IP3 figures, I
would suggest using a very selective front end ahead of it. For a
single band CW receiver some fixed tuned stages might suffice, but
otherwise some tunable input filters should be used.

In Europe, there are several high power broadcasters starting at 7100
kHz, which would easily overload the 40 m receiver. Assuming loaded Q
of 100 and the front end tuned to 7000 kHz, the -3 dB bandwidth would
be +/-35 kHz from the centre frequency with some usable attenuation at
7100 kHz.

Using fixed tuned octave wide front end filters with the 602 is just
asking for trouble.

Paul OH3LWR