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