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Re: [linrad] For general interest
For good passive mixers the noise figure is the mixer loss plus about 1 dB.
The expression SSB noise figure is a silly one. In fact one does say that
one has measured with only a noise test signal in one of the two input
bands. Would one measure with a wideband noise source each sideband would be
converted to the outoput and the indicated noise figure on the meter would
be too good.
But there only is one definition: i.e. the noise factor/figure indicates how
much more noise will be at the output of a real device connected to a 270 K
source in comparison with an ideal device connected to the same source.
Comparing this mixer with a passive mixer of, say, 7 dB NF is to use with
this mixer a good preamp ( say with an NF of 1 dB) and to calculate the gain
of that preamp required to arrive also at 7 dB for that cascade.
Lets take 16 dB ( 40) as the SKY mixer NF. In order to arrive at 7dB (5)
with the 1 dB (1.25) preamp NF the preamp must have a gain of 10.66=10,3
dB. If we neglect the IM properties of the preamp, the combination now has
10,3 dB worse intercept values than those of the SKY mixer alone.
Now you can do a comparison with the passive mixer.
The SKY, of course seems to have other intriguing possibilities.
----- Original Message -----
From: Ron Skelton <ron-skelton@xxxxxxxxxxx>
Sent: Sunday, August 24, 2003 2:18 AM
Subject: Re: [linrad] For general interest
> I was somewhat concerned about the noise figure myself but I don't
> know how this device compares with other techniques and products on
> the questions of noise or leakage. The SKY data doesn't mention
> leakage and the data I have on Mini-circuit mixers doesn't mention
> noise. Neither am I sure how to interpret the SKY noise
> specification stated as a SSB Noise figure in dB. I plan to obtain
> more info.
> As I am interested in HF, noise requirements are more relaxed than
> for higher frequencies and large signal issues seem more important.
> I understand that the chip is priced at $9.95 in 500 unit quantity
> and I am trying to find out what they would cost in the 1-10 range.
> >Tks vy much for the info.
> >The ( probably expensive) mixer, however, may have impressive IP3 figures
> >but one has to account the rather bad 16-19 dB noise figure is order to
> >an idea of its dynamic range.