Thanks for the receiver theory discussion.
How would you compare a Corsair 1 to a Corsair 2? Thanks
73, Millard H. Qualls, K9DIY
Dr. Gerald N. Johnson wrote:
> I've never heard any Triton or Omni A, D, or C owner complain about
> performance. Though by my circuit analysis, I think the Corsair II is a
> superior receiver with better dynamic range, especially for handling
> strong adjacent frequency signals. That's because it uses a transformer
> feed back circuit with RF power type bipolar transistors for the RF and
> first IF stage and double balanced diode ring mixers that have good
> strong signal characteristics. I think the IF gain of the Triton/Omni C
> is a little on the low side, but that gives it a cleaner sound. Having
> only one mixer can give it a cleaner sound, but it may not quite hear
> the weakest 10m signal. I doubt there's a detectable difference on 75
> meters or 80 meters in weak signal detection because antenna noise can
> be so much greater than RF stage noise. But strong signal handling
> capability helps get a good signal to noise after the detector because
> that way neither adjacent channel signals nor strong static overload the
> radio to gain more emphasis than their relative power deserves. Not
> having a second RF mixer (other than the mixer to audio, called a
> product detector) the RF section gain can be lower in the Triton. Low IF
> gain may not be all bad, as that can reduce the noise on the opposite
> side band contributed at the product detector. Then an audio lowpass
> filter and quiet audio stages can make up for the low IF gain... There
> are a lot of trade offs.
>
> The Corsair II has double conversion with IF's at 9 and 6.3 MHz. More
> oscillators means more birdies. With 8 poles of filter in each IF
> there's pretty good skirt rejection and the pass band tuning allows
> shift the edges independently so the effective bandwidth can be narrowed
> to almost nothing. And 8 poles of filter causes more delay to make AVC
> without pops harder to accomplish.
>
> Some days I'd like to compare a Triton and Corsair II side by side under
> various conditions both for weak signals on 10m and on 80 or 160m and
> alongside strong signals. I suspect that the Triton will hear as well
> on 80 as the Corsair II but will be bothered more by strong close
> frequency signals due to active devices not as capable of handling big
> signals and fewer filter poles. I suspect that the Triton may not hear
> as well on 10m due to a bit lower overall gain, BUT I'M not sure of
> that.
>
> I'd kind of like a receiver to use the Corsair II RF stage, mixer, first
> IF stage and 9 MHz filter, then have some gain and have another SSB
> filter before the product defector so it sees only IF noise at
> frequencies that have passed through the first filter. I'd like there to
> be a bandpass filter between the RF stage and mixer for the same reason,
> and that's lacking in the Corsair II. Its probably in the Triton because
> of the impedances needed for the double gate MOSFETs. The I'd like that
> receiver to have a good low noise (perhaps passive) low pass filter
> cutting off to match the SSB receive filter, then another at the speaker
> (again passive) to reduce the high frequency noises contributed by the
> audio stages. All those things help signal to noise without affecting
> the signal. I know the speaker filter helps and I think the others can
> help by reducing the RF stage and IF stage gain required to develop
> system noise figure and the best possible signal to noise at the
> speaker. My Yaesu VHF/UHF multiband multimodes fail miserably at both of
> those compounded by lots of intermod from local oscillator phase
> noise...
>
> I don't think without comparing a Triton and a Corsair II side by side
> with a quick antenna switch for an extended period of time that one will
> ever come to a sure conclusion of which is better for all situations. I
> suspect each will excel on some occasions and conditions. I know that
> was the case when I compared a Corsair II, to an Omni V, and a Cubic 102
> one Saturday when 10m was barely open for DX. One of the features of the
> Cubic is a separate front panel IF gain control which the owners tell me
> does wonders in improving signal to noise ratio at the detector. One
> other feature is continuously variable bandwidth which though
> uncalibrated in the Corsair II is what the bandpass tuning control
> effective accomplishes.
>
> 73, Jerry, K0CQ
>
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