At 10:56 AM 3/20/2006, you wrote:
>At 20% you are on your best output, if the frequency is high enough
>you need even less so it's effectively off by the time you reach the 25% mark.
>
>Still, something else is brewing in Lala land, the SoftRock V7 is
>getting good performance with the same switches at 10 meters, they
>tested as high as 70MHz and it worked., but is not using a QSD
>detector. But it will need a small pre-amp to boost the sensitivity
>up to par with commercial rigs.
Cecil, the softrock ver 7 does not use a QSD at 28 MHz. So, it's not
quite what you think it is. Of course, no one quite knows what's in
it yet-to the best of my knowledge, Tony has not released the schematic.
>I'm still of the opinion that if you want good performance at 10
>meters or higher you need;
>
>1. A good pre-amp running 10dB gain, a Norton amplifier will give you
>high IP3 figures.
>2. Doubly Balance Diode for the detector, or FET switches acting the same.
>
>The QSD maybe coaxed into working at those frequencies, but it might
>not be worth the hassle. Either way you are going to need a pre-amp.
Maybe::>
>I don't know why there is such aversion of a pre-amp on the forum,
>all the commercial receivers have them, even the $11,000 Icom radios
>need them for good sensitivity and noise factor at 10 meters.
Sorry, but of course there is going to be reluctance to include a
preamp! If the circuit really needs a preamp, then it needs a preamp though!
If however, optimization of the switch timing allows good performance
without the preamp, then the receiver will be much better off without
it. It's all experimental and part of the experiment is making sure
the switch is getting optimized control signals. Better to optimize
the existing hardware than to add preamps.
Regards,
Art
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