At 10:37 AM 3/20/2006, you wrote:
>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 don't understand, I said it does not use a QSD detector, I have a
copy of the schematic, it emulates a diode mixer.
> >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.
At 29MHz it's very hard to make a quadrature that has a 20%/80% duty
cycle, the turn on period is less that 8ns, but it's doable if your
willing to add more high speed logic.
Even if you optimizes so it works OK, which I suspect it's more
trouble than it's worth. The simple fact is that at 10M the noise is
so low that component noise becomes a problem and a pre-amp will be
needed no matter what, to have adequate sensitivity and noise figure.
Even the big brand radios have not escaped that in spite of all the
engineers they have.
But the fun is in the trying so I'm going to give a shot, once the
QSD is working as good as it can get, then I will make the decision
about a low noise, high IP3 Norton pre-amp. I have one SR-5 that I
have saved for that purpose.
I purchased a 2M to 10M transverter today so I will have some signals
to play with.
>Regards,
>
>Art
>
>
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>Yahoo! Groups Links
>
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>
Cecil Bayona
KD5NWA
www.qrpradio.com
I fail to see why doing the same thing over and over and getting the
same results every time is insanity: I've almost proved it isn't;
only a few more tests now and I'm sure results will differ this time ...
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