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.
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.
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.
Today I will be buying a 2M to 10 meter transverter, so I will soon
start working on getting a QSD SoftRock to work at 10 meters. I will
also be buying some fast logic to replace the HCT logic of the softrock.
SNIP
>I have the new software installed, but haven't run it yet. My new
>computer died and I have to go out an look for a power supply this
>morning to get it back up and running.
>
>Lately I've been spice modeling QSD circuits, studying the impact of
>an analog switch that has a slow turn off time on a QSD circuit.
>
>The results are preliminary, but my simulations show that analog
>switches do not have to conduct for 25 percent of the time, a much
>shorter than 25 percent conduction time is almost as good.
>
>Also, it appears that conduction time greater than 25 percent (which
>is the norm for the FST cmos switches we currently use) is
>devastating to the output! It is possible that a great deal of
>additional performance and higher frequency operation of the QSD is
>possible with existing technology if the analog switches were
>controlled with a quartz based multivibrator (to insure the switch
>conduction is less than 25 percent, not more).
>
>More info later, I'm still running simulations.
>
>Regards,
>
>Art
>
>-SNIP
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 ...
[Non-text portions of this message have been removed]
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