Re: Daylight again schematic error(?)
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Barry, The 1K resistor? at the input of the RX mixer provides the correct termination for the bandpass filter. The bandpass filter is terminated with 1K on the mixer side and 50 ohms on the other side. If you sweep it with a nanovna which provides 50 ohms on both ends, the plot is bound to show much loss as the ending resonator is loaded down. As I had stressed in my talk, we let go of the 50 ohms standard to simply things. This is one of those gotchas.
On Thu, Sep 8, 2022, 5:37 AM barry halterman < kthreebo@...> wrote: Group, I believe there is an error in the schematic of the daylight again radio. The RX first mixer has the PTO going to the gate with the high impedance input, while the RF input is going to the gate with the 1K resistor.?
I think they need to be reversed.?
The band pass filter should be terminated into a high impedance and not low impedance. A low impedance termination will degrade the filter and the sensitivity becomes poor. This is what I have experienced in this build after many hours of tinkering.
Plots of the filter show about 10db loss when terminated into 50 ohms. I have not done plots with a higher termination impedance. In my build, flipping the two signals improved the performance dramatically. I have not increased the PTO gate termination resistor from 1K to a higher value. The PTO signal measured 3.4Vp-p with the 1K.
All in all, the receiver sounds pretty darn good!!
73
Barry
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