Allison

Am I correct in that all of the following amateur bands are affected?

18.068 - 18.168 MHz
21.000 - 21.450 MHz
24.89 - 24.99 MHz
Something around 26-27 MHz (varies by region)
28.000 - 30.000 MHz

The bands from 18MHz - 21.450MHz at least will have the offending spur stripped out in the LPFs after the finals.?? I agree that amplifying these spurs is not ideal and adds to the problem of drive...? I speculate that this is why there may be a low in power output around these frequencies??

However, the spurs generated at 26MHz and above won't be stripped out by the finals LPF at all, nor by the BPF (actually an LPF) built for RX as these all fall below the desired signal frequency.? This makes it likely that 28MHz is non-compliant with at least US emission standards.

At a minimum, an HPF needs to be switched in for 24MHz and above in series with the RX LPF.

It may be that two filters could be substituted for the RX filter with a single digital line controlling the switch over:

Below 22.5 MHz, a LPF cuts in with a threshold just above 22.5 MHz, killing off all the unwanted mixer products.
Above 22.5 MHz, a HPF cuts in with a threshold just below 22.5MHz, again killing off all the unwanted mixer products.

On Rx the exiting LPF is inserted.?? No new data line is required to switch the RX LPF in/out.? This can be controlled by the TX line.

Inserting new filters in the TX line would require a couple of cuts on the board either side of the existing RX 33MHz LPF filter.

Overall then - 2 relays, and 2 filters (1 LPF and 1 HPF) to solve the problem.

What do you think?

Mike ZL1AXG


On 3/06/18 1:28 PM, ajparent1/KB1GMX wrote: