At 40m band, the SWR at amplifier input is very good. It shows 1:1.2.
But on lower band, 80m and 160m, the SWR increased exponentialy. So, here is the note during attempt to improve the input SWR.
Measure the impedance at gate shows Zin = 6 ohm.
With 6 Ohm, the transformer impedance ratio needed is 9:1, that is 3 times more turn on primary compared to secondary.
After adding transformer, the input impedance at primary transformer is not flat, and only matched around 7MHz.
After several tries, it was found that adding 15 ohm resistor across secondary input transformer giving a very good result.
Here is the input impedance
And here is the final SWR graph
The result of adding R15 ohm is that SWR that unusable on 80m and 160m now can be kept as low as 1:1.2.
Input power that was around 11W for 500W, now need to be around 14W. It should be no sweat for a 100W transceiver. The input power is still low enough that transceiver will be kept cool during operation.
On air test show no degradation, but in the other hand, modulation report says better linearity compared to previous test.
But on lower band, 80m and 160m, the SWR increased exponentialy. So, here is the note during attempt to improve the input SWR.
Measure the impedance at gate shows Zin = 6 ohm.
With 6 Ohm, the transformer impedance ratio needed is 9:1, that is 3 times more turn on primary compared to secondary.
After adding transformer, the input impedance at primary transformer is not flat, and only matched around 7MHz.
After several tries, it was found that adding 15 ohm resistor across secondary input transformer giving a very good result.
Here is the input impedance
And here is the final SWR graph
The result of adding R15 ohm is that SWR that unusable on 80m and 160m now can be kept as low as 1:1.2.
Input power that was around 11W for 500W, now need to be around 14W. It should be no sweat for a 100W transceiver. The input power is still low enough that transceiver will be kept cool during operation.
On air test show no degradation, but in the other hand, modulation report says better linearity compared to previous test.
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