President McKinley, European model ¨Optimizing Modulation". An excellent video.
The original video by ¨nomad" was deleted for an unknown reason.
My intention is to keep this interesting video available.
SMD component experience and soldering skills required.
Index
00:03 PART I
28:34 PART II
44:03 TESTS
45:47 CONCLUSION
Modulation optimization (all modes FM/AM/SSB):
Step 1 of 2: Change the following components:
C254 = change from 330pF 16v to 1000pF
C257 = change from 47nF 10v to 100nF
R270 = change from 270K 1/16W to 330K
(Errata: Service manual states R267 and R270 are 100K, that is wrong as both are actually 270K)
Step 2 of 2: Adjust RT207 according to your preference.
Observations:
C257 is in the path to FM but also influences SSB. Changing it to a higher value such as 470nF (which offers lower resistance for audio frequencies) causes FM to be very loud and prompting you to lower the mic gain. You would then have to increase the mic gain when switching to SSB which is inconvenient.
C254 is a capacitor for high frequencies and it short-circuits high frequencies to ground. So, increasing the value to 1000pF causes it to short-circuit all frequencies to ground hence, frequency response is flat however, overall signal is smaller. But then comes the genius part of President Group engineering: R270 and R267 are voltage dividers and signal can go either positive or negative where, in this radio, negative is used with negative feedback loop. So, with these two resistors, you can adjust when the feedback loop is activated.
1 окт 2024
