Re: Strange peaks in S11 with load
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Jerry
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I posted this frequency analysis on message #894 on this list. I too thought second harmonics were used but they are not¡.. at least in the 900 MHz, two-trace firmware. This chart was previously attached to msg 894 and shows the range of Si5351 frequencies and which harmonics are used for each of the 300 MHz segments. Fundamental frequencies are used from 55 kHz to 300 MHz. The third harmonic is used from 300 MHz to 900 MHz. In ranges where the third harmonic is used the fundamental is boosted about 6 dB. The attached chart was made using ¡°Peak Hold¡± mode on the spectrum analyzer so each group of frequencies could be easily identified. The Si5351 in my unit is capable of a stable 300 MHz output. It is not stable however at 325 MHz. Warren Allgyer WA8TOD On Aug 17, 2019, at 3:55 PM, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:
Hans Summers has experimented with pushing the Si5351 PLL chip beyond its 225mhz max spec, he got up to around 290mhz before it crapped out. /g/BITX20/message/52046 Apparently some chips (at some temperatures and at some supply voltages) can do 300mhz, but not all. Hugen's solution of reducing the max frequency out of the si5351 from 900/3=300mhz down to 800/3=266.66mhz is apparently enough to make it work across all devices. Given that there was a spike at 600mhz (in addition to 300mhz and 900mhz), it is apparently using the 2'ed harmonic, in addition to the fundamental and 3'rd harmonic. Perhaps the firmware could allow the user to attempt going all the way to 900mhz on the third harmonic, with the understanding that it may fail up near the very top. But continue to have gear-shifts at 266.66mhz and 533.33mhz as per the 800mhz firmware. Jerry, KE7ER On Thu, Jul 4, 2019 at 05:55 PM, <hugen@...> wrote: Peaks occur because si5351 is working at the limit£¬I will update an 800MHz |
Warren Allgyer
