Thanks Wayne and Alan, for that super detailed info. The radio side of things are still very magical to me! I'm a software guy, not a hardware guy. :)
I don't own a K3, but two KX3's for my "knob" radios. I use a Flex 6700 and 6300 for home use. I'm assuming the 6700's -147 dBc@10kHz, -152 dBc@100kHz phase noise values are pretty good then, if anything higher than -140 dBc is acceptable. Even the 6300 is spec'd at -140 dBc@10kHz. I do agree that my old (and sold) 3000 was messing up the bands during Field Day last year. This year we are using a K3, two 6300's, and a 6700, so I'm hoping for better performance all around. Again, thank you for the info! On Jun 9, 2014, at 9:08 AM, Wayne Burdick <n...@elecraft.com> wrote: > Chris Johnson <elecr...@ozy.us> wrote: > >> 1) Is phase noise the measurement of the instability of an DDS? > > That's one contributing factor. But the DDS signal drives a mixer, and the > other input to the mixer may be the larger source of phase noise in transmit > mode. > > >> 2) How does this impact TX only, and why does it create such an issue to >> nearby listeners? > > In the case of the KX3 and Flex radios (e.g. Flex 1500/3000/5000), the > limiting factor is probably the transmit D-to-A converter. Its performance is > limited by quantization and sampling noise, setting an upper bound on phase > noise. The KX3 has an advantage in that its synthesizer uses a DDS-driven > PLL, while the Flex radios are DDS only, without a following PLL. But the TX > DAC is still a factor in both cases. > > In a well-designed superhet like the K3, the TX DAC's noise floor affects > only the in-band portion of the transmitted signal, i.e. the portion within > the I.F. crystal filter passband. The K3 has two crystal filters in series in > transmit mode, which results in very high rejection of noise outside the SSB > passband (typically 100-3000 Hz). This means that the limiting factor on > wideband transmit noise is not the IF injection into the mixer -- it really > *is* the synthesizer. > > The K3's synthesizer is extremely clean at wide offsets (another DDS-driven > PLL), and that is why its transmit phase noise is so low. > > >> 3) Does phase noise go down if you use a faster master clock? The Flex 6700 >> uses a 983.04mhz vs a 122.99Mhz clock in the 6300. > > That is a completely different design (direct digital up/down conversion), > which requires very high clock speeds, very expensive ADC and DAC components, > and high current drain in receive mode. It can be made clean in transmit and > receive modes, although in receive mode this architecture will still have > typically 15-20 dB lower blocking dynamic range than a well-designed > superhet. None of this is applicable to the KX3, which is obviously intended > to be an ultraportable radio with low current drain and low cost. > > >> 4) Do low phase noise radios allow in-band use, such as someone on CW on 20M >> and someone up on voice on 20M? > > Yes. In general this is only a problem if you have stations in very close > proximity. In this situation, the K3 is better than any other radio on the > market. This is why the K3 is highly favored for Field Day and DXpeditions. > > 73, > Wayne > N6KR > > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
