Hi Wayne If 2 X K3's can be phased locked ON TX and then combined with a Hybrid combiner, it should be possible to substantially reduce the TX IMD. This is a feature that the R&S Series 4100 DSP transmitters use to improve TX IMD performance. They do the same with their 1KW PA's combining and phase locking the amplifiers with powers upto 4kw of output.
I am no expert in area, so I am not entirely sure if it is as simple as they indicate. It would however prove very interesting if this could be achieved with two K3's? A good reason to buy more K3's! Is phase locking 2 K3's transmitters possible? John --- On Tue, 11/17/09, Wayne Burdick <[email protected]> wrote: > From: Wayne Burdick <[email protected]> > Subject: Re: [Elecraft] K3 frequency accuracy versus displayed precision > To: "ab2tc" <[email protected]> > Cc: [email protected] > Date: Tuesday, November 17, 2009, 2:04 PM > Here are the technical details > regarding the K3's VFO tuning accuracy: > > The K3's PLL synthesizer is phase locked to its 49.38 MHz > reference > via a DDS chip used as a precision divider. The DDS output > is in the > 3.6 MHz range, with a step size of 0.184 Hz (49.38 MHz DDS > clock > divided by 2^28 DDS word size). > > Taking the 8.215 MHz 1st IF into account (added to the VCO > on 160-10 > m, subtracted from the VCO on 6 m), this translates to a > VCO step size > of about 0.5 Hz on 160 m, 1 Hz on 20 m, and 2 Hz on 6 m. > Other bands > are between these values. > > Example: At RF=14 MHz, the VCO is running at around > 22 MHz. The ratio > between 22 and 3.6 is about 6, and 6 * 0.184 = about 1 Hz. > This is the > worst-case DDS-related tuning error on 20 m. > > If REF CAL (in the CONFIG menu) is not set to the exact > frequency of > the reference oscillator, there will be a small additional > offset on > all bands that is proportional to the operating frequency. > > In diversity mode (main/sub VFOs and filter bandwidths > set > identically), the DDS chips on the two synthesizers are set > to exactly > the same tuning word, and the VCO outputs are at exactly > the same > frequency. The two synths are phase-locked to the same > signal, so > there is never any beat note between the two. This is > critical for > diversity use, and is lacking in some other transceivers > with a sub > receiver. > > 73, > Wayne > N6KR > > > On Nov 17, 2009, at 10:05 AM, ab2tc wrote: > > > > > Hi, > > > > First time I have heard about this. How much frequency > shift are we > > talking > > about here? A fraction of a Hz, 10Hz? I have certainly > never noticed > > this, > > but of course on speech anything less than 10Hz is > practically > > inaudible > > unless you do a USB/LSB comparison on an AM station. > > > > AB2TC - Knut > > > > > > > > Wes Stewart wrote: > >> > >> Guys, > >> > >> I've mentioned this caviet before: > >> > >> http://n2.nabble.com/Ref-Osc-Cal-Method-4-td2595451.html#a2595451 > >> > >> The way the K3 implements the passband shift, the > same signal, with > >> the > >> same VFO setting, will have a different audio beat > note if the SHIFT > >> control is changed. * > >> > >> <snip> > >> > > > > -- > > View this message in context: > > http://n2.nabble.com/K3-frequency-accuracy-versus-displayed-precision-tp4016138p4020213.html > > Sent from the Elecraft mailing list archive at > Nabble.com. > > > ______________________________________________________________ > > Elecraft mailing list > > Home: http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/mmfaq.htm > > Post: mailto:[email protected] > > > > This list hosted by: http://www.qsl.net > > Please help support this email list: http://www.qsl.net/donate.html > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
