Kjeld: Any sidebands or trash on your 10 MHz reference, that are within the bandwidth of the Phase Lock Loop reference multiplier in the DDS will appear on the local oscillator in the 1500. Which means that they will appear on both transmitted and received signals.
Analog devices does not specify the bandwidth of their DDS reference PLL, but I assume it is on the order of 1 MHz or so. So, if you want to preserve the performance of the receiver, the 10 MHz reference will need to be clean to greater than -80 dBc within a megaHertz of 10 MHz. Any spurs that are further away, such as harmonics of 10 MHz are not an issue. --- Graham / KE9H == On Wed, Apr 13, 2011 at 8:29 AM, Kjeld Bülow Thomsen <oz...@mail.dk> wrote: > Hello Graham, > > > > Looking on the specs of my Isotemp 134-10 oscillator showed that spurious > attenuation should be >60 dB. Looking at the 10 MHz signal on the 1500 > showed a lot of spurii about 60 dB down. In my scrapbox I found a 10 MHz > 8-pole quarzfilter. Putting this filter in line with the 10 MHz signal > cleaned it up. I do not have ground loops and the power supplies are clean. > But the 60 dB attenuated +/- 10 kHz spurious are still there when I lock > the > 1500 to the GPSDO. And they disappear when using the internal reference. > > > > Kjeld/OZ1FF > > > > Fra: gra...@flex-radio.com [mailto:gra...@flex-radio.com] På vegne af > Graham > Haddock > Sendt: 2011-04-13 05:07 > Til: Kjeld Bülow Thomsen; FLEXRADIO > Emne: Re: [Flexradio] Flex-1500 spurious when using external reference > > > > Kjeld: > > Do you have access to another 10 MHz reference that could be substituted > and > used > to compare? It does not have to be high accuracy for the comparison test. > > I suspect a 10 kHz switching power supply or some other 10 kHz source > associated with your GPSDO as causing the problem. > > You might also try making sure the case of the FLEX-1500 shares a common > ground with the GPSDO. Do not depend on the shield of the 10 MHz coax, > since > it floats at the FLEX-1500 input, to allow the 1500 to reject ground loop > noise. > > --- Graham / KE9H > > == > > On Tue, Apr 12, 2011 at 10:23 AM, Kjeld Bülow Thomsen <oz...@mail.dk> > wrote: > > I’m using my Flex-1500 with transverters on 1,3 – 24 GHz. The radio and > most > of the transverters are locked to a 10 MHz GPS-disciplined oscillator. When > working weak signals there are only very few spurious frequencies. During > the last weeks there has been tropo conditions with signals in the 59 > +20-30 > dB range. All these signals appeared full of spurious +/- 20 kHz. As all > signals was looking in the same way when exceeding S9 I decided to > investigate the problem. > > > > The pictures on http://www.oz1ff.dk/pages/flexradio.html a screen dump of > a > -60 dBm signal on 28,2 MHz from a clean source. Dia1 is with external > reference and shows +/- 10 kHz spurious. Dia2 shows the signal with the 10 > MHz reference switched off. Increasing the signal generator level to more > than -40 dBm with 30 dB preamp gain overloads the receiver. But that is as > specified. The level from the external 10 MHz source is +2 dBm and sine > wave. > > > > The external reference is essential for weak signal work. I don’t expect > this to be a software problem. Any suggestions for a solution to this > annoying problem? > > > > Vy 73 de OZ1FF - Kjeld > > > > Phone +45 7352 6050 > > SMS +45 4021 1119 > > Skype oz1ff-1 > > > > <mailto:kj...@oz1ff.dk> mailto:kj...@oz1ff.dk > > <http://www.oz1ff.dk/> http://www.oz1ff.dk > > > > _______________________________________________ > FlexRadio Systems Mailing List > FlexRadio@flex-radio.biz > http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz > Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ > Knowledge Base: http://kc.flexradio.com/ Homepage: > http://www.flexradio.com/ > > > > _______________________________________________ > FlexRadio Systems Mailing List > FlexRadio@flex-radio.biz > http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz > Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ > Knowledge Base: http://kc.flexradio.com/ Homepage: > http://www.flexradio.com/ > _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/
