In general I've found the spurious performance of the K3 to be pretty good, but I've noticed something today that I thought it would be worth asking more widely if anyone else has seen and fixed.
I was calling CQ on 40m around 7014 kHz and I noted that several skimmers also reported me weakly on c. 600 Hz either side of this frequency. Sometimes skimmers have bad spurious responses, but seeing this on more than one skimmer caused me to look more closely at my transmit spectrum. I discovered that - particularly on 40m - there were specific frequency ranges where a pair of sidebands appeared that move at 150% of the change in carrier frequency. So on 7012 kHz they are at roughly +/- 500 Hz, at 7011 kHz they are at roughly +/- 1 kHz, at 7010 kHz they are at roughly +/- 1.5 kHz. They cross over with the carrier just below 7013 kHz. Similar patterns recur in other parts of 40m, but they are strongest near the bottom of the band. There are dramatic step changes in the level of the spuria at the boundaries between synthesiser segments - So I see spurii from 7000-7004, none from 7004-7009, spurii 7009 -7015, etc. They peak in strength when they are about +/- 500 Hz from the carrier, but drop significantly in level as you get further from the carrier. The level of these spurii is what was concerning - at their worst they were less than 30dB down on the transmit signal. They grow somewhat non-linearly with power. At 5W they are -40dBc, at 12W they are -32dBc, at 13W they are -35dBc and at 100W they are a little less than -30dBc. I can see the same style of spuria in some segments on 80m and 160m - but at lower levels. I assumed this was a fault with that specific radio - and in some ways it is - but the same spurii are present on both K3s that I have here - but on the second radio they are no worse than -45dBc. I've disconnected everything connected externally from the radio, tried different power supplies, and recalibrated the synthesiser and Tx gain with no significant change. Both radios have the original synthesisers - not the KSYN3A. Any leads from anyone on this one? 73, Andy, G4PIQ ______________________________________________________________ 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 Message delivered to [email protected]
