I have just fitted a 4m internal transverter into my KX3 today. I wanted to check the signal stability and quality on a load before putting it on the air, and used my SDR as a spectrum analyser to examine the output. I have used this SDR in the past for examine other transmitters so know it's limitations and strengths.
Here are my observations so far: 1) There is on frequency carrier leakage from the receiver. This isn't a big deal, and is explained in the manual. 2) When in transmit on SSB or CW with no keying or audio input, there are a forest of spurs close to the operating frequency, they are independent of the power setting. Perhaps 50 dB or less down on PEP. This is concerning. I will do more accurate tests. 3) When modulated there are products either side of the main signal that do vary with modulation. They are again not very many dB down. This is very concerning. 4) I tried a transmission at 3W for a couple of minutes, and the PA temperature quickly rose to the cut off point. Yes, I have tightened the screw on the PA to the side wall. This will be a problem if using the rig on high duty cycle modes like JT65. The PA of the transverter is a FET bolted to the side wall of the KX3 and does not directly make use of any third party heatsink that may be bolted to the top. 5) Mysteriously a couple of times I have seen a High SWR warning briefly at start of transmission. On the positive side the frequency stability is acceptable for SSB and CW. It may even be for JT65 or FSK441. I have not found any specification for the spectral purity of the 4m transverter, so don't know if this is what Elecraft expect or not. It certainly isn't up to my standards for a commercial amateur transmitter and I wouldn't subject my friends to such a signal on the air. The only thing in the installation manual that was unclear is the exact routing of the LO cable from the RF board to the transverter by the heatsink and the filter board and battery holder. I suppose there is a small possibility that the routing of that cable may affect the levels of Spurs on the signal. I may try some small adjustments and see. I was going to build a medium (30 W) or high power (150 W) amplifier for the transverter, but clearly I would not like to amplify a signal as impure as this. My plans for 4m have now changed to an IC7300, and I may keep the KX3 4m transverter as a backup or for portable work with QRP. If anybody else has tested their 4m or 2m internal transverter for spectral quality I would be interested in their comments. 73 from David GM4JJJ ______________________________________________________________ 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]
