Paul wrote: hank you for your response, Ron. (and also Don). I am aware that the test I described is only a quick check to see if the ability to hear weak signals is being masked by internal receiver noise. However, the K2 is the only receiver (that I have owned) that has ever "failed" this test on 10 meters (meaning that more gain was needed so the preamp should be turned on) and I am wondering if others experience the same thing or there is something not right with my particular K2. So far, I have not been able to get an answer to that question. I do own the XG2 and have performed MDS measurements on my K2 using the XG2 and also a milspec signal generator I have. The numbers agree very closely with published specs ON 20 METERS. On ten meters I measured an MDS of -124 dbm (preamp off) and -130dbm (preamp on). IMHO, an MDS less than -130 dbm is not acceptable for weak signal reception. Which means to me that on 10 meters the preamp is absolutely required.
---------------------------------- I think "failed" is a misnomer. It sounds as if the only receiver in your comparative tests that is behaving ideally is your K2. The last thing you want is excess "front end" gain. All you want is just enough to bring signal levels up above the internal receiver noise and then have the bulk of the gain *after* the i.f. filters where only the signal of interest is being amplified. The K2 exhibits that characteristic, as you observed. On the lower frequencies no pre-amp is needed. The band noise easily over-rides any internal receiver noise. But on 10 meters it does not until you turn on the preamp. That means the K2 does not have excess front end gain on the lower bands that will limit its dynamic range. It sounds like the receivers you're using to compare the K2 with have a less-than-ideal gain distribution. To the "heart" of your question, yes, on my K2 at least, the preamp is needed on 10 meters. I've not tested the MDS on that band, but at the narrowest bandwidth my receiver's ability to "hear" is limited by the external noise under the quietest band conditions, as indicated by the "DeMaw test": removing the external antenna and noting a significant drop on QRN. That means that seeking a better MDS is a waste of effort for me with my antenna system. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
