Hi Klaus, My understanding is that the iso amp is identical to the 10 dB preamp but with a reduced gain (there is a "iso amp hi" control signal which seems to be used to set the overall gain of that stage). So I would expect the IP3 to settle somewhere between the "no preamp" and the "10 dB preamp" value if the iso amp is on. Turning on the iso amp should increase the noise figure but I don't think this is a big issue (and applies only if you use otherwise no preamp). I would not expect OSB suppression to change because the amp affects both quadrature channels the same way.
Concerning the "local oscillator crossmod theory", and your measurements, I would say it doesn't seem to apply in your case. I think you could make a final check for AM on the vfo leakage signal with your JRC rx in a situation where you are experiencing breakthrough, just to be sure, but I believe it is not very probable in your case. I just finished a measurement of the vfo leakage. I connected the antenna output of the KX3 directly to the input of my Perseus SDR (which provides an accurate level meter). With no preamp, the level is between -75 dBm (S8) on 160 and 80 meters and increases to about -50 dBm (S9+20dB) on 17 meters. With the 10 dB preamp on it is barely detectable (less than -110dBm) Given these numbers, assuming something like -20dB of "gain" for the AC wiring "antenna" and some "free space attentuation", the signal that is re-radiated from the AC wiring should be to weak to be detected in most setups and the local oscillator leakage is not likely to explain the AM breakthrough. Vy 73 Ralf, DL6OAP Am 30.07.2013 um 11:20 schrieb Klaus Dittrich <kla...@arcor.de>: > Again, thank you all for taking the time to contribute to > the issue. > > Ken, there was a relay of Radio China in Albania but > I don't know if it is actually active. > > Ralf, this morning I "measured" the vfo leakage with my > second receiver a NRD-535 connected to a R&S active antenna > positioned at about two meters distance from the feedpoint > of my dipole. > > At 15m the received vfo signal was about S3, dropping down > to just noticeable if I switched on the isolation > amplifier. > > I wonder why this isolation amplifier is off by default, > but assume the reason is to save battery power which > does not matter in case of use as home station. > > So I would like to know if there are any degradations > in IP3 or more probable in opposite sideband suppression > if this amplifier is permanent in the signal path because > of additional phase shifts. > As far as I remember this case is not included > in the OSB adjustment procedure. > > I was astonished to see during OSB adjustment how > sensitve the procedure is to frequeny dependend phase > shifts which I never thought they could be of importance. > > Every 10th mm on the circuit board and every ns in software > seems to matter. > > Wayne, could you please drop a few words about this? > > I assume such small rf-levels are not able to cross-modulating > the local oscillator's "carrier" in the AC mains. > In general I agree with your technical analysis and hope we met > us on the bands some day for a longer talk. > > "If the AM breakthrough is a real (direct rectification) one, the 90 degree > phaseshift between the two quadrature "channels" would probably not occur (in > contrast to "true" signals). This could probably be used for suppressing it > by software (?)" > > I such a direction my hopes went. > > Wayne, thank you very much for answer, technical statements, clarification > and your offer. > > Now the reason of this AM-breakthrough is determined by the relevant > authority. > > Good to hear as well that the dynamic range at 2 kHz drops not as far as I > assumed because of the data measured by Sherweng. > > To your offer, which is much appreciated, I have several technical > questions but these we will handle in separate e-mails as desired. > > > Igor, I agree the problem is not a permanent one, as I already > wrote and in no way my intention was to cast a bad light on the KX3. > > I already had a lot of fun and fine dx qso's with it. > But if your are in a cw-qso at 15m and suddenly because of this > AM-breakthrough you can't complete it, that's annoying. > > "Did you send message to elecraft technical support? Or do you expect them to > answer your concerns here on the reflector? They sure are not obliged to do > the latter." > > Shure they are not, but in practice they do. :-) > > I contacted qrp-project (main Elecraft distributor in Germany) before. > They told me the problem is already known but the reason unclear. > > Now, now it is clear. :-) > > "BTW, later you may discover couple of other issues with KX3 which are not > that obvious and which I have already discovered. Or you may just search this > reflector and find out." > > I will look at your contributions to find out or contact you direct. OK? > I am always interested in problems. :-) > > -- > 73 es mny tnx > Klaus DF1TL > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
