Hi Geoff, --- Geoffrey Mackenzie-Kennedy <[EMAIL PROTECTED]> wrote:
> Hi Gian, > > Your messages have arrived!! I am glad you got the message. > > I experience the same problem here with the K2 on > 40m all the time when the > BC stations above 7100 kHz are being received at S9 > ++, and have to use > another receiver which uses H-Mode mixers etc. If we have problems in Italy certainly the same is in UK on 40m. > > Understood. Without running IMD tests on my K2/100's > receiver and its IF > cascade I can only guess that this might not be > enough protection when the > BC station carrier levels are up in the -10dbm > region, and you are trying to > copy a signal that is in between them. This is the > situation that I have > when using SSB between 7150 and 7197 kHz. The > situation improves of course > if the beam is pointing away from the BC stations. Yes, ointing the bem to another direction is like inserting an attenuator > There is also the > question of roofing filter linearity and Rx phase > noise. I am not sure we can call the first K2 Xtal filter a roofing filter as this is the main Bandpass filter. The second filter I believe it is an IF noise limiting filter to reduce IF noise. I believe the linearity problem is in the 2N5109 stage more than in the xtal filter. You need to do measurement to see which is the stage. In the CDG2000 we have linearity problems with passive components like front end coils and transformers. There is not much > that we can do about BC station Tx phase noise! Sometime they overmodulate > >> Although you may have not "enough improvements" > > because the stahge is limited by the phase noise > ... I > > believe it is better than having both the mixer > and > > the PLL limitations. > > Understood! > > >> NO. The H-Mode Squarer has a balance adjustment > and > > you do not need to put your hands in the PLL. Also > the > > HMM require 0dBm drive or less, so youmay have > less > > spurs. The BFO 50-50 balance is not necessary as > the > > LO frequency is low and the squarer gives quite a > good > > 50/5o outputs. > > I understand, but I was looking at the Squarer as > part of the circuitry to > be added to the K2's LO (VCO) *output* which > provides injection to the TUF-1 > mixer. Yes, the squarer is the one that square the LO signal to drive the FST3125 switches in the mixer. The STAR has the same squarer that drive the 3t or 2t H-Mode Mixer the user like to implement. > > -------------------------------------------- > From your second message: > > > Agree about terminations, but there is a limit!! The > SD5000 FET array (now > obsolete) with three transformers yields an Input > IP3 of +50dbm or better at > the worst case input levels below compression, but > my test equipment is > becoming stretched. Perhaps the newer arrays will > provide the same > performance. Yes... The SD5000 was good at its time... the problem is that it required several adjustments and this is not a good solution for people without proper test equipment. THe FST3125 H-Mode MIxer is very simple, it does not require adjustments like the original mixer. Exception the balance if you are looking for the highest IP3. The other aspect of 3125 vs SD5000 is the lower insertion losses, > -4.5dB vs -8dB or more. That's why it gives you a very hot front end not needing preamp. If you look at the measurements done by PA3AKE on the H-Mode Mixer with 3 and 2 transformers using FST3125 and new switches like FSA3157, the average IP3 can be +40 to +45dBm with 0dBm drive or less. I had the idea to use FST3125 and the like in mixer in 1998, at this time ... 10 years ago; SD5000 was implemented in the G3SBI H-Mode Mixer in 1993, 15 yeas ago. Now the search for new switches in the H-Mode Mixer are to reduce DDS spurs as all the other parameters are already good ... hi Nothing is perfect... > > Have you measured the filter's input IP3 with the > varicaps' back bias at the > minimum value used? Receiver IP3 measurements were done, before and after mixer and roofing filter mods, with IF xtal filter in its widest bandwidth. > > Good luck and many thanks. Thanks to you and best 73 Gian I7SWX > 73, > Geoff > GM4ESD > > > ____________________________________________________________________________________ Sucker-punch spam with award-winning protection. Try the free Yahoo! Mail Beta. http://advision.webevents.yahoo.com/mailbeta/features_spam.html _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net 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
