Re: [time-nuts] how to find low noise transistors
Rick wrote: When you raise the source impedance, you also have to reduce the collector current. Your analysis didn't take that into account. Refer to page 83 of the first edition of Low Noise Electronic Design. Equation e. states that optimum noise figure is a function of the ratio between base spreading resistance and (beta)(r-sub-e). If base spreading resistance is high, you make r-sub-e high by reducing collector current. Equation f. states that doing that will increase optimum source resistance. Agreed, you can adjust the noise resistance of a BJT (the ratio of its voltage noise to its current noise). However, minimum noise figure is frequently not the way to obtain the least added noise voltage from an amplifier. That is the fallacy I mentioned -- the mistaken notion that increasing the resistance of the source to achieve a better NF will improve the S/N ratio of the amplifier output. That will be true only if (i) one can arbitrarily vary the intrinsic resistance of the source without changing the source's intrinsic S/N ratio, and (ii) one is stuck with a certain BJT input device. Neither is almost ever the case in real life (aside from increasing the source impedance with a transformer). Furthermore, reducing transistor current to raise the noise resistance causes undesirable collateral effects (including reduced bandwidth, which increases phase noise due to baseband noise modulation of transistor capacitances and generally increases nonlinearity). BJTs are readily available with noise resistances of less than 50 ohms (see The Art of Electronics, 3rd edition, Chapter 8). The only reason to increase the source impedance with a transformer is if the intrinsic source impedance is lower than the lowest available BJT noise resistance -- for example, in the case of microwave transistors (remember, this thread started in reference to LN preamps for 100kHz LORAN antennas). Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] LORAN on the air 89700 been a good day so far
Hi Bill, it is very dependent which is closer to the receiver here in the Bay Area sometimes you can't hear local AM stations either. 73 Alex KJ6UHN On 7/21/2015 3:15 PM, billriches wrote: Hi Alex, 100 Khz is not protected however the interference from SMPS is annoying but will not bother loran transmissions as it is much stronger than that interference. 73, Bill, WA2DVU -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Alex Pummer Sent: Tuesday, July 21, 2015 11:58 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] LORAN on the air 89700 been a good day so far Hi Bill , is the Loran frequency 100kHz protected? because there are may switching mode power supplies which generate lots of Loran replacementsthe same is with wwvb 's 60kHz 73 Alex KJ6UHN On 7/21/2015 4:26 AM, billriches wrote: Alex - are you referring to the test of eloran in progress from Wildwood NJ? That of course is on 100 Khz. There is no Loran in California at this time. 73, Bill, WA2DVU Cape May -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Alex Pummer Sent: Monday, July 20, 2015 9:03 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] LORAN on the air 89700 been a good day so far Hi Paul where could I find the frequency of our Loran [the Californian Loran ] I have an old HP3586 radio receiver 73 Alex llow the instructions there. --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Austron 2200A
While I may be counting chickens, I'm likely to take delivery of an Austron 2200A in the next week. Somewhat predictably the antenna isn't included and I've seen the extensive thread from this mailing list circa 2007 where the thread seemed to peter out at the end. Worst case I could probably pillage the (working) rubidium oscillator that's inside it, ideally it would be nice to get the unit working as is. Did people end up getting their Austron's up and running ? At the moment I'm looking at options to make a down converter to deliver the 75.3Mhz required for the Austron and to power a timing antenna with 5v LNA that I have sitting on the shelf. There are some 23cm amateur kits that would be adapted for the mixer unless there is a 'simpler' solution I've missed. Any suggestions ? Cheers -- -- Teach your kids Science, or somebody else will :/ ja...@ball.net vk2...@google.com vk2f...@google.com callsign: vk2vjb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] HP 3581A question
Corby ,have you checked the Keysight tech support site? I didn't have time to investigate completely, but they have a 3581a/c operating and service manual pdf. John -- Original Message -- From: cdel...@juno.com To: time-nuts@febo.com Subject: [time-nuts] HP 3581A question Date: Mon, 20 Jul 2015 11:33:08 -0700 Hi, I have an HP 3581A and I need to replace the top right hand frequency pot. My unit has a dual pot with a concentric shaft. The only manual I have shows a single pot. If anyone has a manual that shows the dual pot could you let me know the values of the pots? Thanks, Corby Dawson ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. Old School Yearbook Pics View Class Yearbooks Online Free. Search by School Year. Look Now! http://thirdpartyoffers.juno.com/TGL3131/55afd326151c953171946st01duc ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
