Hi Gain without an input termination will very much depend on the source you are driving it from. With a "proper" 50 ohm source, the gain will be 6 db high without the input resistor. If it's got more gain than that, your source is not 50 ohms. There are a lot of OCXO's out there that are not "true" 50 ohm sources.
Input termination or not depends a *lot* on what you are going to use it for. In my case, I'm after a high input impedance to low output impedance conversion. I need to deal with some gear that was made back before 50 ohms was "how it's done". Bob -----Original Message----- From: time-nuts <time-nuts-boun...@lists.febo.com> On Behalf Of Taka Kamiya via time-nuts Sent: Wednesday, March 25, 2020 2:49 PM To: Discussion of precise time and frequency measurement <time-nuts@lists.febo.com> Cc: Taka Kamiya <tkami...@yahoo.com> Subject: Re: [time-nuts] Noise Floor I've been playing around with Clifton amplifier as well. Mine, input is terminated with 50 ohm register, and rest is unmodified, so it has 6dB gain. I have a 10dB pad on input side. I, too, noticed there will be a severe clipping with driving it too hard. I plan to zero the gain and retest. Without proper termination on input side, it showed phantom gain of 10dB.....? I stayed conservative and output is 7dBm. I with there was a little more room there.... Looks pretty clean spectral density wise. (frequency is 10MHz) --------------------------------------- (Mr.) Taka Kamiya KB4EMF / ex JF2DKG On Wednesday, March 25, 2020, 2:00:08 PM EDT, kb...@n1k.org <kb...@n1k.org> wrote: Hi So, here we have a couple of plots of a Clifton Labs Z10000 amplifier board. It's a part that several list members (including myself) have recommended using. The board has the "stock" high input impedance and has been modified for 0 db gain (470 ohm resistor so just over 0 db ...). There is a 6 db pad between the splitter and the amp to terminate things. The run is fairly short so the data is a bit rough. For a better look, an overnight run would show a bit more detail. Phase noise looks pretty good. ADEV has some weird "stuff" going on. Time to start tearing the board apart to see what's wrong with it? Maybe there's some noise in those resistors .... let's go !!!! Well..... maybe not so much. If you go back and dig up the original plots in this thread, the ADEV is *essentially* at the "noise floor" of the measurement system. There are sure to be some wobbles in a shorter ADEV run so it's not a 1:1 sort of thing. Phase noise wise, everything from about 80 Hz and lower is at noise floor. The data out at 100 KHz offset suggests that for a low phase noise system, this board would degrade the typical 10811 by a slight bit "wideband". Since noise floor likely changes with things like drive level and frequency, to be 100% sure of the floor, one would need to repeat the original test at this frequency and these levels. I'm not that ambitious 😊 What I have tells me pretty well when I've hit the limit. It keeps me from going crazy "debugging" a board that actually does not have a problem. (or if there's a problem, my quick test can't see it ) Some other Z10000 trivia: If you drive this board so it has a couple db more output, it goes into clipping. When that happens .... yuck. Noise and ADEV both are massively impacted. You very much do *not* want to overdrive this board. (This is also true of most amplifiers) At ~14 dbm out at 5 MHz you are in clipping. I would stick with 12 dbm or less (at 5 MHz ... who knows about other frequencies ...). Dropping gain to zero db with the resistors on the board is better than doing the same with a pad on the input. The wideband phase noise is a bit better when done with the resistors. Very much like the front end on a radio .... Fun !!! Bob -----Original Message----- From: time-nuts <time-nuts-boun...@lists.febo.com> On Behalf Of jimlux Sent: Tuesday, March 24, 2020 7:31 PM To: time-nuts@lists.febo.com Subject: Re: [time-nuts] Noise Floor On 3/24/20 2:17 PM, John Miles wrote: >>> It would be interesting to know what ADC was used and if there's an >>> SDR-board out there that uses the same ADC. >> >> Uh.. I remember John telling me what ADC it was, but I forgot, sorry. > _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.