Magnus Magnus Danielson wrote: > Bruce Griffiths skrev: > >> Pete wrote: >> >>> Arnold, >>> >>> I have had good experience with the SYPD series >>> from Mini-circuits. I have not seen any used, but >>> their new cost is reasonable. They do several things >>> well e.g. the DC offset on the units I received is >>> <1mV & they produce >2V p-p when driven @ >>> +7dBm. >>> >>> Pete Rawson >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >>> >>> >>> >> Pete >> >> These are OK except when one needs to isolate the IF ground from the RF >> grounds to avoid low frequency ground loop problems. >> The RPD and MPD through hole series are better in this regard as they >> allow the IF ground to be isolated from the RF grounds. >> > > It should be noted that several of their SMB mixers have separated > grounds, but it is not documented in their datasheets. > > >> The flicker phase noise characteristics of the mixer/phase detector >> should be measured as some mixers/phase detectors have lower flicker >> phase noise than others. >> The termination of the IF port will affect the mixer phase noise. For >> offset frequencies < 100kHz a capacitive termination of the IF port >> which reflects the sum frequency back into the mixer reduces the mixer >> phase noise. >> > > It essentially sees a very low impedance at those frequencies. > > My experiments with capacitive loading of mixers basically indicates > that the actual low-frequency slope of an unloaded mixer does not > change, but the capacitor load filters the sum-frequency (with > overtones) while a resistive 50 ohm load just loads the amplitude down > and gives no significant change to performance. Optimum performance out > of a mixer in my experience comes from fairly high-impedance load at low > frequencies with a direct capacitive loading for filtering effects. > > A non-filtered response is quite interesting to see with a fairly slow > beating frequency occuring. Kind of soothing waveforms floating slowly > as waves over the scope. > > The effect of reflecting the sum frequency back into the mixer is documented in some Watkins Johnson and HP/Agilent appliction notes. It can be very effective even at microwave frequencies.
>> The tradeoff is that the mixer output at higher offset >> frequencies is attenuated by the IF port termination. >> Terminating the IF port in a capacitor reduces the RF port impedance, so >> that a low value series resistor (22 to 39 ohms - select for lowest >> VSWR) is then required to improve the RF port VSWR. >> > > Which in improves phase-stability as reflected waves has less impact. > -3 dB pads have also been used by the good folks over at NIST at one time. > > The best combination is a series resistor plus an attenuator pad. >> Terminating the IF port with a capacitor also alters the mixer gain (as >> a phase detector) so this needs to be measured in conjunction with the noise >> > > Well... the normal 50 Ohm loading alters the mixer gain... not the cap. > But since the normation is towards 50 Ohm... ah well... > > >> 10514 and 10534 mixers using discrete diodes supposedly have lower >> flicker noise than mixers using integrated quad diodes. >> > > They however has common ground in their every day laboratory variants. > There exist variants meant for production. However, they are not made > out of that exquisite components, so their performance should be > replicable, as have been pointed out before. > > The B versions intended for through hole PCB mount have separate grounds for all ports. These don't seem to be as widely available as they once were although I have an HP10534B one. > Cheers, > Magnus > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > Bruce _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
