Re: [time-nuts] Looking for high reverse isolation amplifier
On 1/30/2014 7:50 PM, John Miles wrote: Exactly, for unity gain you'd design for +6 dB and series-terminate the output with 50R. Good for capacitive loads as well as isolation. Do you run it in inverting or non-inverting configuration? I've only used the non-inverting configuration (figure 1 from the datasheet). Takes about 20 minutes to dead-bug with 0603 resistors over bare copper. -- john, KE5FX Miles Design LLC The LMH6702 has 50 dB of reverse isolation at 200 MHz (good) but the phase noise is 15 dB above my DUT, so the search continues. Rick ___ 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] Looking for high reverse isolation amplifier
Depending on how much forward gain you're after, I'd suggest looking at the LMH6702 current feedback opamp. I keep a few of them around in Hammond boxes, powered by NiMH rechargeables. Measured S12 is about 70 dB at 100 MHz, and I'm sure it could do at least 40 dB at 200. If I remember correctly the 3 dB point is about 400 MHz in a stage designed for +8 dB of gain, and unity gain is about 700 MHz. Residual PN at 80 MHz is around -135 dBc/Hz @ 1 Hz, flicker corner around 1 kHz, floor around -165 dbc/Hz. You can do better with discretes but you can also do a lot worse... -- john, KE5FX Miles Design LLC -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts- boun...@febo.com] On Behalf Of Richard (Rick) Karlquist Sent: Wednesday, January 29, 2014 10:25 PM To: Discussion of precise time and frequency measurement Subject: [time-nuts] Looking for high reverse isolation amplifier Can anyone direct me to an amplifier with: 1. High reverse isolation (over 40 dB). Note: the spec of interest is *reverse* isolation, not port to port isolation in a distribution amplifier. 2. Low phase noise (less than -100 dBc/Hz at 1 Hz offset) 3. Works at 200 MHz The Q-Bit QBH-1401PM seems promising...if I can get one. If necessary I will build the amplifier if I can get a known good schematic to follow, but prefer to buy one. Thanks in advance. Rick Karlquist N6RK ___ 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.
Re: [time-nuts] Looking for high reverse isolation amplifier
On 1/30/2014 12:30 AM, John Miles wrote: Depending on how much forward gain you're after, I'd suggest looking at the LMH6702 current feedback opamp. I keep a few of them around in Hammond boxes, powered by NiMH rechargeables. Measured S12 is about 70 dB at 100 MHz, and I'm sure it could do at least 40 dB at 200. If I remember correctly the 3 dB point is about 400 MHz in a stage designed for +8 dB of gain, and unity gain is about 700 MHz. Residual PN at 80 MHz is around -135 dBc/Hz @ 1 Hz, flicker corner around 1 kHz, floor around -165 dbc/Hz. You can do better with discretes but you can also do a lot worse... -- john, KE5FX Miles Design LLC Great suggestion! TI has eval boards available for them so I can get up to speed quickly. I guess the idea is that I set it up for a gain of 2, and put a 50 ohm resistor in series with the output. Now it is a unity gain buffer in a 50 ohm system. A signal trying to go through it backwards has a source impedance of 100 ohms driving the output impedance of the amplifier, which is spec'ed at 30 milliohms, at least at low frequencies. That works out to 70 dB, which is what you observed. So I can see how it could have good reverse isolation. Do you run it in inverting or non-inverting configuration? Rick N6RK ___ 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] Looking for high reverse isolation amplifier
Great suggestion! TI has eval boards available for them so I can get up to speed quickly. I guess the idea is that I set it up for a gain of 2, and put a 50 ohm resistor in series with the output. Now it is a unity gain buffer in a 50 ohm system. A signal trying to go through it backwards has a source impedance of 100 ohms driving the output impedance of the amplifier, which is spec'ed at 30 milliohms, at least at low frequencies. That works out to 70 dB, which is what you observed. So I can see how it could have good reverse isolation. Exactly, for unity gain you'd design for +6 dB and series-terminate the output with 50R. Good for capacitive loads as well as isolation. Do you run it in inverting or non-inverting configuration? I've only used the non-inverting configuration (figure 1 from the datasheet). Takes about 20 minutes to dead-bug with 0603 resistors over bare copper. -- john, KE5FX Miles Design LLC ___ 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] Looking for high reverse isolation amplifier
Can anyone direct me to an amplifier with: 1. High reverse isolation (over 40 dB). Note: the spec of interest is *reverse* isolation, not port to port isolation in a distribution amplifier. 2. Low phase noise (less than -100 dBc/Hz at 1 Hz offset) 3. Works at 200 MHz The Q-Bit QBH-1401PM seems promising...if I can get one. If necessary I will build the amplifier if I can get a known good schematic to follow, but prefer to buy one. Thanks in advance. Rick Karlquist N6RK ___ 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.
