[time-nuts] Looking for high reverse isolation amplifier

[John Miles]

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-bounces at febo.com [mailto:time-nuts-
> bounces at 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
> 
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