Some years ago I bought some dividers from Wenzel. For each arm, we have x256 and a x64 divider. Wired in series, that means we can divide each IR beat by 2^14.
The highest frequency we can read in our digital system is ~8100 Hz. This corresponds to an RF frequency of ~132 MHz which as much as the BBPD could go, but less than the fiber PDs.
Today we checked them out:
- They run on +15V power.
- For low RF frequencies (< 40 MHz) the signal level can be as low as -25 dBm.
- For frequencies up to 130 MHz, the signal should be > 0 dBm.
- In all cases, we get a square wave going from 0 ~ 2.5 V, so the limiter inside keeps the output amplitude roughly fixed at a high level.
- When the RF amplitude goes below the minimum, the output gets shaky and eventually drops to 0 V.
Since this seems promising, we're going to make a box on Monday to package both of these. There will one SMA input and output per channel.
Each channel will have a an amplifier since this need not be a low noise channel. The ZKL-1R5 seems like a good choice to me. G=40 dB and +15 dBm output.
Then Gautam will make a frequency counter module in the RCG which can do counting with square waves and not care about the wiggles in the waveform.
I think this ought to do the trick for our Coarse frequency discriminator. Then our Delay Box ought to be able to have a few MHz range and do all of the Fast ALS Carm that we need. |