Instrument cables.

[cicastol]

I wonder if this causes the difference in plots when cables are directly swapped without re-calibration?

Yes, higher capacitance smoothens too much the pulse, i also had used the Thermax RG400 2 years ago, switched for a 75Ohm lower capacitance Radiall KX6A .

[Pavel M.]

Hi guys,
my cables finally arrived, so I was able to do some basic testing.

As I said, my current setup uses two separate lines for HV (BNC-BNC) and signal (Gx16-Gx16).
During the testing, I mainly focused on the capacitance, because if the capacitance is too high, it can "flatten" your pulses.
I measured it with a simple DIY Arduino-based meter, which turned out to be accurate enough for this purpose.

For HV, I've tried 11 cables of various lengths from different suppliers. I chose 1m, 2m, 3m and 5m. All of them were either the standard RG58 coax, or the SYV-50 (Chinese equivalent). Most of them were around 40-50pF/m, the best 1m cable was 30pF, and the worst 5m cable measured as high as 257pF. There were no noticeable differences in performance, so it basically doesn't matter which one I use.

For signal, it was a different story. The higher quality cable from Cordial was only 58pF for like ~1,5m (I'm not 100% sure about the exact length since I don't have the cable at hand right now), and it significantly outperformed everything else I've tested so far. For generic 5m cables, the capacitance can reach some crazy values (over 550pF!).

The capacitance varied greatly, but surprisingly enough, I was still getting good results even with the "worst" cables. Although those longer (higher capacitance) signal cables do indeed slightly lower your count-rates, the resolution stays the same. However, just like Andrey said, I also had to adjust the calibration every time I swapped a cable.

As a conclusion, it really comes down to your setup and how does it process pulses, but shorter, more expensive, premium cables do generally work better for GS.

-Pavel

[James Luck]

Figure I'll let everyone who comes across this discussion know.

I've started producing my own cables with success, and no longer am in search of a supplier, ends up I can produce most of mine on my own for about $10usd.

Thank you to all of you who has replied to me.

James